Building my own Eurorack module

 For my birthday I got a NiftyCase with various modules, and I also bought a Mr Phil Ter and a Monsoon for it. However, it lacked envelopes. I started looking for possible solutions, On my youtube channel you can see a bit more about the synthesizer, here I will describe the design and making of the module. The basic circuit I came up with is as follows:

There's two inputs and an output, one of the inputs is the gate signal, which starts the decay, and the other is the control voltage, which uses and LED to control a photoresistor which is in parallel with a potentiometer, both of which control the length of he decay. The output is multiplied by a certain amount (currently 1.55x, but I may go back to the idea of multiplying by 2x as in the circuit above.

The 85k resistor was changed to 1M, and I added a LED and 470 resistor to show the decay working after the OPAMP (an TL072). This circuit worked, but unfortunately most gate signals are terrible, so I had to add a special PIC10F206 circuit to clean that up. This circuit also discharges the capacitor quickly between uses, avoiding a wait time that was necessary otherwise.

The only improvement still needed is handling of triggers: if the gate signal is too short I want to change the behavior into a release instead of a decay, possibly with a check that the output signal has grown small enough.

Here is what it looks like on the outside, which required some drilling, which was definitely a new experience, and quite scary.

By now I learned that the CEO of the company that makes these specific panels isn't a very nice person, so I may have to reconsider my purchasing strategy here.

Syncing the Arturia MicroBrute with the Pocket Operator 32

 Today I wanted to do the reverse of the previous project: having the Arturia MicroBrute control the Pocket Operator 32. This is relatively easy (one video states it takes only 17 seconds) by just hooking up the MicroBrute's Gate Out to the Pocket Operator Sync In, but as I previously mentioned the issue here is that the output is 10V peak-to-peak and the input is 5V peak-to-peak maximum. It still works, which is great, but there have been reports of Pocket Operators freezing at certain battery levels and in general it isn't a good idea to run something out of specification.

Fortunately the circuit I made has a very lenient input, and can also be used to convert the 10V of the MicroBrute into the 5V necessary for the Pocket Operator. I plugged everything in, switched the PO-32 to sync mode 2, and everything worked fine.

You can see it working in the following video:

Soldered version of the PO-32 to Arturia MicroBrute sync

 As I still had a few prototype PCB boards I decided to make a soldered version of the syncer I previously designed. I added a power plug to it, so I can splice the power off the MicroBrute into this circuit. The power circuit is the usual LM7805 implementation seen elsewhere on this blog. As you can see from the pictures, my soldering skills haven't improved, but they suit the purpose, which is to make a nearly unbreakable version of the board.

I like my trick of putting the connectors at the edge of the board like this, so I don't need to drill larger holes for the pins. I chose pink for the connector to the PO-32 because Teenage Engineering sounds more playful, and because that plug is red, so I know what to match it to. Next will be to set this up and start making a song with it.

There was one soldering mistake that I had to fix, a blob of solder had fallen between two of the lines. This caused the circuit to just play a single note initially. But with my multimeter it was easy to figure out.

Video for the PO-32 to MicroBrute sync project

I made a short video showing how the sync circuit of the previous post works:

I've not made many of such videos yet, and I clearly need some work on figuring out how to set this up better, but hopefully it shows the most important aspects.

The details are as follows:

• 3.5mm stereo male to two 3.5mm mono male splitter cable, one goes to the circuit as shown, the other to a MouKey MAMX3 mixer.
• The PO-32 is in SY1 mode, which can be done using the * button combined with the BPM button.
• The Arturia MicroBrute is in "gate" mode, this can be configured with the program on a PC hooked up through the USB port.
• The Arturia MicroBrute has a recorded sequencer pattern, ideally with a length matching the drum pattern (16 beats, usually).
• The first note of the pattern will be the note played on the keyboard.

In the schematic the 100k Ohm resister IS the Arturia MicroBrute. There is no need to actually put the resistor in the circuit. I added it to aid the simulation.

Pocket Operator (PO-32) to Arturia Microbrute sync

Two birthdays ago I received an Arturia Microbrute which I did very little with so far. Instead I worked on a system combining a Yamaha CS, the Pocket Operator PO-32 by teenage engineering and a TASCAM digital recorder/mixer. However, lately I've become interested in Eurorack modular synthesizers and I discovered that the Arturia Microbrute has some (quite limited) patch options. I also became curious whether it would be possible to include the PO-32 into the modular system and discovered that it has a sync signal, both going in and out and I was curious if I could use this to have the PO-32 control the Arturia Microbrute.

The Internet has quite a few resources here, most of which have the Arturia Microbrute's Gate Out connected to the sync in from the pocket operator (e.g. https://www.youtube.com/watch?v=WIobsEA-_cA). Although this seems to work, if you research it closer there are some warnings here. The Arturia Microbrute's Gate Out is rated 10V peak-to-peak, whereas the pocket operator manual states that the sync signal should not exceed 5V peak-to-peak. From all the youtube videos on this it seems it usually works, and definitely doesn't destroy the pocket operator, but there are reports of the pocket operator freezing at certain battery levels. I suspect this all can be easily voided with a resistor network, and I'll work on that soon. However, I was more curious whether it was possible to have the Microbrute get the sync signal from the Pocket Operator through the Gate In.

Unfortunately the Gate In of the Microbrute expects a 5V peak-to-peak minimum (I suspect it can handle up to 12V) and the Pocket Operator seems to output not more than 1V, as shown on p0k3t0's blog. As you know, I faced a problem like this in the past with the RS-232 conversion for the PIC microcontroller, and I thought that I could use the same circuit here. Unfortunately the RS-232 conversion also required an invert, which is not useful here, so I decided to link two together to form the following circuit:

I'm sure a smaller version is possible, but as shown it is very lenient, it's very accepting to different voltages, and the output's voltage is basically whatever voltage you run the circuit at. 4.5V seems to be enough for the Arturia Microbrute, though.

 

Here is a picture of the working prototype I made. I can make a video later.

I used circuitlab to make this circuit diagram, also because it allows you to simulate the result:

It shows that a 0V input voltage results in a 0V output, and a 1V input results in a 4.5V output. When you change the voltage of the circuit to 12V it will adjust accordingly.

The simulator also allows me to measure current usage, which is 2.3mA, which seems acceptable.

Updated source for SERVO.ASM

Will Collier has updated the source code for my servo controller (described in my post here). It should now be able to reach its full range.

PS/2 keyboard to MIDI translation

In 2011 I made a PS/2 keyboard to MIDI converter. It came with a sample source code, but this source code had some issues as it was originally meant for a regular keyboard read, not one that is MIDI specific. So at the encouragement of Oscar I wrote a better version of the source code that has the following additional features:

• It allows mapping of every key on the keyboard using two tables, one for the regular keys (BaseKeyboard) and one for the keys whose scan codes start with 0xE0 (SuperfluousKeyboard). Setting a key is as simple as giving it a note (1-127).
• It removes the auto repeat that some keyboards have that could create notes with an annoying echo.
• It allows assigning of MIDI CC messages. This is done by adding 128 to the channel you wish the CC message to be sent over. By default it will send key presses with 127 and releases with 0. This can be changed globally, but not per CC.
• It has various fixes that make the code run smoother and be less error prone.

The source code is available here. Remember to keep the spacing intact, as otherwise the file may not compile. It is intended for a PIC16F690. The wiring is described at the top, and in the original article.

The biggest flaw so far is that upon startup it sends a few random MIDI sequences out, because the keyboard sends its start up sequence to the PICmicro. This can be avoided by mapping those specific keys to 0, or by adding a startup delay.