Please don't laugh at my SMD soldering skills

I made a first PCB using the original pcb-layout from the git repo, but the combination of a printer driver that produced a fuzzy mask and less than perfect etching skills didn't produce a satisfactory result. I then re-drew the GND copper-fill and some other traces on the PCB for bigger clearances and easier etching. Printed from adobe acrobat on windows the mask also has much better resolution than when printing from Document Viewer/Ubuntu.

Here are my modified masks in PDF format: hardware_etched_2011dec04 (note that the board outline is enlarged)

The PCB is clearly made for commercial production. There are vias under the microcontroller, which you can see from the pictures I have filed down after soldering so that the chip will fit on top. This isn't an issue with a commercially produced PCB where the vias are plated. Also, I noticed while starting to assemble the board that the large pad on the 3.3V regulator in the upper right corner will short out the trace drawn under it. Thus the silicone tape as insulation in the following picture. This is also not an issue with a commercial PCB since it will have an insulating soldermask.

Then on to programming. From the servodrive adventure I have an ICD2 programmer/debugger. However using it was challenging. I first tried 64-bit Windows 7. The latest Microchip MPLAB IDE does ship with 64-bit drivers, but they are hidden away in a special place, and require manual installation. No luck here, from device-manager/update-driver I couldn't get Win7 to recognize a valid driver using the instructions supplied.

I then tried 64-bit Ubuntu11.10. They have a Java version of MPLAB, called MPLAB X. It installs and runs nicely, but when I started digging in the documentation it turns out that product only supports the newer ICD3 programmer/debugger, not my older ICD2! (there might be ICD2 support in some old beta-version of MPLAB X, but I didn't search).

Oh well, it's nice we keep those old 32-bit Windows XP machines around in the lab! So I repeat for the third time the whole download and installation process on an old XP machine. That seems to work. The C-compiler which I vaguely remember being free previously now has a 60-day trial period after which Micrchip proudly proclaims it will stop producing nice binaries and start producing crap binaries. Strange. There's both a bootloader and a firmware project in the colorhug firmware repo. My guess is I only need to build and deploy the bootloader, and the firmware can be flashed from any machine after that. The bootloader requires a USB-library, which I didn't manage to find before I had to quit for the day... To be continued.

Note to self: future projects should use ATMEL or other microcontroller which (a) has a free/open-source toolchain for building the firmware, and (b) can be programmed directly over USB. The 6-pin ICSP connector is just big and ugly on a cute little board like this.

The circuit is based on the TCS3200D color-sensor which RS had on their website when I made the order, but the delivery note lists the parts as "discontinued". So these have to be sourced from somewhere else.

I should do a test on the bike later. Maybe include the Garmin 405cx and older C7 phone also?

The touch-screens on these devices are different: Edge 800 works fine with gloves, N9 doesn't work at all with gloves.

Cropped from original like this:

#!/bin/sh
mencoder video.mp4 -oac pcm -o test.avi -ovc lavc -lavcopts vcodec=msmpeg4v2:vpass=1:vbitrate=5160000 -vf crop=370:300:200:100

The first circuit is based on the 555 and produces a square waveform with variable frequency depending on the resistance of a thermistor. At room temperature the thermistor resistance is 100 kOhms and the output frequency is below 1 Hz, and when the temperature is suitable for extrusion the thermistor resistance is about 200 Ohms which produces an output frequency of around 25-30 Hz. If the EMC2 base-thread runs with a 50 us period then it should be possible to record the frequency of this square wave using an input pin on the parallel port with an accuracy of roughly 1/500 (half a degree C?), which should suffice.

Testing the heating side of things, a wire with about 6 ohms of resistance wrapped around the extruding head, showed that a suitable DC voltage is around 8 V and produces a current of 1.3 A. The idea is to use a HAL PWM-generator to drive the base of a 337 transistor which drives the gate of an IRF610 FET that controls the current through the heating wire. By adjusting the PWM duty cycle it should be possible to control the temperature using a PID controller based on the temperature measurement.

We have a 1994 LPKF Protomat S91 PCB mill in the lab for making prototype PCBs. Here it was used to cut a circular part (not a PCB) which was first drawn in CorelDraw, then saved in HPGL format, and then opened in BoardMaster which is the program that controls the mill through a quirky serial protocol. I think the original LPKF design has a solenoid for the up/down z-movement of the tool. The solenoid would become unreliable during a long run, because it was getting very hot, so on our mill it has been replaced with a more reliable pneumatic cylinder. The spindle is a Proxxon hand-tool, and tool changes are manual.

Tried to order some CUI encoders (102-1307-ND pic) and cables from digikey, but got these IC sockets instead... FAIL.

The heating elements on this heater just kept on heating and heating independent of the temperature. I first checked the thermocouple that measures temperature - but that seemed OK, so the next thing I suspected was the solid-state relay that turns on/off the heating. Turns out this initial guess was right, and I was lucky we had a replacement on the shelf, so now the heater works again. The picture above shows the broken SSR on the right.

New SSR in place.