Pranam Tries To Make Things

MAS.863 - 2016

Week 11: Interface Programming

Writing a Potential Output Program for the FabSpec

Yeah, this week didn't go very well. Coming back from Thanksgiving, I didn't have much time to do the interface programming project. The goal was to desing the final photogate circuit and build an application for it to graph voltage, which will read cell density. Still bad at Eagle, the board took me 3 days to design, and a real challenge to export. I didn't even get to mill it.

I spent a long time figuring out a good design for the photogate circuit. The final iteration was to have a 9 V battery powering both the 5 V ATTiny microcontroller through a 5 V regulator, as well as a bright white LED (indicated by a transistor since I need through-holes). On the other side, connected to an ADC pin, is a phototransistor, which can read the amount of light passing through a tube.


Figure 1. Eagle schematic of Photogate.

Then, it was time to route. With so many connected components, I took Hisham's advice and took a guess at the orientation of the board that would yield the fewest overlaps, and then used the best autorouter design. I settled on a design that needed only 1 0 ohm resistor.


Figure 2. Eagle board design.

From here, I really struggled with exporting the file, and realized it was the dimension layer 20 that did not allow me to export a concise png file. After figuring that out, I tried to mill the board, but something seemed off. Perhaps the endmill was too dull, or the Modela was malfunctioning. No clue, but I have to keep trying.


Figure 3. Failed milling.

I will continue making the final project board, and then program it with the folliwing short application I wrote in Sublime. This is just a starter program I wrote from scratch. Basically, I read in the voltage from the photoresistor every minute (no need to monitor it for too long), and then I store the value in an array of fixed value (perhaps read voltage every minute for 1 day), and then export the array as a CSV, which can be opened by MatLab or Python and graphed for the user to see.


Figure 4. Program to interface with Photogate board.

Activity Tools Used
Designing The Board Eagle
Milling The Board Modela
Stuffing the Board Soldering Stuff, Electronics
Reading the Board Arduino, C, Sublime