Found in a 1970 EEE, this circuit can be applied to TTL ports. The supply is 5 V and the frequency, which depends on the crystal, can be between 1 and 3 MHz.
In the figure we have the way to use the LM3914 as a scale of bar LEDs or moving point. The...
We found this circuit in a European publication of the 1980s. The transistor could be the BC549. The...
We found this simple continuity tester in a 1995 documentation. It uses two LEDs to indicate...