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The circuit below is designed to be used with the bi-directional lamp sequencer shown above on this same page. Two additional transistors are used to increase the current from the 74HCT138 decoder to control 12 volt 25 watt lamps. A 6.8 volt/1 watt zener diode is used in series with the ground connection of all the CMOS ICs (74HC14, CD4516 and 74HC138s) so that the total voltage across the CMOS devices will be about 5.2 volts and the outputs will move from +12 to about +7 when selected.... [read more]

This is a variation on the astable multivibrator. Circuit was recently developed to test for N-mosfets(the power kind e.g irf830)... [read more]

This simple and inexpensive circuit can produce a dual (positive and negative) voltage from a single supply input. It is therefore extremely useful for powering opamp and other circuits that require a dual voltage from a single battery. The circuit will operate at an input voltage from around 5V to 20V and produce a output from +-2.5V to +-10V.... [read more]

This circuit is not a novelty, but it proved so useful, simple and cheap that it is worth building. When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate. Reversing polarities the Green LED will illuminate. Connecting the probes to an AC source both LEDs will go on.... [read more]

Designs for audio amplifiers with DC coupling to the load are not often encountered these days, even though they offer definite advantages.... [read more]

The circuit turns on a light corresponding to the first of several buttons pressed in a "Who's First" game. Three stages are shown but the circuit can be extended to include any number of buttons and lamps.... [read more]