Progress Report (Sort Of)

So I have not updated my blog in a while. Grad school is keeping me pretty busy. Most of what I do with electronics now is related to the local hackspace I joined. I was able to use some tools there to shorten the bolts for the case of my RPN Scientific Calculator and I also have access to a laser cutter and 3D printer that I eventually want to use to make keys for it. One of the members there and I decided to start on a project together. We have not made enough progress yet to post about but we did finish a schematic of what we plan to do. For this we have both EPROMs and EEPROMs. The EPROMs have a small window and can be erased with UV light, though the lamp we have does not seem to be working. They would also need a higher voltage source to write them and I want to make a voltage multiplier when time allows. If I can get that working, it might also help me with another project that needs -27 volts for LCD contrast.

Another neat thing I have experimented with at the hackerspace is the Spark Core. One of our members was able to get a hold of several of these for us. These tiny little boards let you connect a microcontroller to Wi-Fi pretty painlessly. This would work really well for a project idea I have that I have not started on yet. One thing I don't like is the Arduino-like environment used to program them with but I think I could get used to it since I would probably use my own microcontroller for everything but Wi-Fi. Another idea would be to simply use the CC3000 chip the board uses without the Spark Core board, though that may be too complicated to be worth it. It seems that the newer Spark Photon uses a different chip which could be easier to use by itself, though Spark Photons are not scheduled to ship until March.

One thing I have been working on on my own is a sombrero with LEDs. It was supposed to be part of a Halloween costume, but I did not finish it in time. Each color (red, green, and blue) is soldered as a 4x4 matrix that has its own shift register. It might have been possible to solder all 48 LEDS (16 each of red, green, and blue) as a 6x8 matrix and use one less shift register, but this way lets me keep each LED on three times longer. NeoPixels would have worked well for this project but just one of them costs almost as much as all of the LEDs. The board for controlling everything is finished. Now all the LEDs just need to be sewed to the sombrero and the firmware written to control their flashing. In order to save time I only soldered buttons to the board for controlling the patterns of the LEDs, but I do have some nice potentiometers I bought that I now have time to use instead. Reading their value with an MSP430 worked great on the first try and I displayed it on my one wire debug display.

One Wire Debug Display

Lately I haven't had much time to work on hobby projects but I did manage to do a few things. Sometimes for debugging I use an LED if the UART pins are not free to output to a serial terminal. This works alright for simple things but gets complicated when I start outputting different patterns of flashes. Instead I decided to wire a small screen to a microcontroller so that I can bitbang out debug information with just one pin.

WM-1611-62C

At the beginning, I considered using a WM-1611-62C LCD from Russian telephones that I have had for the last two years. It runs on 1.5v, so I haven't been in a hurry to do anything with it. The documentation for it shows Vdd supplied by 5v through a 4.7k resistor with two standard diodes between Vdd and Vss. Running from the 3.6v of the launchpad, the voltage between Vdd and Vss was well under 1.5v and the display was very dim. Adding another diode brought the voltage up and resulted in the clear display you see on the right. Poking at the pins revealed what some of them do and I was able to bitbang some characters to the screen. This was possible even at 3.6v through diodes since the inputs are open drain. Unfortunately, other than 0-9, only a few other specialized characters are possible. Displaying anything in hexidecimal would not be possible, so I scratched the idea of using it.

The next idea I had was to use a cell phone screen. In Kyrgyzstan I found some 1202 cell phone screens for about $2 and I tried soldering 0.10mm wires to one of them. At 700°F the iron was way too hot and even at 550°F I managed to destroy the tiny ribbon cable of the LCD. The next LCD I tried was from a Nokia 3510i but I managed to lift the pads off of that LCD. It seems that the temperature displayed by the soldering iron might be wrong. Even at 350°F the iron melts solder very quickly.


Another idea I had was to use some small green 7 segment displays I have lying around. With one MSP430 I could multiplex all four of them. Even at the 6mA that a single pin can supply, these displays were very dim. Maybe it has something to do with running green LEDs at 3.6v. Next I tried a red 7 segment display from an answering machine that was very bright even at 1mA, so I soldered everything to perfboard like you see on the left. The MSP430 on there waits for data to come in on the purple line and flashes a number out digit by digit. It is probably not practical for displaying 32 bit numbers in decimal but seems to work well enough for 8 and 16 bit numbers in hex. The headers on the right are for relaying incoming data to a PC over UART, even if the UART pins on the main microcontroller are in use.