[altusmetrum] NMEA input to a TeleMini?

Bryan Duke bryan at thedukes.org
Sun Sep 3 22:53:48 MDT 2017


Thanks Keith, this helps a ton! It’s great to hear that those pins are exposed & there aren’t any giant road blocks. The EEPROM logging would definitely be nice, but the lat/long telemetry is priority 1.

I’ll start digging through the code once I hit go on a TeleMini order & get it in.

Thanks!
-Bryan

> On Sep 3, 2017, at 9:44 PM, Keith Packard <keithp at keithp.com> wrote:
> 
> Bryan Duke <bryan at thedukes.org> writes:
> 
>> Hi everybody. I posted on the Facebook group, but someone there suggested I try the mailing list instead…
>> 
>> I’m putting a TeleMini in a nosecone for a 24mm rocket that I’m hoping
>> to break the TRA G-motor record with. There isn’t enough room in the
>> nosecone for anything bigger than the TeleMini, but it looks like
>> there will be just enough room for a separate little GPS. Is there a
>> way to feed the TeleMini a NMEA stream & have it send GPS coordinates
>> over its telemetry? It looks like several of the STM32's pins are
>> accessible....I'm ok writing some code to make it happen.
> 
> This should be reasonably straightforward. TeleMini has a 6-pin
> connector. Four of those are our standard debug connector (debug
> data/clock, reset and ground). The other two are normally a regular USB
> connection. You can hook those to a USB cable. However, those same two
> pins can be re-configured to talk to a serial device, such as a GPS
> device.
> 
>        Pin 1 is TX
>        Pin 2 is RX
>        Pin 3 is gnd, and the pad around that is square.
>        4,5,6 are the debug connectors.
> 
> The source code for AltOS has GPS drivers for u-blox, sirf and skytraq
> already available, and the radio driver has all of the necessary
> bits to send our regular digital telemetry as well as APRS.
> 
> So, if you're up for building the firmware, what I'd suggest is:
> 
> 1) Leave the USB running for a while when the device boots. This will
>    make reflashing a ton easier as the alternative is to reflash over
>    the debug link, which is really slow.
> 
> 2) After 'a while' (maybe 10-20 seconds?), turn off the USB and then
>    reconfigure the pins to talk to the GPS device.
> 
> Normally, we log GPS data to the eeprom, so eventually you'll want to
> add that, but it's a bit of work. Doing the GPS telemetry is quite easy
> though, along with making APRS work.
> 
> There are 33ohm resistors on the board for the USB port; I don't think
> those will hurt communication with the GPS chip, but you should be aware
> that they are present.
> 
> -- 
> -keith



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