We found this circuit in the National Semiconductor's Linear Applications Handbook of 1994. The circuit uses an operational transconductance amplifier.
This circuit was obtained from Linear Technology documentation from the 80's. Powered by 5 V it...
Only when the programmed key sequence is activated, and within a minimum time determined by the...
This circuit is from a 1981 publication. The DC supply can be made with voltages from 6 to 12 V...