Water activated alarm (CB7993E)

This rain, flood or leak sensor was found in a 90s Popular Electronics. All the components used are common today. The transistor can be the BC548.

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Battery discharge indicator (CB9549E)
This circuit is based on an operational window comparator. We found it in a documentation from the...
Electronic Roulette (CB7002E)
Found in a Popular Electronics from the 90s, this game can be seen in other configurations on this site. The...
Microphone Signal Conditioner (CB15601E)
In the figure we present a circuit of a microphone signal conditioner using the SSM2167 integrated...