Stage 1: Getting the parts
While we were planning the purchases for our mendels, we wanted to solder the electronics ourselves, because we thought it would be cheaper that way. But it turned out that the do-it-yourself kits from makerbot are much cheaper than the PCBs and components, even with import tax, and since the PCBs are only available from makerbot anyway, it was clear that we would get the kits.
When I made the cost calculations I noticed that the complete kit would only be 20$ more, so we decided to get them complete as soon as they were in stock.
But I wanted an extra extruder controller to be able to work on my granulate extruder or maybe a frostruder or whatever came to my mind, while still having a functional extruder. So when the electronic kits were back in stock I waited a little to see if the extruder controller would come in as well.
20 hours later ALL electronic kits were sold out. I was really pissed!
So we went back to plan A and ordered the PCBs from makerbot, the components from mouser (because they are included in the reprap parts lister, which makes shopping so much easier) and the chips from farnell (because I know them from work and they had those in stock). In the end the costs were roughly the same as the complete kits, but since I didn't expect makerbot to get them back in stock soon, there was nothing else to do.
But of course I was wrong. Even before the package from makerbot was here, they got a whole bunch of electronics back in stock.
So what, we had already ordered everything, there was no going back.
Stage 2: Soldering
Since my old soldering iron was broken and the new one not really suitable for smt soldering, I decided to try the hot plate reflow technique.
I started with the extruder controller, because we have one of those extra. I applied the solder paste and set the components. That was not so difficult, even if I don't have the best equipment.
The only problem was the 180 ohm terminal resistor, the documentation says this is needed for one extruder in the system, but it is not listed. However it is listed for the mainboard, where it is optional, so it's not so bad. But I still think it should be the other way around.
Another problem was because I had to order other LEDs, the green ones I got are a little confusingly marked, so I put them on the wrong way.
For the hot plate I prepared my multimeter with a thermistor and monitored the temperature of the plate, which was a good thing. It should not get over 200°C to save the epoxy of the PCB, but more than 180°C are needed to melt the solder paste. I think by now I know the correct setting, but the first try should not be attempted without a thermometer.
After soldering in the through hole components the controller was finished and ready for a test.
Stage 3: Testing
I had to dig a little in the wiki to get the procedure for programming, but after I got the arduino software set up I was ready.
I connected the USBtinyISP to the board and burned the bootloader, which seemed to work well. (This was the point where I noticed the LEDs were not working.)
I tried to connect the serial cable, but I could not programm the controller. I tried the USBtiny again just to be sure the chip was ok, and it did not work any more. The interfaces are rather simple, and we tested the circuits and could not find anything amiss, but I must have shorted something somwhere so the chip was fried when I connected the serial cable.
I'll try a stepper driver next and I hope that works out better.