Core Electronics Forum

Automatic dispenser for water

I’m trying to find out if I can get these components to make an automatic dispenser for water. This is not an Arduino project. I’m not sure what motion or proximity sensor listed on core electronics will be the right one for this project. Can someone help me with the ordering of the appropriate parts if they are available? This is a project for University. thank you

Hi Aisha,

Welcome to the forum!!

If this project is aimed for uni students I would recommend getting in touch with a lecturer/tutor for some guidance.

Ultimately understanding why they will work together is the main outcome of the assignment. It would definitely be worth reading through how the sensors work, getting into the fundamentals of how each part interacts with the next, simulating the circuit on SPICE or Falstad would be an awesome idea.

That kind of sensor goes by a few names, reflectance sensor, line sensor, digital IR sensor(the analog ones usually have 4 pins)
I found this one; but haven’t tested it in that circuit so cant confirm if it will work and it doesnt have any form of adjustment so you wont be able to fine tune it: RedBot Sensor - Line Follower Australia

There are a couple of catches with using the schematic given, it doesnt look like they make use of the diode (stops the motor generating back EMF) anywhere which will definitely be necessary (A computers USB port is generally attached to some other expensive stuff so grab a USB power supply or portable USB power bank)

This module has all of the supporting circuitry around the MOSFET so will take the resistor out of the equation.

PS: Cheers to Bob for finding that module^^


Hi Liam,
thanks for your reply. My project is for an art project, not an electronic project. I have no knowledge of circuits or electronics. I just need a customer service officer to advise me what part of core electronics to buy. They suggested I would post this here but they are not really helping me. I’ll call in (again) tomorrow. thanks

Hey Aisha,

I’ve had a chat with the guys at Core and I think the forum is the best spot for tech support.

They can do some testing to confirm but I think we should first narrow down some parts.

The hours are 9-5 so I’m sure they’ll help out tomorrow🙂

1 Like

Hi Aisha,

I’ve had a little while to read through what you’re trying to do after your phone call and I think @Liam120347 's advice is spot on, I was going to suggest a PIR motion sensor but a reflectance sensor like Liam suggested will perform even better. If you need a digital threshold instead of an analog reading to be interpreted by an Arduino then something like this may work best.

Liam has pointed out a real flaw in the design of the tutorial you’re trying to follow and I’d recommend swapping the transistor for the transistor module he recommended.


Hi Liam
The circuit Alsha refers to uses a PNP transistor as a high side switch. The Mosfet module you link (thanks for the acknowledgement) is an NPN device and would be used on the low side with a complete circuit change. Also it would appear that the sensor output goes to ground and would need to go high to use the NPN Mosfet. This would be OK if the sensor could be configured to do this otherwise would require another interface transistor.

The 1N4007 diode is not suitable to catch the opposite going spike at motor switch off. It is far too slow and needs to be a Schottky diode… Maybe the author did get away with not using a diode in his product but it should be used as any damage is cumulative and the transistor will eventually fail.
Cheers Bob