We found this circuit in a 73, magazine for radio amateurs of the 90s. The circuit is passive and most telecommunications receivers can be added.
This circuit is from 1995 documentation. When the phone is lifted, the relay closes its contacts by...
This astable NAND TTL provides complementary signals. The circuit must be powered with 5 V and...
This photo-relay uses a Darlington stage to increase sensivity. Any photo-transistor can be used....