Photocardiograph (CB21738E)

We found this circuit in a 1969 Popular Electronics. It measures the heartbeat by changing the transparency of the finger.

Acid Rain Monitor (CB25037E)
Written in an article in Radio Electronics magazine in April 1987, this circuit triggers an alarm...
IR Remote Control Receiver (CB25785E)
This is the receiver circuit for the previous transmitter. The circuit has a programming key to...
Temperature Sensor TMP390 (CB20399E)
This is an example of a temperature sensor shield using the Texas Instruments TMP390 obtained from...