This circuit also detects IR, providing LED indication. The circuit is used to indicate humidity in bench tests. We found it in the Radio Electronics magazine of February 1990.
This circuit is from old documentation. The operational amplifier is uncommon nowadays. The...
September 2017 - Semtech's proximity sensors SX9310 with Specific Absorption Rate (SAR) can be...
Found in a 90’s Popular Electronics, this circuit can use other power MOSFETs. The transformer has a...