Parallax 433Mhz Transmitter/Receiver questions.

Morrolan

Hi all,

I am about to embark on a project that requires me to be able to receive GPS data wirelessly from multiple sources. The idea is to track multiple Boe-Bots via GPS as they navigate an outdoor obstacle course.

I already have a Parallax GPS Receiver outputting data to a serial LCD on a BOE-Bot, but I would like to send the data via a serial connection to a PC which will log movements of the Boe-Bots over time.

My question is, how many incoming signals can a Parallax 433Mhz Receiver handle? Can I have 4, 433Mhz transmitters sending data to one receiver attached to a Stamp and then output data to the PC from there, or are the transmitters/receivers paired in some way?

I would greatly appreciate any help, as I don't want to splash out on the transmitters/receivers if they are not suited to the task.

Many Thanks in Advance,
Ian

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Flying is simple. You just throw yourself at the ground and miss.

"I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image."
Stephen Hawking

Mike Green

It's like with any other radio transmitter. You have a particular frequency that you're listening to. If there are two transmitters transmitting at the same time, they interfere with each other and the receiver can't separate the signals. Since the transmitter can be turned on and off, it's possible for several transmitters to share the frequency over time, but how would the transmitting units know what time slot is theirs and when they can transmit?

There's only one frequency used and the units cannot be tuned to another frequency. The chip manufacturer (Linx Technologies) makes transmitter/receiver chips for three different frequencies, 433MHz, 418MHz, and 315MHz. You could have a separate receiver / transmitter pair for each frequency running at the same time, but Parallax doesn't make a version of their complete unit for the other frequencies.

You might be better off with something like xBee which is designed for use on a network where there are multiple units. The xBee transceiver is controlled by its own internal microprocessor which takes care of sharing the single frequency over time among several units. Each unit is configured for a particular address and you address messages from one unit to another.

Chris Savage

There is another option if you want to use the 433 MHz system, but it will require each BOE-Bot to have a transmitter and receiver as well as the ‘base station’. The base station can query each BOE-Bot for its position by sending out a message with the ID of a specific BOE-Bot. Only that BOE-Bot would respond, preventing any issues with multiple transmitters. I have used this concept many times and it works great. Each BOE-Bot will have a unique ID that it will respond to. Essentially all bots hear the message, but only the one spoken to responds. The base station then queries the next bot, and so on…

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Chris Savage
Parallax Tech Support

Morrolan

Thanks Chris, that's a good idea! As long as I can accommodate the costs, that would be a much neater solution.

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Flying is simple. You just throw yourself at the ground and miss.

"I think computer viruses should count as life. I think it says something about human nature that the only form of life we have created so far is purely destructive. We've created life in our own image."
Stephen Hawking