PaulS wrote:
What does "design the interfaces for the controller and the programming" mean?
Quote
I've sketched out a prototype fairly well
Can you share that?
Two separate things: by "interfaces" I was referring to circuitry; I'm not up to speed on how to connect a controller to switches, relays, thermistors, etc.
Programming would be just that; the code to make it all run.
Controller would have a few inputs: Switch or switches to set the number of desired cycles (probably in multiples of 20 -- i.e., one push sets it to 20, two to 40, etc.), to start the cycling, and probably a cancel/reset. Thermistor input to monitor when sample reaches a certain pre-programmed high temperature, and to hold it there.
Outputs would be:
a display to show the number of cycles set/remaining
an output to switch a control relay from "cool" (its default position) to "heat" (i.e., an i/o output)
an output to run another power relay (actually controlling the power to the thermoelectric unit -- another i/o)
Programmed cycle would be something like:
user - set desired number of cycles
user - start first cycle
controller:
apply power to "cool" themoelectric unit, hold for programmed time
switch to "heat" function
monitor temperature
as programmed temperature is approached (within perhaps 5°C), pulse heat control at 50% cycle
as programmed temperature is approached closer (perhaps within 2°C), pulse heat control at 25% cycle
when programmed temp is reached, begin timer, shut off heat
monitor temperature during programmed hold time, throttle heat control as above (if it drops 2°, pulse heat at 25%, etc.)
after programmed hold time is complete, step down one cycle count, and begin the next cooling phase
continue cycling until counter reaches zero, then shut off.
I figure that all the calibration and programming of the cycle parameters would be done using a PC hookup, then the unit could function on its own during normal operation.
I've looked a little more at the actual operation of specific thermoelectric units, and considered some power supply and mechanical setups, but that is all within my skill set, and won't lay out all the details unless someone asks. What I need to add to my repertoire is how to stick an Arduino on top of it all and make it run itself!
Having the UI include the ability to change the temperature settings or hold times might be "fun", but I have the feeling that our sample thermal masses will usually be similar, so one successful programming while the machine was being set up will probably suffice.