Sally Williams @ Fab Academy 2015

Assignment: 

• Add an output device to a microcontroller board you've designed and program it to do something


Background

I wanted to use Output Device week to make a useful contribution towards my final project.

In essence I was developing a wrist wearable digital mala for recording and training the mind in mindfulness. This concept could include a secondary device which would be place in the home. This wrist wearable would connect with the secondary device which would interpret and express some of the accomplishment of time recorded as mindful during the day. There are three ways I wanted to translate this information:

1    light
2    rotation of prayerwheel (prayerwheels are traditional Buddhist sacerd objects which can contain 1000s of sacred mantras; as the prayer wheel is rotated - traditionally spun on a spindle by hand, the auspiciousness of the prayers are said to be caught and carried by the elements.
3    statistics to demonstrate progress in graphs

So, here, in Output Device week, I would use a DC H-Bridge Motor Driver on my board to enable and simulate the rotation of a prayerwheel. I used the 'hello.H-bridge.44' board as a basis. For the purpose of testing, I added 2 buttons to enable me to rotate the motor both clockwise and anti-clockwise (although a prayer wheel only rotates clockwise).

Configuring the Schematic in Eagle

The first part of the weeks' assignment was taken up by trying to find the components in the Eagle libraries. One of the items cited on the hello.H-bridge.44 board is "IC3 A4953". I went on a wildgoose chase trying to find this part. It was not listed in any of the Eagle libraries that I had downloaded from the earlier electronics weeks, including the ng library and the fab.lbr. Although I understand that I could have substituted with another part with same footprint, as beginner I did not have conviction over making the right choice. Thankfully, I received another fab.lbr database from a global peer, where the part was listed as an unique part with its specific footprint. I could now proceed to complete configuring the schematic with confidence that I was on track again.
 



  Board with airwires ready to plan:



Routed board:



Correcting routes in Gimp:

In some places on the board, the routes looked too close to footprints and some additional routes needed thickening to take into account an increase in power supply. I made these alterations in Gimp with the drawing tools.

 

Corrected file :



The board was extended by 40 pixels on both x and y axis and 'trace' and 'interior' versions were saved ready for milling.

Milled board:




Stuffed board ready to test:



Initial continuity tests showed shorting-circuiting on the board

After revisiting the board in Eagle, a connection was spotted bridging the capacitor. I realised that I had forgotten to run a design rule check, which would have shown this error:



As this was easily fixable on the board itself, I desoldered the capacitor, removed the copper layer on the board by blade, and then bridged a tinned copper wire section to create the right route:



Once this correction had been made, the board made all the right nosies under the mulitmeter.  From the terminal window, changed directory to inside this new folder and then ran the 'make program-usbtiny' command which showed to be 100% succesful.

As soon as this was done, when the power supply was connected, the motor ran its sequence of varying rotations and rhythms from "hello.H-bridge.44.DC.c".

See green blurr below:




Modifying the sample code

Using NG code as a basis, and with the help of a tutor, I was able to amend the code so that the 2 buttons could be used to rotate the motor. "Button L", whilst being pressed, would rotate motor clockwise; and conversely "Button R", whilst being pressed, would rotate in reverse the direction. It was noted that the motor struggled to turn with the delay set at 5µs; this was changed to 3µs and worked succesffully both ways.

 

Download files:

hello.H-wheel.44.DC.c

makefile2

(After downloading makefile2, you must rename as "makefile", removing the "2"). (This is because the command instructions for C programming are taken from a "makefile". As I have more than one makefile in my webfolder, I chose to name them "makefile1", etc.

HelloWheeltraces

HelloWheelinterior

Eagle file - schematic - board