Hall effect sensor to trigger relay

Hi! I have a project that needs to sense whether water is flowing through a pipe. I bought a water flow sensor on Amazon (https://www.amazon.com/gp/product/B01LVWHJP0/) thinking I could use it as a basic switch, however, it's got a hall effect sensor and I don't understand how to deal with the voltage output.

Measuring from the pulse signal to ground, the sensor swaps the polarity each time it's triggered: With water running, I see a positive voltage. Turn the water off and back on, voltage goes negative. My control system can't deal with this.

What I need is a simple circuit to turn the sensor's pulse output into a contact closure. Can anyone help?

Thank you!


You can get dirt simple models that use a spring loaded flap.
Once water flows the flap opens either partially or fully, depending on the flow.
The output for those is either none at all or a just a simple reed contact activated with a magnet on the flap or axle.

If you need only positive signals: Did you at any stage consider using a simple rectifier between output and your control system?
The pulse are proportional in speed to the rate of flow, so the higher the flow the faster the impulses.
If you just need a "on-off" signal:
Add a rectifier.
Use the output from the rectifier to drive a simple delayed transistor switch.
The pulse charges a capacitor and once charged the charge should be sufficient to keep the transistor "ON" till the next pulse comes.
Depending on the charge time and capacitor size you can control at what minimum flow rate the "switch" stays on without interruptions.
Once the flow stops the capacitor will fully discharge and the transistor "turns off".

rpdubz (author)  Downunder35m1 month ago

Thank you for your response! I am a capable backyard electrician but have no circuit design experience and didn't know what a rectifier was. I will look into this solution. Thank you again!

+1