I learned today about Diode Transistor Logic, which was the predecessor to Transistor-Transistor Logic (TTL), which was replaced by CMOS. This goes back to the 60’s, but was the technology that put men on the moon. With DTL, the logic gate is a set of diodes, with a transistor providing the amplification. The circuit above and below is an AND gate:
The basic idea, as I understand it: if either input is 0V (logic low) then current runs through the diode, pulling down the voltage on the base of the transistor. But if both inputs are 5V (logic high) then the diodes do not conduct, and the base of the transistor remains at +5V, turning on the transistor and the LED.
This is a poor quality video, but I needed something to show it works. In the video, INPUT1 is a 1 Hz square wave signal, and INPUT2 is an 8 Hz square wave signal. When brought together in an AND gate, the combined signals cause the LED to blink 4 times for the first half of each second.
There is no Arduino IDE package for Guix. I asked why once, but I forgot what the reason was — something to do with the way that Arduino build process works I think. Anyway, this is how I get it running on my systems. I suspect this is not the best way, but it works for me. The process is a little convoluted, but I don’t use the IDE very often, so I haven’t been motivated to figure out something better. Typically all I need is avrdude, in order to load Forth firmware onto the chips, and there is an avrdude package available in Guix, as well as a avr-toolchain package and a few other tools.
First you need to make a clone of the git repo:
git clone https://github.com/arduino/Arduino.git
Specifically I am using the some old commit bf24880d7c559751765a43cd1669d893bba267e8, which is the commit for Arduino IDE version 1.8.14, but maybe a newer version would work also.
After changing into the build directory, you must setup the proper build/run environment. I do this by having the following manifest file saved at ~/Manifests/arduino-ide-run.scm:
If you want to use the same environment as I am using right now, prefix the command above with guix time-machine --commit=079a7f2c65c51da7b53b0e5ef44c516dc8eaab6e --. (I’m running Gnome DE, but I’m not sure if that makes any difference.)
Then run the command ant run &. In a minute or so you should see the IDE appear.
I problem I have at this point is that, although the IDE runs, you are not able to compile sketches, because the executables in the avr-gcc toolchain are looking for linker & glibc stuff in the wrong place on your system. I fix this by running the following script after the IDE starts, which I have saved in the file ~/Scripts/arduino-patchelf.sh:
You will need to adjust the variables on top according to the location of things on your system. Unfortunately, it is necessary to run this script every time you call ant run, or at least I haven’t figured out a way to get around that. I’ve been told it is possible instead to just set a symbolic link from the “standard” location glibc location to the actual location, but I didn’t want to do this for fear that there might be some effect on the purity of my other build environments.
Hopefully somebody will put together a Guix package soon, but this is a workaround in the meantime.
I’m not getting paid to say this, but I bought this ISP Shield for Arduino and found it to be convenient:
This setup is the same as programming using two Arduino boards and the Arduino ISP sketch, but a more compact and convenient, since you don’t have to figure out where the wires go, and you can clip the chip into the ZIF socket.
I like this better than the other programmers I have used, at least for burning 328P chips. To use it, you must (one time) load the Arduino as an ISP sketch onto the 328P chip, and then afterwards attach the shield. When burning chips with avrdude, use the stk500v1 programmer type.
So far, I have a demo-pitches word that plays c4, e4, g4, and c5 frequencies, but I can set other frequencies ranging from a4 to g#6, using the words I have so far. There is no system yet for setting duration, so I can’t play notes proper. But it was fun setting up a system for setting the equal temperament pitches.
In microcontroller programming, it is much easier to justify efforts to save memory. I needed to store the precalculated frequency register data values for each pitch. Originally I had a table like so:
With each line (two 16 bits words) representing one pitch. However, the first two bits in each 16-bit word are actually not frequency data, but register addressing bits, which can easily be added in later. Also, the second 16-bit word in each pair has (in my application) only two bits of actual frequency data, which are the two right most bits. So, I cut the table memory usage in half by packing those two bits into the left-most two bits of the first word in each pair:
\ packaged freq register data for equal temp
\ pitches from A4, A#4, B4 , ... , G#6
\ format numbered from lsb to msb:
\ 0-13: the 14 LSBs of the lsb register load
\ 14-15: the 2 LSBs of the msb register load
$1274 , $138d ,
$14b7 , $15f2 ,
$1740 , $18a2 ,
$1a19 , $1ba7 ,
Now each line in the table is actually two separate pitches. Then I just need a few words to separate the bits back out into separate words, and recombine them with the frequency register addressing bits:
In testing, I have some trouble with some pitches getting distorted when I set the volume to higher levels. I suspect the problem is that I am still using the USB power supply and need to feed in my +5V from an external PS. I plan to try that next week, God willing.
The PCBs I had ordered from OSH Park arrived, and my co-worker Mike was nice enough to solder the components on for me. The module works, and I was able to produce 1000Hz and 2000Hz audio using FlashForth to drive the SPI signals. The sound output sounds pure and pleasant, although when I twist the volume above halfway, my ears detect what sounds like a very slight overtone or distortion, but it still is pleasant-sounding enough.
The module is a step above the usual cheap piezo buzzer circuit, the latter having the grating, distorted sound which is usually undesirable. But it is a few steps below having an actual programmable sound generator chip or a full blown sound card.
The actual PCB design here would not be used in a commercial product as it is very large for its functionality (about 6 cm wide). But it could be constructed easily by any hobbyist as the components are all through-hole and spaced far apart.