Price reduction!

Well, despite the fact that no one has yet actually bought one, I've decided to get a bulk order of Toast-R-Reflow parts. This bulk ordering has allowed me to drop the price 20% on the power board. So if you don't mind doing a little soldering (none of it surface-mount), you can get a complete TRR kit (consisting of a power board kit and a backpack controller "quick kit") for just $50. All you need to add is a 7-12 volt @ 250 mA power supply, a K type thermocouple and a toaster oven.

Step right up, don't be shy!

The Toast-R-Reflow boards and kits are available if you want to convert your own toaster oven into a reflow oven. It's not that hard. I've even written a nice instruction manual you can peruse before you take the plunge. Assembling the power board is just about the easiest through-hole soldering I've ever done, and the controller comes with all surface mount parts pre-assembled and the controller pre-programed. All you need to do to finish the "quick kit" is attach the through-hole connectors and mount the LCD. And all you need after that is a K type thermocouple and a toaster oven.

Who'll be the first?

RGB LCD Backpack

I'm a little torn about this.

I've been buying my RGB LCD backpacks from Chris over at the OpenEVSE store. The downside of this is that when people want an EV Sim or a reflow oven standalone controller, they can't just do one-stop shopping. Additionally, if I had an absolutely free hand, there are a couple of tweaks I'd make to the design:

1. LiquidTWI2 supports a piezo element on the last unused pin of the MCP23017. It'd be nice if there was a spot on the backpack for that.
2. There's probably a simpler layout for the button pin connections.
3. I want to include a 2 way solder jumper for the backlight common pin to accommodate both common cathode and common anode backlit modules.
4. Since I happen to have a pile of them, I'd use the SSOP derivative of the MCP23017 instead of the SOIC one. That leaves more room (should it be desired) to add stuff down the road (for example, Chris added a Dallas Semi i2c RTC chip to his).

So I've posted a design for my own version of the i2c RGB backpack. It feels slightly, I dunno, mean to steal his thunder like this. I'm not really trying to take food from his mouth or anything like that. My own latest trend has been to replace ATTiny85 + MCP23017 designs with ATTiny84s directly wired to the LCD. It saves quite a bit of firmware space, and about a dollar off the price, and for most of the designs to which I've applied this, the RGB backlighting hasn't been needed anyway.

But once the prototype comes and the design is validated, I'll add my version of the backpack to my square-up store just so folks won't have to buy from two different places. The i2c connection will be pin-compatible with the OpenEVSE backpack, and it'll work with the LiquidTWI2 library. If you want to take a look at the board, the design is in my OSH Park profile.

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.

LCDuino update

The LCDuino shield adapter prototype boards arrived. With them, I got the LCDuino prototype to take over the GPS clock duties using the GPS shield

The Shield Adapter board worked perfectly on the first attempt. The prototype lacks a 3.3 volt power supply, so the 3.3 volt shield pin is NC, but the GPS module doesn't care.

It did point out a second wiring error in the prototype - the blue and green backlight control lines are reversed. I worked around that too in software for now, so the v0.3 LCDuino board will be the keeper.

The LCDuino ribbon cable mating into its plug on the Shield Adapter rides just a bit high - so the first shield in the stack winds up hitting it. I will probably use a right angle DIP header to work around that for the next one.

But LCDuino is well on track. I just hope it winds up being useful to more than just me.

The Hacker Dojo reflow oven

The oven is complete and operational. In case folks want more information, I'll put up this page as a clearing house.

While I was there, I ran through a cycle while someone took a video. When that video gets posted somewhere, I'll link to it here.

The gist of it is that you need to supply the oven itself with 120vac (just like its makers intended), and the controller board (with the LCD) needs 7-12 VDC @ 200 mA, 2.1mm center positive.

The normal waiting state will show "Waiting" and the thermocouple temperature on the left side of the display.

The thermocouple is the brownish wire-looking thing snaking up from the bottom of the oven. You want to put your boards as close to the end of that wire as practicable, but you want the thermocouple in air, not touching your board or any other part of the oven.

There is a button on the back left (when viewed from the front) side of the controller. Press it to start a cycle. The display will show four pieces of information. Top left is the name of the current step in the cycle. The steps are "Pre-Heat," "Soak," "Reflow," and "Cool." The bottom left will show the current temperature and the bottom right will show the current set point (target temperature) of the oven. The top right will show the elapsed time from the start of the cycle.

The way the firmware works is best illustrated with the concept of a graph. The axes of the graph are time and temperature. The beginning and end of each step represent points on that graph. The end of one step is the same as the beginning of the next. The set point of the oven will gradually move along the graph described by line segments joining each of the points.

The points are:

1. The beginning of pre-heat starts at 0 seconds, 25 ºC. Pre-heat lasts 90 seconds and ends at 150 ºC.
2. Soak lasts 60 seconds, and ends at 180 ºC.
3. At the end of Soak, the line has a discontinuity. It breaks and immediately snaps to a set point of 225 ºC.
4. The Reflow step stays steady at 225 ºC for the duration, which is 75 seconds.
5. The Cool step goes downwards from 225 ºC to 150 ºC for 60 seconds. In reality, the oven will cool slower than this left on its own. Impatient users may wish to open the door a crack to speed cooling, but there is a danger of thermal shock if the cooling proceeds too quickly. The cool stage will attempt to prevent this by heating the oven further if cooling is proceeding too quickly.

This profile is appropriate for Sn-Pb solder paste. I have not attempted RoHS soldering with this oven. I am skeptical that it can make it up to 260 ºC in a reasonable amount of time, but I'd be happy to be proven wrong.

The low voltage cable coming out of the oven to the controller is directly connected to a pair of optoisolators with a common cathode (the green wire). There are no series resistors - you must add them yourself. The target is 20 mA of current. Do not exceed 50 mA or you'll damage the optoisolators. If you want to experiment with alternate control systems, the optoisolators are MOC-3020s. The thermocouple is a K type. Note that the K type thermocouple lead color code is yellow for positive and (perversely enough) red for negative.

The controller board that's there is a prototype for the backpack controller design. There is a wiring error in the LCD wiring that was worked-around in software. You must modify the LiquidTWI2 library to reverse the order of the LCD data bus lines for this particular board. I have an order into OSH park for corrected boards and will bring one in when they arrive.

See you Saturday

I will be at Hacker Dojo this Saturday at noon. I'll be there to do the Toast-R-Reflow conversion operation in person. I'll leave the completed oven there for folks to use too. I'm not a member, so I can't reserve a room or create an event or anything like that. But I visited (for the first time) this evening and met some folks there who dug it and they said that Saturday at noon-ish was a good time, so that's the plan.

I've already set aside most of the parts. I'll be using the standalone controller and an LCD backpack, but I will eventually replace that with the ATTiny84 backpack design as soon as the boards arrive from OSH park.