Clock Controlled Relay Driver. Design Trick 14



Don’t miss your favorite TV programme or don’t forget to irrigate garden. This clock controlled circuit will actuate a relay to switch on the AC load to perform the function at the right time. Operation of the circuit is simple. It receives the triggering pulse from the buzzer terminals of the clock and an SCR triggers to activate the relay. The only drawback of the circuit is that, it is necessary to switch off the load manually by turning off the power. You can do experimentation to make an automatic operation also.

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Simple Solar Charger. Design Trick 13


You can use this Solar charger to charge 12 volt Lead Acid or Tubular battery. It is voltage controlled and charge the battery when the output from Solar panel exceeds 15 volts in bright sunlight. The open circuit voltage of a 12 volt solar panel is around 20 volts in full light and the 12 volt battery requires around 14-15 volts for charging. The circuit also prevents the discharge of battery into the solar panel when the sunlight is low.
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Tuning free AM Receiver. Design Trick 12


You can hear a local AM station clearly with this IC radio. It is tuning free so only the strongest nearby station will be available. Only a few components are necessary to build this Matchbox size radio and can be assembled quickly on a common PCB. No coil, No Gang, No professional touch. But still it is a Radio. See the trick to use the Gain pins of an amplifier IC as Signal receiver.
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Live Wire Scanner. Design Trick 11



Try this single IC circuit for Non contact detection of current in live wires. It can detect the presence of AC from a distance of 30cm or more without touching the bare points of live wire. It is ideal to detect cable break, switch board faults, earth leakage etc. The circuit detects the e.m.f (called AC hum) present around the live wire when the electricity passes. Only a single IC CD4033 can do the trick.
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High Current Battery Charger. Design Trick 10


Lead Acid and Tubular battery sometimes require boost charging with high current to remove the memory effect. In Inverter battery, the charger delivers low current since the charger is always on to charge the battery. If the line voltage is low, the charging will not be complete and battery gets only partial charge. This leads to memory effect and the battery remembers this partial charge as full charge in the subsequent charging. The best method to remove the memory effect is boost charging with high current for a short period. It is better to boost charge the inverter battery once in a month using an external charger after removing the battery connection from the inverter. This charger will do a quick charging and is ideal for Automobile battery and Inverter battery.
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Time reminder.Design Trick 9



This simple transistorized timer can be used to remind an activity such as telephone use, heater on, pump on etc. It beeps at an interval of one minute to remind the activity. The circuit is too simple and can be assembled in 10 minutes.
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Simple Alarm Generator. Design Trick 8


You can make a simple alarm generator based on an oscillator to use in burglar alarm circuits. It uses only two transistors and a few other components. Oscillator is a circuit that generates AC pulses from DC. The AC pulses thus generated can be converted into audio frequency using a speaker. Let us see how it works.
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