Driving doorbell (DC motor) with my Particle Photon - MOSFET problems!

Getting Started
1

I am in the process of wifi enabling my old fashioned doorbell (smartphone notifications, home automation etc.). My problem lies in the most basic feature of a doorbell – making the bell ring!

The originall doorbell is driven by two 1,5V DC batteries (D size). Powering the Particle Photon of a USB charger / USB cable I plan to power the bell of the 3V3 and GND pin. Connecting the wires directly to the pins makes a reel clean and powerfull ring.

My problem lies in controlling the ring with the Particle Photons digital pins. I bought a MOSFET N-channel transistor (irfz44n) but can’t get it to work!!

Connecting the transistor leaves the bell ringing half force and connecting the gate to a HIGH or LOW digital pin makes no difference in ring speed/force.

How do I control/trigger the bell using my Particle Photon? Any ideas?

IMG_0688.JPG2016×1512 662 KB

Picture/Wire explanations:
RED/YELLOW 3V3
GREEN GND
BLUE Digital pin connected to GATE
WHITE deliberate shortcut of the original doorbell trigger switch

2

you might need to swap the Green jumper and the green wire going to ground.

The mosfet pin-out is (Gate Drain Source)

Gate --> D4
Drain --> bell
Source --> GND

It’s likely that current is flowing through the diode in the N-fet due to the current wiring, causing the constant ringing :wink:

3

Kenneth! You are completely right! Thanks … Unfortunally the D4 pin is not powerfull enough to open the gate. But if I connect the gate (blue wire) to the VIN pin the bell rings (even after I disconnect the wire) and stops when connected to GND. Any suggestions to this? Is my MOSFET the wrong choice or do I need a second transistor trigging the IRFZ44n?

4

What happens if you connect the gate to 3V3 instead of Vin?

5

Nothing

6

The Vgs of the IRFZ44N is 4V so applying Vin which is around 4.7/5v turns it on fully, which makes sense…

Do you have an NPN transistor around? It might be a simpler solution since the current draw in this case shouldn’t be too high.

This N-fet might work well with 3V3 devices - https://www.sparkfun.com/products/10213

7

I tried using a 2N5401 That works (OFF on HIGH) - but it gets really hot an smells burned! Not good! I look for a NPN.

Is my wiring wrong? should a place the switch where the white wire is placed ?

THANKS!!

8

Put a 10K resistor between Vin and the gate. When you switch your I/O pin (5V tolerant) to input, it will raise the gate voltage to 5V shutting it off. Switch it to output and low to ring the bell.