Voltage probe (CB8184E)

Found in a 90s Popular Electronics, this circuit uses general-purpose transistors, serving to indicate the polarity of circuits.

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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...