Wireless Communication :: RF Recievers + Transmitters

[Michelle Kirby]

Hello!

I'm working with a wireless transmitter and a receiver, but the two
aren't communicating with each other. I'm using the LINX HP series
(RXM - 900 - HP3 - PP0, TXM - 900 - HP3 - PPS). This is my first time
working with wireless communication and I'm having trouble figuring
out where I'm going wrong. The two chips are being run from an arudino
and the data they are sending is from an IR sensor. I actually don't
need to send all the numbers from the IR, I just need to send a
digital 'yes' when someone is standing in front of the sensor.

These are some troubleshooting areas where I think the problem might
be coming from : The transmitter has a clear-to-send switch that goes
to high when its ready to communicate, from the data sheet it seems
like the chip should do this on its own, but when I monitor the CTS,
it never goes to high. Also, right now I don't have an antenna for the
two, but I just ordered two and they should be here today! Also, I'm
not sure if I need anything else to make these work?

This project part of a procedurally generated art piece based around
the idea of observation. The sensor tracks when someone is viewing the
animation, and then starts a clock to time how long they stand in
front of the piece, the animation distorts proportionally to the
amount of time the viewer is viewing. I have the animations built in
open frameworks. Originally, the sensor / computer / projector were
all locally connected, but because of the nature of the presentation
space, I need to seperate the sensor so there isn't a massive
extension cord running over the gallery ;p

I just bought an xbee1 and an xbee explorer, but I have no idea where
to begin with those. For starts, I'm working on a mac, so that's an
issue for sure. It seems like its possible to work with a mac via
moltosenso (http://www.moltosenso.com/#/pc==/client/fe/download.php)
(which I learned about from here http://www.tristantech.net/articles/xbee_tutorial/1.php)
but this direction is really confusing to me and I would rather stick
with the LINX chips.

I'm hoping somebody can help me or possibly meet with me via skype or
in person. I have code written that I can send as well ( I didn't want
to paste it here, this is already pretty long :) I am a hardware
novice and appreciate any help! Thanks so much! - Michelle

[Matthew Guindin]

I didn't read the entire post, but I've done transceiver work in the
past with microcontrollers, you're hooking them up to protoboards and
not breadboards, right? Breadboards have metals clips that add
capacitance to RC circuits and can cause them not to function
correctly.

-Matt

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[Paul Strohmeier]

not sure how to help you, as you dont really state a problem. I have no experience with LINX 

you say you have "an Xbee1 and an Xbee Explorer" ? You mean you have *one* radio and *one* breakout board? (if so, you do realize why this wont work, right? :-D ...)

*

anyway, when building something similar I had following setup:

Explorer for connecting to computer http://www.sparkfun.com/products/8687

XBee Pro for receiving the signal, attached to the Explorer: http://www.sparkfun.com/products/8690

A second XBee Pro for sending the signal, attached to a Arduino Fio http://www.sparkfun.com/products/10116

The cool thing is, you can program the Fio via the wireless link using a very simple hardware mod. 

I used this tutorial to get myself set up:

http://funnel.cc/Hardware/FIO

*

Dont know if this helps - I am no expert at all, but this is how I solved a similar problem.

Cheers

p.

--
paul strohmeier
          [web] paulstrohmeier.info

[blog] fkeel.blogspot.com
[mail] paul.st...@gmail.com

[derek enos]

Hi Michelle,

As you suspected, figuring out why the transmitter is not pulling CTS high is a great place to start.

Looking at the Typical Performance Graphs on page 3 of the TXM-900-HP3-PPS data sheet, the transmitter will pull CTS high about 7.2mS after power is applied to both VCC and PDN, or just VCC if the PDN line is floating (not connected).  The PDN (power-down) line, when pulled low, will cause the transmitter to enter a low-power state (or just never become active when power is applied to VCC). While in this state, the CTS signal will be held low.

Checking the state of PDN on power-up is a good first step. If you don't anticipate needing to put the transceiver in the power-down mode, the easiest thing to do is leave this pin disconnected. The transceiver automatically pulls this signal high if nothing is connected (datasheet page 5 -> Pin Descriptions -> PDN).

If PDN isn't the issue, I'd then look at the power supply. Make sure that all 4 of the transmitter's GND pins are actually connected to your power supply's GND and that you're applying the correct voltage to the transmitter's VCC pin. Since the transmitter has an internal voltage regulator, its VCC pin can accept any voltage in the range of 2.8 - 13.0VDC

Also, this transmitter definitely needs an external antenna to function. It's possible that not having one connected will prevent it from fully powering up / asserting CTS.

The Typical Applications diagrams in the datasheet make the TXM-900-HP3-PPS appear fairly easy to implement but it's certainly not the most friendly, or most affordable, of wireless solutions. I've had good luck with Nordic's nRF24L01+ 2.4Ghz transceiver breakout boards which MDFLY sells for $6.95/ea. There's an Arduino library for it here, with more info here and here.

Good luck!

Derek