After a lot of debugging and testing the current state of the hardware design I decided I needed to go back to the drawing board. I was having a major problem trying to get TX data over the SPI bus to the pic. I don't have a proper logic analyzer, but I did try a lot of things to figure out what was going on and after several days of fiddling around with it I'm still stumped.

However it looks like it's all for the better. My new design uses a dsPIC33FJ64GP802 as its core. It has a built in Audio DAC which fixes the problems with the 2.2k PTT resistor loading down the signal because it has built in reconstruction filters and output drivers. So there is no longer a need for an external low pass filter or driver op amp. In addition to that now that all the processing is happening on the PIC im free to choose a cheaper lower power Bluetooth Low Energy module. The new PIC costs about $4.30 more than the old one but the new BLE module I'm looking at (AMS002), only costs $5.86 starting at a minimum of 1 module. The RFDuino cost $14.99 for a minimum of 1 and $12.79 when you get to the 500 unit volume. This lower's the overall cost down to about $15 a board. So we will also be cheaper than before.

So far I have the PIC sending and reciving APRS packets no problem on a breadboard. Better than what I had before. (RX Only) I dont have the Bluetooth Low Enery modules yet but they look very solid and have a simple serial interface for communication to the master device.

One important point about this design. I've looked around a bit have have yet to find a TNC that works with iPhones or iPads. I believe this is primarly because of the lack of Serial Port Protocol capability. There are apps out there that will use the phones headset jack to get the radio data and to the modulation but I would imagine that would put a significant drain on the devices battery. This device because of the low enery aspect will be able to communicate with iPhones and iPads. There are test applications for the ACKme modules available on the app store so I'm quite sure its doable. I however do not have any apple devices so I will most likley not be writing and app to communicate with this device. If anyone want's to write an app for the iPhone/iPad to communicate with my device or has an APRS app and would like to integrate compatibility with my device in addition to the headset modem send me a message.

Things are looking pretty great for me to have a fully functional prototype ready to show off in about 2 weeks. The only things left are to test the Bluetooth LE Module, design and make new board, and finaly tune up and streamline the code and the device communication protocol. Hooking up the breadboard prototype to the computer via serial port allows me to recive and send packets quite well.