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Old Aug 08, 2012, 05:12 PM
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Auckland, NZ
Joined Sep 2009
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Sounds good, my vote for rssi value should be in dBm.

Many thanks for your effort.



Quote:
Originally Posted by SimonChambers View Post
Hi Bingo,

The RSSI output is PWM based. It is an averaged value of RSSI over the last complete received channel hop sequence. Invalid packets or corrupt will reduce the RSSI value.

I couldn't find any form of standard whatsoever, so I came up with the following formula:
PWM duty cycle = ([RSSI_dBm] + 128) * 2

The PWM is 8bit - so generated internally from 0 to 255.

IIRC, the RSSI dBm signal strength in the receiver is between -120dBm (minimum received signal) and -10dBm (receiver saturation). Above -10dBm the receiver becomes saturated and is unable to process packets (so signal loss). However the only way I can get these park flier receivers to saturate is by putting the receiver antenna right next to the transmitter antenna, in the same polarisation plane - not recommended to be done btw, as you could damage the receiver RF front end.

If all packets are lost for 2 complete channel hopping frames, RSSI will drop to zero - i.e. Failsafe/no signal mode. By default the receiver will stop outputting PPM on the loss of 2 complete channel hopping frames, unless if the failsafe is set, then the receiver PPM will output the failsafe positions. Each channel hopping frame = 21 channels. So 2 complete channel hopping frames = ~1 second.

Anyone who has a better RSSI algorithm, let me know and I can change it to it! One possible problem is that the dBm scale is logarithmic - so at low signal levels, the RSSI will vary by not a lot.

I've got some interesting stuff going on behind the scenes , unfortunately I am restricted due to commercial reasons from saying exactly what I am doing.

I really can't say more than that (I'm sticking my neck out by saying what I have here already), as I don't want to risk damaging all the work that has gone on. Rest assured, if everything is eventually successful, it should be good and hopefully people will be happy!

Cheers,

Si.
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