Infrared detector (CB7814E)

This circuit was found in a Popular Electronics of the 90s. The operational amplifier admits equivalent and the phototransistor can be of any type.

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Mini amplifier (CB21958E)
Found in a publication by Gernsback from 1960, this circuit makes use of germanium transistors of the time....
Isolated Shield for Motors or Relays (CB23724E)
To control relays or DC motors safely with double isolation via the parallel port, we suggest the...
Guitar Expander and Compressor (CB13995E)
This circuit is from a 1975 Sperimentare (number 11). The circuit uses optical coupling for a...