This circuit of a 1964 Electronic Design uses a photodiode from the time. Modern equivalent can be used. The standby current is 1.2 mA.
The suggestion for using this circuit from an old American documentation is to use small antennas...
November 2016 - The new wireless power modules for use in wearables from Semtech can now be...
This TTL module can be used in counter and many of them can be cascaded to counts up to 99, 999,...