Hardware Is Hard

Where I live there aren’t really any options for electronics shopping, so I was resigned to do it mostly through mail order. Fortunately I discovered that Kjell & Co., which is probably the closest thing to Radio Shack we have in Sweden, not only carries a lot of Arduino stuff, but also has an shop in the next town over (Luleå, about 50km away).

So I got myself a soldering station, some lead-free solder1 some sensors and grab bag of diodes, resistors and cables to play with. It must be something like 25 years since I last had a soldering iron in my hands, but putting the T-cobbler together I all just came back to me. Even the smell was exactly as I remembered it.

I had some problems getting the DHT11 sensor up and running. All the examples I could find had a four-legged sensor, but mine came pre-mounted on a board with only three. Also, the configuration of the legs had been switched around. That one took some figuring out.

The DS18B20 however, just plain refused to show up as a device in /sys/bus/w1/devices. I tried everything: reflashed the SD card, checked the kernel messages, double-checked my connections (twice), moved things around on the bread board in case there was a break (which incidently there is; the vertical strips break in the middle, but this didn’t affect my wiring) and tried every combination of power and GND I could find on the breakout board in case I had done a bad soldering job (which I hadn’t). I did countless reboots. Still nothing.

I had just about written that sensor off when I discovered that the pullup resistor2 I’d used wasn’t yellow-purple-red as specified, but yellow-purple-yellow. 470K instead of 4.7K. Oops.

Hardware is hard.

  1. Which everyone seems to think is terrible, but I haven’t had any problems with. Yet.

  2. I confess I have no idea what a pullup resistor actually does.