How to control DC relay module?

Question

I have a remote controlled battery box (Lego) that I want to use to control a relay module. Having limited electrical knowledge and tools, I opted for a ready made relay module (bistable, because I don't have a continuous power source).

The issue I have is that the module I purchased has separate contacts for the relay's power and the two buttons to control it:

My battery pack only provides power until the button is pressed but allows to reverse the flow. Playing around with the module I found that I can make it work by plugging DC+ to the IN connector (lower outlet) and DC- to one of the COM outlets.

My solution would then require plugging two different wires (corresponding to two buttons on the RC) to the IN connector + and then one - to each COM.

Am I right that I will need something (e.g. zener diodes) to prevent the current flowing backwards to the controller? Something like this would work?

EDIT: I'll try to clarify. The relay module itself works with any polarity and has protections in place. It works both when powered as intended (first picture) or powering one of the two IN and COM. The problem is my RC controller: I one plugged some LED directly and it started to smell (I probably fried something). I imagine that connecting the + from two different lines of the RC together would be bad for it, so I need to prevent that?

Edit 2: here is a picture of the RC box. It's meant to control motors or lights but I would like to use it to control the relay.

Answer 1

It would appear that the board expects a voltage and ground on the "in" connector and then it will provide that voltage to the connectors 1 and 2, and the ground to COM. This is where you pick up a multimeter and "beep" to ensure this. If this is true, then the connections you've drawn might be wrong.

1 and 2 would be the + on the relay coils. This is a 2 coil latching relay with nominal 12VDC (Hongfa HFD2). The board is apparently designed so that you should only connect physical switches on that connector. One coil is used to set the relay and the other to reset.

The IC might be an optocoupler, in which case it is there to protect your "in" device from reverse EMF. Or it might also be a diode net with 2 diodes in one package, which would achieve the same thing. Though in case it is an optocoupler, it means that the "1 2 COM" connector still has the reverse EMF, which will become an issue in case you connect anything but a physical switch there.

Again, here comes the handy multimeter, measure diode forward voltage across the pin pairs, to figure out if it's a diode or optocoupler. Now if we could read the IC print we could also tell it that way...

In case it's an optocoupler you have to provide two "flyback diodes" with their anodes on 1 and 2 and their cathodes on COM. If you get some standard through-hole 1N4007 diodes, they can likely be placed directly into the connector without the need to solder anything. In either case they won't cause any harm.

Also the relay coils are rated 200mW typical, meaning your switches need to withstand at least 200mW / 12V = 16.66mA. That should go for most switches out there, though I have no clue about what "lego" ones can handle.