Circuit electrinic

Here is a tester for on-board testing of IR receiver modules used for remote control of TV sets and VCD players. The circuit is very simple and can also function as a remote tester. IR receiver modules are miniature IR receivers sensitive to pulsed infrared rays. These have a pin photo-diode and a preamplifier stage encased in an epoxy case that acts as the IR filter.

Infrared (IR) Receiver Module Tester Circuit Diagram

Internally, the module has an AGC, band-pass filter, demodulator and control circuit. Its output has a bipolar transistor with 80- to 100-kilo-ohm resistor in the collector. Normally, the collector output of the transistor is high and gives 5V at 5 mA. The output of the module is active-low and hence it sinks current when the pin photo-diode senses the presence of pulsed IR rays.


The IR receiver module is designed with high immunity against ambient light and is capable of continuous data transmission at up to 2400 bps or higher. The band-pass filter and AGC suppress unexpected noise to avoid false triggering. The module responds to the IR beam only if its carrier frequency is close to the centre frequency of the band pass.

IR Receiver Module Pinout

Working of the circuit is simple. Three mini crocodile clips are used to connect the circuit to the positive, negative and output of the module. If the module is properly working, its output remains 5 volts. This makes the cathode of LED1 high. So LED1 doesn’t glow and the buzzer remains silent. When you focus the remote handset onto the IR receiver and press any switch, the output of the IR receiver sinks current.

So LED1 starts flashing and the buzzer beeps in sync with the pulsations of the IR beam. On the other hand, if your IR receiver module is faulty, the output of the module does not sink current when you focus the remote handset towards the module and press any switch. So neither LED1 flashes, nor the buzzer beeps in sync with the pulsations of the IR beam.

Power to the circuit is obtained from a 9V PP3 battery and regulated to 5 volts by zener diode ZD1. Most of the IR receiver modules work only between 3 and 6 volts. Storage capacitor C1 releases current to make LED1 flash brightly. (EFY Note. We had used a TSOP1738 IR receiver module while testing. Fig. 2 shows the pin configuration of TSOP1738.)

Assemble the circuit on a small piece of matrix board and enclose in a small cabinet. Use a high-brightness red LED and a small buzzer for audio-visual indication. Connect points A, B and C to the crocodile clips using red, black and blue wires to connect to the pins of the module easily. For easy identification of pins, the pin assignment (front view) of some common IR receiver modules is shown in the table.

 It also has a special mode for pictures of contacts and a World Card Mobile application

for capturing and reading business cards.
Videos can be captured in normal and MMS modes. Format options include MPEG4 and H.263. Highest resolution can be set at VGA (640x480 pixels). Recording limit has a number of options such as 10

seconds, 3 minutes, 2 MB, etc.This is a gadget which can add extra capability to your cellular phone. A cell phone booster with

a Bluetooth contrivance can set up a wireless connection with some other detailed devices with the same capability. Hence, it abolishes the requirement to use physical cables.This accessory help

you in providing the strong network along with the huge connectivity. Antenna Booster will help you in many ways. It provides the good connection so that you can easily talk to your relatives or

family members.Faceplates are generally used to give the trendy, classy, amazing, stylish, and the glossy look to your touchtone phones. They are available in the market in great abundance. You can

get them according to your need and make your cell also luxurious.
This is all about the accessories and its benefits, I hope after reading this article you will surely purchase the good and the stylish accessories for your handsets.
 Schools are looking to purchase mobile phone signal boosters. The misuse of cell phone boosters during class is causing the teachers to fight back. Not only is it a huge distraction during class

while teachers are trying to actually teach, but there is also concern that cheating is more prevalent with the ongoing texting.
In Des Moines, Iowa, one school board member was quoted by the Des Moines Record. "I dont think they have a place in the educational environment. The educational environment is supposed to be

about students learning and teachers teaching and teachers cant teach over a mobile phone. If a student is busy on the cell phone booster they arent learning. Its a distraction... and we need to

minimize the distraction."
What is the solution? With the FCC controlling signal boosters as well as signal boosters, and the law limiting signal boosters to use only by federal authorities, schools dont have much of a

chance to fight back that way.
One reader responded to the article in the Des Moines Register with an amusing suggestion to the problem. "Oh, For Crying-out-load. Just hang one of those shoe organizers next to the door and

require each student to check in their phones on entering the classroom, then they can retrieve them after class.

The antenna determines the shielding range of cellular phone jammer. 
Should implement prevention unit is responsible, focused, ensuring safety "approach, in accordance with the principle of" who is in charge, who is responsible for the development of safe production responsibility system. Security work into the performance appraisal. A month to conduct a safety check, make a record, identify problems and timely rectification. Check the results and linked to the income of employees, through the specification and inspection to ensure the implementation of various rules and regulations. Pre-job of the salesperson, business training, security, confidentiality, and legal education, and pass the examination can be employed. To develop a cell phone store receipts, cash-carrying on the way the anti-robbery prevention and emergency response plans, and the familiar, once the incidence, rapid and effective processing solutions. The direction of cell phone jammer is decided by the antenna.
Security facility configuration, capital safety, electrical safety, fire safety management with reference to the business hall of Jiangsu Mobile Communication Co., Ltd. safety regulations "file execution. The information security manager responsible for the confidentiality of sales information: information security education on a regular basis, and stores the information security implementation of the supervision and inspection. For all types of business documents, internal company documents, work information, technical data and statistical analysis data, non-license led by the higher authorities, all employees shall not be privately available to any individual or entity shall not be privately copied, disk copy, or network transmission other ways out of the workplace. Systems Engineering in the case of stores people personnel changes, job transfers and permission to adjust the situation. The antenna and battery of cell phone jammer are the built in type.
The store manager shall promptly submit an application to the higher authorities, with the completion of work the application, close, permission to adjust the work in accordance with the requirements of the higher authorities. Business accepted members in their daily work involved in customers personal data, cost information, call list information must be kept strictly confidential and shall not be divulged. Customer data to strict management, the timely entry of the BOSS system. The raw data shall be properly kept on time and returned to the company. Place of business must be set within the computer power-on password may not be equipped with floppy drive must be disconnected from the network after work. Business computer, the timely replacement of the BOSS job number passwords should be based on the requirements of the higher authorities.

This is why it is a good idea to get a universal gift that all people will love. Here are some reasons why a booster is the perfect

present.
Shopping for a teen or a pre-teen can be an exceedingly difficult task. A person has to be updated on the latest gadgets and the hottest fashions. Instead of catering a gift to preconceived notions

of what teenagers might like, a person should buy a present based on what these teens will need. All young people use cell phones and the onset of smart phones has increased their prevalence. A

cell phone booster is a great gift because a teen is guaranteed to use it. Anything that allows them to talk and text for longer periods of time will keep them happy and satisfied for years to

come.
If a person has a businessman on his or her gift list, a cell phone booster is a terrific option. People who work in business rely on their phones in order to communicate with clients. There is

nothing more embarrassing than consistently dropping or missing calls. A cell phone booster will reduce the propensity for dropped telephone conversations. Any businessman will be thankful for a

device that allows them to conduct business in an easy and effective manner.
Shopping for ones parents can also be a perplexing experience. People often rely on flowers for their mothers and ties for their dads. A person should instead use some ingenuity and purchase a

cell phone booster for their parents. Although this technology has been around for a number of years, it will seem revolutionary to most parents. Many of them will marvel at the fact that they can

talk in any part of the house. This is a great present for parents that love to talk and communicate over the phone.
So for the upcoming holiday season, look for something that every person will love. Since most people have mobile phones, a cell phone booster is the ideal gift. They are terrific for any age group

and any demographic. So pick up a booster and reward the ones you love.If you have trouble talking on your cell due to a weak signal on the road, at home, or in the office, then a cell phone signal

booster can improve your reception and call quality. Do you need a booster for your weak signal? Many people report poor cell signals when traveling to different areas. Cellular boosters help you

by improving call quality and reducing dropped calls while being very easy to install.

The Over-the-Top type of operational amplifier is ideal for use as a current sense for battery charger applications. The design described here can be used with chargers for rechargeable batteries (Lead/acid or NiCd etc). The 5V operating supply for the circuit is derived from the battery on charge. The circuit uses a sense resistor R8 to determine the value of current flowing in or out of the battery.

Battery Charging Indicator Circuit Diagram

An LED output shows whether the battery is charging or discharging and an analogue output displays the battery charge or discharge current. The circuit can also be altered to shown different ranges of charging current to cater for higher capacity cells. IC1a and IC1b together with T1 and T2 form two current sources, which produce a voltage across R5. The voltage across R5 is proportional to the current through resistors R8 and R1 (for IC1a) or R8-R3 (for IC1b).


The current source formed by IC1a and T1 is active when the batteries are discharging and IC1b and T2 is active when the batteries are being charged. In each case the inactive opamp will have 0V at its output and the corresponding transistor will be switched off. IC1d amplifies the voltage across R5, which is proportional to the sense current. The component values given in the diagram produce an amplification factor or 10.

A sense current of 0.1 A will produce an output voltage of +1 V. The supply voltage to the circuit is +5 V so this will be the maximum value that the output can achieve. This corresponds to a maximum charge/discharge current of 0.5 A To display currents from 0 to 5.0 A, resistor R7 can be omitted to give IC1d a voltage gain of 1. Higher currents can be displayed by using a lower value of sense resistor R8. A DVM or analogue meter can be used at Vout to give a display of the charge/discharge current.

The constant current sources can only function correctly when the supply to the voltage regulator circuit (UBatt. e.g. 6V or 12V) is greater than the operating voltage of the opamps (+5 V). The supply voltage to the LT1639 can be in the range of +3 V and +44V and voltages up to 40V over the supply voltage are acceptable at the inputs to the opamp. IC1c controls the charging/discharging LED output. The inputs to this opamp are connected to the outputs of the current source opamps and its output goes high when the battery is being charged and low when it is discharging.

This simple circuit allows a 12V battery pack to be charged via a bike generator. The generator is rated at 3W and with this voltage multiplier circuit provides about 200mA at about 15km/h. A 12V system was chosen because it allows the use of a car horn (get noticed)! Two 6V 3W globes in series provides adequate lighting and they last more than six months

A notch for a narrow frequency band of a few per cent or even less normally requires close-tolerance components. At least, that’s what we thought until we came across a special opamp IC from Maxim. In filters with steep slopes, the component tolerances will interact in the complex frequency response. This effect rules out the use of standard tolerance components if any useful result is to be achieved. The circuit shown here relocates the issue of the value-sensitive resistors that determine the filter response from ‘visible’ resistors to ready available integrated circuits which also make the PCB layout for the filter much simpler. The operational amplifiers we’ve in mind contain laser-trimmed resistors that maintain their nominal value within 1‰ or less. For the same accuracy, the effort that goes into matching individual precision resistors would be far more costly and time consuming. The desired notch (rejection) frequency is easily calculated for both R-C sections shown in Figure 1.


Dividing the workload:

The circuit separates the amplitude and frequency domains using two frequency-determining R-C networks and two level-determining feedback networks of summing amplifier IC2, which suppresses the frequency component to be eliminated from the input signal by simple phase shifting. IC1 contains two operational amplifiers complete with a feedback network. The MAX4075 is available in no fewer than 54 different gain specifications ranging from 0.25 V/V to 100 V/V, or +1.25 V/V to 101 V/V when non-inverting. The suffix AD indicates that we are employing the inverting version here (G = –1).

These ICs operate as all-pass filters producing a phase shift of exactly 180 degrees at the roll-off frequency f0. The integrated amplifier resistors can be trusted to introduce a gain variation of less than 0.1 %. They are responsible for the signal level (at the notch frequency) which is added to the input signal by IC2 by a summing operation. However, they do not affect the notch frequency proper — that is the domain of the two external R-C sections which, in turn, do not affect the degree of signal suppression. In general, SMDs (surface mount devices) have smaller production tolerance than their leaded counter-parts. Because the two ICs in this circuit are only available in an 8-pin SOIC enclosure anyway, it seems logical to employ SMDs in the rest of the circuit as well. Preset P1 allows the filter to be adjusted for maximum rejection of the unwanted frequency component.

R-C notch filter:

Using standard-tolerance resistors for R1 and R2 (i.e., 1%, 0806 style) and 10%-tolerance capacitors for C1 and C2 (X7R ceramic) an amount of rejection better than that shown in Figure 2 may be achieved. The notch frequency proper may be defined more accurately by the use of selected R-C sections. Pin 3 of IC2 receives a signal that’s been 90-degrees phase shifted twice at the notch frequency, while pin 1 is fed with the input signal. These two signals are added by way of the two on-chip resistors. IC2 is a differential precision operational amplifier containing precision resistor networks trimmed to an error not exceeding ±0.2‰. Here, it is configured as a modified summing amplifier with its inverting input, pin 2, left open.

For frequencies considerably lower than the resonance frequency f0 = 1 / (2 π R C) the capacitors present a high impedance, preventing the inverting voltage followers from phase-shifting the signal. At higher frequencies than f0, each inverting voltage follower shifts its input signal by 180 degrees, producing a total shift of 360 degrees which (electrically) equals 0 degrees. The phases of each all-pass filter behave like a simple R-C pole, hence shift the signal at the resonance frequency by 90 degrees each. The three precision amplifier ICs can handle signals up to 100 kHz at remarkably low distortion. The supply voltage may be anything between 2.7 V and 5.5V. Current consumption will be of the order of 250µA.

Output voltages are frequently 5V and below with 3.3V probably the most common requirement, and 2.5V gaining in popularity. If a processor is on the card, voltages as low as 1.3V are not unlikely. One common approach is to regulate a distributed power bus, say the 5V rail, and then use non-isolated DC/DC converters to generate lower voltages. With the tendency away from 5V, the 3.3V rail is beginning to serve as the distributed bus, although, from the power supply designer’s perspective, this is not the most of desirable situations.

Fairchild has recently introduced a family of high voltage MOSFETs ranging from 80- to 200-V drain voltage specifications. This application note will provide information helpful in the proper selection of FETs for primary side switches – available in various types of 48V power converters.

Most cars do not have delayed interior lights. The circuit presented can put this right. It switches the interior lights of a car on and off gradually. This makes it a lot easier, for instance, to find the ignition keyhole when the lights have gone off after the car door has been closed. Since the circuit must be operated by the door switch, a slight intervention in the wiring of this switch is unavoidable. When the car door is opened, the door switch closes the lights circuit to earth. When the door is closed (and the switch is open), transistor T1, whose base is linked to the switch, cuts off T2, so that the interior light remains off. When the switch closes (when the door is opened), the base of T1 is at earth level and the transistor is off.

Capacitor C1 is charged fairly rapidly via R3 and D1, whereupon T2 comes on so that the interior light is switched on. When the door is closed again, T1 conducts and stops the charging of C1. However, the capacitor is discharged fairly slowly via R5, so that T2 is not turned off immediately. This ensures that the interior light remains on for a little while and then goes out slowly. The time delays may be varied quite substantially by altering the values of R3, R5, and C1. Circuit IC2 may be one of many types of n-channel power MOSFET, but it should be able to handle drain-source voltages greater than 50 V. In the proto-type, a BUZ74 is used which can handle D-S voltages of up to 500 V.

A simple 9 Volt 2 amp supply using a single IC regulator.

The circuit will work without the extra components, but for reverse polarity protection a 1N5400 diode is provided at the input, extra smoothing being provided by C1. The output stage includes C2 for extra filtering, if powering a logic circuit than a 100nF capacitor is also desirable to remove any high frequency switching noise.

Circuit diagram:

 9 Volt 2 Amp PSU Circuit Diagram

Notes:

There is little to be said about this circuit. All the work is done by the regulator. The 78S09 can deliver up to 2 amps continuous output whilst maintaining a low noise and very well regulated supply.

Author : Andy Collinson Copyright : zen22142

Dynamic flip-flops ignore pulses at their inputs that are shorter than 40 ns or do not have TTL levels. This means that TTL flip-flops are poorly suited to capturing noise pulses having unknown durations and magnitudes. Anyone who has ever tried to observe very short laser pulses (15–25 ns) is familiar with this problem. By contrast, this circuit can detect impulses with widths less than 8 ns and amplitudes between +100 mV and +5 V. The heart of this circuit is formed by a MAX903, a very fast comparator with internal memory. The IC has separate supply pins for its analogue and digital portions. The analogue portion is powered by a symmetrical ±5-V supply.

This allows the detector to also handle input voltages that are negative relative to ground. The internal memory and output stage operate from a single-ended +5-V supply, so the output signal has proper TTL levels. The MAX903 (IC1) has a special internal memory circuit (latch). The latch either connects the output of the internal comparator directly to the signal output or stores the most recent TTL level and blocks the output of the internal comparator, causing the most recent TTL level appears at the output. This allows short input pulses to be stretched to any desired length. Despite its extremely short switching times, the MAX903 consumes only a modest 18 mW.

In the quiescent state, the voltage on the Latch input (pin 5) is at 1.75 V. This reference voltage is provided by LED D1, which draws its current via R2. In this state the latch is transparent, and a positive edge at the input appears will appear as a negative transition on the output after a propagation delay of 8 ns (tPD). This only happens if the peak voltage on the input is more positive than ground potential. C1 passes this change in the output voltage level to the Latch input (pin 5). As soon as the voltage on the Latch input drops below 1.4 V, the internal latch switches to the Hold state. In this state, the output is no longer connected to the comparator, and the output remains low for the duration of the latch hold time, regardless of what happens with the input signal.

The latch hold time is determined by the time constant of the C3/R1 network; it has an adjustment range of 100–500 ns. Pulses of this length can be readily observed using practically any oscilloscope. This latch function in this circuit is only triggered if the input signal has a rising edge that crosses the zero-voltage level. The internal latch remains transparent for signals in the range of –5 V to 0 V, so such pulses will not be stretched. If only positive input voltages are anticipated, the negative supply voltage is not necessary and the circuit can be powered from a single +5-V supply. A fast circuit such as this requires a carefully designed circuit board layout. All connections to the IC must be kept very short.

Decoupling capacitors C1 and C2 should preferably be placed immediately adjacent to the supply pins. Pin 3 of the IC can be bent upward and soldered directly to a length of coax or twisted-pair cable (air is still the best insulator). If a coax cable is used, the unbraided screen must not be formed into a long pigtail. It’s better to peel back a short length of the screen, wrap a length of bare wire around it and solder it directly to the ground plane. The supply traces for the analogue and digital portions must be well separated from each other, and each supply must be well decoupled, even if only a single supply voltage (+5 V) is used. The preferred solution is to use two independent voltage regulators.

Depending on local regulations and the telephone company you happen to be connected to, the voltage on a free telephone line can be anything between 42 and 60 volts. As it happens, that’s sufficient to make a diac conduct and act like a kind of zener diode maintaining a voltage of 38 V or so. The current required for this action causes the green high-efficiency LED in the circuit to light. Line voltages higher than about 50 V may require R1 to be changed from 10 kΩ to a slightly higher value. When the receiver is lifted, the line voltage drops to less than 15 V (typically 12 V) causing the diac to block and the LED to go out.

The circuit diagram indicates + and – with the phone lines. However, in a number of countries the line polarity is reversed when a call is established. To make sure the circuit can still function under these circumstances, a bridge rectifier may be added as indicated by the dashed outlines. The bridge will make the circuit independent of any polarity changes on the phone line and may consist of four discrete diodes, say, 1N4002’s or similar. Finally, note that this circuit is not BABT approved for connection to the public switched telephone network (PSTN) in the UK.

The preamplifier is intended for use with dynamic (moving coil–MC) microphones with an impedance up to 200 Ω and balanced terminals. It is a fairly simple design, which may also be considered as a single stage instrument amplifier based on a Type NE5534 op amp. To achieve maximum common-mode rejection (CMR) with a balanced signal, the division ratios of the dividers (R1-R4 and R2-R5 respectively) at the inputs of the op amp must be identical. Since this may be difficult to achieve in practice, a preset potentiometer, P1, is connected in series with R5. The preset enables the common-mode rejection to be set optimally. Capacitor C1 prevents any direct voltage at the input, while resistor R7 ensures stability of the amplifier with capacitive loads.

Circuit diagram:

 

Balanced Microphone Preamplifier Circuit Diagram

Power supply:

Power Supply For Balanced Microphone Preamplifier

Resistor R3 prevents the amplifier going into oscillation when the input is open circuit. If the microphone cable is of reasonable length, R3 is not necessary, since the parasitic capacitance of the cable ensures stability of the amplifier. It should be noted, however, that R3 improves the CMR from >70 dB to >80 dB. Performance of the preamplifier is very good. The THD+N (total harmonic distortion plus noise) is smaller than 0.1% with an input signal of 1 mV and a source impedance of 50 Ω. Under the same conditions, the signal-to-noise ratio is –62.5 dBA. With component values as specified, the gain of the amplifier is 50 dB (´316). After careful adjustment of P1 at 1 kHz, the CMR, without R3, is 120 dB. The supply voltage is ±15 V. The amplifier draws a current at that voltage of about 5.5 mA. Note the decoupling of the supply lines with L1, L2, C2–C5.

Author: T. Giesberts - Copyright: Elektor Electronics 1998

Turn ON or OFF electrical devices using remote control is not a new idea and you can find so many different devices doing that very well. For realization of this type of device, you must make a receiver, a transmitter and understand their way of communication. Here you will have a chance to make that device, but you will need to make only the receiver, because your transmitter will be the remote controller of your tv, or video …This is one simple example of this kind of device, and I will call it IR On-Off or IR-switch.

How it works:

Choose one key on your remote controller (from tv, video or similar), memorized it following a simple procedure and with that key you will able to turn ON or OFF any electrical device you wish. So, with every short press of that key, you change the state of relay in receiver (Ir-switch). Memorizing remote controller key is simple and you can do it following this procedure: press key on Ir-switch and led-diode will turn ON. Now you can release key on Ir-switch, and press key on your remote controller. If you do that, led-diode will blink, and your memorizing process is finished.

Instructions:

To make this device will be no problem even for beginners in electronic, because it is a simple device and uses only a few components. On schematic you can see that you need microcontroller PIC12F629, ir-receiver TSOP1738 (it can be any type of receiver TSOP or SFH) and for relay you can use any type of relay with 12V coil.

click on the images to enlarge

Click here to download source code for PIC12F629-675 . To extract the archive use this password extremecircuits.net

Here is a simple circuit that starts playing the car horn whenever your car is in reverse gear. The circuit (1) employs dual timer NE556 to generate the sound. One of the timers is wired as an astable multivibrator to generate the tone and the other is wired as a monostable multivibrator. Working of the circuit is simple. When the car is in reverse gear, reverse-gear switch S1 of the car gets shorted and the monostable timer triggers to give a high output. As a result, the junction of diodes D1 and D2 goes high for a few seconds depending on the time period developed through resistor R4 and capacitor C4.At this point, the astable multivibrator is enabled to start oscillating. The output of the astable multivibrator is fed to the speaker through capacitor C6.

Car reversing horn diagram:

Car Reversing Horn Circuit Diagram

The speaker, in turn, produces sound until the output of the monostable is high. When the junction of diodes D1 and D2 is low, the astable multivibrator is disabled to stop oscillating. The output of the astable multivibrator is fed to the speaker through capacitor C6. The speaker, in turn, does not produce sound. Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet.Connect the circuit to the car reverse switch through two wires such that S1 shorts when the car gear is reversed and is open otherwise. To power the circuit, use the car battery.

Flasher diagram:

Flasher Circuit Diagram

The flasher circuit (shown in Fig. 2) is built around timer NE555, which is wired as an astable multi-vibrator that outputs square wave at its pin 3. A 10W auto bulb is used for flasher. The flashing rate of the bulb is decided by preset VR1.
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. The flasher bulb can be mounted at the car’s rear side in a reflector or a narrow painted suitable enclosure. EFY note. A higher-wattage bulb may reduce the intensity of the head-light. You can enclose both the car-reversing horn and flasher circuits together or separately in a cabinet in your car.

Author: Ashok K. Doctor - Copyright: Electronics For You Magazine

This simple programmer will accept any device thats supported by software (eg, IC-Prog 1.05 by Bonny Gijzen at www.ic-prog.com). The circuit is based in part on the ISP header described in the SILICON CHIP "PIC Testbed" project but also features an external programming voltage supply for laptops and for other situations where the voltage present on the RS232 port is insufficient. This is done using 3-terminal regulators REG1 & REG2. The PIC to be programmed can be mounted on a protoboard. This makes complex socket wiring to support multiple devices unnecessary. 16F84A, 12C509, 16C765 and other devices have all been used successfully with this device.

Circuit diagram:

Simple Universal PIC Programmer Circuit Diagram

Author: Luke Weston - Copyright: Silicon Chip

Life in the 21st century would be almost unbearable without some of the computer peripherals that PC users now look on as essentials - take for example the USB powered teacup warmer; this device is obviously an invaluable productivity tool for all users but it could prove a little tire some if the extra current it draws from the USB port is sufficient to produce a localised meltdown on the motherboard. In a slightly more serious vein a similar situation could result from a carelessly wired connector in the design lab during prototyping and development of a USB ported peripheral. What’s needed here is some form of current limiting or fuse to prevent damage to the motherboard.

  

The MAX1562 shown in Figure 1 is a purpose-built USB current limiter from the chip manufacturers Maxim. The device operates with a supply voltage from 4.0 to 5.5 V with an operating current of typically 40 µA or 3 µA in standby mode. The circuit introduces a very low resistance in the power line (typically 26 m but guaranteed less than 50 m) from an internal MOSFET. The FET gate bias voltage is generated on-chip from a charge pump circuit.

The chip can distinguish between an overload and a short circuit condition in the supply line by measuring the voltage drop across its internal resistance; if the voltage is less than 1 V a short circuit is assumed and the chip pulses a (limited) output current every 20 ms in an effort to raise the output voltage. This approach will eventually be successful if the short circuit was caused by a large value capacitor across the USB supply pins or an external hard drive which have a high in-rush at start up. If the supply rail is not pulled up within the first 20 ms the FAULT output (pin 2) is driven low. The output current limit is set by a single resistor on pin 4 (ISET): LIM = 17120 / RSET.

The circuit diagram shows a fixed 5.6k resistor in series with a 10k preset giving an adjustable current limit between 1.097 and 3.057 A. This range should be sufficient for the majority of applications. Increasing the preset resistance reduces the current limit level. Any intermittent connection in the preset (caused by a dirty track etc.) will switch the chip into shut down. The MAX1562 also contains a thermal cut out which turns off the output when the chip temperature exceeds 160 degrees C.

Figure 2 shows a diagram of the manufacturer’s application circuit. The FAULT output drives an LED via a series limiting resistor which reduces the LED current to 2 to 3 mA. The MAX1562 is available in a HESA variant (with an active high ON signal) or ESA version (with an active low ON signal). The chip is packaged in an 8-pin SMD outline. Figure 3 shows a small PCB layout for the circuit using mostly SMD components.

COMPONENTS LIST

Resistors
R1 = 5k6 (SMD 1206)
R2 = 1k5 (SMD 1206)
P1 = 10k preset
Capacitors
C1 = 1µF (SMD 1206)
C2 = 4µF7 10 V, tantalum
C3 = 220nF (SMD 1206)
Semiconductors
D1 = LED, low current
IC1 = MAX1562ESA

Author: Andreas Köhler - Copyright: Elektor Electronics

You can take this white LED-based night lamp on your picnic outings. The lamp has sound trigger and push-to-on facilities and gives ample light during a walk at night. It will also prove useful in locating the door of your tent in the darkness. A click of the fingers will switch on the lamp for three minutes to help you in a strange place. The circuit uses low-power ICs to save the battery power. JFET op-amp TL071 (IC1) amplifies the sound picked up by the condenser microphone. Resistor R1 and low-value capacitor C1 (0.22µF) make the amplifier insensitive to very low-frequency sounds, eliminating the chance of false triggering. VR1 is used to adjust the sensitivity of the microphone and VR2 adjusts the gain of IC1. The amplified output from IC1 is coupled to trigger pin 2 of IC2, which is a monostable multivibrator built around low-power CMOS timer IC 7555.

Resistor R4 keeps trigger input pin 2 of the monostable normally high in the absence of the trigger input. Timing elements R6 and C4 give a time delay of three minutes. Reset pin 4 of IC2 is connected to the positive rail through R5 and to the negative rail through C2 to provide power-on-reset function. The output of IC2 powers the white LED (LED1) through ballast resistor R7. The circuit can be easily assembled on a perforated board. Make the circuit assembly as compact as possible to enclose in a small case. Use three 1.5V pen-light cells to power the circuit. Adjust VR1 and VR2 suitably to get sufficient sensitivity of IC1. Toggle switch S1 can be used to switch on the lamp like a torch.

This simple circuit proves to achieve surprisingly good results when used with the IR–S/PDIF transmitter described elsewhere in this site. The IR receiver consists of nothing more than a photodiode, a FET and three inverter gates used as amplifier. The FET is used as an input amplifier and filter, due to its low parasitic capacitance. This allows R1 to have a relatively high resistance, which increases the sensitivity of the receiver. The bandwidth is primarily determined by photo-diode D1, and with a value of 2k2 for R1, it is always greater than 20 MHz. The operating current of the FET is intentionally set rather high (around 10 mA) using R2, which also serves to ensure adequate bandwidth. The voltage across R2 is approximately 0.28–0.29 V.

The combination of L1 and R3 forms a high-pass filter that allows signals above 1 MHz to pass. L1 is a standard noise-suppression choke. From this filter, the signal is fed to two inverters configured as amplifiers. The third and final inverter (IC1c) generates a logic-level signal. This 74HCU04 provides so much gain that there is a large risk of oscillation, particularly when the final stage is loaded with a 75-Ω coaxial cable. In case of problems (which will depend heavily on the construction), it may be beneficial to add a separate, decoupled buffer stage for the output, which will also allow the proper output impedance (75 Ω) to be maintained in order to prevent any reflections.

When building the circuit, make sure that the currents from IC1 do not flow through the ground path for T1. If necessary, use two separate ground planes and local decoupling. Furthermore, the circuit must be regarded as a high-frequency design, so it’s a good idea to provide the best possible screening between the input and the output. With the component values shown in the schematic, the range is around 1.2 metres without anything extra, which is not especially large. However, the range can easily be extended by using a small positive lens (as is commonly done with standard IRDA modules). In our experiments, we used an inexpensive magnifying glass, and once we got the photodiode positioned at the focus after a bit of adjustment.

We were able to achieve a range of 9metres using the same transmitter (with a sampling frequency of 44.1 kHz). This does require the transmitter and receiver to be physically well aligned to each other. As you can see, a bit of experimenting certainly pays off here! It may also be possible to try other types of photo-diode. The HDSL-5420 indicated in the schematic has a dome lens, but there is a similar model with a flat-top case (HDSL-5400). It has an acceptance angle of 110°, and with the same level of illumination, it generates nearly four times as much current.

The current consumption of the circuit is 43 mA with no signal and approximately 26 mA with a signal (fs = 44.1 kHz) That is rather high for battery operation, but it can handled quite readily using a pair of rechargeable NiMH cells. Incidentally, the circuit will also work at 4.5 V and even 3 V. If a logic-level output is needed, C3 at the output can be replaced by a jumper. Finally, there is one other thing worth mentioning. With the HSDL-5400 that we had to play with, the cathode marking (a dark-blue line on the side below one lead) was on the wrong side (!). So if you want to be sure that the diode is fitted properly, it’s a good idea to measure the DC voltage across R1, which should be practically zero.

Operating a stepper motor using a fixed (constant) voltage supply results in poor torque at high speeds. In fact, stepper motors tend to stall at fairly low speeds under such conditions. Several approaches can be used to overcome this problem, one of which is to use a constant current supply in place of the more conventional constant voltage supply. A disadvantage of many constant current supplies is that simple circuits are inefficient but that doesnt apply to switchmode supplies such as the circuit shown here.

Basically, this circuit is a conventional switchmode regulator adapted for constant current output and is specially designed for stepper motor drivers - although it could be used for other applications as well. The circuit works as follows: IC1 (LM2575T) and its associated components (D1, L1, C1, etc) operate as a switchmode power supply. Normally, for constant voltage operation, the output is connected - either directly or via a resistive divider - back to the feedback input (pin 4) of IC1.


In this circuit, however, Q1 senses the current flowing through R1 and produces a corresponding voltage across R3. This voltage is then fed to pin 4 of IC1. As a result, the the circuit regulates the current into a load rather than the voltage across the load. Only one adjustment is needed: you have to adjust VR1 for optimum stepper motor performance over the desired speed range. The simplest way to do this is to measure the motor current at its rated voltage at zero stepping speed and then adjust VR1 for this current. The prototype worked well with a stepper motor rated at 80O per winding and a 12V nominal input voltage. Some components might have to be modified for motors having different characteristics.

This circuit was designed to produce an audible alarm when the mains power is interrupted. Such an alarm is essential for anyone whose livelihood depends on keeping perishable foodstuffs in cold storage. The circuit is powered by a 12-V mains adapter. LED D5 will light when the mains voltage is present. When the mains voltage disappears, so does the +12 V supply voltage, leaving the voltage regulator IC1 and relay driver T1-T2 without power. The relay driver, by the way, is an energy-saving type, reducing the coil current to about 50% after a few seconds. Its operation and circuit dimensioning are discussed in the article ‘Relay Coil Energy Saver’. The value of the capacitor at the output of voltage regulator IC1 clearly points to a different use than the usual noise suppression.


When the mains power disappears, Re1 is de-energized and the 0.22 F Gold-cap used in position C4 provides supply current to IC2. When the mains voltage is present, C4 is charged up to about 5.5 volts with IC1 acting as a 100-mA current limit and D10 preventing current flowing back into the regulator output when the mains voltage is gone. According to the Goldcap manufacturer, current limiting is not necessary during charging but it is included here for the security’s sake. The CMOS 555 is configured in astable multivibrator mode here to save power, and so enable the audible alarm to sound as long as possible. Resistors R5 and R6 define a short ‘on’ time of just 10 ms. That is, however, sufficient to get a loud warning from the active buzzer. In case the pulses are too short, increase the value of R5 (at the expense of a higher average current drawn from the Goldcap).

This circuit uses a complementary pair comprising NPN metallic transistor T1 (BC109) and pnp germanium transistor T2 (AC188) to detect heat (due to outbreak of fire, etc) in the vicinity and energise a siren. The collector of transistor T1 is connected to the base of transistor T2, while the collector of transistor T2 is connected to relay RL1.

The second part of the circuit comprises popular IC UM3561 (a siren and machine-gun sound generator IC), which can produce the sound of a fire-brigade siren. Pin numbers 5 and 6 of the IC are connected to the +3V supply when the relay is in energised state, whereas pin 2 is grounded. A resistor (R2) connected across pins 7 and 8 is used to fix the frequency of the inbuilt oscillator.

Circuit Diagram

Automatic Heat Detector Circuit Diagram

 

The output is available from pin 3. Two transistors BC147 (T3) and BEL187 (T4) are connected in Darlington configuration to amplify the sound from UM3561. Resistor R4 in series with a 3V zener is used to provide the 3V supply to UM3561 when the relay is in energised state. LED1, connected in series with 68-ohm resistor R1 across resistor R4, glows when the siren is on. To test the working of the circuit, bring a burning matchstick close to transistor T1 (BC109), which causes the resistance of its emitter-collector junction to go low due to a rise in temperature and it starts conducting. Simultaneously, transistor T2 also conducts because its base is connected to the collector of transistor T1. As a result, relay RL1 energizes and switches on the siren circuit to produce loud sound of a fire-brigade siren.

Note.

• We have added a table to enable readers to obtain all possible sound effects by returning pins 1 and 2 as suggested in the table.

 Author:Sukant Kumar Behara Copyright:Circuit Ideas

This circuit will illuminate a LED if one of your telephones is in use. It should work in all countries (Including UK) that have a standing line voltage above 48 Volts DC. Please note that it is illegal to make a physical permanent connection to your telephone line in some countries (this includes the UK and Ireland). If building this circuit it is advisable to use a plugin cord so that the unit can be unplugged should a fault occur. If in doubt consult either your telephone or cable operator.

If all extension phones are on-hook and the line voltage is around 48 V, Q1 will conduct thus effectively shorting the gate of Q2 to its source, so it will be off and the LED will be disabled. Lifting the handset of any phone on the line causes the line voltage to drop to 5-15 V. The gate voltage of Q1, equal to some 6% of the line voltage, will then be too low and Q1 will be turned off. So Q2s gate is now biased at approximately 1/2 of the line voltage, Q2 turns on and the LED indicates that the line is in use. The circuit itself is practically invisible to the other telephone devices using the same line. LED1 must be low-current and its current-limiting resistor must be 2k2 or more.

The other components ideal values may vary slightly, depending on the local telephone line parameters. The circuit is powered off the telephone line. If other types of MOSFETs are used, the 500k trimmer can be adjusted to ensure that Q1 is biased fully on while the line is not in use (LED1 off), and vice versa. If Q2 is not a BS108 but some other 200 V MOSFET with a higher G-S threshold voltage, it might be necessary to increase the value of the lower (or decrease the value of the upper) one of the two resistors connected to the gate of Q2. Plain (bipolar junction) transistors can be used instead and the circuit also works fine.

But the resistor values are then much lower - letting ten times more microamps of current pass through while the line is not in use, and even this MOSFET design still could not meet formal minimum on-hook DC resistance specifications. Both prototypes PCBs were 4x1 cm. The current-limiting resistor for LED1 is 2k2 in both cases. DO NOT ground any of the leads or conducting surfaces in this circuit. A more reliable design would also include some kind of over-voltage protection etc.

Warning:

In their normal course of operation, telephone lines can deliver life-threatening voltages! Do not attempt to build any of the circuits/projects unless you have the expertise, skill and concentration that will help you avoid an injury. There are also legal aspects and consequences of connecting things to telephone lines, which vary from country to country. Keep away from telephone lines during a lightning storm!