Saturday, January 4, 2014

Toast-R-Reflow schematic round-up

So here are the schematics for the Toast-R-Reflow project so far. For the Eagle .brd files, you can go to my OSH Park profile.

First, the power board:

This has remained, more or less, constant throughout the whole project. The design is quite simple, and taken straight from one of the data sheets (for either the BTA-20 triac or the MOC-3020 optoisolator. I forget which). The only possibly controversial aspect is the inclusion of a snubber (the .01 uF cap and 39 ohm resistor on each output). The loads are not particularly inductive, and the triacs are billed as being "snubberless," but I included it anyway. It doesn't do any harm, and it's not like the components are pricy.

But once that's done, to what do you connect it?

That's the first controller design. It was intended to connect to an OpenEVSE style RGB LCD backpack or to an AdaFruit RGB LCD shield. It works perfectly, but I imagined folks railing against the need to buy two pieces of kit. So I came up with...

This design combines the backpack's circuit with the controller. That worked too, but it occurred to me shortly after I finished it that the price of an ATTiny84 was going to be less than the price of the 85 and the MCP13027 GPIO chip. And that led to...

That's what's in at OSH Park right now being fabbed as we speak.

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