Transmitting data over APRS radio with the HX1 transmitter using APRS protocol.

I want to transmit the location of a high altitude balloon payload. I have a radio license and an HX1 transmitter for transmitting over the APRS network. I'm a bit confused on how to implement the protocol properly. Do I just hook it directly to the arduino's TX RX pins and tell it to send data exactly as if it were the serial monitor? I'll be using software serial to use different pins so I don't transit debugging stuff by accident. I found this, which gives me a pretty good idea of what to transmit, but I don't quite trust myself to get all the rules right. I found some firmware that looks like it should help me out. What steps would I take to use this firmware in my project? Will it work just like any other library?

The APRS protocol is quite complicated. You might find this firmware helpful.

The APRS protocol needs a bi directional radio link, usually a half duplex system is used, where each end has both a transmitter and a receiver, in most cases its simply a voice FM radio. Do you really need to use APRS? The issues you have to consider is what error rate can you tolerate in your data transmission, and what data rate you need. If you only need a slow data rate, you can implement some kind of forward error correction in the data you send to check for errors.

mauried: The APRS protocol needs a bi directional radio link, usually a half duplex system is used, where each end has both a transmitter and a receiver, in most cases its simply a voice FM radio. Do you really need to use APRS? The issues you have to consider is what error rate can you tolerate in your data transmission, and what data rate you need. If you only need a slow data rate, you can implement some kind of forward error correction in the data you send to check for errors.

What alternative to APRS would you suggest? Pure telemetry is not allowed on the amateur bands (at least, not in the US). APRS lives in a gray area. :)

The Trackuino firmware should do just what you need. It sends the audio on Pin 3 using PWM. You connect that to the Tx pin on the HX1 and you don’t need a receiver.

Pete

el_supremo: The Trackuino firmware should do just what you need. It sends the audio on Pin 3 using PWM. You connect that to the Tx pin on the HX1 and you don't need a receiver.

Pete

That's what I was hoping.

aarg: What alternative to APRS would you suggest? Pure telemetry is not allowed on the amateur bands (at least, not in the US). APRS lives in a gray area. :)

So is it illegal to use aprs for telemetry? All my research pointed me to the HX1. This transmitter is made for the american APRS band and was made for only transmitting. The arduino receives commands over the cellular network and It can send text messages once it's landed in case the APRS fails.

mauried: The issues you have to consider is what error rate can you tolerate in your data transmission, and what data rate you need. If you only need a slow data rate, you can implement some kind of forward error correction in the data you send to check for errors.

It's only transmitting a GPS location and maybe its status, so I need almost no speed or bandwidth. It could have a 99% error rate as long as 1 transmission an hour is successful. Even then, there's the SMS back up after landing.

So is it illegal to use aprs for telemetry?

In the U.S. lots of people use it for balloon and model tracking, satellite data telemetry, model rocketry, repeaters, etc. Evidently there are exemptions for low power telemetry from models. Look up and obey the rules on using unattended transmitters!

Do you have a suitable receiver for this transmitter? The specs are a bit vague on how the actual data is modulated. It appears to be direct FSK, but theres no detail on the data shaping used which is needed to keep the transmission narrow band.

mauried: Do you have a suitable receiver for this transmitter? The specs are a bit vague on how the actual data is modulated. It appears to be direct FSK, but theres no detail on the data shaping used which is needed to keep the transmission narrow band.

I'm also unsure how the signal is modulated, but it's handled by the transmitter module. A receiver isn't necessary because the data will be transmitted to stations on the ground that will automatically upload the data to the internet.

So is it illegal to use aprs for telemetry?

For this application, no. The regulation issue mainly concerns control over the station. You are supposed to be able to shut it down if something goes haywire. But people (and the FCC) stopped sweating over the tiny details a long time ago. Just have some respect and observe the correct transmission protocol so you won't wreak havoc on the repeater network.

It would be polite to attempt to contact some of the APRS repeater operators for the stations you expect to use, tell them what you are up to. They will probably react positively, and help you integrate your system.

Cool, so I don't need a last minute complete redesign!

Now I'm concerned with how to use this firmware. I've extracted it and opened all the .ccp's and .h's in the IDE, but I can't tell if these are examples or the actual firmware. There's a lot of code I'm unfamiliar with. It looks like the stuff going on behind the scenes in the libraries. My application is far simpler than what the program can do. All I need is to transmit location periodical. This software transmits sensor data, uses buzzers, and takes the raw NMEA sentences. I'm just hoping to take what I need.

I have experience with parsing GPS sentences, working with tons of sensors, I2C, SPI, logging data, multiplexing, binary counters, and a few other things. So I'm not completely clueless. I just need to be pointed in the right direction.

It's been a while since I played with this, but I believe the APRS standard already has a specific syntax for location reporting, so you should comply with that.

Can you please elaborate on this .

I'm also unsure how the signal is modulated, but it's handled by the transmitter module. A receiver isn't necessary because the data will be transmitted to stations on the ground that will automatically upload the data to the internet.

What are these stations on the ground and what are they using to receive the transmitted signals. You MUST have a receiver thats specifically designed to demodulate the transmitted data.

mauried: Can you please elaborate on this .

I'm also unsure how the signal is modulated, but it's handled by the transmitter module. A receiver isn't necessary because the data will be transmitted to stations on the ground that will automatically upload the data to the internet.

What are these stations on the ground and what are they using to receive the transmitted signals. You MUST have a receiver thats specifically designed to demodulate the transmitted data.

Are you quoting without using quotation marks? That is terribly confusing.

Anyway, just Google APRS and you will get the answers to your questions. You do not need any receiver, because the repeater network usually passes on data to the internet.

The APRS signal is audio frequency shift, 1200 baud, using tones of 1200 and 2200 Hz.

If you go balloon hunting in a remote area, you will need a receiver. This site has the best overview, and DIY/purchase modems for use with handheld radios. The BaoFeng UV-5R handheld is incredibly cheap, popular and works well for APRS.

jremington: The APRS signal is audio frequency shift, 1200 baud, using tones of 1200 and 2200 Hz.

If you go balloon hunting in a remote area, you will need a receiver. This site has the best overview, and DIY/purchase modems for use with handheld radios. The BaoFeng UV-5R handheld is incredibly cheap, popular and works well for APRS.

I do live in the eastern sierra mountains, so that would very useful, although it is one of the stronger network locations. Would I use themodem with the baofeng and a laptop to interpret that data packets?

Yes. APRS packets can go online only targeted appropriately AND if a APRS radio receiver is listening at the correct frequency, so most likely that you will be on your own for data and/or recovery.

I've been slowly putting together a similar setup and this is pretty much my choice of equipment. People often use good antennas, too -- you will need a Yagi beam antenna on the receiver to get the maximum range.

For a completely different approach, consider (as I am) the Iridium satellite network and the RockBlock satellite modem. The results of those transmissions do go directly on line, less DIY hassle and it is seems pretty cheap, including data charges.

Edit: on the other hand, there is this unbelievably cute 144 MHz APRS tranceiver, probably the world's smallest.