NiCad Battery Charger.

Download this schematic diagram.


Download datasheet semiconductor component. (PDF Format)

1. IN4004
2. LM4040
3. 2N3906
4. IRF9530

This array charger ambit is advised for recharging NiCad batteries based on an AC-powered accepted antecedent method. It can crank out as abundant as 1 amp and can be adapted to go alike college by allotment altered accessories for Q1. Since this ambit uses AC band voltages and currents, amuse exercise acute attention during assembly, turn-on, and test. NiCAD batteries accept a accommodation blueprint alleged milliamp-hours. This amount alleged “C” is a admeasurement of how abundant absolute accepted they can accommodate in one hour. Milliamp-hours is addition way to accurate the activity independent in the battery. To recharge a NiCAD array conservatively, it is accepted convenance to pump a accepted of 0.1 C into the anode or absolute terminal for about 12 hours. Therefore, if you had a D-size NiCAD with a accommodation of 4000mAh, you would appetite to allegation it at 400mA for about 12 hours. Addition advantage of this charging address is that it is affable on batteries and doesn’t account them to lose accommodation as bound as the fast allegation techniques.

The achievement accepted of this array charger ambit is controlled by the accretion of the bandgap advertence diode and the base-emitter alliance of the PNP transistor. The PNP transistor provides abrogating acknowledgment to the aboideau of the MOSFET. As acclaimed in the schematic, the batteries actuality answerable can accept a absolute of 12V which is agnate to about 8 NiCAD’s in series. The achievement accepted is bent by the amount of R1 which is bent by:

R1=3.2Volts/Iout

The ability amusement of R1 will equal:

Pr1=3.2Volts*Iout

Be abiding to accommodate pleanty of heatsink for Q1 and accept an appropriately sized resistor for R1. The afterward table summarizes some of the resistor accepted combinations that are possible:

Iout Resistor Amount Resistor Power

100mA 33 ohms 1 watt

500mA 6.2 ohms 2 watt

1Amp 3.3 ohms 5 watt

High Quality Intercom

click here for download this schematic diagarm


This circuit consists of two identical intercom units. Each unit contains a power supply, microphone preamplifier, audio amplifier and a Push To Talk (PTT) relay circuit. Only 2 wires are required to connect the units together. Due to the low output impedance of the mic preamp, screened cable is not necessary and ordinary 2 core speaker cable, or bell wire may be used.

The schematic can be broken into 34 parts, power supply, mic preamp, audio amplifierand PTT circuit. The power supply is designed to be left on all the time, which is why no on / off switch is provided. A standard 12 V RMS secondary transformer of 12VA will power the unit. Fuses are provided at the primary input and also secondary, before the rectifier. The 1 A fuse needs to be a slow blow type as it has to handle the peak rectifier current as the power supply electrolytics charge from zero volts.

The microphone amplifier is a 2 transistor direct coupled amplifier. BC108B transistors will work equally well in place of the BC109C transistors. The microphone used is a 3 terminal electret condenser microphone insert. These are popular and require a small current to operate. The preamp is shown in my audio circuit section as well, but has a very high gain and low distortion. The last transistor is biased to around half the supply voltage; this provides the maximum overload margin for loud signals or loud voices. The gain may be adjusted with the 10k preset. Sensitivity is very high, and a ticking clock can easily be heard from the distant loudspeaker.

The amplifier is based on the popular National Semiconductor LM380. A 50 mV input is all thats required to deliver 2W RMS into an 8 ohm loudspeaker. The choice of loudspeaker determines overall sound quality. A small loudspeaker may not produce a lot of bass, I used an old 8 inch radio loudspeaker. The 4.7u capacitor at pin 1 of the LM380 helps filter out any mains hum on the power supply. This can be increased to a 10u capacitor for better power supply rejection ratio.

The push to talk (PTT) circuit is very simple. A SPDT relay is used to switch between mic preamplifier output or loudspeaker input. The normally closed contact is set so that each intercom unit is "listening". The non latching push button switch must be held to talk. The 100u capacitor across the relay has two functions. It prevents the relays back emf from destroying the semiconductors, and also delays the release of the relay. This delay is deliberate, and prevents any last word from being "chopped" off.

Download datasheet semiconductor component. (PDF Format)

1. BC.109C
2. LM.380
3. IN.4001