Anyone have experience with BIM1's


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Thread: Anyone have experience with BIM1's5416 days old

  1. #1
    poke_
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    Default Anyone have experience with BIM1's

    Hi All,

    I've just bought a couple of BIM1's from Radio Metrix.

    http://www.radiometrix.co.uk/products/bim1.htm

    I've noticed it mentioned a few times here in the forum, but does anyone have any tips / advice / sample code for getting started with them.

    Thanks

    Anthony

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  3. #2
    poke_
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    Ok... so I'm guessing not

    Anyone have experience with tranceivers in general under proton that would like to offer some sage advice?

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  5. #3
    david
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    Hi,
    For what it is worth....
    Use the "Junk, sync, data" format to send your information. The junk bit is to wake up receivers and alert RSSI outputs. This part of the packet is expendable. The "sync" part is the bit you lock on to and could be a Tx address such as "Tx1". The data bit is the information payload.
    At the receive end use a serial format that waits for the "Tx1" to appear, rejecting all else and effectively making it a unique "channel". Then collect your data following the wait field.

    For aerials I suggest a vertical half wave dipole. OK it's not matched and should be a balanced drive but will still beat a 1/4 wave whip with an undersized groundplane.
    The 1/4 wave whip only works properly with a 1/4 wave or better groundplane and even this needs to be angled down at about 40 degrees to get a 50 ohm match. If you need a small antenna then a normal mode helical may be OK. At 434MHz this is about 165mm close wound on about a 3.2mm mandril - a bit like a spring out of a ballpoint pen.

    A simple Tx (+4dB) and Rx (-98dB) pair at 434MHz is good for over 1Km with matched antennas and line of sight operation but most applications have severely compromised antennas and are lucky to get 100m.
    Have fun.

    Cheers,
    David

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  7. #4
    poke_
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    Thanks heaps David.

    I'm using the 151.3mhz BIM1. It runs at a max speed of 1200baud. The suppliers have tested the 10kbps model and had it work effectively at over 10km with a half wave dipole, so I'm hoping that with the lower speed, I should be able to get 3-4km with a 1/4 wave.

    I've read quite a bit on the net about RF comms, and it seems that most people recommend a manchester encoding.... but I'm still not sure about that. All I'm transmitting is a station id, and then GPS location data.

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  9. #5
    david
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    Hi,
    Path loss at 151 will be less than at 434 so your range will be better. Ground effects will become more important due to longer wavelength and you may need to factor this in to your antenna radiation pattern.
    I don't know much about Manchester encoding but I believe it will effectively double your data rate. Try sending the truncated GPS serial strings as is at 1200 baud- you have plenty of time as your GPS data update is probably only 1Hz.
    Are the modules FSK or ASK? FSK should be better due to full time carrier, capture effect and amplitude noise rejection at the Rx side.

    Cheers,
    David

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