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.
This simple thermostat circuit was found in the September 1976 issue of Radio Electronics...
We found this circuit in the 1982 SGS Linear Integrated Circuits manual. The integrated circuit used...
This circuit uses a FET to drive an LED with constante currente. The current up to 20 mA can be...