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Topic: XBee RSSI Signal (Read 2001 times) previous topic - next topic

UNTEngineer

Could I use the RSSI signal to determine signal strength? Can someone suggest a simple circuit that I can visually display the signal using a LED bar graph.
Working on a Smart Home Management System. Visit my blog: http://tae09.blogspot.com/ to find out more, and to keep track with the project.

oric_dan

According to my d/s, RSSI is a PWM output. You can filter this using a simple RC low-pass filter, and feed
to an LM394 or LM3915. They apparently still make these things.

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_24230_-1
http://www.jameco.com/1/1/2533-lm3915n-1-lm3915-dot-bar-display-driver.html

For ckts, do a google image search on LM3914 or LM3915,

http://www.google.com/imghp

UNTEngineer

Well I have a PCF8574N. Will that work?
Working on a Smart Home Management System. Visit my blog: http://tae09.blogspot.com/ to find out more, and to keep track with the project.

oric_dan

Ok, take at look at the chips I mentioned and see how they compare to your [what I presume is an]
I2C expander. You want a display, no?

UNTEngineer


Ok, take at look at the chips I mentioned and see how they compare to your [what I presume is an]
I2C expander. You want a display, no?


I looked at the LM3916, and I realized the difference after I posted that. One is a multiple LED/LCD driver and the other is an I2C expander for an LCD.

What values would you suggest for the Low Pass Filter?
Working on a Smart Home Management System. Visit my blog: http://tae09.blogspot.com/ to find out more, and to keep track with the project.

UNTEngineer

Working on a Smart Home Management System. Visit my blog: http://tae09.blogspot.com/ to find out more, and to keep track with the project.

oric_dan

You need to know the PWM frequency out of the RSSI pin, and then select a cutoff frequency
roughly 10X lower, according to

F3db = 1/(2*pi*R*C)

Use R=4.7K or 10K as a starting point and calculate C accordingly. That's where I'd start.

betomax

take a look to dev interface schematic, were a lm339 is used to drive 3 leds (basic comparator) feed with rssi output through RC filter


http://ftp1.digi.com/support/images/XBIB-R-dev%20schematic.pdf

Jack Christensen

I'm working on a project right now that does this. Connect the XBee RSSI pin to a digital input pin and use pulseIn() to read the PWM pulse width.

S1 or S2 XBees?
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

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