mono stabile (one shot) generator with 2 transistors (experimental circuit)
I found this circuit in a book from the sixties and tested it. It has some flaws: 1) the 27 K base resistor to TS 1 proved to be necessary to make the circuit function on low frequency (2 Hz or so) trigger frequencies (AC via a coupling capacitor). The circuit did not function properly on AC input signals without this resistor that gives the base a small + positive forward voltage (in case of this - NPN ! - transistor) 2) when you want to drive TS 1 with a DC voltage a resistor from 1 K or more in series to the base from TS 1 is absolutely necessary, TS 1 is very quick defective with a too high base current, the same applies to TS 2 (also defective very easily for unknown reasons) 3) the "fixed" pulse at the output (fixed in time) is only available when the input has a fixed frequency, so it does not act so properly as a one shot generator (limited frequency band), when the input is "random" DC or AC the pulses are not regulary available due to the recovery time from the time dependent capacitor and 4) the input is only sensitive enough in the 0,6 - 0,8 V (AC) range, so not usable to be triggered by your fingertip/hand. But: a very interesting circuit for experiments, especially with an AC coupled pre-amp. More electronic circuits in my books, available on the Lulu website, author Ko Tilman.
