Toast-R-Reflow - yet another toaster -> reflow conversion
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Toast-R-Reflow - yet another toaster -> reflow conversion

by nsayer on Fri Jun 13, 2014 6:36 pm

I've got a bit of a story... When I was young, I put lots of HeathKits together. But towards the end of the 80s, the whole electronics industry went to SMT and I sort of regarded that as the end of the hobbyist era in electronics, more or less. Back then I tried to make a simple through-hole PCB myself with an etch resist pen and acid and a tiny drill bit, and that didn't work out so well (even with a drill press it was nearly impossible to get the holes to line up).

Fast-forward 20 years and I buy an electric car. From there, I discovered OpenEVSE and that led me to Arduino and then to OSH Park, and now I've rediscovered the hobby I abandoned in my youth. The culmination of that was a thing I call the J1772 Hydra which lets you share an EVSE with two cars. It was on show-n-tell last week.

But the first versions of that were through-hole. Last fall, I decided to see what SMT was really like, so I converted a very small thing - my EV Sim (a piece of test gear for charging stations) - and designed an SMT board for it, ordered the parts for it (what must DigiKey have thought when they got an order with *single* 0805 resistors??) and sat down at a professional soldering lab at the office. It took me 2 hours to hand-solder what took me 20 minutes as a through-hole version. I said, "oh the hell with that!"

But then I wrote about my experience on the OpenEVSE group and the answer came back, "Oh no, don't do it THAT way..." and I discovered the concept of reflow.

I set out to make my own toaster oven conversion. Step 1 was to search for and see what others had done. A lot of folks used solid-state relays. I didn't really like those as they're quite costly (at least for those that can switch enough current for a toaster oven). Others didn't separate the high voltage and low voltage portions of the project enough for my tastes (I want to not get electrocuted while debugging the control stuff). Long story short, I made my own. I call it Toast-R-Reflow.

It comes in two parts - a power board with two opto-isolated triacs with VERY beefy heat sinks - and a controller board, which has an ATTIny84, a thermocouple amplifier, power regulator and is a backpack on a 2x16 LCD module.

The power board is still through-hole, because there aren't that many parts, and they're high-powered parts anyway. The power-board is made to be embedded within the oven itself in place of the original controls. It has two channels on it. Originally that was because with the heatsinks I used I could only really handle around 800 watts of switching thermally. Using two triacs let me divide and conquer, since most toaster ovens have separate top and bottom elements (or separate pairs). A 3 wire cable comes out to your controller. The controller is powered separately with a 7-12 VDC @ 200 mA wall-wart. The controller has an AD8495 thermocouple amplifier, the LCD, outputs for the optoisolators on the power board, and a single button. Push the button and the firmware runs a Sn-Pb profile. It's worked perfectly for me for nearly a year now.

You can get more info from my blog: http://www.geppettoelectronics.com/sear ... t-R-Reflow

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Joined: Thu Aug 08, 2013 10:45 am

Re: Toast-R-Reflow - yet another toaster -> reflow conversio

by adafruit_support_bill on Sat Jun 14, 2014 5:56 am

Great project! Thanks for posting.

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Joined: Sat Feb 07, 2009 10:11 am

Please be positive and constructive with your questions and comments.