[TriEmbed] Coffee roaster sanity check

[Shane Trent]

Craig,

The optoisolators allow the microcontroller to switch AC connected loads
while isolating the microcontroller from the AC lines. Your AC solid-state
relay for the heater coil has the optoisolation built-in. Actually you
could use a DC solid-state relay for controlling the cooling fan as well.
The only other components you would need to add are the input current
limiting diode and the reverse-biased kick-back diode across the motor
terminals. The IXYS DC solid-state relay below is $3 in singles (and IXYS
makes nice parts). The diagram I shared in my previous message is basically
how you would build your own solid-state DC relay.

https://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/CPC1706Y/CPC1706Y-ND/3077519


Shane

On Thu, Jan 2, 2020 at 7:00 PM Craig Cook via TriEmbed <
triembed at triembed.org> wrote:

> >I was actually talking about the voltage rating of the optoisolator used
> to drive the FET gate. The image below more fully describes what I meant. I
> expect your final circuit for the fan would include most of the items shown
> below (I am not sure that you would need D2).
>
> Ah, I was working off this tutorial.
>
>
> https://itp.nyu.edu/physcomp/labs/motors-and-transistors/using-a-transistor-to-control-high-current-loads-with-an-arduino/
>
> Their example uses a 12V motor. Mine is ~20V. I thought I was "close
> enough" to make it work.
>
> You are suggesting I need more components, i.e. at least add an optoisolator
> into the mix.
>
>
> > How many popcorn makers have you been through on this project? :-)
>
> LOL. Two have died from natural causes. I fried the heater on the third by
> running without a fan.
>
> > the heater might just be overheating a little bit each time, gradually
> weakening itself until it breaks.
>
> Yes, that sounds like a great theory as well. The wire on the coil breaks,
> close to where the windings start. It may be due to the number of heat and
> cool cycles it goes though.
>
> >Also bear in mind that your $30-or-so popcorn popper simply isn't built
> for longevity.
>
> Yes. It's supposed to last 12 months of popcorn usage. For most units it's
> probably rare to be used many times in a 12 month period.
>
> The system I design needs to be reasonably easy to swap out the failed
> parts, which so far seems to be the heating element.
>
> Thanks
>
> Craig
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*Shane D Trent*
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