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Author Topic: Collecting Telemetry for APRS  (Read 5690 times)
K0GDI
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Posts: 7




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« on: August 05, 2013, 06:30:57 PM »

I am wondering how I can get telemetry out via APRS?  I have a Samlex power supply that has a 25 pin D-Sub connector and has the capability of remote monitoring of volts, amps, and a few other things.  What kind of device do I need to read this information and get it to the computer and then out to APRSISCE?  Any ideas?
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N3HFS
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« Reply #1 on: August 05, 2013, 07:56:23 PM »

Review the following items' documentation. These are APRS trackers which are able to generate telemetry packets for APRS:

https://www.argentdata.com/products/tracker3.html:
Quote
Extra analog inputs and digital I/O lines, plus a Dallas 1-wire bus, allow connection of a wide variety of devices.

http://www.byonics.com/tinytrak4/:
Quote
Analog & Digital Telemetry - TinyTrak4 can read temperature, battery voltage, and other analog and digital sources.

I have a couple of Tiny Trak 4's, although I don't use them for telemetry.  From my point of view, Byon's APRS smart modems come highly recommended!  Scott at Argent Data Systems has never let me down either - I have his weather station setup and simplex repeater and other hardware from him.

Hope this helps!
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K0JEG
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« Reply #2 on: August 05, 2013, 08:06:47 PM »

Once you get it set up aprs.fi will graph telemetry for you automatically:

http://aprs.fi/telemetry/a/ANVIL

This is a solar powered repeater our club operates just west of Rifle CO, giving statistics on charging and battery voltage. The telemetry is produced using a Kantronics KPC-3. I think the telemetry signals are just a simple A/D converter and you set a calibration factor in software, but it's been a while since I've looked at one.
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N3HFS
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« Reply #3 on: August 06, 2013, 04:19:15 AM »

Yes, an analog voltage range is converted to a number (e.g., 0-255) for transmission in a packet.  The units I linked above do this as an adjunct to their primary chores (digipeating, tracking, etc).
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K0GDI
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« Reply #4 on: August 06, 2013, 06:21:21 AM »

http://www.samlexamerica.com/documents/manuals/SEC-40BRM_60BRM_80BRM_100BRM_230V_Manual_Feb2008.pdf

Look at page 5, will I be able to monitor my power supply via APRS?
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N3HFS
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« Reply #5 on: August 06, 2013, 10:35:35 AM »

http://www.samlexamerica.com/documents/manuals/SEC-40BRM_60BRM_80BRM_100BRM_230V_Manual_Feb2008.pdf

Look at page 5, will I be able to monitor my power supply via APRS?
I should think so, but there may have to be some voltages dropped - a little beyond my expertise.  From your linked manual:

Quote
A provision has been made for remote signaling and monitoring of the following operational
conditions and parameters:

1. Operational status of the 5 Power Supply Modules (PSM)
2. Failure condition of the cooling fan(s)
3. Availability of AC input power
4. Output voltage measurement
5. Output current measurement ( Voltage across an internal shunt with Shunt ratio of 50 mV / 100 A or 0.5 mV per Amp)

Signaling of operational conditions as at serials 1, 2 and 3 above is opto coupled with open collector, NPN transistor outputs. The collector and emitter of each opto coupled transistor are accessible to the external user interface through the 25 pin D-Sub connector. Each open collector, opto coupled NPN transistor can provide a maximum of 50 mA with a collector to emitter
voltage of up to 35 V.

Outputs for voltage and current measurements at Serials 4 & 5 above are direct analogue voltages.

1, 2, and 3 are basically "YES/NO" telemetry, so I'd think that a reading near 0 or near 255 would provide the desired status.

4 and 5 are meter readings, and a provision to drop the voltages to a linear range of 0V thru 5V to represent the power supply's 0V-35V scale would be needed.

I, probably quite obviously, don't have much EE background or experience - those who do, please chime in!
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K7RBW
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« Reply #6 on: August 07, 2013, 06:57:47 AM »

It looks like pins 1, 2, and 3 are digital outputs that you'd need to measure to see what open (high) and close (low) mean. Typically an open-collector output is an active-low such that you'd put a current-limited voltage to the pin (e.g. 5-v through a 10-K resistor). When the output is active, you'll see 0 volts at the pin and when it's not, you'll see the 5-v from the supply. What's not clear is what either level means, but that's easy to measure.

The other 2 pins look like analog signals that you'd need to digitize somewhere along the way before sending it to the APRS device. I don't recall if the TinyTrak has an analog input or not, but A-D converters are easy enough to come by.

If these are the only specs you have to go on, you'll need to do some experimenting to match the power supply's outputs to your APRS inputs, but its nothing you couldn't do with a breadboard and a digital volt meter.

An Arduino board might be the easiest way to interface the two devices in that they have digital and analog inputs ready to go and they can be programmed to convert those inputs to any manner of digital and analog outputs.
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K0GDI
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« Reply #7 on: August 07, 2013, 09:33:50 AM »

This is almost sounding like too much work and not really worth it.  I may just shelf this idea.  Sad
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N3HFS
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« Reply #8 on: August 07, 2013, 12:15:08 PM »

I don't recall if the TinyTrak has an analog input or not, but A-D converters are easy enough to come by.
The way I understand the documentation, the Tiny Trak periodically samples a voltage from 0V - 5V (which is a continually variable analog signal) and assigns to it a value of 0-255 (digitization) for transmission as telemetry.  A 0V reading would yield a "000" telemetry value, and a 5V reading would yield a "255."    That would make it an A-to-D converter.

If the sampling works in a completely linear fashion, then the resolution would be approximately 20mV, that is, about fifty possible values between each volt from 0 to 5, for a total of 256 possible values.

I believe the Tiny Trak has at least three available channels that do this for totally separate inputs, so that three different voltages may be read and sent as digital telemetry.
« Last Edit: August 07, 2013, 12:19:40 PM by N3HFS » Logged
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