9. Input Devices Assignment

Input Devices Assignment

This assignment was significantly frustrating and the learning curve for it has not been entirely gone through as I am writing this, a lot to do left.

For this particular assignment, the work was clear, measure something, the real thing about it was in the how, so I made this first approach to a workflow before starting:

The first was to understand how the different types of sensors work in the example boards and how do they interact with the Microcontroller attiny 45v we found in the lab inventory to make the boards.

This time, the initial designs were kind of made, so I started by downloading the traces files and customize them, I chose three sensors for testing: light, load and txrx. I milled first load and then txrx, building on previous assignments, I sent the path to the modela using offsets = 8, this would not bring a good result, since an horizontal trace is too close to a pad, and when it was milled it was reduced to a nealy hairline width (marked in red) so just too much offsets.The second time I chose offsets= 5 and it worked fine.

milling hello load

Then, it was time for the other board, this time I used directly offsets = 5, learning from previous experience, however, other problems occurred. This time the double contact tape was not properly bonded into the milling machine table, so, eventually it got loose and I lost the milling.

Finally, I got it right and milled the board, however, as I was removing it, something curious happened, the traces were milled at a particular angle. So finally, after trial and error, I got two boards made, one almost made and one completely lost. It was time for soldering. But first, get the parts for the assembly.

board before soldering

Welding was, apparently no problem, since the parts were quite simple, in the space of time I had in the lab I was able to weld completely the load and txrx boards without incident. It was time for testing. So I downloaded the C code and makefile for the boards and tried tu run it using my FabISP board without success.

programming sensor borads failure

The welding, it was now clear, was not as well done as I supposed, to checking again was in order, however as I was reviewing and resoldering some parts of my txrx board, one of the traces got loose and the connection was lost, so long to my board. Fortunately, Roberto had some spare boards I could work on, I got soldered another txrx and a light board:

sensor boards, after soldering, ready for testing

So, time of truth, to see of the soldered boards were actually functional. I tried the hello C code for each board, without success... again. So it was time to recheck, review and redo the soldering, until I got those boards running right. It took a while, and I was specially careful checking on the Tiny 45 pins. In the end, I may never really know which solered pin was the faulty one, or if I tripped welding a resistor or a capacitor, but, however, the boards worked.

programmed TxRx

In order to program the boards, both FabISP and the AVR ISP Mk II were used, as I was not entirely certain that the connections were right, I used the AVR ISP to check using the LED in it.

Sensor board programmed with AVR ISP

Programming a Board from FabISP

After finding that everything was set right, I downloaded the Python scripts for operating the sensors and started working with them and checking how the measurement works. They worked fine.

I checked all three boards using the Python scripts, first he TxRx, using a pair of copper plates connected to some wires to the board, the readings changed as I pressed them.

measuring Txrx

I used the same plates to test the load sensor, this was not as responsive as the first, probably becasue of the system used.

measuring load

Finally I checked the hello light:

To-Do

-Prepare a customized board to make an acceletometer sensor.

-Get my Fabbed Arduino Board done, more to come in the "Output Devices" assignment

Conclusions?

Design, Design, Design... Still a lot to learn about this

Second, No matter how simple the board, soldering is Key

Third, this i cannot emphasize enough,read the datasheets before making the boards

Fourth, as previously stated, take into account Hofstadter's law into assignment planning, it -painfully- works.