Another Corretto roaster build (PC controlled)

[jbrewster]

I generally prefer to code to bare metal and just use the boot loader for convenience! I also hate using the delay function, at least any blocking delay function anyway.

Yeah, fair enough, I do the same unless it's a quick hack or something I expect other people might use. I generally avoid blocking delays too. Changing the timers also impacts millis() in Arudino land.

With a little work you could slow the PWM speed right down and turn on for a few seconds and then off again etc. Could potentially get some finer control by using the fan speed?

Most PWMs won't go that slow, on those timescales you'd be better off toggling the line on and off yourself. Not sure how much control varying the fan speed would give you.

[nicovington]

There is code on Arduino Playground to change the relevant registers (there are caveats though as you're changing timer prescalers and such), the actual available frequency depends on which PWM pins you're using, ISTR there are three timers and hence three different "modules" I usually use 9/10 which ISTR if you set the prescaler to 1 gives ~16kHz, and doesn't impact the delay() function and friends.

I generally prefer to code to bare metal and just use the boot loader for convenience! I also hate using the delay function, at least any blocking delay function anyway.

With a little work you could slow the PWM speed right down and turn on for a few seconds and then off again etc. Could potentially get some finer control by using the fan speed?

[jbrewster]

From Memory most Arduino's have a PWM freq of 490Hz, which is quite ridiculous since the uC is capable of far more, 62.5kHz is easily obtainable, and even higher with a reduced resolution.

There is code on Arduino Playground to change the relevant registers (there are caveats though as you're changing timer prescalers and such), the actual available frequency depends on which PWM pins you're using, ISTR there are three timers and hence three different "modules" I usually use 9/10 which ISTR if you set the prescaler to 1 gives ~16kHz, and doesn't impact the delay() function and friends.

[jbrewster]

The left relay will drive the heating element via PWM signal from the Arduino.

Unless that SSR is a "random switching" type PWM control won't do what you think it will. The vast majority of those SSRs I've seen are "zero crossing" types (which is generally better for on/off applications and hence typically more common) http://www.fotek.com.hk/solid/SSR-1.htm says it's zero crossing.

If it's a zero-crossing unit it will only turn ON with the signal supplied, and will not turn off until the mains goes back through the "zero" point (or it might be that it doesn't act on the input until it sees a zero crossing... I'm a little rusty here), so driving it with PWM >50Hz won't do anything for you.

The only way this sort of thing works with zero crossing devices is if you do "phase angle" control (which is how your average light dimmer works). Basically you need feedback to tell your uC when the mains crosses the zero-point, then you wait x amount of time (0-10ms in the case of 50Hz mains) to turn the relay back on, effectively supplying a partial waveform to your load.

[DesigningByCoffee]

Sounds cool
Having just done two roasts - poking the HG button manually at the same spots each roast does get a bit tedious after a while - with your system then you should just be able to say "at 90° on the DMM increase gun temp 10% etc etc…?

Look forward to seeing the development
Matt

[fg1972]

Hi Matt,

Thanks for the offer to help, I'll definitely read through your thread.
No, not using the CS software. I'm using Artisan instead to read TC temperatures and control outputs manually and then hopefully build some profiles.
I'll upload some screen shots and maybe a short video as it progresses a bit more.

[DesigningByCoffee]

Appreciate the kind words - it has been a great thread! Thumbs up to all the contributors who made it happen

Hi fg1972
While I can't really help in any of your tech development (wish I could!) - I'm really interested in what parameters you'll use to set your profiles - will it be reading time? DMM temp? RoR? Input power or temp? A combo? Are you planning to use the CS software?

This is a whole new world of programing for me! But with a little more info, I can possible help with some profile parameters? Happy to send through CSV files too - but not sure if they would be suitable for your output?

Cheers Matt

[Dimal]

Excellent recommendation chokki'...

One of the best Corretto home-roasting threads around I reckon...

Mal.

[chokkidog]

Have a read of Matt's excellent work here:

http://coffeesnobs.com.au/home-roast...justments.html

It will, hopefully, get you going with some parameters.

Remember that every setup and situation is unique; some trial and error, fun and games are ahead for you!

Happy roasting!

[fg1972]

Thanks Mal.

Whilst I'm sorting out the controller I'm also starting to think about creating some sort of roast profile to begin with.
Since I've never roasted with a corretto before, roughly what kind of heat ramp up is generally used in a generic roast profile for a covered and insulated corretto?
For example;
- Drying phase, how long, high/low/medium heat?
- Approaching 1C, heat setting?
- During 1C, heat setting?
- Approaching 2C, heat setting?

Cheers

[Dimal]

Sounds good mate....

Doubt you would ever head below 50-60% of Fan Speed for any kind of meaningful profile. Ditto for the Heating Element... Although, I do go down to about 40% for some beans/batch sizes...

Mal.

[fg1972]

Hi nicovington,
Thanks,
I've been using a Futek SSR on my Behmor each week for the last few months with no issues so far.

In regards to the Arduino problem, it appears to be a limitation with the front end java application (RoastLogger) and not the code loaded on the Arduino.
It's easy enough to define the extra output just like the existing outputs in the Arduino code but it looks like the java application does all the controls via serial commands to the Arduino.

Today I've found a much better solution,
I downloaded and installed Artisan software and reflashed the Arduino with the Artisan firmware.
Artisan doesn't do very much out of the box without some proper configuration unlike RoastLogger which is easier to get going,
But
Very quickly I've found Artisan much more flexible for custom stuff and after a bit of stuffing around, I've created a custom button to turn on the stirrer relay and another button to turn it off.
This has enabled me to also create an event which automatically turns on the relay when the roast starts and turn it off at the end of the roast, perfect.

The default PWM frequency via my basic transistor circuit works well controlling the DC fan motor speed right down to about 20% speed where it then sounds a bit funny but I don't expect to drive it this low.
Constant 100% fan speed probably would suffice but I suspect it will cool the heating element too much during lower heat settings.
Having the luxury of variable fan speed should work nicely though.

[nicovington]

You could buffer the output of the PWM via a suitable capacitor to provide smoother control of the motor. If it's a high frequency output PWM though, probably won't matter...

Mal.

From Memory most Arduino's have a PWM freq of 490Hz, which is quite ridiculous since the uC is capable of far more, 62.5kHz is easily obtainable, and even higher with a reduced resolution.

I'm guessing the fan load wouldnt be that high so in practice is probably wouldnt matter, however it might make a slightly audible hum as the speed "wobbles" if the PWM freq isnt high enough,

[Dimal]

How well does the heatgun fan run with PWM? I think I'd be more inclined to run it full tilt most of the time

You could buffer the output of the PWM via a suitable capacitor to provide smoother control of the motor. If it's a high frequency output PWM though, probably won't matter...

Mal.

[nicovington]

Awesome project, I think i'll have to take one of these on when I get a little more space/time.

I'm interested in the reliability of those Futek SSR's, I have a bunch waiting to be used and at $3-4 they are a bargain. One of the PID units I bought claimed to be SSR output, but it's got relay outputs, and the seller refunded half the cost which brought it down to $12 ( it's the Rex C100 unit), but I can easily remove the relays and simply route the relay coil trigger to the output terminals and it'll work nicely with the SSR's.

I wonder if there is any advantage running PID on the coffee bean temp?


Regarding your Arduino problem, is it that you dont know how to code, or is there any other roadblock? It should be fairly simple to configure another output if all the code is open source.

How well does the heatgun fan run with PWM? I think I'd be more inclined to run it full tilt most of the time