Liz McCormick

HOW TO MAKE [ALMOST] ANYTHING_MAS.863

Week 08 - Input Devices

 

Project 02b
This weeks assignment was to measure something: add a sensor to a microcontroller board that you have designed and read it.

Project Planning & Prep

 

Project 02a
The data sheet for this sensor was much more straightforward than the ATtiny data sheet... except for all the Japanese.
Project 02c
Project 02b
Here's the schematic from Eagle.
Project 02b
This is the most complex board I've ever designed, and I had a hard time getting all the traces in order without overlapping eachother. I did try the autorouter this time for some ideas but ended up figuring it by hand using trace paper and colored pencils (trying to keep the VCC and GND straight).
Project 02c

Milling Struggles

 

Project 02c
Milling feels pretty easy at this point, so I'm happy about that. If only I could stop making dumb mistakes with my files or the setup. This board took longer to cut than any of my other boards (~30 minutes for traces).
Project 02c
The image on the left was my first attempt. Some of the traces were too fat and there was a lot of overlap. Also, the holes that I drilled for the DHT22 were way too big.
The image on the right was my second attempt. The holes were still too big but I decided to go with it. Lesson learned here: don't solder while hungry. I had a really hard time attaching the chip - I couldn't get it lined up with the copper pads, and once I finally did, I couldn't control the solder. I tried to create a big glob and use braid to clean it up as Neil recommends, but I couldn't get the solder out from between the pins, so everything was connected. I found a bit of success in scraping the solder away with a knife and some tweezers (since the soldering iron point wasn't sharp enough) but after being a little too foreceful, I broke one of the pins and ripped the copper off the board, so it was all over after that point.
Project 02c
dumb dumb dumb. After making it through the traces in 30 minutes, I sent the frame .png to the mill without changing it to 500 dpi - it was on the default 72 dpi. It cut right across my traces. Bummer.

Stuffing & Soldering

 

Project 02c
These temperature/humidity sensors were a little expensive, so I was sensitive about fully anchoring it to the board when I wasn't sure that it would work, given all the milling issues I was having. One of the TA's suggested that I connect it with wires, so that it's easy to desolder and I don't need to trim the pins. In the end, I decided that this was ugly and I wasn't entirely sure how to connect it to the board, so I opted to solder it directly to the board upside down (but without trimming the pins)
Project 02c
Soldering this on was easier than I thought. Now I need to figure out how I'm going to use it in my environment box before I decide if I'm going to use the wires or not. As a side note, I had to rotate the sensor in order to keep it with the correct paths.
Project 02c
When meeting with the TA, she drew this little sketch for me so I could add it to Neil's Hello.Arduino board from the embedded programming week. I need to follow up on the "100 MF capacitor". I assumed it was 100 UF, but I could only find 100 PF. I'm not really sure what any of it really means, so I don't know if I've installed the correct piece.
Project 02c
And here's the final board.

Programming & Measuring

I will try this using some of the code available in the Arduino library and see how that goes.