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Almost all 24V power systems in trucks, 4WDs, RVs, boats, etc, employ two series-connected 12V lead-acid batteries. The charging system can only maintain the sum of the individual battery voltages. If one battery is failing, this circuit will light a LED. Hence impending battery problems can be forecast. The circuit works by detecting a voltage difference between the two series connected 12V batteries. Idle current is low enough to allow the unit to be permanently left across the batteries.... [read more]

Attach this circuit to the door of an unattended shop - or reception area - and the sound of the buzzer will tell you when you have a customer. Add a siren - and it becomes a simple intruder alarm. Photo... [read more]

If the unit is brought close to a live conductor (insulated, and even buried in plaster) capacitive coupling between the live conductor and the probe clocks the counter, and causes the LED to flash 5 times per second, because the 4017 IC divides the mains 50Hz frequency by 10. When remote from a live line, the unit stops counting, the LED resulting permanently off.... [read more]

This circuit uses a CA3420 BiMOS op amp to form a picoammeter with 4 ranges. The exceptionally low input current (typically 0.2pA) makes the CA3420 highly suited for use in a picoammeter circuit. Input transient protection is provided by the 1 megohm resistor in series with the input.... [read more]

A very simple circuit of indication of level, with 10 Led. Is used the circuit of half-wave rectification of precision round the IC2, with gain one. With switch S1, we can select the indication of Led. The level of entry is 60 mV-1.25 V.... [read more]

There are times when a little light inside the car would greatly assist one of the passengers but the dome light is too bright for safe driving.... [read more]