AVR-Chat

I've been using a cheap toaster oven for a while. It has two heater 
elements, top and bottom. It's 600 W, which is just enough.

When I got it, I ran a few tests and noted down the temp curve at 
several points, with the plan of making a controller with and AVR.
But, the runs showed that the oven was fairly similar to a real reflow 
oven, and that there was no need for a controller.
I simply out in the board, and set the timer for 2 minutes. The board is 
then up at about 120-130 deg C. I then leave it for about 1-2 miutes so 
the flux can do it's job, then finalize it all by turning the oven on 
for another 3 minuts. This will take it over the top at about 230-240 
deg. Open the door and let cool. Serve with a chilled chardonnay.
Works great, have made quite a lot of boards now with no problems, even 
though I suspect heat distribution withing the oven isn't all that great.
So, you may not need to make a controller after all.

But, back to the type K question. I did another project with a type N, 
which is similar. Thermocouple input was amplified 200 times with an 
opamp, so it would suit the A/D.
I used a Dallas DS18B20 as a temp reference, mounted where the connector 
to the thermocouple entered the board.

/Jesper

Kathy Quinlan wrote:
> Hi all,
> 
> Well I have to make 100 units (and pot them in Epoxy Resin) of an octopus lure 
> I designed for a proto run.
> 
> I am now thinking SERIOUSLY about building my SMD oven (as it is mainly SMD 
> only 4 through hole solder connections and 2 through hole non solder 
> connections (fishing line to hold the lure in the pot))
> 
> I also have a lot of "other" projects including a run of 200 units for my 
> speed alarm unit for the Au Targa Rallys.
> 
> So I need a circuit for Type K to AVR. I know there was a design note in the 
> Atmel applications Journal, unfortunately the WRONG schematic was placed in 
> there :(
> 
> So if anyone knows of a good easy schematic (with cold junction compensation) 
> I would love to see it. I do not need high accuracy, as solder does not mind 
> if it is 310C or 315C so anything to within +/- 2.5C is fine (I think the over 
> will have problems in coming up quick enough ;) (if so more elements and more 
> insulation is in order ;)
> 
> This will be an OPEN SOURCE Design. FULL PCB artwork (in Gerber and Protel 
> 99SE format), Schematics, Photos, source code, etc. will be on my site.
> 
> I will also be recognising all who contribute to this design.
> 
> I know I can buy chips like the MAX6675 as used in the Elector Jan06 issue, 
> but these are not at hand ATM and I am running out of time.
> 
> I will also use the over for post curing of the epoxy etc. so I would like to 
> build something that can have MULTIPLE presets.
> 
> I will design around the Mega 128 (huge overkill, BUT I have them in stock ;)
>