Trigger a relay with multiple inputs on same screw terminal block

Projects General Guidance
1

Stupid question, I should be able to figure this out, but I'm blanking: I have a simple 2-channel relay board, with wires going in to channel 1, triggering relay 1. I need to add a second input to trigger the relay. Can I simply wire in two additional wires (HIGH pin + ground) on the same screw terminals as the other input? So basically two sets of (input) wires will always be touching each other...

Thanks!

1 Like
2

What are you trying to do? Do you have two inputs to the Arduino that control two Arduino outputs to control the relay? You seem to want the relay to close if Arduino output one OR Arduino output two is active. You can do the OR function in code and send the result out on one Arduino output pin. That is my best guess without more information. Let's see your code and actual wiring.

3

No, I'm trying to add an Arduino "into the mix" with a controller for a door that I have in my office. The controller, with a keypad, triggers a relay which opens the door. I want to connect into that same relay so the Arduino can also open the door, but there's only one set of screw terminal inputs into the relay, so I just wanted to see if I can add my Arduino output + GND into those same screw terminals.

So terminal A would have wire from controller + wire from Arduino, terminal B would have GND from controller, and GND from Arduino.

Thanks!

4

You are tying two outputs together into one input. That is bad. If one output is high and the other low, what happens? If the output high voltages are close you can use an or gate (74HC32). That will isolate the two outputs from one another and if either is high the or gate output will be high. Or disconnet the keyboard output from the controller and feed it to the Arduino (with appropriate signal conditioning) and just have the Arduino output control the door based on keyboard OR Arduino.

1 Like
5

That makes total sense. I knew I was blanking on a simple solution :-).

Thanks!

6

add a second relay? no problem if you are ONLY using the relay as SINGLE THROW.

let the Arduino be the ONLY thing connected to the relay and have the 'other' device tell the Arudino to change state.
that way, one way, the other, or both, it all goes through the Arduino.

7

Hi,
The existing relay that you want to work with, what does its output switching do?
Is it just a COM and NO switch terminals that connects 2 wires or does it operate as a change over, using COM, NC and NO switch terminals?

Tom..... :slight_smile: