Astable

IC1 is a 555 timer in astable mode, sending approx. 10 ms pulses to decade counter IC2. IC2 is continually reset through R3, until pin 15 is taken low through the "Fire" button. IC2 then sequences through outputs Q1 to Q7, to feed power transistors TR1 to TR4, which fire electromagnets L1 to L4 in rapid sequence...

It can be helpful to rapidly and easily determine the polarity (npn or pnp) and function of a transistor. The pocket-transistor tester in Figure 1 is ideal for quickly testing without regard to such parameters as gain and frequency response. You connect the transistor, or device under test, between the collectors, T, of an astable multivibrator. Thus, the VCE voltage of the device under test is alternately positive and negative...

Most of the strobocopes designed for commercial use (light effects, theatrical lighting, DJ-lights) have a external trigger connectors on the back of the strobocope. Those connectors trigger input are typically 6.3 mm jacks or XLR connectors. Sometimes there is one input and one output jacks so that many stroboscopes can be easily wired to one controler by just connecting the first stroboscope to controller and wiring next strobocope to the output of he first stroboscope etc. Voltage level is typically 2-12V, a positive pulse triggers the stroboscope. Input impedance is typically 1 kohm So if you generate for example 5-10V pulses at frequnecies from 1 Hz to 15 Hz you get a a nice stroboscope controlling signal. This stroboscope controller is a simle adjustable multivibrator which gan easily generate frequencies at frequency range 1..15 Hz and output suitable control signal pulse to trigger the stroboscope. The circuit diagram is a little bit modified standard 555 based astable oscillator circuit with some extra electronics added to the output side...

This self-build project can simulate a telephone call / connection between any two local telephone devices. This for a fraction of the outlay of some commercial units, many with cost-increasing features that usually are not required. The circuit is centred on two cascaded binary counters clocked by a 555 astable multivibrator. Several of the counters` outputs provide the frequencies, tones and time delays required. A pair of operational amplifiers detect on / off hook conditions at both ends of the simulated line. To detect call answering, a third op-amp monitors the ringing current. R/S latches and logic gates provide event storage and signal control. Discrete circuits provide the voltage multiplication and DC to AC conversion required for the ringing signal. A pair of miniature relays, switch each end of the simulated line between connection and ringing...