This circuit was found in a Popular Electronics from the 90's. The CMOS integrated circuit used is not very common nowadays. The range depends on the infrared LEDs. R7 can be changed.
This circuit of the 80's makes use of components of the time. The circuit is from an American...
With this circuit general purpose diodes and rectifiers can be tested with ease R has 100 ohm for...
This three-transistor amplifier uses a JFET at the input to increase the input impedance. The...