Use JST port for I2C and add new JST port for I2S/Expander

hardware/surface-mount/bill_of_materials.md

@@ -10,7 +10,9 @@ You will also need one 3.5mm cable (normal Eurorack patch cable) to perform the
 | SW1 - SW2 | 2 | D6RXX F1 LFS | C&K Tactile Switch (Non-Illuminated) | [Thonk](https://www.thonk.co.uk/shop/radio-music-switch/)<br>[Mouser (Black)](https://www.mouser.co.uk/ProductDetail/CK/D6R90F1LFS?qs=WS%2FiepCTwPDejJXcQ7Ir1g%3D%3D&countrycode=US&currencycode=USD) |
 | OLED1 | 1 | 0.91" SSD1306 | I2C OLED Display | [CPC](https://cpc.farnell.com/winstar/wea012832fwpp3n00000/oled-display-128x32-white-i2c/dp/SC15661)<br>**Note: The surface-mount build does not support 'The Pi Hut' style OLEDs, they WILL NOT WORK due to different pinouts.** |
 | J1 - J8 | 8 | PJ398SM | Thonkiconn 3.5mm Mono Jack | [Thonk](https://www.thonk.co.uk/shop/thonkiconn/)<br>[Mouser](https://www.mouser.co.uk/ProductDetail/Adafruit/4031?qs=u16ybLDytRatVTT4ndlXOw%3D%3D)<br>[Banananuts](https://www.thonk.co.uk/shop/bananuts/)<br>[Cosmonuts](https://www.thonk.co.uk/shop/cosmonuts/) |
-| CONN0 | 2 (pairs) | 20x1 2.54mm | Pico Connection Header (Male + Female) | CPC:<br>[Male](https://cpc.farnell.com/harwin/m22-2012005/header-vertical-1row-20way/dp/CN14644), [Female](https://cpc.farnell.com/multicomp/2212s-20sg-85/socket-pcb-1-row-20way/dp/CN14539)<br>Mouser:<br>[Male](https://www.mouser.co.uk/ProductDetail/Amphenol-FCI/10129378-920001BLF?qs=0lQeLiL1qyYln8p37ftVpg%3D%3D), [Female](https://www.mouser.co.uk/ProductDetail/Samtec/CES-120-02-T-S-RA?qs=0lQeLiL1qyZzf%2Fbgtv%2FkJg%3D%3D) **NOTE: If you're actually buying these and don't already have more lying around, buy an extra *Male* header to snip down to 4 pins if you want to fit the i2c header** |
+| CONN0 | 2 (pairs) | 20x1 2.54mm | Pico Connection Header (Male + Female) | CPC:<br>[Male](https://cpc.farnell.com/harwin/m22-2012005/header-vertical-1row-20way/dp/CN14644), [Female](https://cpc.farnell.com/multicomp/2212s-20sg-85/socket-pcb-1-row-20way/dp/CN14539)<br>Mouser:<br>[Male](https://www.mouser.co.uk/ProductDetail/Amphenol-FCI/10129378-920001BLF?qs=0lQeLiL1qyYln8p37ftVpg%3D%3D), [Female](https://www.mouser.co.uk/ProductDetail/Samtec/CES-120-02-T-S-RA?qs=0lQeLiL1qyZzf%2Fbgtv%2FkJg%3D%3D) |
+|| 1 | JST-PH (4 Pin) | I2C Expansion Header (Optional) | [CPC](https://cpc.farnell.com/jst-japan-solderless-terminals/b4b-ph-k-s-lf-sn/header-top-entry-4way-2mm/dp/CN14075)<br> **Note: This is an optional JST-PH header that can be used to connect extra I2C peripherals such as sensors. Not soldering it will not affect function of the module other than you being unable to connect these.** |
+|| 1 | JST-PH (6 Pin) | GPIO Expansion Header (Optional) | [CPC](https://cpc.farnell.com/jst-japan-solderless-terminals/b6b-ph-k-s-lf-sn/header-top-entry-6way/dp/CN14077)<br> **Note: This is an optional JST-PH header that breaks out the remaining GPIO pins of the Pico as well as providing 3.3V power so you can experiment with expansion boards or sensors. Not soldering it will not affect the function of the module.** |
 | | 2 | T18 Shaft | Knobs | [Thonk](https://www.thonk.co.uk/shop/1900h-t18/)<br>**NOTE: If you buy D-Shaft potentiometers, the knobs must be 'Reverse-D-Shaft' type.<br>Any knobs which fit may be chosen, but Mouser does not stock the standard suggestion sold by Thonk** |
 | | 1 | 10 - 16 Pin | Eurorack Power Cable | [Thonk](https://www.thonk.co.uk/shop/eurorack-power-cables/)<br>**Note: Mouser does not stock the correct cable at time of writing. Other suppliers will provide the correct part, but always double check that the polarity is correct (red stripe is always -12V)** |
 | | 1 | | Micro USB Cable (Capable of Data Transfer) | [CPC](https://cpc.farnell.com/pro-signal/psg91562/lead-usb-a-male-micro-b-male-black/dp/CS32732), [The Pi Hut](https://thepihut.com/products/usb-to-micro-usb-cable-0-5m)<br>[Mouser](https://www.mouser.co.uk/ProductDetail/Teltonika/PR2US08M?qs=9vOqFld9vZXl90mLcdqZXQ%3D%3D) |

hardware/surface-mount/build_guide.md

@@ -25,9 +25,9 @@ If you want to build this version of the EuroPi, you can buy the PCB directly fr
 1. Now it's time to solder the OLED, which is easily the most difficult part of this build. You need to apply a small amount of solder to each of the pins while holding the OLED in place with your other hand, so it can help to use some kind of desk clamp. Run the soldering iron over each of the 4 pins quickly enough that the solder on all of them stays molten, and use your other hand to make sure the display is straight while the solder cools. The pins should only just be flush with the back of the PCB, so I find it easier to solder from the top (but make sure none of the pins are bridged together).
 
     ![IMG_4560](https://github.com/user-attachments/assets/07483aa2-d90e-465d-aa1f-b427b1db0e30)
-1. Solder the Eurorack power header and (optional) I2C header by fitting them and turning the board over to solder from the other side. If they're a bit loose you might need to use an elastic band to hold them in place while you solder one pin, then remove and solder the rest.
+1. Solder the Eurorack power header, (optional) I2C header, and (optional) GPIO expansion headers by fitting them and turning the board over to solder from the other side. Note: If these photos don't match your module, you likely have an older revision which does not have the GPIO expansion header and only requires a 1x4 2.54mm male header for the I2C port. The module will work identically but doesn't require the extra JST-PH headers.
 
-    ![IMG_4564](https://github.com/user-attachments/assets/11308b06-3f1b-49c0-9650-565ddf0fca48)
+    ![EuroPi-Back](https://allensynthesis.co.uk/images/europi/assembled/Allen-Synthesis-EuroPi-Back.png)
 1. Follow the [programming instructions](/software/programming_instructions.md) to set the module up for however you want to use it, calibrate it if you want higher accuracy, and have fun!
 
     ![IMG_4566](https://github.com/user-attachments/assets/aed31128-227d-4bcb-9529-86b588602962)