September 17, 2022: I’ve updated the assembly manual to include the latest changes in the hardware. If you’ve downloaded v1.0 please download this one to build your Mini.

You can build the CTR2-Mini from the PCB kit I supply and through-hole components from purchased from Mouser, or I can supply fully assembled and tested units (minus the Wio Terminal). Use the CTR2-Mini Order Form to order the PCBs or assembled units.

For builders I’ve created automated bill-of-material lists on Mouser so you can easily order the through-hole components you’ll need to populate the PCBs. You can find the BOMs and schematics here.

Building the kit is pretty simple since the only parts you need to install are through-hole connectors and a few resistors. All of the SMT components are pre-installed for you (with the exception of the optional micro-USB connector on the Radio I/O board.

I do recommend that you should have moderately good soldering skills to build the kit. This is primarily because of the small pins on many of the connectors. As long as you use a temperature controlled soldering iron and have solder braid to eliminate any solder bridges you should be fine.

I have created an assembly manual for the Mini that goes over each step. This will give you a good idea of what’s involved in building one. Schematics can be found in Appendix A at the end. You can review it here or click the link below to download it.

I have posted a video on my YouTube channel that goes over the construction of the Mini. Click the photo below to view the video.

Main Board v1.2 Headphone Jack Fix

I made a mistake when I added the headphone jack header to v1.2 of Mini’s main PCB. I inadvertently connected the sleeve of the jack to GROUND on header J2. Unfortunately, when wired this way the sidetone cannot be heard when headphones or an external speaker is plugged into this jack. This is because the sidetone output requires +5 volts along with the switched ground (SPKR) from Q1. Basically the sleeve of the headphone jack needs to be connected to +5 volts instead of ground. The following document shows the necessary steps needed to modify an existing board or build a new one.

This problem has been fixed on the v1.3 PCB.


With this modification the sleeve of the Mini’s headphone jack is “hot” (+5 volts). Plugging the Mini’s headphone jack into a powered speaker or amplifier will short your PC’s USB +5 volt supply to ground. You must use an inline isolation transformer if you want to feed an amplifier with this output.