This Schmitt trigger was found in old documentation. The transistors can be of the general-purpose type like BC548 or even 2N2222.
This proximity sensor was found in a 90s Popular Electronics. The base is a PLL567 that operates...
In this circuit, we have a sensor that consists of a phenolite plate with a labyrinth of fillets that...
This circuit is from a 1976 technical documentation. In it we have the way of tuning a circuit using...