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Electronics => Electronics => Topic started by: fast96pgtze-T on December 22, 2006, 06:06:54 PM

Title: Newbee with some wireless questions
Post by: fast96pgtze-T on December 22, 2006, 06:06:54 PM

Hello All,

I am building a dual axis camera positioning system using two different stepper motors.  This is not hard to do, however the system has to be wireless.  Now bluetooth and wifi are out of the question cause the distances needed are slightly farther than the those two are capable of.  I was looking at the following link:

I am currently controlling the system from a laptop running Labview software.  The software outputs the necessary pulses to run the stepper motors.  I was wondering if these telemetry modules were capable of interfacing with all programs and if they are capable of performing the need tasks.  If not, is there anything else I am overlooking that is capable of doing this at a relativly low cost and with out any major programming?

Thanks in advance.
Title: Re: Newbee with some wireless questions
Post by: Militoy on December 22, 2006, 07:50:56 PM
I haven’t personally used one of these units – but I would be a little bit suspect of their “up to 250m” claim as to line-of-sight range. The 900 MHz band they use is the same set of frequencies used by many portable phones and wireless intercoms and speakers in the USA, as well as some wireless LAN systems. They seem in their literature to claim power output of 1-10 mW – that’s 0.001 to 0.010 Watts of power. Some US wireless phones have up to 100 mW of power, and they rarely get much over 100m of range, even with a full Watt "range extender" under real-world conditions. The USB protocol they use should be a good medium for wireless serial control. I would e-mail the company, and ask how they get so much better range than a 900 MHz garage door opener, with so little power.
Title: Re: Newbee with some wireless questions
Post by: R.O.V.E.R on December 30, 2006, 06:59:41 PM
I plan on implementing 80211b/g wireless on my bot, as that is what I'm familiar with and the design centers around a PC motherboard.

The text you're seeing in my response was shot outdoors over the distance of a football field to the access point using a simple grid antenna and a pci card.   I've read stories online of guys going over 1 mile clear line of sight with small amplifiers on the antennas.  Just food for thought.
Title: Re: Newbee with some wireless questions
Post by: dunk on December 31, 2006, 05:29:41 AM
hey fast96pgtze-T,
i have used the easy-Radio Transceiver Modules in the past.
note that i used the Transceiver Modules on their own rather than the pre-built boards that Active Robots are selling.
specs here:
i got around 50 meters range out of these indoors, with random furniture and partition walls in the way without paying any particular attention to areal mounting location, etc.
while it would definitely be possible to get better range than i did with a bit more care when designing circuit boards and mounting aerials, i'd say the quoted "Range up to 250m (line of sight)" range applies only to out door applications and you would only get this in ideal situations with some sort of flow controll in software to test for mistransmitions.

as for using these modules with other software,
they are fairly easy to use in any application that uses your computer's serial port.
in my project, i had a PIC microcontroller, attached to a PC's serial port using the PIC's UART using a max232 to change the voltages between the TTL of the PIC and the RS232 voltages of the PC's serial port..
once i got the application working using a serial cable it was a simple matter of inserting the easy-Radio modules between the PIC and the MAX232.
when the distance between the easy-Radio modules was small the whole project worked first time without any other changes.
at longer ranges occasionally a bite would not arrive or be the wrong value, presumably due to radio interference. as a result i implemented a checksum at either end of the link. when ever data was transmitted i would also transmit a checksum .(i just added the values of all bites transmitted and transmitted that total at the end.) if the message did not match the checksum then the receiving end would request a retransmission.

so in answer to your question:
I was wondering if these telemetry modules were capable of interfacing with all programs and if they are capable of performing the need tasks.
that all depends on how your application is connected to your laptop.
if you are using the serial port then yes, these modules would be usable without changing your application much.
at short ranges you can think of them as a replacement for a serial cable only wireless.
at longer ranges you will have to accept that occasionally a transmitted bite will not arrive or be corrupt.

all the pre built boards i have seen using these modules also use the serial port.
Active Robot's "Radio Data Modem - USB Radio Telemetry Module" for example appears to the PC it's plugged into as a serial port. it has in effect a USB to serial converter built in.

so, some questions about your application:
how are you connecting your project to your laptop?
do you need 2 way communication or is simply sending information to your motors enough?
what sort of environment are you dealing with? will there be obstacles in the way? will the remote end be moving or in a fixed position?