Radio-Computer Interface

Sound card interface PCB v01

So I’m back on the topic of interfacing a radio to your computer – this time with a bit of a twist. In the past, I’ve discussed methods by which you could decouple your radio from your computer (and the importance of this) and I’ve even gone as far as to design a couple of interface printed circuit boards – one of which even includes push-to-talk (PTT) functionality as well as CAT control by a microcontroller.

I felt there was one major flaw with my previous designs – both required the user to supply a sound card (ideally one other than the computer’s built-in one!). Yes there are products out there which cost ~$109 which have a USB sound card built-in, but I am dissatisfied with both the price and the fact that I can make one myself!

Radio to computer interface schematic v011

Thus, a new project is born. I will be attempting to design and fabricate my very own full radio to computer interface which will include a USB sound card on-board. The goal of this project is to provide the following functionality:

• radio-computer sound interface with built-in sound-card
• PTT control of radio
• CAT control via either PC or on-board MCU
  • allowing control of such tasks as Doppler corrections, ALC / drive level management, and GPS-based program memories (repeaters)
• single USB cable to client computer

Texas Instruments one of a few fantastic companies which offers free engineering samples to independent design engineers. I’ve ordered a number of samples from TI before and they offer incredibly quick response / service all in the hopes of your future business. Because of the phenomenal service of Texas Instruments, I endeavoured to find a USB codec chip made by TI which would serve my design needs. Without too much trouble, I was able to find the PCM2912A chip which appears to be absolutely perfect for my needs.

Texas Instruments samples

Along with the PCM2912A I ordered a number of samples to handle USB-hub functionality since I wish to provide the end-user a single-USB cable connection to control multiple USB-host functions. Naturally, I selected TI parts and place a single sample order which took a mere two days to arrive! All for free! I really can’t speak highly enough of the companies which are willing to provide free samples. They make affordable hobby design possible!

PCM2912A USB codec TQFP-32

My project is currently in the bill-of-materials (BOM) gathering stage along with the preliminary schematic phase. Most of the parts which I intend to use will be surface mount (SMD) components which may cause a few people to cringe.

Let me assure you that with proper techniques, SMD soldering / kit building is actually very easy! I’m trying to design around fairly large-sized passive components to help ease neophytes into surface mount soldering. As you can see, the USB codec chip is quite a bit smaller than a nickel – rest assured it is actually quite simple to solder!

I hope to have a chance to sit down at the design bench for a few hours some time in the next few days so that I can make some serious headway on this project. I’ll need to order some surface mount passive kits (resistors, capacitors, inductors, LEDs) to aid in the first build once the completed design is fabricated by the PCB fab-house.

I think that this will be a really fun and perhaps rather challenging endeavour. Now off to reading more about analog and digital ground planes and how to keep them separate!