My FrSky telemetry project

Telemetry is the new "big thing" in RC systems. If you've got something to say or a question to ask, do it here.

Re: My FrSky telemetry project

Postby takilara » Sun Sep 11, 2011 8:49 pm

seaman wrote:Do you have any interference ? A think that FRSKY and Bluetooth use the 2,4Ghz.


No. I have not been able to notice any inteference. I expected to have inteference on the return channel. (As the return channel is not frequency hopping), but I guess it is far enough from the BT transmission to work without inteference. This might be different for different RS232-BT bridges though.

Note, i have not done very extensive testing with this, but i logged RSSItx and RSSIrx both using cable to computer, and using BT to cell phone. (different flights). And I was unable to see any noticeable difference in the numbers.
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Re: My FrSky telemetry project

Postby igo88 » Thu Sep 15, 2011 3:15 am

Thank you very much for this 43 pages...they have been very instructive for me.

I am thinking about ordering a DIY kit of a frsky 2.4ghz with telemetry...is this project still alive??...i have seen a hub in the frsky page...is this one?

Thanks again!
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Re: My FrSky telemetry project

Postby jhsa » Wed Sep 21, 2011 1:28 pm

Bodmer wrote:
lm317 wrote:I actually don´t see a prob with the voltage divider.


Agreed, on it's own it is a simple circuit that is easy to make and calculate the values with no design flaws when considerend in isolation. The complications arise when it is connected directly to the battery in the more complex setups, for example where an independant BEC is used or a BEC within the ESC.

The diagram below illustrates a bad setup. This diagram has been simplified to illustrate a point, the heavy black lines are the 0V wires. The 0V line to the motor is electronically commutated normally but for simplicity it is shown as a direct connection. The line shown as carrying 1.5A is the 0V line of the voltage divider sensor:
Parasitic paths.jpg


There are multiple reasons why this is particularly bad:
1. A parasitic current path exists from the ESC through the receiver back to the battery. In a setup using 14AWG wire for the main battery and 26AWG wire for the receiver and voltage monitor circuit the parasitic current could be 2 Amps or more if the motor current is 50A. If 20AWG wire is used in the receiver leads the parasitic current approaches 5A!
2. There is a parasitic path via the sensor return that bypasses any common mode choke in the power feed from the BEC/ESC to the receiver (typical in switched mode BECs). The common mode choke now makes supply noise much much worse since it couples noise spikes on the battery lines straight into the power feed to the receiver, this could easily reduce the operating range of the receiver and hence cause loss of control at a distance......
3. The parasitic current path can upset switched mode BECs that use a significant level of common mode output filtering, affecting their output regulation and causeing "pulse skipping" that typically results in very brief brownouts in the receiver supply, again likely to cause loss of control when the servos start working hard.
4. If the battery to ESC has a connector and if the +ve line to the battery connects first (even very briefly during a 2 pole connector mate) the receiver is likely to experience a brief voltage surge of the full battery voltage and very high transient currents will be routed via the receiver while the bulk decoupling capacitors at the input of the ESC charge up (brief capacitor charge curents in excess of 100Amps are not unusual and this charge current will try to go via the voltage divider 0V line!!!!!!)

So don't be surprised if things mysteriously fail with this setup.......

Here is a setup that deletes the parasitic path:
Divider monitoring.jpg


In this circuit the OV line from the resistor divider is NOT connected to the battery. The parasitic current path through the receiver is now removed and the battery voltage is sensed relative to the 0V that is routed via the BEC. The capacitor fillters the ground noise resulting from transient voltage drops in the 0V line. The 4K7 resistor limits the discharge current from the capacitor into the analogue channel input to the microcontroller in the case where the capacitor is charged and the receiver is off. (Note: even a very brief current of more than 2mA into the receiver pin will destroy or reduce the life on the receiver.)

The problem with the high power electrical systems that are used in model aircraft is that with the high currents and high transient voltages (that are invisible in a simple electrical analysis of the system) make wires look like resistors and inductors. Also low parasitic capacitances start to couple significant currents into sensitive electronic components.

ATB,
Bodmer

Hi Bodmer, don't know if you're still following this thread. Didi you manage to built that differential voltage sensor? You said that you'd build one. I've read all the thread but couldn't find it.
I have the er9x radio with frsky telemetry on screen. Copied the frsky voltage sensor, and guess what... I fried my tricopters receiver. I wish I'd read your post earlier :cry:

Anyway How are you guys connecting your voltage sensors. I'm using an old D8R receiver. How can we avoid that the noise from the motors fry the receivers when we connect the sensor to the battery?
Regards to you all
Thanks,
João
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Re: My FrSky telemetry project

Postby jhsa » Thu Sep 22, 2011 11:29 am

I'Ve designed this voltage sensor that will work with 2 and 3s lipo battery. I didn't test it yet and I would like some opinions on it.
I will try to test it today. Hopefully this will stop receivers from get fried ;)
The sensor ratio is 4:1 and is ,meant to work with the frsky D8R, D8R V2 (A2 pin ), and the new D8R-II receivers.

Regards,
João
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Re: My FrSky telemetry project

Postby sindre » Sun Nov 06, 2011 9:55 am

Hi Bruce and all other fellow RC enthusiasts. Greetings from Norway. I have a question on the FrSky telemetry system, has anyone confirmed that the FrSky transmitter actually outputs RS232 levels ? It would seem much more logical that it outputs TTL levels IMHO. When I've looked at schematics for interfacing telemetry data with the Turnigy 9X ER firmware I've seen MAX232's or similar circuits used. Are they really neccesary ? (And yes; I've seen that the FrSky "manual" says RS232, but TTL connected to a RS232 Rx line will also give the correct results ... )
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Re: My FrSky telemetry project

Postby takilara » Sun Nov 06, 2011 10:58 am

I think this is confirmed yes. I cant find the link right now, but that confirmation is why i use a RS232 bluetooth bridge instead of normal TTL bluetooth bridge
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Re: My FrSky telemetry project

Postby SidGates » Mon Dec 26, 2011 9:12 pm

I stumbled onto this thread a couple days ago and spent about one day reading all the post and then when I get to page approx . 41 all posts be the author have ceased. Can anyone tell me the status of this project???
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Re: My FrSky telemetry project

Postby A10FLYR » Tue Dec 27, 2011 8:04 am

Maybe Bruce sold it to FrSky?
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Re: My FrSky telemetry project

Postby ergocentric » Wed Dec 28, 2011 2:33 pm

A10FLYR wrote:Maybe Bruce sold it to FrSky?


eventually FrSky had to develop their own design, looks hackable, that way you don't have to chase down all the parts
http://www.frsky-rc.com/ShowProducts.asp?id=104
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Re: My FrSky telemetry project

Postby SidGates » Wed Dec 28, 2011 4:44 pm

I looked at FrSky product and since I can't see any pitot equipment I assume the "Speed" is ground speed from the GPS. Can anyone confirm this?

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