This relay shield circuit for old computers was found in January 1983 Radio Electronics magazine. The relays are sensitive types with currents up to 200 mA.
If the transistor is PNP, keep a good NPN in place. If it is NPN, keep a good one in the...
This circuit indicates variations in room temperature around a few degrees on a bargraph scale. The...
Found in a 90s 73 magazine for radio amateurs, this circuit makes use of common operational...