We found this circuit in the Texas Instruments optoelectronics manual. Field effect transistors can be BF245 and bipolar BC548. The sensor is a photodiode in the photo-generator mode.
We found this circuit in an English documentation from 1979. It shows how you use a 100 uA...
This circuit for high-impedance magnetic headphones was suggested as an experimental amplifier for hearing...
This circuit was found in a 1987 publication. A 4017 sequentially counts time in steps set by...