10Pcs 1 Channel DC 3V/3.3V Relay Power Switch Module with Optocoupler Relay Module Isolated Drive Control Board for IOT ESP8266 Microcontrollers Development Board 3v Logic Level Boards

Making a simple ESP thermostat device, this works for my application. Here is my simple drawing of the input side of this board. You may be able to pull the jumpers and use the pins to inject your own separate switching source. Not sure why you'd want to do that.

I had a very hard time getting these to trigger with an output at 8-20 mA. The listing claims 3mA. If you look at the schematic and resistors on the board, it is going to draw far higher in order to trigger. If there weren't an optocoupler and LED in series and a low value resistor, it would probably work. Look for other relays that are at a higher voltage. They can still accept a 3V TTL signal. The 3V simply is not enough to reliably trigger the relay.

This works sometimes, but doesn't work other times. When it doesn't work, the led does light but the relay doesn't activate.

The 2 jumpers obviously due something, but I can not tell what. I am running 3V through the signal side and 24VAC through the switch side. The current is <3 amp, so it is not over the limit, but it keeps resetting and causing the ESP32 controller connected to the signal side to reboot. This has been repeated with 3 units. The use case is a thermostat I made to work with Home Assistant.

There are 2 unmarked jumpers on the board. There is no documentation. So if you buy this item, then you will need to reverse-engineer it.