Popcorn-Popper -> Coffee Roaster Mod

the-few writes "Tom Gramilas (Toms-roaster@columbus.rr.com) created a computer-controlled coffee roaster using an old West Bend Poppery I popcorn-popper (popular among home roasters with a modding mindset), a few thermocouples, and an old DOS computer. The code he wrote to control it is available from his site on request, and uses a flexible control algorithm to control roasting segments. Pictures and roasting profiles included."

Comments

TC hookup is non-standard

[deacon]

From TFA:

I actually have four thermocouple in the rig: each of the TC's in the roaster has a reverse connected TC attached to it, This helps to eliminate stray thermoelectric voltages, and is, I'm told, the most accurate way to use a thermocouple. Because of the reverse junction thermocouples, the voltmeters sense the difference between room temperature and the temperature of the sensor. The use of high quality voltmeters here, with low DC offsets, is important since the TC's generate only 22uV or so of signal per degree F.

That's an unusual way to hook up TCs, unless you put the extra TC in an ice bath (for the ice point). All TC meters (as opposed to generic voltmeters) have an artificial ice point voltage generator inside.

In the design of this roaster, the extra TCs shold be in an distilled ice/water bath, otherwise the roaster temp depends on room temp, which is not what you would want. The roaster temp should be independant of the room temp variations (that is the whole point of a control system.)

The other choice would be to use a surplus ISA based TC meter board (which has it's own ice point) in the PC, then you would only need 2 TCs and these would read the temp directly.

Still, I think I speak for all of /. when I say that this project deserves praise and admiration for not only its pointless complexity, (really, a requierment of any GOOD project) but also for the use of very expensive and obscure (GPIB voltemeters and an A_D converter? WTF?) components.

Sort of reminds me, in spirit anyway, of the weed burner I made out of an oil burner for a house furnace, and the snowblower made from the front half of a subaru station wagon...