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Using RSSI pin on #27982 433Mhz Transceiver modules — Parallax Forums

Using RSSI pin on #27982 433Mhz Transceiver modules

RobotWorkshopRobotWorkshop Posts: 2,307
edited 2010-07-08 17:07 in Accessories
I've looked the datasheet for the Parallax #27982 433Mhz Transceiver modules and also at the datasheet from Linx on their LT module but haven't seen any examples on using the RSSI pin. It is supposed to provide an analog voltage out as it relates to the received signal strength. I'd like to find out how much current that pin can safely supply. I'd just like to use it to drive and LED to help with diagnostics. I'll probably have a jumper to enable/disable the LED to save power when not needed. Does anyone know if it will drive a standard RED LED if I use 510ohm resistor in series?

Robert

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-06-23 20:07
    Robert,

    It is not designed to drive an LED. Its output is an analog signal corresponding to the data being received. If you were to hook up the Data line and the RSSI line to a scope you would see that the RSSI somewhat follows the Data line, with the exception of varying with the signal strength. The data line is driven so that it can always generate a 1, so the RSSI at the moment of the Data line going high can tell you the relative signal strength. It could be read with an ADC.

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    Chris Savage

    Parallax Engineering
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  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2010-06-23 21:04
    Chris, thanks for the clarification. I'm working on a new project where I think the modules would work out well. The board it would be replacing happens to have a diagnostic LED which can be enabled by a jumper to show a relative signal strength for testing/troubleshooting. Since I'll need to design a carrier board that the #27982 module would plug into I wanted to replicate the same feature. The output of that pin acts the same as the device it will be replacing. Since it can't drive the LED directly do you know if there are any examples that people have used that would do something similar? Perhaps something as simple as a transistor and a couple resistors?

    Robert
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-06-23 22:08
    Robert,

    That depends on what the input voltage range to what you're trying to drive is. You could use a transistor...or you could use an op-amp. At unity gain it would be a buffer and drive the LED directly, if that's what you want to do.

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    Chris Savage

    Parallax Engineering
    ·
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2010-06-23 22:53
    The voltage range will be whatever the RSSI pin usually puts out. Ideally it would be off for no signal, dim for a weak one, and on for a good signal. Looks like some experimentation is on order. Have to break out the breadboards....

    Robert
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2010-07-01 19:13
    I noticed on the Linx website that the chip used on the board is offered in three different frequencies. Can these RF transceiver boards be ordered in 315Mhz and 418Mhz versions too?
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-07-07 18:24
    The IC from Linx can, however the modules we sell are fixed frequency.

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    Chris Savage

    Parallax Engineering
    ·
  • kwinnkwinn Posts: 8,697
    edited 2010-07-07 20:58
    Take a look at the lm3914 bar graph driver. It is a bit much to add to the board permanently but with a led bar graph it makes a nice little plug in for testing something like that.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2010-07-08 17:07
    kwinn,

    The LM3914 by itself will not give a good visual indication on a pulsing line. You'll need a sort of sample and hold circuit. Or better yet, just place a 1M resistor and a 0.1uF capacitor across the signal line to ground. That should stabilize the display and give a much more consistent feel to the signal.

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    Chris Savage

    Parallax Engineering
    ·
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