I have bought this Grove relay: Grove - Relais | Kiwi Electronics. I use it to drive a low-power water pump with a 9v battery. So the pump circuit is isolated from the Arduino circuit. When the Arduino sends 'high' to the relay, this relay begins to stutter. Contract-release at high frequency. This only happens if the pump is attached. I have bought multiple relays and they all behave in the same way. When I use a non-grove relay, such as Twee-kanaals 5V relais module | Kiwi Electronics I do not have this issue. I made a small film of both relays: https://photos.app.goo.gl/szHHE5EGqjHzJy3f7 (shared google photo's album). Why does this happen? What can I do to correct this issue with the Grove-relais? I want to use these Grove-relays because they need to be used by students that are used to work with Grove components. Please help!

The code:

void setup() {
  pinMode(7, OUTPUT);

void loop() {
  digitalWrite(7, HIGH);
  digitalWrite(7, LOW);

This is the schema: enter image description here

  • Please try the grove relay again with the exact same connections and code as the other relay. If it then still happens, then the relay board is probably broken
    – chrisl
    Commented Feb 22 at 13:59
  • I use the exact same code and arduino setup. I tested it with multiple different Grove relays. They all have the same issue.
    – mvermand
    Commented Feb 22 at 14:40
  • could be bad code
    – jsotola
    Commented Feb 22 at 14:51
  • The circuit works properly when I switch to the non-grove relay. And it's just setting a digital output port high. Can't be much bad about that, i think. :-(
    – mvermand
    Commented Feb 22 at 14:59
  • maybe the arduino is resetting
    – jsotola
    Commented Feb 22 at 15:17

2 Answers 2


The Grove relay in your photo (the black one) clearly says DC3V: you are presumably energising the coil, as well as controlling it, with DC5V.

Perhaps you should try their 5V version:

enter image description here


I would suspect that the switching of the pump motor causes a decently high current spike that messes with your control side. Switching inductive loads always comes with issues.

Try adding a freewheeling diode and bypass cap (1-10µF) to the pump like:


Though If possible, I'd still reccomend using a relais that's less likely to generate interference. With this relais I'd suspect the close proximtiy of input and output traces to be a good part of the reason it's doing what it does.

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