AA3RP wrote: ↑Sat Nov 18, 2023 10:45 pm
Just received a MD-390 with GPS which seems to work fine when I am out of the house. I get between 7 to 10 sats in 1 to 2 min from a cold start.
My query is, are the files from 5-6 Oct 2023 for the CPS and firmware the ones I need for getting APRS up and started testing ?
I have some GPS antennas and chips on the way for mods to a pair of my MD-9600s. One I want to the antenna internal, and the other I hope to set up for external antenna input.
Final question about the MD-9600. Does it have a +5V anywhere that is easily accessible internally. I would like to use +5V for the external antenna if possible rather than 3.3Vcc, but this is not a show stopper.
Looking forward to checking this APRS aspect out.
The files for APRS beacon are posted at the beginning of this thread.
On the MD9600, you'd need to poke around to see if you can find a 5V.
Howver, as the CPU chip in these radios is a 3.3V device, if your GPS is outputting 5V serial data, it could potentially damage the CPU.
i.e some CPU pins are "5V tollerant" but not all, and you would need to check is pins PA9 and PA10 are 5V tollerant.
If your GPS has its own internal regulator from 5V to 3.3V, often they will accept 3.3V , or failing that, just bypass the regulator
The GPS voltage is normally switched via a 2 transistors located inside the front panel of the radio, so the best way to power the GPS is to solder to the pads where the official GPS is located, on the front panel PCB, this also is where its best to feed the serial data from the GPS.
If you power the GPS from somewhere else in the radio, its likely to be drawing power all the time, because the MD-9600 does not actually have any master 12V power switching. Its On all the time.
When you appear to turn it off, all that's actually happening is that the display is cleared and the CPU is put into its sleep mode to save power consumption.
Possibly a few hundred mA of current doesn't matter to you, but if you leave that sort of load on a car battery for a few weeks, e.g. while in an airport parking lot, you may find that the battery won't have enough energy to crank the engine when you return.