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Friday, October 8, 2010

Mobile Cellphone Battery Charger Circuit Using 555

This diagram is a series of circuits Mobile Cellphone Battery Charger. Stops charging when battery is full charged, Portable unit Charging of the mobile phone, cellphone battery is a big problem while traveling as power supply source is not generally accessible. If you keep your cellphone switched on continuously, its battery will go flat within five to six hours, making the cellphone useless. A fully charged battery becomes necessary especially when your distance from the nearest relay station increases. Here’s a simple charger that replenishes the cellphone battery within two to three hours. Basically, the charger is a current-limited voltage source. Generally, cellphone battery packs require 3.6-6V DC and 180-200mA current for charging. These usually contain three NiCd cells, each having 1.2V rating. Current of 100mA is sufficient for charging the cellphone battery at a slow rate. A 12V battery containing eight pen cells gives sufficient current (1.8A) to charge the battery connected across the output terminals. The circuit also monitors the voltage level of the battery. It automatically cuts off the charging process when its output terminal voltage increases above the predetermined voltage level.
Part :
P1 = 20K
P2 = 20K
R1 = 390R
R2 = 680R
R3 = 39R-1W
R4 = 27K
R5 = 47K
R6 = 3.3K
R7 = 100R-1W
C1 = 4.7uF-25V
C2 = 0.01uF
C3 = 0.001uF
D1 = 5.6V-1W Zener
D2 = 3mm. Red LED
Q1  =  SL100
S1 = On/Off Switch
B1 = 1.5vx8 AA Cells in Series
IC1 = NE555 Timer IC
Timer IC NE555 is used to charge and monitor the voltage level in the battery. Control voltage pin 5 of IC1 is provided with a reference voltage of 5.6V by zener diode D1. Threshold pin 6 is supplied with a voltage set by P1 and trigger pin 2 is supplied with a voltage set by P2. When the discharged cellphone battery is connected to the circuit, the voltage given to trigger pin 2 of IC1 is below 1/3Vcc and hence the flip-flop in the IC is switched on to take output pin 3 high. When the battery is fully charged, the output terminal voltage increases the voltage at pin 2 of IC1 above the trigger point threshold.
LED Status
This switches off the flip-flop and the output goes low to terminate the charging process. Threshold pin 6 of IC1 is referenced at 2/3Vcc set by P1. Transistor Q1 is used to enhance the charging current. Value of R3 is critical in providing the required current for charging. With the given value of 39-ohm the charging current is around 180 mA. The circuit can be constructed on a small general-purpose PCB. For calibration of cut-off voltage level, use a variable DC power source. Connect the output terminals of the circuit to the variable power supply set at 7V. Adjust P1 in the middle position and slowly adjust P2 until LED (D2) goes off, indicating low output. LED should turn on when the voltage of the variable power supply reduces below 5V. Enclose the circuit in a small plastic case and use suitable connector for connecting to the cellphone battery.
Source :

Simple AM Radio Circuit using Transistor

This is a circuit diagram AM transmitter, where the AM transmitter using ceramic resonator / filter of 3.587 MHz is presented here. This circuit is based on the core to the operation of the transistor circuits. Resonators / filters such as the frequency of 5.5 MHz, 7 MHz and 10.7 MHz may also be used.

Using a different frequency filters / resonators will involve corresponding variation in the value of inductor used in the oscillator tank circuit is connected to the collector of transistor T1. AF input for modulation is inserted in series with the emitter of transistor T1 (and resistor R4) using a transistor radio type audio transformer such as a driver on the circuit. In the picture above the modulated RF output is developed across the tank circuit which can be tuned to the resonance frequency of the filter / resonator with the help of gang condenser C7. Next two stages formed with low-noise RF transistors BF495 is, in fact, connected in parallel for amplification of modulated signal coupled from collector of transistor T1 to the base of the transistors T2 and T3. Combined output from the collector of T2 and T3 is to the antenna feed through 100pF capacitor C4. Circuits that can be easily collected in the general-purpose PCB. Range from transmitter is expected to be one to two kilometers. Circuits that require regulated 9 volt power supply for operation.

2 Cell Lithium Ion Charger Using 555

This circuit is a circuit diagram was build to charge a couple series Lithium cells (3.6 volts each, 1 Amp Hour capacity) installed in a portable transistor radio. The charger operates by supplying a short current pulse through a series resistor and then monitoring the battery voltage to determine if another pulse is required. The current can be adjusted by changing the series resistor or adjusting the input voltage. When the battery is low, the current pulses are spaced close together so that a somewhat constant current is present. As the batteries reach full charge, the pulses are spaced farther apart and the full charge condition is indicated by the LED blinking at a slower rate.   A TL431, band gap voltage reference (2.5 volts) is used on pin 6 of the comparator so that the comparator output will switch low, triggering the 555 timer when the voltage at pin 7 is less than 2.5 volts. The 555 output turns on the 2 transistors and the batteries charge for about 30 milliseconds. When the charge pulse ends, the battery voltage is measured and divided down by the combination 20K, 8.2K and 620 ohm resistors so that when the battery voltage reaches 8.2 volts, the input at pin 7 of the comparator will rise slightly above 2.5 volts and the circuit will stop charging. The following is a schematic drawing:
The circuit could be used to charge other types of batteries such as Ni-Cad, NiMh or lead acid, but the shutoff voltage will need to be adjusted by changing the 8.2K and 620 ohm resistors so that the input to the comparator remains at 2.5 volts when the terminal battery voltage is reached. For example, to charge a 6 volt lead acid battery to a limit of 7 volts, the current through the 20K resistor will be (7-2.5)/ 20K = 225 microamps. This means the combination of the other 2 resistors (8.2K and 620) must be R=E/I = 2.5/ 225 uA = 11,111 ohms. But this is not a standard value, so you could use a 10K in series with a 1.1K, or some other values that total 11.11K Be careful not to overcharge the batteries. I would recommend using a large capacitor in place of the battery to test the circuit and verify it shuts off at the correct voltage.

Low Noise Balance Microphone Pre-Amp using a TL071

Simple circuit diagram which is very low noise. In the circuit diagram in the design of circuits that consist of a combination of differential pairs of transistors with a common mode (floating) gain control connecting the emitters of the pair. The plural pairs of 2N4403 and BC549s far longer than one transistor. In the different circuits in and outside and therefore requires a balanced to unbalanced buffer to give the appropriate output for the next stage in the signal from the channel mixing desk. This is provided by high-performance op-amp differential gain stage, which can be a TL071 or similar IC of your choice. Stage has a profit of six or 15 dB and maximum input level is set about 1.5 volts RMS before clipping. This is the same with an SPL of 150dB typical over the microphone.Operation on the input stage circuit is configured to at least the noise and this is not to approach IC. There are some special ICS that can be used for microphone pre-amps, they include circuits such as this, except on one chip fabricated. All components must be available except for 10 k ohm pot to get control. This need to be a reverse log taper – or if not using the multi-position switch with 6 dB gain steps to cover 60 dB range of circuits. Make sure before making a break already. The + / -15 Volt power supply is too important, should be regulated and low noise. If the voltage regulator usually used ICS I recommend fitting a post filter consists of a 10 ohm resistor and capacitor 470 UF to remove all noise generated in the ICS. A 100nF capacitor (C6) should be installed as close as possible to the op-amp supply pins – a ceramic cap is recommended to cut the best performance on high frequency.
the source of Phil Allison

AC Power Supply Low Voltage

Here’s AC power supply circuit with low voltage output (step down transformer converter). Warning! This project involves the use of dangerous voltages. You must make sure all high-voltage (120 volt household power) conductors are safely insulated from accidental contact. No bare wires should be seen anywhere on the “primary” side of the transformer circuit. Be sure to solder all wire connections so that they’re secure, and use real electrical tape (not duct tape, scotch tape, packing tape, or any other kind!) to insulate your soldered connections. If you wish to enclose the transformer inside of a box, you may use an electrical “junction” box, obtained from a hardware store or electrical supply house. If the enclosure used is metal rather than plastic, a three-prong plug should be used, with the “ground” prong (the longest one on the plug) connected directly to the metal case for maximum safety.

Before plugging the plug into a wall socket, do a safety check with an ohmmeter. With the line switch in the “on” position, measure resistance between either plug prong and the transformer case. There should be infinite (maximum) resistance. If the meter registers continuity (some resistance value less than infinity), then you have a “short” between one of the power conductors and the case, which is dangerous!
Next, check the transformer windings themselves for continuity. With the line switch in the “on” position, there should be a small amount of resistance between the two plug prongs. When the switch is turned “off,” the resistance indication should increase to infinity (open circuit — no continuity). Measure resistance between pairs of wires on the secondary side. These secondary windings should register much lower resistances than the primary. Why is this?
Plug the cord into a wall socket and turn the switch on. You should be able to measure AC voltage at the secondary side of the transformer, between pairs of terminals. Between two of these terminals, you should measure about 12 volts. Between either of these two terminals and the third terminal, you should measure half that. This third wire is the “center-tap” wire of the secondary winding.

Differential Analog Circuit Switch

This circuit is a differential analog circuit switches. The FM1208 monolithic dual differential multiplexer used in applications where the RDS (ON) must be the same match. Since RDS (ON) for monolithic dual tracks at better than 1% of the broad temperature range (-25 to 125 C) is making an unusual choice, but ideal for a multiplexer accurate. This greatly reduces the close tracking errors due to common mode signals. OP-Amp used are LM107. Here is a schematic drawing:

Electronic Shutdown Circuit

Electronic Shutdown Circuit
September 29th, 2010 | Author: admin
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Electronic shutdown circuit uses a practical method of shutting down the LM340 under the control of a TTL or DTL logic gate. The pass transistor Q1 operates either as a saturated transistor or as an open switch. With the logic input high (2.4V specified minimum for TTL logic) transistor Q2 turns on and pulls 50 mA down through R2. This provides sufficient base drive to maintain Q1 in saturation during the ON condition of the switch. When the logic input is low (0.4V specified maximum for TTL logic) Q2 is held off, as is Q1; and the switch is in the OFF condition. The observed turn-on time was 7.0 µs for resistive loads from 15O to infinity and the turn-off time varied from approximately 3.0 µs for a 15O load to 3.0 ms for a no-load condition. Turn-off time is controlled primarily by the time constant of RLOAD and C1.
*Required if the regulator is located far from the power supply filter
**Head sink Q1 and the LM340

FM Tracking Transmitter Using a 555 Timer

Circuit diagram is designed for tracking transmitter audio tone in FM frequency band. Circuits that can be used the signal transmitter or remote control transmitter. In circuits that use only components that are available. Transmitter’s range is 100 m in the distance using the 9V power supply and matching the antenna. 

Circuit diagram is built by IC timer 555 to produce audio and tone based on the JFET in the circuit as the core. JFET circuit operation is the first (Q1) is the cable as a Hartley oscillator frequency modulated by the audio tone. The second (Q2) JFET is wired as a buffer to isolate the oscillator from the antenna based on the Q1. Diode D1 is used as varactor here.
The diode is reverse bias voltage generated by slim on pin 2 & 6 of IC1 results. This change in capacitance of the junction diode reverse bias, which in turn change the frequency of the oscillator to achieve frequency modulation.   For inductor L1 can be made by winding 5 turns of 18 SWG enameled copper wire on 3 / 8 inches long, 3 / 16 inch diameter plastic tube. The coil must be tapped in the center. The antenna can be a 20cm long wire.