View Full Version : HAM Radio Connection

06-10-2005, 08:24 PM
I'm working on a cutdown system for a high altitude balloon. I've spent a little while learning how to use the basic stamp, and now I'm trying to integrate it to cut down the ballon.
For the entire duration of the flight, we should have communication with a HAM radio...and we would be able to send it a string of text like "cutdown" or some passcode. Anyway, I was wondering if anyone knew if it was possible to connect the stamp to the ham radio.

If not, it is also possible that we can connect the HAM to a computer. My question then would be...is it possible to control the Stamp with the computer using some programming language.
Any links etc. would be appreciated.

Beau Schwabe
06-10-2005, 08:45 PM

I think the Stamp is very capable of what you are asking. There are several ways that you could go about doing something like this... On the receiving end you could have a tone decoder IC
to indicate a mark (logical 1) or space (logical 0) <--- I would use two separate tones representing a 1 or 0 for this. On the transmission side, you could use the built in DTMF out capabilities
of the Stamp (if you used a DTMF decoder on the receiving Stamp) to "talk into" the ham radio. As far as using some programming language, there are several different flavors that you could
use depending on how involved you wanted to get. A dumb terminal program might work, or you might want to get a little more sophisticated by using a Visual Basic program or what ever your
preference is. There are tons of applications where a Stamp "talks" back and forth to a PC.

Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

06-10-2005, 09:39 PM
Don't know what you mean by the expression of a cutdown system unless you are refering to a method of causing the flight termination and trigger the balloons desent.

If that is the case and you want to manually trigger desent the use a dtmf encoder on the ground station which most stamps have built in, and a stamp with a dtmf decoder chip in the ballon electronics.. Set it up to decode a secret 3 to 5 digit
sequence. So that someone listening on your frequency can not shoot you down .

Be sure to test it well before using in flight. And do not reveal the trigger code to anyone but the immeadiate recovery crew.

06-10-2005, 09:44 PM
By the way. Another thought. If you have a electronic baraometer on board. You could use the same touchtone system with a decoder added on the ground station to send back by radio, the barometric pressure from the balloon so you would have a record of it just in case the balloon was never recovered.

Iin a case at roper mtn science experimenters group (sc) the balloon was recovered over a year later when a hunter shot it out of a tree.

A year till it hit the earth again. Wow......


06-10-2005, 09:56 PM
Some more thoughts.

You are going to have to have a very small transceiver like a handie talkie in the balloon. Also most mobile/base stations now have touchtone (dtmf) built into the mike's. Just key in the preset code that the balloon stamp/dtmf decoder sequence will activate on.

You would still need the stamp and dtmf decoder on the ground to receive the barometric pressure and send to a serial printer or a serial to parallel adapter feeding the printer.


06-14-2005, 08:14 AM
Thanks guys. I ended up building an audio based cutdown system using the stamp COUNT function to look for a certain frequency sent in the coded pattern of my choice.
- cjkogan111