Build a 3v Relay Module Answered
Would love a 3v relay module that can be drive by PIRs that output 3v signal. Thought I finally found what I needed on Ebay, but discovered this is a bogus product that actually needs 5v to be driven. http://www.ebay.com/itm/5PCS-3V-3-3V-Relay-High-Level-Driver-Module-optocouple-Relay-Module-for-Arduino-/331413255692?hash=item4d29c4f60c:g:6koAAOSwfcVUDuEJ Buyer Beware. Advertised relay PCB as 3v relay. While the relay on the board may trigger independently with only 3 volts, the circuitry of the board demands a higher voltage to trigger the relay. Relay PCB has a EL817 opto-coupler for the input signal, it requires a 5V drive voltage on the Input in order to drive the onboard transistor which controls the relay coil current. With only a 3v drive, there is insufficient current to drive the opto and transistor. The module that the relay is mounted to is falsely advertised as 3.0V because the components on the board need more than 3 volts. In order to drive this relay with a 3v signal device, voltage level shifting needs to take place between 3v device and relay PCB.