Building the Euclidean


The new PCB has the name “Euclid2-31” on the back top right corner of the PCB. The only differences are:

  1. BAT54S instead of transistors on the outputs.
  2. Circuitry for 3 analog/digital inputs or digital outputs, including jacks. These are wired to A5, A6, and A7 through previous expansion port (which is still there).

The code is exactly the same. Nothing has been done with the code except to verify that the new analog inputs work. The panels will also need new holes drilled for the jacks.

Github repository:

BOM: (new PCB amounts) Does not include components for the three optional inputs.

Qty Value Device Package Description
1 Header 1X08 Exp. Header (optional)
1 8×8 LED Module 8×8 LED Segment Displays: Row = Cathode
2 100k Resistor 0805
2 100n Capacitor 0805
4 100r Resistor 0805
1 100uF Capacitor Through-hole POLARIZED CAPACITOR
9 10k Resistor 0805
2 10uF Capacitor Through-hole POLARIZED CAPACITOR
2 1k Resistor 0805
2 1n4007 1N400X.3 DO41 Rectifier Diodes
4(0) 2n3904 Transistor SOT23 Generic NPN BJT
1 4.7k Resistor M0805 Replaces 10K
1 7805TV 5V Regulator TO220V Positive VOLTAGE REGULATOR
1 ARDUINO NANO Arduino Nano v3
2(6) BAT54S Input Protection SOT23 Schottky Diodes
1 5×2 Header 2X5-SHROUDED Eurorack 10-pin power
6 3.5mm socket 3.5mm socket
2 8-pin female headers 1X08 For LED Matrix (optional).
2 15-pin female headers 1×15 For Nano. Cut from female header strip.
1 IC Socket DIL24-3 For MAX7219

BOM Notes:

  • DIP MAX7219 readily available from Digikey, Tayda, etc.
  • LED Matrix is Row:Cathode Column:Anode (Tayda A-1316). I haven’t tried any others. Be aware that although they look the same some matrix displays have different pinouts.  They also can vary in size.
  • Thonkiconn style 3.5mm sockets (I use Erthenvar). Tayda sockets can be used with a bit of modification.
  • Rotary Encoders. I use EN11-HSM1BF20 from Digikey which seem to have the most common footprint and pinout BUT not all encoders have the same footprint/pinout — it’s a big pain. These TT-Electronic/BI EN11s seem to have the best availability and work well.
  • The 10K resistor at the MAX7219 should be replaced with a 4.7K. This resistor controls the LED brightness, and although with the 10K the LEDs are very bright, they also consume much current and the 5V regulator which can supply up to 1.5A gets very hot (but not hot enough to require a heatsink or trip the thermal cutoff). The brightness can be controlled in software as #define brightness around line 170.


New Schematic:

Clean PCB with Isopropyl alcohol to degrease to make soldering easier.

The 10K resistor at the MAX7219 near the capacitor should be changed to 4.7K.

MAP_6564_lznSolder the surface mount devices first. There’s a single SMD capacitor on the front as well (opposite power connector).

Soldering can be done with either hot air or iron.



After soldering remove any solderballs that may have formed from using solder paste.

Check that no solder is bridging the components underneath.

Add the through-hole power components and power connector.

Visually inspect the soldered components for shorts.

Test the power connector for shorts between ground, +12, and -12, and also between +12 and -12.

Apply power and check for +12 and +5 on both ends on the indicated diode.

If using “Kobiconn” style 3.5nn jacks, trim the ends as shown so they’ll fit in hole. There should be enough pin left to come through the other side.

MAP_6578_lznUse a discarded lead (diode leads are perfect) to connect the Kobiconn ground to the PCB.

Shown here: Thonkiconn and Kobiconn jacks.

MAP_6585_lznIf the encoders are low-profile (doesn’t meet the panel at the same level as the 3.5mm jacks), add extra nuts or washers to fill the gap. This is optional but will the the knobs more durable and prevent presses from stressing the PCB.


Add the six jacks and three encoders, then temporarily place the panel over the parts for alignment.

MAP_6579_lznCarefully turn the panel upside down and place on two supports. The supports should prevent the encoders from touching the table. Be careful not to scratch the panel.

If using low-profile encoders, then encoders should drop a small amount with less than a half millimeter showing through the hole. Make sure to solder the side “snap ins” for strength once aligned.

Solder the jacks and encoders.

MAP_6586_lznSolder the two 8-pin female sockets for the LED module. This is optional but recommended. However the module will stick out of the panel by 1mm.

Alternatively, the LED module can be soldered directly. DON’T DO THIS NOW. The module will need to be aligned to the front of the panel.

Add the sockets for the IC and Nano.

The Nano socket is and odd size and will need to be cut from a strip of female headers.


Visually inspect the solder connections for bridges.

Use a multimeter and check again for shorts on the power connector.

Apply power and check for +12 and +5 at the indicated points.

If soldering the LED Module, add it now. Align the module with the panel as shown earlier. Make sure the orientation is correct before soldering because it will be almost impossible to get out without damaging the module or PCB.

Add the programmed Nano (sketch location listed above), MAX7219 IC, and LED Module. Ensure proper orientation. Pin 1 for the module is marked by a small DOT on the front (panel side) of the board on the lower left (may not be readily visible).

If mounting the LED module on headers, it will need to be secured with hot-glue.

Apply power, and you should see the display light-up and begin with the default pattern. Yeah!

If it doesn’t work, check that everything is oriented properly.

MAP_6595_lznOnce working secure the front panel to the encoders and jacks.

The encoders should have enough room for a washer and nut. Watch that the nut isn’t pulling the PCB towards the panel. If using a second nut as a spacer, tighten that nut against the panel, then tighten the top nut. This will put all of the button-pushing stress onto the panel and not the PCB.

The PCB can be held to the panel with just the jacks alone, but keep in mind that any stresses on the encoders are going directly to the PCB. This isn’t a problem with normal everyday operation, but if something falls onto the encoder knobs it could damage the PCB.

Add the knobs of your choice.

MAP_6600_lznKnobs up to 20mm will fit without obscuring the legend.