Lock code unit with auto reset

The code unit, which operates with was designed to control an electromagnetic door lock with a four-digit code. It resets automatically after a short period. The keys that set code are designated S1-84 in the diagram. Each of them is linked to a bistable (flip-flop) in IC1. The connections are arranged so that when key[…]

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Small power converter

The converter enables an existing positive supply voltage to be raised, to be lowered, or to be changed into negative potential. The new voltage is electrically isolated from source by a DIY transformer wound on a G2-3FT12 toroid. The primary winding consists of 30 turns. The number of secondary turns, n, is calculated from n= […]

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Zero suppressor for IC17106

Many people are irritated by the superfluous zero that precede a number on, for instance, a liquid crystal (Lc) display. To them ‘1’ is clearer than ‘001’. In systems where the ICL7106 display is used, this irritation may be removed by the present suppress. Both the backplane (BP) and the segment of a 1CL7106 arc[…]

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Telephone monitor

It is sometimes necessary to make a telephone conversation audible to more than one person at either end or to make a tape recording of it (as in many businesses). Often, this is done with the aid of a microphone fitted with a suction cup. This does not work very well, though, hence the present circuit.[…]

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Low-drop a.c. switch for 12 V halogen lights

Because of their inertia, power consumption, contact wear, and often size, relays are not really suitable for switching alternating voltages. Moreover, they cannot be used in phase control circuits. Replacing them by triacs may give problems owing to the forward voltage drop across these devices. A much better solution is the use of anti-series-connected SIPMOS transistors.[…]

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