Midibro soldering guide

Before you start


Building Midibro is quite easy, even for a beginner. If you’re new to soldering, I recommend reading this tutorial.
Please also check this page that will help you identify bad solder joints.

Needed tools

You will need basic tools to complete the build. This is the bare minimal recommended setup:

  • 20-30W soldering iron
  • leaded solder (way easier to work with than non leaded solder – just wash your hands after soldering and you’ll be fine)
  • a set of pliers
  • a basic voltage meter, or multi meter


Take your time, read this guide twice or even thrice before warming your soldering iron.

Work in a clean place with enough space to do things properly.
Take your time and be patient, you will have a fully functional device if you follow this guide thoroughly , but a single little mistake can turn a few hours build into a days/weeks build.

We are not responsible for anything wrong (including electric shocks, malfunctions, fires, accidents involving a soldering iron) that might happen during the assembly of the kit. Everything you do while assembling the kit is at your own risks.

Step 0

First, solder the LCD headers on the top side of the PCB, as this is easier to do it now.
The longer side of the headers should be placed at the back (this means that on the picture, you are looking at the shorter side).
Do not solder the other components shown on the pic yet – this has been taken at a later stage of the build.


Step 1

Let’s solder the bottom-sided components.
Start with the 4x 220 ohms resistors. The top ones are here to ensure proper MIDI communication. The bottom ones are the current limiting resistors for the 2 LEDs.

ERRATUM: R2 is mislabeled 220 on the PCB and in the following picture.
Do not solder a 220-ohm resistor for R2, leave it empty for now.



Step 2

Then solder the 2x 10k resistors (Brown Black Orange Brown or Brown Black Black Red Brown).
R2 (mislabeled 220 – remember the previous step?) is a pull-up resistor for the optocoupler and R8 is a pull-up resistor for the reset switch.

On the following picture, if you look at R2, you will notice its value is 220. This is not correct, do solder a 10K there.



Step 3

Add the 4x 100nF (0.1uF) filtering caps.
Note that C6 is left unpopulated, as the EEPROM circuit is not used by the original MIDIpal, and components not supplied in the kit.


Step 4

Then solder the 2x 33pF caps (these are labelled 22p on the silkscreen, but the kit provides 33pF caps, as the provided crystal needs higher value caps.


Step 5

Then add the 20MHz crystal.
And the 2 diodes, D1 and D2. Those are polarized, the ring on the component must be placed like indicated on the silkscreen.


Step 6

Then place the 2 IC sockets.
Pay attention to the orientation, the notch on the socket must correspond to the notch printed on the PCB.


Step 7

Now solder the reset switch and the the 10K contrast trimmer


Step 8

First, solder the 5V regulator. It is “polarized”, the metal plate is indicated on the PCB by the big white line.
Then solder the 2 electrolytic caps. These are polarized too, the longest lead goes to the hole with a (+) sign.


Step 9

Add the DC connector.
The easiest way is to solder one leg first, then adjust its position (flat to the PCB). Once OK, solder the other legs.


You can check that your power supply section is working by connecting a power supply and measuring the voltage between the +5V and GND points. You should read a voltage between 4.95V and 5.05V.

Step 10

The LCD provided with the kit already has a current limiting resistor built-in. Use a trimmed lead from a resistor or capacitor and solder it in place of R4.


Step 11

Solder the 2 MIDI sockets


That’s all for this side. If you plan to reprogram the chip with an AVR programmer, you can solder the 2×3 ISP header.

Step 12

Solder the 2 LEDs. These are polarized, the longest lead goes into the hole labelled with a (+) sign on the PCB.
Once done, insert the 2 single headers for the LCD without soldering them yet.


Step 13

Place the LCD, and solder it. Do not forget to solder the 2 single header pins you’ve been asked not to solder in the previous step. Now you can do it 🙂
Once done, place and solder the encoder.


Step 14

Insert the 2 ICs. Be careful with their orientation, carefully check the following picture


Step 15

Add the headers to mount the case.
The 4 M3x10mm MF spacers are on the side of the LCD screen, the 4 M3x25mm FF ones on the other side.


Before mounting the case, let’s test our Midibro.
Connect a 9V center positive power supply. The Midibro will boot into the monitor app. Press the encoder for 2 seconds and you are back in the app menu.
If you have nothing on the screen, turn the contrast trimmer once you see something.

You can check that MIDI is working by selecting the monitor app, insert the Midibro between a MIDI keyboard and a sound module, play a few notes, the Midibro should display the incoming MIDI messages while letting them thru, so if your sound module and MIDI keyboard are on the same MIDI channel, you should be able to hear it.

Everything’s OK, then go to step 16.
Have a problem? Check all your solder joints, polarized components orientation, etc. If still in trouble, please use the forum to get some help.

Step 16

It’s time to encase our Midibro.
First, remove all protective foils from the 6 panels. You can wash them with with water and a small amount of dish soap to remove the laser engraving dust.
Building the case should be pretty straight forward. Start with the bottom panel (there is hole for a small screwdriver to adjust the contrast trimmer), secure it with M3x6mm screws.
Then place the top panel (remove the screen protection sheet before doing this). Add the 4 M3x6mm screw, but do not tighten them for now.
You can now place the side panels, they are secured with a M2.5x12mm screw and a nut. Once OK, Gently tighten the 4 top screws, and you’re done!


And don’t forget the encoder knob, and the 4 rubber feet.

Enjoy your Midibro!