This Linear Technology circuit can measure currents from 100 pA to 100 uA. The circuit is from the 80's, using a component of the era. Transistors are general purpose types.
This circuit is from Popular Electronics of the 90's. It makes use of NO and NC sensors. The relay...
This circuit can be enabled and disabled by a TTL signal. The relay is a low current reed type and...
This low-frequency oscillator was found in a 1963 documentation. Capacitors determine frequency. The...