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Phase 4 (Revise): What happened to phase 3?

Getting a little ahead of myself in skipping to a partial phase 4 as writen up back in my intermediate uber post .

Based on a lot of the Q's for the in and outputs of the MPET (Paul does permit me to use some of his terms like GOZINTA and COMZOUTA), I want to go more detailed with photos and diagrams like Chuck did for his great Poorman’s Binary Coded Decimal (BCD) Switch post. So look out for a proper phase 3 post before the next "Where in the world is K2GOG trip"

I will call my phase 4 project for now the AX.25 Packet MPET.

For a just completed trip out west for the RSA conference (For all you cyber security people out there) , I was "hoping" to have my finished MPET for AX.25 completed, but instead I used the TNC2 by Mobilinkd for some APRS tracking for which I got the idea from in the first place.

**Head over here for the TNC2 product review. **

Here is the list of parts I will use to add AX.25 ( Packet) capability to the MPET. Only some are hyperlinked because many are easy to source from many places ( or I already had on hand and I dont know how to hyperlink to my junk boxes!)

  • Arduino Nano v3 (Generic Arduino Nano NOT the Micro)
  • 10KOhm Resistor (Qty 3)
  • 100KOhm Resistor
  • 1KOhm Resistor
  • 2.2KOhm Resistor (maybe)
  • 10nF Capacitor
  • 100nF Capacitor
  • NPN Transistor (2N2222 or equivalent. I may also go with a MOSFET instead)
  • 3.5mm 4-pole jack (Like the connector on many Yaesu HT's)
  • 2.1mm female coaxial power jack (with inbuilt Normally closed switch)
  • Prototype boards (Why bother with a breadboard sometimes, just go right to the PCB!)

Courtesy of Rob (The maker of the Mobilinkd TNC1 and TNC2), for my starting point:

Features on my take of getting the MPET to do "packet" include:

  • Use a step up buck converter to take 5V USB to 8V to give minimal power to the MPET to be self powered from a PC or laptop. Note: The USB 2.0 spec provides up to 500mA at 5-5.2V. This means on transmit, I probably wont "blow up" a USB port. I could also use a powered USB hub if I really wanted to as a back up plan. Most likely, I will use the MPET when powered from the PC/laptop in RX mode with very lite duty TX, which makes this "OK". I would not normally think to have a long QSO powered from a PC USB port!

  • Use the 2.1mm power jack (see above parts list) to allow the MPET to run from the USB power for low RF output (by bringing pin 5 to ground)

  • When plugging in 8v or greater up to 15V power source, permit the MPET to be powered from external power to allow for high RF output (5W). This does not bring pin 5 to ground, making it high power.

  • There will be no need for any further interface to the host PC/laptop aside from just a USB cord (and optional power for high RF output) This is great to not have to twiddle with audio cables since the Arduino sketch does all the hard work in the software.

  • The software defined modem (what the above parts assembled create) will operate as a KISS TNC, so will be great for standard packet (1200 or 9600baud) with the appropriate software running on a laptop, PC, or a smartphone with USB On The Go adapter even. It will also allow for use in a WinLink configuration to send email or by adding a USB GPS to the PC/laptop, as a APRS system with live GPS.

  • The mic jack will be used to operate the MPET for voice mode and will be switchable for a voice/data mode so the MPET is "one or the other at a time, not both". I figure this is a safe way to do things.

  • Channel control will be with a 8 position BCD that gives me all the data/simplex channels listed below eventually:

  • 144.390MHz = US APRS
  • 144.800MHz = EU APRS (May replace with 147.420 as a local mixed data/voice simpelx channel)
  • 146.520MHz - US FM CALLING
  • 145.500MHz = EU FM CALLING (May replace with the 145.800/144.490 pair for ISS Voice contact)
  • 145.825MHz = ISS APRS
  • 145.010MHz = US PACKET COMMON
  • 145.050MHz = US PACKET COMMON

Will get some pictures up once I bust out the soldering iron out during the coming week.

If you want more details on the original project, here is the back reading for it plus what I will be "flashing" into the Arduino to make the software magic work.


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