2HPico-Eurorack-Module-Hardware

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2HPico-Eurorack-Module-Hardware

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2HP Eurorack module based on Raspberry Pi Pico 2

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  - Pico 2HP_Audio.net
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  - 4HPico Panel.stl
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- - 4HPico panel_for_JLCPCB.zip
  - 4HPicoDSP.zip
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- - 2HPico Panel.stl
- - 4HPico Panel.stl
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README.md

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# 2HPico-Eurorack-Module-Hardware
2HP and 4HP Eurorack modules based on Raspberry Pi RP2350 Pico 2

December 2025 - added Version 1.0 2HPico KiCad design files, BOM, Gerbers for main board and panel board and 3D printable panel.

Jan 28/2025 - added Version 1.0 2HPico DSP PCB design files and FR4 front panel design files and gerbers.

Feb 16/2026 - JLCPCB assembly files are now verifed. Minor BOM changes to 2HPico DSP as a result of further testing.

April 13/2026 - added 4HPico DSP PCB files. PCB fabbed, tested and working with 1 jumper.

May 6/2026 - updated 4HPico DSP PCB to V1.1 which corrects missing GND plane connection from middle to bottom of PCB. I have no plans to order these because V 1.0 is fine for me. Changes are minimal so not much risk in ordering V1.1.
Added .stl file for 3D printed panel. No plans to do a PCB panel at this point - I'm happy with the 3D printed panel.

July 2/2026 - added 4HPico PCB files

2HPico, 2HPico DSP, 4HPico and 4HPico DSP are complimentary designs intended for different uses:

The 2HPico has 1 or 2 CV inputs and 1 or 2 CV outputs depending on how its jumpered - see notes below. Its dual DAC CV output(s) can also be used for audio generated by the RP2350 processor. 2HPico can be used to process triggers, gates and CV inputs and can generate CV or audio out - its well suited for sequencers, LFOs,  oscillators etc.

2HPico DSP has an audio ADC and DAC to enable signal processing for audio effects like delays, reverbs, chorus etc.

2HPico and 2HPico DSP use the same front panel and control panel PCBs.

4HPico is the 2HPico with 2 dedicated CVin, 2 dedicated CVout and two jumperable CV in/outs. Encoder with a 64x32 OLED display instead of pots for setting parameters. This is a single PCB design which requires a 3D printed panel or PCB panel.

4HPico DSP is basically the 2HPico DSP with stereo audio in and out and two dedicated CV inputs. Encoder with a 64x32 OLED display instead of pots for setting parameters. This is a single PCB design which requires a 3D printed panel or PCB panel.

See the repository https://github.com/rheslip/2HPico-Sketches for Pico Arduino sketches to run on the 2HPico.

See the repository https://github.com/rheslip/2HPico-DSP-Sketches for Pico Arduino sketches to run on the 2HPico DSP.

See the repository https://github.com/rheslip/4HPico-DSP-Sketches for Pico Arduino sketches to run on the 4HPico DSP.

See the repository https://github.com/rheslip/4HPico-Sketches for Pico Arduino sketches to run on the 4HPico.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0607.JPG)

***General notes on the designs***

Waveshare (and others) make small form factor RP2040 and RP2350 boards which make stuffing one into 2HP possible. The RP2350 has much better performance but for simple things like sequencers, ADSR, LFO etc the RP2040 should work OK. Core 0 runs the main processing loop for the UI and control,
core 1 runs the DSP and sends samples to the I2S driver. The code has an option for monitoring the performance of core 1 with a scope. If enabled you will see a pulse on GPIO 8 that indicates how much time core 1 is spending processing samples. If its high more than 100% of the time you will get audio dropouts - time to overclock or optimize your code some more!

The PT8211 16 bit stereo R2R DAC used on the 2HPico and 4HPico is very inexpensive and has proven so far to be quite accurate and consistent from one chip to another (provided they aren't defective - see caveats below). It has no internal antialiasing filters but it works down to DC so can be used as a CV out as well. U6 is a DC coupled antialiasing filter and it also amplifies the DAC output to +-5V eurorack levels.

The 2HPico DSP uses a PCM1808 24 bit stereo audio ADC and a PCM5102A 24 bit stereo audio DAC. The top panel jack is connected to both channels of the PCM1808 and one of the RP2350 ADCs. There is a "DC Input" jumper on the back of the board which shorts the input blocking cap so the top jack can be used for CV input. It adds an approximately 1.6V offset to the input signal so could cause high level audio inputs to clip. Its is recommended to leave the blocking cap in the circuit for audio processing applications.
As with the 2HPico, if the "DAC" solder jumper is shorted audio is sent to both of the lower front panel jacks. Both the PCM1808 and PCM5102A have internal antialiasing filters. Note that the 2HPico DSP can not generate CV outputs because the PCM5102A DAC must be AC coupled.

2HPico DSP build is pretty much the same as the 2HPico but you will be populating a couple of different parts - see the BOM.

***Panel PCB Build notes***

Solder the .1u cap and the RGB LED. Note pin 1 location is NOT the lead with the 45 cut on it - check the picture in the BOM. Hopefully you bought the right pinout! Note these are 5V parts but I haven't had any issues running them at 3.3v - and they are still way too bright!

Solder the jacks - note that the two bottom ones have the same GND via to save real estate

Solder the button. Glue the button cap on with a dab of superglue.

Solder the pots. You can clip the brackets near the bend to make soldering a bit easier but its not required. Make sure they are lined up vertically and horizontally before you solder the brackets to the pads. A Panavise is handy for this step.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0590.JPG)

***Main PCB Build Notes***

Solder all the 0603 Rs and Cs first

Solder diodes, R1, U3 regulator, U4 voltage reference and power connector J4. Hook it up to power and check that the 5V, -12V, +12V and -10v reference voltages are OK

Solder in all the chips, the larger caps and the trimpot RV1 (2HPico only).

The Waveshare RP2350 board cannot solder directly to the main PCB because it has components on the bottom side and must stand off a bit. You can solder .1" headers to it and solder the headers to the main PCB or solder .1" header pins in the corners and make the rest of the connections with short wires.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0595.JPG)

Power up the PCB again and check that the 5V and 3.3V rails are OK.

Solder right angle connectors J1, J2 and J3. The shorter pins solder to the main PCB as shown.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0593.JPG)

Plug the long end of the right angle connectors into the panel PCB and solder.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0599.JPG)

Clip the pins on the bottom side of the main PCB so they don't interfere with adjacent modules - a 2HP module is supposed to be only 10.16mm wide.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0596.JPG)

Solder one of the jumper pads on the bottom to select jack 2 on the panel as either DAC right channel out or a second CV/Gate input. This depends on what the module is supposed to do.

The 2HPico DSP board has a "DC Input" solder jumper that should be shorted if you want to use the top jack as a CV input.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0601.JPG)

It should be ready to go. You can load up the HWtest sketch and run it to check the pots, button, inputs and DAC functions.

***2HPico only - Trim the DAC output***

Load up the ADSR app or mod the HWtest sketch so the I2S code is sending the value 0 to the DACs. Measure the level at the output jacks or at U6 pins 1 and 14 and trim RV1 to get as close to 0V as possible. There will probably still be a few mV difference between the channels. 
Its set up for +-5V output corresponding to -32767 and 32767 DAC values respectively (output amp inverts the DAC signals). If you want higher output levels you can mod the output stage gain but keep in mind the offset and the lowpass filters also have to be recalculated.

***Notes on the PT8211 DAC chips for the 2HPico***

I bought 10 on Aliexpress and I got a couple of defective ones. Symptom was no output from either left or right DAC, just a low amplitude glitch at the opamp outputs U6 pins 1 and 14. I also got some that were not linear enough for accurate pitch CVout. I suggest you buy from a couple of different vendors and cross your fingers. Alternatively Sparkfun and PJRC sell PT8211 kits for a few dollars that include a PT8211 presumably from a reputable source.

***Notes on the PCM1808 and PCM5012A chips for the 2HPico DSP***

The PCM1808 ADC is 24 bit only wheras the PCM5102A works with either 16 bit or 24 bit I2S audio. Since they are on the same I2S interface they must both run the same format. I was not able to get 24 bit I2S working with Arduino Pico but it does work with 32 bit I2S. The additional overhead is minimal since the processor and DMA are 32 bits.

***Notes on the Panels***

STL file is included for a 3D printable panel which includes a collimator that sits over the RGB LED. I glued a short piece of transparent filament inside the collimator as a light pipe - for some reason commercial acrylic light pipes are stupidly expensive. The RGB LED is very bright even on 3.3v so I cut the level back in the code. I will probably design a silkscreened FR4 panel for it at some point.

FR4 front panel gerbers are also included. You will have to make a collimator from a small piece of plastic tubing to direct the RGB LED light to the hole in the panel.

![](https://github.com/rheslip/2HPico-Eurorack-Module-Hardware/blob/main/Images/IMG_0608.JPG)

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