Wavelink - CM108 Soundcard with PTT

# CM108 Soundcard with PTT Support ## Project Thesis Often times in amateur radio, it would be helpful to interface the radio with your personal computer, whether it be for packet radio like WinLink or APRS or for using digital modes like FT8. This can be achieved by connecting the radio's sound input and output to the computer through a dedicated soundcard, if the radio does not support audio over USB (as most don't). To that end, existing devices like the DigiRig have the capability to do so, but often are extremely bulky and not very convenient for hyper-light portable scenarios like backpacking. This project serves as an extremely lightweight Digirig replacement device which uses the CM108 USB audio interface as the soundcard driver, but leverages the GPIO3 pin of the CM108 to provide PTT support. This provides much more support compared to traditional CM108 soundcards, which do not have a way to effectively trigger PTT without modification. Instead of having to solder wires and whatnot directly to the CM108 like you would, this board aims to combine everything together. In addition, the CM108 boards commonly are "USB dongles" instead of standalone devices. This puts a fair amount of stress on the USB connectors of most devices and modern devices may not even have USB-A ports. That's why this device opts to replace the USB dongle portion with a simple USB-C port that's adaptable. Much like the Digirig Lite, this version aims to use a single TRRS jack for input/ouput/PTT. To prevent confusion, this device is made compatible with existing Digirig cables (like the ICOM HT cable). However, in my opinion, those cables are extremely bulky for what they need to do and defeat the purpose of the device. To that end, I'm making custom cables for myself, which follow the same pinout as the Digirig ones (they have their pinouts published), but omit the resistors between PTT and Radio_Out. In my mind, it makes no sense to have the resistor soldered within the cable itself, but rather would be better placed on the PCB. Therefore, there is a slide toggle switch that needs to be changed between using a cable with a built-in inline resistor if needed and without. It's best to consult Digirig's own documentation on their cables. If there is an inline resistor as part of the hookup cable, then either the cable needs to have the resistor, or you need to toggle the switch to the resistor position. If the cable doesn't need a resistor, then the switch should be left to the "no resistor" side. As well, there is a built-in -20dB attenuator based off an L-Pad design for when the radio presents a signal that is too high. This attenuator can be enabled by sticking a small object like a toothpick or screwdriver and actuating the side switch on the device. I find that the switch is typically set and forget, but if you juggle around a bunch of radios, some that need it and some that don't, you may enjoy having the feature readily accessible on the side. The case is considered to be made of CNC aluminum and certain ESD protections have been taken into consideration for that specific purpose. However, if you wish to use a 3D printed version, the PCB woul still work fine and no changes need to be made. Personally, I recommend a CNC version in order to properly laser mark the top.