how to make an automatic paper towel dispenser?

I'm trying to build my own, but I'm not exactly sure how it works. I currently have a 12v power source, a PIR sensor, and a 12v motor. I've read online to try to figure some things out and a came across a set reset flip flop. i figured this will make the motor run then stop and reset the circuit. but when i try to connect everything nothing happens. in its simplest form i want it to dispense for probably about 3-5 seconds then turn off. is there an easier way to achieve this?

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-max-2 years ago

The easiest solution, one that will probably be the most easy to integrate, would be a small microcontroller, programed such that when a sensor detects something, that can be like a sonar module, or PIR thing, a output to a motor driver is turned on, and it stays on for a certain number of cycles.

If the output of the PIR sensor is a really basic HIGH when a change in surrounding is detected, LOW when nothing moving is detected, then using discrete logic may be just as simple.

As other's have mentioned, a monostable 555 will trigger off of something, and the output will stay on a certain time afterwards. This can also be done very easily with op amps. have a RC circuit, where a capacitor and highish value resistor connects between a op amp non-inverting input, and a zener diode reference voltage connects to the outer input. You could also use a resistor divider for that other input if the voltages are already regulated or stable enough.

Anyway, you would activate the trigger be allowing the capacitor to charge fully to the Vcc, and then allow it to slowly discharge though the resistor, all in the meantime, keeping the output on, and keeping a MOSFET or motor driver / ESC activated. Eventually, the capacitor will discharge below that of the reference voltage, and the op amp will turn off, and the motor will likewise turn off. That is probably the simplest, cheapest solution.

daric111 (author)  -max-2 years ago

Thank you, this was quite insightful.

JM19992 years ago

You need an old weedwakka motor, attach it to the roll and fire it up!

JM1999 JM19992 years ago
Vyger2 years ago

A bored cat could do it for you except probably not on demand. They do really good with toilet paper.

+! lmao

Maybe use that motor and PIR to lower some teats or a toy mouse? :P or even use the PIR to trigger a Laser pointer :D

Yes, you need a "one-shot" circuit, or monostable. You can find them made with 555 timer chips like the circuit in this excellent instructable

Beware: your motor will draw so much current it will destroy the switches in your PIR sensor and 555. You MUST use a relay.