Hi
I have build a controller for a toaster oven to turn it into a reflow oven.
I was inspired by this
http://thomaspfeifer.net/backofen_smd_reflow.htm guy and more or less recreated his circuit and designed a PCB for it, which you can see in the attachments.
On the hardware-side the circuit has the capabilities to use i2c-connected H44780 LCDs (can be found on ebay for under 10€ with free shipping) and 4 buttons to control it.
Unfortunately, the ATtiny461 isn't supported really well in Arduino, so the advanced function pretty much went down the drain when I realized that a few hours ago. -.-
So I will probably resort to just coding the most basic control and then send it to the chip via the ISP-Connector with the 2 pins for i2c connected to 2 LEDs to show the mode (Preheat, Soak, Reflow, Finished) and using one button to start a cycle until the chip is supported by the Arduino libraries.
Or maybe one of you guys would like to have a crack at it. I currently don't have the time to adapt one of the ATtiny-libraries for Arduino (
https://code.google.com/p/arduino-tiny/ &
http://highlowtech.org/?p=1695), as I am occupied with finishing the project I did this little side-project for, as well as University.
As a little incentive, I'm offering 4 of my remaining 9 (bare) boards to the one who makes the Arduino IDE compatible with the Attiny 461 and 3 boards to anyone who then writes a software that allows the User to program custom temperature-profiles with the available interface/display-combination. These have to be open source and shared with the community of course
A few words about the circuit: It uses 2 Solid State Relays (S202S02 Opto-Triacs made by Sharp) to switch the 2 heater-banks inside the oven on and off. The SSRs are able to handle 8A, which is enough for a 1KW oven (standard seems to be between 900W and 1,2KW).
Temperatures are measured with a diode: Voltage-drop across the diode has a more or less linear dependency, which gives enough accuracy for this kind of application.
Power-Supply is provided by a 7805 that in turn is fed by any power-source within the limits of the IC (Battery, Transformer + Rectifier, dynamo for the guys who want to work out when doing electronics XD).
High Voltage-Path can be protected by a fuse on board if not already available in the casing.
If the controller is used externally, one of the SSRs can be left out of the circuit and the two free pins then used for something else.
User Interface can be made with a i2c-connected Display of some sort and the connectors provide enough pins for 4 GPIO-Ports and one Output (5 GPIO-Ports if the internal PullUp-Resistor of the Attiny is used).
Programming is done via the ISP.
For further information, see the attached schematic.
The used components should be readily available to everyone here: 0,1µF Ceramic Caps, 10K, 1K, 330/220Ohms Resistors (all in 0802-Package), 1 Axial 47µF Electrolytic Cap, 1 7805, some Pin-Headers, a few cables and a LED. The remaining parts: The SSRs, buttons, Display and the Attiny461 can be found on ebay for less than 15€ combined. Bringing the total system-cost to about 20€, including 1PCB and a short thermal resistant cable.
The total BOM comes down to 35€ - 40€, including the oven and adding some reserves for shipping etc.
Well... I hope you guys like this little device and hopefully someone can come up with a solution to use its full potential.
In the attached Zip-File you will find the schematics.
PS: I know, the traces for the high voltage-stuff have pretty small gaps. My father's Fluke says "OL" between them an the protective Ground Layer, but next time I will make the gap a lot bigger
Note: The ZIP-File contains the updated circuit and looks a lot different from the pictures.
The pictures have been left in there only to make the following conversation more understandable.