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Old Oct 01, 2009, 06:25 PM
Alexander/Sweden
Tuven's Avatar
Hemavan/Sweden
Joined Nov 2006
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R617FS RSSI problem whit remzibi OSD

Hi

I have made the RSSI hack on the R617FS reciever and i use a 4.7kohm resistor to connect to the Remzibi OSD.

But i have some strange values when iam going to polling the adc values.

When i turn on the tx the values it jump very much, the values between 11-43 and then a big jump to 360-380 adc value and then back to the lower values then upp again.....,

If i turn of the tx i get some lower values and they donīt jump around that quick, geting the values between 11-25.

But i tried to calibrate the RSSI as good i could, then i went out to my flying field and fired up and voila the RSSI was working and showing 160% +/- very stable, and i fly away and the RSSI went weaker and showed around 125% at 1km/0.6mile.

So it worked,

The inside test showed 0% and then jumped to 100% when tx on and then back to zero and than back to 100%........

when tx off the rssi showed around 0% +-- and no jumping upp. wierd

One tought i have about this strange values could be the wireless networks.
I have one 200mw router on my roof and one weaker in my apartment, plus the neigbors nets.

So maybe the FASST must work realy hard to filter out the noise and the diversity between the antennas could be one problem between the jumping values?

Hmm i forget to mention that i have measure the rssi whit my voltmeter and it showed a stable high/low value when tx on/off. but maybe the remzibi osd can measure more precise? or something i have made wrong.

So if you guys have some tips and tricks it would be great.

Regards Alex
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Last edited by Tuven; Oct 01, 2009 at 06:32 PM.
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Old Oct 01, 2009, 06:34 PM
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I use a different approach, because strong disturbing signals may fool rssi.

I use a "packet loss indicator". There is a red led on the receiver, it is on if a packet lost. The more it light the worse the reception.

I connected a RC low pass filter (150kOhm, 10 uF) on the led's pin, and connected the average voltage to the A/D. It diplayed as 0% to 100%.

Works pretty well.
Time to worry above 30%, but you can't feel it, the servos are smooth at that level. Above 70% the servos are jumpy.

My test video (check the % vs the movement of the servo):
Untitled (1 min 37 sec)
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Old Oct 01, 2009, 06:58 PM
Alexander/Sweden
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Hemavan/Sweden
Joined Nov 2006
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Okey i see, thatīs realy smart and fool prof, the RSSI is not that precise then.

Must test it out tomorrow and see how the red led behave and record whit my webcam.

But shouldent the lowpass be on the OSD? because the voltage dropp ??
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Old Oct 01, 2009, 07:09 PM
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Quote:
Originally Posted by Tuven
But shouldent the lowpass be on the OSD? because the voltage dropp ??
Of course I soldered the R and C part to the OSD's pcb.

I attached an oscillogram, the rssi output of the 617 is a series of pulses. If you like to use rssi, you need an opamp voltage follower (to avoid low impedance on the output) and a RC lowpass.
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Old Oct 01, 2009, 07:18 PM
Alexander/Sweden
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Hemavan/Sweden
Joined Nov 2006
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Thankīs alot. very good info.

I will go for the packet loss indicator mod.

But the rssi could be good also. but for me i think the packet loss indicator will do fine. it is simple then opamp.

Have you tested in air yet?

PS. do you have some direct link to the specified cap and resistor?
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Last edited by Tuven; Oct 01, 2009 at 07:28 PM.
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Old Oct 01, 2009, 07:46 PM
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Quote:
Originally Posted by Tuven

But the rssi could be good also. but for me i think the packet loss indicator will do fine. it is simple then opamp.

Have you tested in air yet?
More then a hundred flights in 2 planes. Works very well.
Before this mod I didn't know that there are losses in relative small distances, if my body is between the plane and the radio.

Quote:
PS. do you have some direct link to the specified cap and resistor?
No, sorry, I have resistor and capacitor sortiments, as my job and second hobby is electronics.
You can use any resistor and capacitor with the above values, including electrolyt type (take care of polarity).
I built it with a ceramic one.
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Old Oct 02, 2009, 01:19 AM
Alexander/Sweden
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Hemavan/Sweden
Joined Nov 2006
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Okey good.

No problem i will find the right parts.

And thankīs for the quick answers.
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Old Oct 03, 2009, 10:58 AM
Alexander/Sweden
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Hemavan/Sweden
Joined Nov 2006
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BTW whatīs the formfaktor on the resistor/cap are you using, i have seen three diffrent sizes/package

0603
0805
1206

?
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Old Oct 04, 2009, 02:03 AM
The one and only
dadde's Avatar
Hjo, Sweden
Joined Apr 2004
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Cool find mmormota! One question thou; Is there no need for a D/A converter from the led output to the RSSI input on the OSD? Or does the RC filter make one obsolete?
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Old Oct 04, 2009, 07:26 AM
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Quote:
Originally Posted by Tuven
BTW whatīs the formfaktor on the resistor/cap are you using, i have seen three diffrent sizes/package

0603
0805
1206

?
0805 for most positions, just the 10 uF is bigger.
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Old Oct 04, 2009, 07:28 AM
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Quote:
Originally Posted by dadde
Cool find mmormota! One question thou; Is there no need for a D/A converter from the led output to the RSSI input on the OSD? Or does the RC filter make one obsolete?
No need for additional hardware, just the RC low pass: 150k in series, 10 uF parallel to the input.
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Old Oct 04, 2009, 07:30 AM
The one and only
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Thanks man Awesome
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Old Oct 04, 2009, 10:59 AM
Alexander/Sweden
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Hemavan/Sweden
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Have ordered the stuff
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Old Oct 13, 2009, 06:01 AM
Alexander/Sweden
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Hemavan/Sweden
Joined Nov 2006
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I have it working now. Thankīs mmormota

Peace of cake, my first smd soldering hehe. not that easy.
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Old Oct 19, 2009, 11:24 PM
The one and only
dadde's Avatar
Hjo, Sweden
Joined Apr 2004
503 Posts
Tuven: Did the mod work good for you?

My OSD's RSSI input is made for 0-2.5V and the signal i get from the receiver is 2.8V, would it be possible to add a pull down before the low-pass filter to get the voltage down a tiny bit?
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