I am trying to send Video and GPS data from a model rocket. I have worked out a powersupply (8v 400mA MAX. Battery), and I have a PAL video camera installed in the rocket. I have found a GPS device with a 1.8v UART output - but that only needs the Transmit line.
I am trying to find a way to send both signals back with only 1 transmitter (range 300 - 500 feet) due to weight/space constraints and power limits.
My first Idea was to use a Bluetooth device - Either the RN41 or WT11. This would happily transmit the GPS data, but not easily the video. My idea to solve this was to put a USB video capture card in the rocket and connect that to the USB port on the bluetooth chip (Via a USB host such as the FDTI VDIP1). I am waiting on delivery of the VDIP1, and when that comes will test this idea. However I am somewhat doubtful it will work.
The second Idea is to use a 5.8GHz (or 2.4) video transmitter such as the Airwave AWM680Tx or similar. This would make sending the video simple, but not the GPS data. This is where the question lies…
The Airwave transmitters have 1 or 2 audio lines, and I was wondering if it would be possible to convert the UART Tx of the GPS to a signal which could be sent as an audio signal. This signal would then either need to be converted back to a UART signal at the other end. Or the signal could be converted such that it could be piped into a 56k Modem and then read by software such as Hyperterminal.
Is this possible? and does anyone have a circuit diagram/parts list to make it work.
Yes it’s very possible to transmit data on audio-frequencies. That is what a standard data-modem does.
To get high-data throughput is not easy though. You could modulate the data like 0=nothing and 1=sine 100 Hz (just an example). This is very easy to demodulate, but getting more than 9600 bps could be hard. this you can probably do without even using a DAC-conversion as you can just shoot a square wave into the transmitter.
Read up on data modulation and you will find what you can use with regards to your hardware. First you should probably see what data-rate you really need (and then again what you really, really need).
I forgot to mention that. The data rate of the GPS is only 4800 Baud, which shouldnt be too bad. Do you have any suggestions on a circuit for modulating the data - Would it be possible to get something like a very simple tone generator with an Enable pin, and then pipe the Tx line into the Enable pin?
Presumably I would either need to convert it back at the other end with some circuitry, and put it through a UART to USB converter. Or alternatively, would it be possible to connect the audio out of the reciever directly to a 56k Modem on my laptop?
A tone generator would probably work, but a micro-controller would probably be better as you then will have a way of upgrading the modulation routines in the future.
The RX-part is a bit trickier. I doubt you can use the modem with this simple approach. the easiest as I see it if you just want the data in your laptop is to use the microphone or line-in jack.
I guess it could be hard if you have no programming skills what-so-ever.
An all-hardware solution shouldn’t be that hard to build either. Basically a rectifier circuit and a low-pass filter tuned to the bit-rate and modulation frequency.
I like the idea using a Line-In port. My video capture card has its own line in, do would work well. As for recapturing the signal from the line in, I have no idea. So I guess I will have to have a similar circuit as in the rocket, on the ground to convert the transmission back to UART.
Presumable any old Microcontroller - maybe one of the smaller PICs would do the job of converting the signal. Though at the moment I have had very little experience writing programs, so a more analog method would me more preferable.
After many hours of searching (clearly i dont know what I am searching for) I have come up with nothing. Does anyonne have a circuit which would do the job of taking a Binary UART signal at 4800Baud, and turning it into a signal which can be sent through a 3Vp-p audio line on a transmitter. Then at the other end, a circuit would be needed to convert it back into a Binary signal.
I’m going round and round in circles getting nowhere and would appreciate the help.
Have you asked at an Amateur Radio forum? Some of those guys have been doing this kind of thing for 40 years.
The Amateur Radio angle is an interesting one to follow up. “Audio Frequency Shift Keying”, “AX.25 packet” and “APRS” might be good search terms to find some help.
Here is my stupid suggestion of the day: Have you considered high-speed morse code? It’s very easy to generate the tx side, and reasonably easy to decode.
-73 de br/KT0X
billroy:
Here is my stupid suggestion of the day: Have you considered high-speed morse code? It’s very easy to generate the tx side, and reasonably easy to decode.
-73 de br/KT0X
Interestingly, one of the things i had thought about is to connect the serial data to some sort of switch which turns on and off a tone generator of some description, so 1 is a tone, and 0 is no tone. The problem i see is that 4800Baud seems very fast to use something like a transistor or a relay.
I think i might try that TinyTrak circuit. I have a PIC16F84 to hand, so… we shall see.
I haven’t got the transmitter yet, but will do by the end of the week. I have come up with two other simple ideas which have worked in a simulator, so I am confident. Will keep you posted.
Thanks to the big boom in Iceland stopping air travel, I haven’t been able to do any testing as my GPS device is stuck somewhere in brussels. Hopefully it will come monday and I will be able to do some testing.
I have managed to get my video transmitter working, and can now get a live video stream from my rocket (still need a proper antenna - which is also stuck in brussels). Here’s hopeful about the GPS.
I’ve been using XBee radios to send data from rockets to the ground, and within the kind of range you’re talking about (300-500) feet, they work extremely well. With GPS data you can usually just connect the GPS TX pin to the XBee TX pin, through a very simple (1 transistor, two resistor) inverter circuit.
I didn’t mention this before because it definitely will NOT enable you to send both GPS and video through the same transmitter, at least in the simple way I just described for GPS. But it’s very very easy to use an XBee to transmit serial data, and it does work well from inside a rocket.
I new there were other ways - I was even going to go for bluetooth at one point, but There is very little room in my rocket nosecone (it is only 35mm OD), so I’m endevering for one transmitter. I may end up having to go for two though. We shall see.