This circuit is from a manual from the 80's and the operational one used, uncommon nowadays, can be replaced by a modern equivalent. The power supply must be symmetrical.
In the figure we have the photo-conductive way of using a photocell to control a small motor with...
Pressing S1 the LED glows by a time interval depending on the capacitor. Time intervals in the...
This is a protection circuit in which, under excess current in the load, the SCR trips by shorting the...