AC voltage probe (CB8185E)

This circuit for voltages up to about 20 V was found in a 90s Popular Electronics. The LED can be of any type or color.

DTMF decoder (CB17454E)
The integrated circuits used in this 1999 project are not very common today. However, they can be...
Digital thermometer with the TL505 and TL502 (CB16050E)
This 3-digit thermometer, suggested by Texas Instruments, uses 3 integrated plus the display, with...
200 MHz Amplifier (CB14623E)
This circuit is from the National Semiconductor FET Databook. The coil data is provided with the...