Help on Coffee Grinder Control Circuit

[efr450]

Hello all,

I'm working on a project for a class and we need to control a Mr. Coffee Burr Grinder coffee grinder with a microcontroller.  I accidentally damaged the circuit earlier in the semester  , but we'd rather not buy a new one and waste part of our budget.  I've attached photos which show the main control circuit in question, with the removed (destroyed) timer chip.  We are trying to control the grinder with simple on/off function similar to the Triac circuit shown here: (see datasheet below for Triac on the board)



We have the gate of the triac connected to a 120 ohm resistor, the other end of the resistor connects to the Neut terminal on the board.  We first put in a 10Vpp 60hz sine wave to the input terminals (Neut and Live) and then measured the input and motor output (M+ and M-), which correctly output the same wave form as our input.  We then stepped it up using 120VAC wall power, and measured both the output and input again.  This time we only got a ~34Vpp output and input with the same waveforms.  We measured the wall outlet with a DMM and confirmed that it was 120VAC.  Just to see if it was an issue with our oscilloscope (which can handle 300VAC so we didn't think so), we decided to hook the motor up on the motor output and see if our circuit would run it.  It did not.  So now we are stuck on what to do next!  I'm not sure what other info is relevant, but hopefully I gave enough (and if not, I can give more!).

Thanks in advance for looking this over,
Ethan

[Zero999]

If you got 34Vpp on your oscilloscope then it's possible because you were using a divide by 10 probe.

What's the point of the circuit? That circuit just allows a small, low current switch to control a higher current load. It's not suable for use with a microcontroller, unless the switch is some relay contacts. You can get special optically isolated TRIACs which are designed to trigger a larger TRIAC to switch a load.
https://www.fairchildsemi.com/datasheets/MO/MOC3041M.pdf

There could be various reasons why the motor wouldn't run. One is the impedance of the 10V signal source is so high that the voltage drops too low, when the motor is connected.