Hi there, I'm just wanting to check the feasibility of hacking a hotplate to gain control to adjust the temperature to match a temperature ramp I need.
Specifically I'd like to adjust the temperature control dial by 1 degree (or on click on the dial) after x amount of time. The temperature only needs to adjust in 1 degree increments and would allow me to program the ramp I need.
Looking into this subject I have found tutorials on "hacking buttons" in which I've seen solutions that would work if only the hotplate used a simple on/off switch. This hotplate uses what looks like a rotary encoder. This rotary encoder have very light bumps / clicks when you rotate it and will rotate continuously, the rotary encoder also has a switch that tells the program to use the value that the encoder has been set to.
Might this be possible to hack the hotplate with an ardiuno to control the temperature if it has a rotary encoder?
Sorry, the switch on the encoder is there to tell your program to use the value that the encoder has been set to, not to turn your hot plate on and off.
There are 4 leads to the encoder I think, so I guess it's a standard quadrature encoder so it can tell which way the knob is being turned. For example, the two switches might be commoned and connected to ground at one end and the other ends brought out with the ground - so 3 leads. Then the "axial" switch needs another lead, making 4 in all. Then each active lead would have a pullup in the internal controller.
If this interpretation is correct you could simply disconnect the cable from the switch and have a suitable pin header connected to your Arduino where you generate sequences to emulate the switch operation. Lots of details to think about, like are the switches commoned to the positive rail or negative? What's the logic level? And most importantly safety - you are connecting your Arduino to a mains powered system, is it properly isolated?
I did give this a bash some time ago and shelved it for now. With some help I was able to get the device to notch up 1 click either up or down.
From messing about it seemed one of the 4 cables was for the switch to turn on the hot plate.
I can’t remember the last state but I think that I had to backtrack and try to re-wire the circuit to add in some optoisolators for safety and failed to get the circuit to work again - I might have been my bad wiring or something to do with the value of the resistors used. I am pretty sure I was able to get this to work by plugging the arduino directly into the board even tho this was potentially dangerous.
I realised that there might be a bit more to the way the actual hot plate was programmed as I would get some very strange codes come up when I used different pulse times. The codes looked like test codes possibly used in the factory and definitely not mentioned in the manual at all.
I have yet to revisit this project again. I ended up having to control the hot plate manually to finish the project it was for. One day I will try again I think.
