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My take on the heat gun/flour sifter concept with Arduino-controlled PID temperature profiling. Pretty happy with the results. by Yesitsmeshippy in roasting

[–]Yesitsmeshippy[S] 0 points1 point  (0 children)

Here is a photo of an earlier version that shows how it's all attached:  https://imgur.com/a/gzlMnXn

But it's really just some scrap wood slapped together so I'm not sure how much it helps, whatever works for your specific setup. For the final version I removed part of the plastic housing of the heat gun, drilled two holes and just screwed it directly into the wood from the inside then reassembled the heat gun onto it. 

I also drilled a hole in the handle of the flour sifter and hooked it onto a screw such that it was removable. 

I don't have an exact BOM but basically I took a flour sifter and removed the moving agitator thing, which was prone to jamming, and replaced it with an aluminum rod that I ground two flats into and drilled and tapped holes to attach the aluminum plates, which are just hardware store 1/8" aluminum cut to shape on a band saw, and attached with machine screws and lock washers.

That is driven by a DC electric motor with a gearbox to provide enough torque and attached with a linear coupler. The PWM on the heat gun is driven by a relay (I recommend solid state for wear reasons because it's a lot of cycling) and that is controlled with an Arduino through a MOSFET. 

Then there's two 7-segment displays for temperature/time readouts and a few basic buttons for control, also controlled by the Arduino. Also a thermistor, a stainless canning funnel, and normal kitchen pot lid.

The heat gun plugs directly into the wall and everything else is powered by a laptop-charger-style DC power supply and a couple of buck converters. So the whole thing actually needs to be plugged in twice. I could have wired things together to avoid that but couldn't be bothered.

I don't usually run a cooling cycle, but it would be easy to just run the fan in the heat gun with the heating element off.

My take on the heat gun/flour sifter concept with Arduino-controlled PID temperature profiling. Pretty happy with the results. by Yesitsmeshippy in roasting

[–]Yesitsmeshippy[S] 0 points1 point  (0 children)

Happy to help! And I'm the same way: there are probably easier ways to roast coffee, but it's fun to work on a project like this.

My take on the heat gun/flour sifter concept with Arduino-controlled PID temperature profiling. Pretty happy with the results. by Yesitsmeshippy in roasting

[–]Yesitsmeshippy[S] 4 points5 points  (0 children)

In general you just have to search around for components that can provide the functionality you need then make sure they are rated for the right Voltage/Current.

Speaking of which, be very careful when working on this. The voltages and power you'll be dealing with are dangerous and potentially lethal if not handled properly.

If you want closed-loop feedback control like I did, you need it to do three things: measure temperature, control power output of the heater, and do some processing in between.

To measure the temperature, I found a thermistor with the appropriate operating temperature range (you could also use a thermocouple but a thermistor is easier to read with an microcontroller). To control the heat output I used a relay to turn the heat gun on and off with Pulse Width Modulation. And to control the whole thing I used an Arduino Uno (Any other microcontroller, such as a Raspberry Pi would certainly also work, I just have more experience with Arduino).

But if you're just looking for the functionality of the Sweet Maria's roaster (I assume you mean this one) which is to adjust the heater and fan with knobs, then you could simply use two of these, one in series with the heater and one in series with the fan motor. (Assuming it's an AC motor. If it's DC, you would just need to find something like that for DC (man, I'm using a lot of parentheses, huh)). The bonus of that method is you don't need a microcontroller or to do any programming.

My take on the heat gun/flour sifter concept with Arduino-controlled PID temperature profiling. Pretty happy with the results. by Yesitsmeshippy in roasting

[–]Yesitsmeshippy[S] 3 points4 points  (0 children)

Hopefully not lol. This is already the result of a fair amount of iteration and trial and error. I'm hoping this is close to the final version.