Sunday, December 22, 2013
Balancing LiPo Cells
Things change fast in the electronics world, and that’s also true for recharge- able batteries. The rate of development of new types of rechargeable batteries has been accelerated by the steadily increasing miniaturisation of electronic equipment. LiPo cells have conquered the market in a relatively short time. Their price and availability have now reached a level that makes them attractive for use in DIY circuits.
Balancing LiPo Cells Circuit diagram:
Unlike its competitors Elektor Electronics has already published several articles about the advantages and disadvantages of LiPo batteries. One of the somewhat less well-known properties of this type of rechargeable battery is that the cells must be regularly ‘balanced’ if they are connected in series. This is because no two cells are exactly the same, and they may not all have the same temperature. For instance, consider a battery consisting of a block of three cells. In this case the outer cells will cool faster than the cell in the middle. Over the long term, the net result is that the cells will have different charge states. It is thus certainly possible for an individual cell to be excessively discharged even when the total voltage gives the impression that the battery is not fully discharged. That requires action – if only to prolong the useful life of the battery, since LiPo batteries are still not all that inexpensive.
One way to ensure that all of the cells have approximately the same charge state is limit the voltage of each cell to 4.1 V during charging. Most chargers switch over to a constant voltage when the voltage across the batter terminals is 4.2 V per cell. If we instead ensure that the maximum voltage of each cell is 4.1 V, the charger can always operate in constant-current mode.
When the voltage of a particular cell reaches 4.1 V, that cell can be discharged until its voltage is a bit less than 4.1 V. After a short while, all of the cells will have a voltage of 4.1 V, with each cell thus having approximately the same amount of charge. That means that the battery pack has been rebalanced.
The circuit (Figure 1) uses an IC that is actually designed for monitoring the supply voltage of a microcontroller circuit. The IC (IC1) normally ensures that the microcontroller receives an active-high reset signal whenever the supply voltage drops below 4.1 V. By contrast, the out-put goes low when the voltage is 4.1 V or higher. In this circuit the output is used to discharge a LiPo cell as soon as the voltage rises above 4.1 V.
When that happens, the push-pull output of IC1 goes low, which in turn causes transistor T1 to con-duct. A current of approximately 1 A then flows via resistor R1. LED D2 will also shine as a sign that the cell has reached a voltage of 4.1 V. The function of IC2 requires a bit of explanation. The circuit built around the four NAND gates extends the ‘low’ interval of the signal generated by IC1. That acts as a sort of hysteresis, in order to prevent IC1 from immediately switching off again when the voltage drops due the internal resistance of the cell and the resistance of the wiring between the cell and the circuit. The circuitry around IC2 extends the duration of the discharge pulse to at least 1 s.
Figure 2 shows how several circuits of this type can be connected to a LiPo battery. Such batteries usually have a connector for a balancing device. If a suit-able connector is not available, you will have to open the battery pack and make your own connections for it. The figure also clearly shows that a separate circuit is necessary for each cell.
Author :Paul Goossens - Copyright : Elektor
Source: http://www.ecircuitslab.com/2012/05/balancing-lipo-cells.html
Saturday, December 21, 2013
This is why it is a good idea to get a universal gift
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.
Read More..
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.
Friday, December 20, 2013
Build a Bridge Circuit Diagram With One Power Supply
This is simple Bridge Circuit Diagram With One Power Supply. For systems with only one power supply, two op amps act as instrumentation and buffer amps. The OPA111 AM buffers the reference mode of the bridge and applies that voltage to the instrumentation amps ref terminal. Output is taken between the amplifier outputs to exclude the fixed output offset.
The additional op amp creates a bridge error of 2, where IB=bias current of op amp and R is the resistance of one leg of the bridge.
Bridge Circuit Diagram With One Power Supply
Thursday, December 19, 2013
Battery Charging Indicator
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.
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.
Read More..
 |
| 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.
Wednesday, December 18, 2013
Simple Knight Rider lights Circuit for model cars
This simple circuit drives 6 LEDs in Knight Rider scanner mode. Power consumption depends mainly on the type of LEDs used if you use a 7555 (555 CMOS version).
Simple Knight Rider lights Circuit
Note
That VDD and GND for the ICs are not shown in the circuit drawing.
Simple Knight Rider lights Circuit
Note
That VDD and GND for the ICs are not shown in the circuit drawing.
| Pin-outs: | |||||
| (7)555 | 4017 | ||||
| 1 | GND | 1 | Q5 | 9 | Q8 |
| 2 | TRIGGER | 2 | Q1 | 10 | Q4 |
| 3 | OUTPUT | 3 | Q0 | 11 | Q9 |
| 4 | RESET | 4 | Q2 | 12 | CO |
| 5 | CONTROL VOLTAGE | 5 | Q6 | 13 | NOT ENABLE |
| 6 | THRESHOLD | 6 | Q7 | 14 | CLK |
| 7 | DISCHARGE | 7 | Q3 | 15 | RESET |
| 8 | VDD | 8 | GND | 16 | VDD |
Telephone In Use Indicator
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!
Tuesday, December 17, 2013
Automatic TV Lighting Switch
The author is the happy owner of a television set with built-in Ambilight lighting in the living room. Unfortunately, the television set in the bedroom lacks this feature. To make up for this, the author attached a small lamp to the wall to provide background lighting, This makes watching television a good deal more enjoyable, but it ’s not the ideal solution. Although the TV set can be switched off with the remote control, you still have to get out of bed to switch off the lamp.
Automatic TV Lighting Switch Circuit diagram:
Consequently, the author devised this automatic lighting switch that switches the background light on and off along with the T V set. The entire circuit is fitted in series with the mains cable of the TV set, so there’s no need to tinker with the set. It works as follows: R1 senses the current drawn by the TV set. It has a maximum value of 50 mA in standby mode, rising to around 500 m A when the set is operating. The voltage across R1 is limited by D5 during negative half- cycles and by D1– D4 during positive half-cycles. T he voltage across these four diodes charges capacitor C1 via D6 during positive half-cycles. This voltage drives the internal LED of solid-state switch TRI1 via R2, which causes the internal triac to conduct and pass the mains voltage to the lamp. Diode D7 is not absolutely necessary, but it is recommended because the LED in the solid-state switch is not especially robust and cannot handle reverse polarisation. Fuse F1 protects the solid-state switch against overloads. T he value of use d here (10 Ω) for resistor R1 works nicely with an 82-cm (32 inch) LCD screen.
With smaller sets having lower power consumption, the value of R1 can be increased to 22 or 33 Ω, in which case you should use a 3-watt type. Avoid using an excessively high resistance, as otherwise TRI1 will switch on when the TV set is in standby mode. Some TV sets have a half-wave rectifier in the power supply, which places an unbalanced load on the AC power outlet. If the set only draws current on negative half-cycles, the cir-cuit won’t work properly. In countries with reversible AC power plugs you can correct the problem by simply reversing the plug. Compared with normal triacs, optically cou-pled solid-state relays have poor resistance to high switch-on currents (inrush currents).
For this reason, you should be careful with older-model TV sets with picture tubes (due to demagnetisation circuits). If the relay fails, it usually fails shorted, with the result that the TV background light remains on all the time. If you build this circuit on a piece of perf-board, you must remove all the copper next to conductors and components carrying mains voltage. Use PCB terminal blocks with a spacing of 7.5 mm. This way the separation between the connections on the solder side will also be 3 mm. If you fit the entire arrangement as a Class II device, all parts of the circuit at mains potential must have a separation of at least 6 mm from any metal enclosure or electrically conductive exterior parts that can be touched.
Author :Piet Germing - Copyright : Elektor
Source : http://www.ecircuitslab.com/2012/03/automatic-tv-lighting-switch.html
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