FrSky Telemetry with Er9x; short explanation

All mods related to the frsky telemetry series of the firmware
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Mutchy
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FrSky Telemetry with Er9x; short explanation

Post by Mutchy » Sat Feb 25, 2012 10:56 am

This post describes the Er9x FrSky NOHT firmware when used to display Rx Battery Voltage, Pack Voltage and Altitude when using the Winged Shadow "How High" sensor. This version of ER9x has no Helicopter firmware and no templates. This save space in the ATMEGA chip for the telemetry firmware and more model memory, I suppose.

This description focuses on an electric powered glider or aircraft with either a separate pack for Rx supply or a UBEC connected to the main power pack. Of course the description is generally applicable too. Altitude is important to me as I sometimes compete in F5J where there is a vast increase in penalty for starting altitudes over 200 feet.

No hub is necessary to obtain these displays on the transmitter screen. You will need to buy an altitude sensor and make a voltage divider. I decided to use a stand alone telemetry system for a variometer because I wanted real time audio output without having to look at the screen. My descriptions of this system is here:
http://www.rcgroups.com/forums/showthre ... st20569858
See posts #30 and #36. Of course both the altimeter and variometer are illegal for competition but are very useful for training.

You get the three Received Signal Strength Indication (RSSI) alarms for free, ie without doing anything special or buying sensors. They are not adjustable. As the distance increases you get one beep, then two, then three.  Be aware that when the Rx swops over from ariel to ariel ie is using the built in ariel diversity feature of the Receiver chip you get a single beep at the Tx: nothing to worry about but may still be an indication of good or not so good positioning of the ariel on your model. When circling it can happen twice per circle which gives the clue that it is Rx ariel diversity working.
Get worried when you hear the triple beep in flight. To become familiar with the alarms do a range check by walking away from the model with the Tx in your hand in range test mode. This will give you a sense of the proportions of the distances when each alarm sounds and when you finally lose contact.

To display altitude a Winged Shadow "How High" unit is programmed for the correct output and connected into the receiver as described in the How High documentation. Power is taken from one of the receiver channels and the output, a single lead with a male plug, plugged into the signal pin labelled Rx on the side of the FrSky receiver. Despite the right click 9/10 screen having selectable options for metric or Imperial display the display only works with imperial. So the "How High" has to be programmed to Imperial mode and the right click 9/10 screen selected to display "Imp".

The Rx voltage is displayed on the screens when you put a jumper (shorting plug) across the A1 + and A1 Signal pins on the side of the FrSky receiver so that is easy too. The voltage comes up on the display and has two alarms which you can set as well at right click 9/10 screen. You have to calibrate the A1 voltage multiplier on that screen so that the reading you get with your voltmeter at the Rx agrees with the telemetry displayed value at the transmitter.

To display pack voltage take some leads off the main battery pack connector through a voltage divider to give less than 3.3 Volts at the A2 pins. You then have a readout of the main pack voltage. Again you have to calibrate the voltage multiplier on right screen 9/10 in eR9x so that your voltmeter reading agrees with the screen display.  This voltage readout  is handy for a day's soaring so that you don't run the main pack too low ie do too many climbs. You can set two levels alarms for this telemetry channel too. I suggest using a trim pot for one of the resistors so you can get fairly close to just under 3.3 Volts at the Rx side terminals. A voltage divider is explained in the posts mentioned above for the Variometer.

Just an observation about the right screen 9/10 voltage multiplier values. Highlighting any value using the left side navigation keys and then pressing the top right (enter) key gives you the ability to toggle between a number of alternatives or set numeric values for the voltages alarm numeric values. When finished press the lower right key short to set the value and long to return to the main screens. There's a lower case v and an upper case V option as well as upper case A for current (Amps). For very large multiplier values use V which goes up to 60 Volts I think. For smaller values use v which goes up to 24 Volts I think. The value you have to use is a mystery to me and the value to enter for the v option is about twice the real Voltmeter reading. 

Another point; the minimum and maximum values of the voltages, (and also RSSI and TSSI readings) are shown below the instantaneous value. Also the instantaneous value of A1 drifts a bit while calibrating it compared to the actual Voltmeter reading. I have had to set and reset the multipliers a few times over a period of two or three minutes to get a good average display which corresponds with reality.

Here are the three screens for the FrSky Telemetry.
Descriptions are for the pictures below.

Mutchy
Attachments
FrSky Telemetry Screen 1 sml.jpg
Screen 1: one press down from the start up screen. Clockwise from the top left are Model name and below that is the Tx battery voltage. Then the timer switch identity, timer setting in minutes and seconds, the A2 Pack voltage display, the transmitted signal strength below that and the received signal strength at the receiver to the left. Above that is the A1 Receiver voltage display.
FrSky Telemetry Screen 2 sml.jpg
Screen 2; one press right on the navigation buttons: from top right first row: Model name, Tx Voltage, timer setting. second row: A1 (Receiver) Voltage, A2 )(pack) Voltage. Row 3: Min and max vltages fro A1 and A2. Row 4: Rx and Tx signal strengths. Row 5: Min and Max values for signal strengths above.
Screen 3 Small.jpg
Screen 3 another press right on the navigation keys. I don't have a temperature, fuel gauge or RPM sensor connected so the displayed values are the default with no sensor input.
Last edited by Mutchy on Sun Feb 26, 2012 6:48 am, edited 3 times in total.


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FrSky Telemetry with Er9x; short explanation

Post by Rob Thomson » Sat Feb 25, 2012 11:20 am

Thanks for this post.

I will turn the guts of it into a wiki guide!


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...........if you think it should be in the wiki.. ask me for wiki access, then go add it!

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MikeB
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Re: FrSky Telemetry with Er9x; short explanation

Post by MikeB » Sat Feb 25, 2012 12:25 pm

Thought I'd fixed that A2 display on the third screen.

Mike.
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Mutchy
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Re: FrSky Telemetry with Er9x; short explanation

Post by Mutchy » Sun Feb 26, 2012 4:48 am

MikeB wrote:Thought I'd fixed that A2 display on the third screen.

Mike.
I'll check that I've got the latest FrSky NOHT firmware later today.

Mutchy

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Re: FrSky Telemetry with Er9x; short explanation

Post by Mutchy » Sun Feb 26, 2012 6:23 am

Mutchy wrote:
MikeB wrote:Thought I'd fixed that A2 display on the third screen.

Mike.
I'll check that I've got the latest FrSky NOHT firmware later today.

Mutchy
Sorry All. I had the older version of the firmware. I have updated the firmware and the A2 display is now correct on the third screen. I will now edit the above post to show the third screen with the correct information. The A1 display still drifts when calibrating it to the Voltmeter reading..... ie when adjusting the screen display by varying the multiplier on right click screen 9/10.

Mutchy


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Re: FrSky Telemetry with Er9x; short explanation

Post by MikeB » Sun Feb 26, 2012 10:32 am

The 'drift' you refer to is probably due to the scaling sometimes having more than one setting resulting in the same displayed value.
Suppose you have a 4:1 divder, this means the maximum voltage you can measure is 13.2 volts (4*3.3), so the scaling factor would be set to 132.
Now, suppose the voltage you are measuring is 5.0 volts. This is divided by 4 to give 1.25 volts. This is a proportion of 1.25/3.3 of the analog to digital converter that gives an output of 0 to 255. This will give a conversion value of 96 (its rounded down). When scaled using the 132 above, this results in a reading of 4.9 volts, which is actually correct given the rounding down (4.969 is the floating point calculated value). You most likely then change the scaling to 133, which gives a reading of 5.0 (5.007 if floating point calc). You could also change to 134 or 135, and both these will also give a display of 5.0 (5.045 and 5.082). From one measurement to another there is some variation, and if you are actually close to 5.000, the display will probably drop to 4.9 frequently, while if you are close to 5.099 the display will flick to 5.1 frequently. All this is more noticeable if the measured voltage is a lot less than the maximum for the scaling allowed.
You also have a delay for the screen update, to prevent the display from becoming unreadable due to frequent changes, so the measured value may have changed, but it has not yet been displayed.

BTW, 'v' goes up to 25.5 volts, and 'V' goes up to 51.0 volts (twice).

Mike.
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Re: FrSky Telemetry with Er9x; short explanation

Post by Kilrah » Tue Feb 28, 2012 8:47 am

Hmm, I seem to have a problem I can't find on the forum.
I run r736, and I remember having had the telemetry screens as displayed here the first few times at the beginning. However, at some point I used a receiver with a sensor hub connected and since then the 3rd screen is a different one with latitude, longitude etc, likely for GPS use. Since then, I don't have the A1 and A2 voltages displayed anymore on any screen, even if I use another model memory and receiver.
I have seen in threads devoted to other firmwares that there was a setting to choose a different protocol when using the sensor hub than for the plain RX telemetry, but haven't found a similar one on ER9X. Would the radio have changed protocol automatically because of me connecting a sensor hub once, with no way to get back to normal?

EDIT: Found out, it was simply due to the max scale being set to 0, disabling voltage display. It's by trying Open9x on my TX to see the differences that I understood, the text being explicit in open9x's menu instead of just a seemingly meaningless number next to "A1 channel" on ER9x.
Last edited by Kilrah on Tue Feb 28, 2012 10:21 am, edited 1 time in total.

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Re: FrSky Telemetry with Er9x; short explanation

Post by Mutchy » Tue Feb 28, 2012 10:09 am

MikeB wrote:The 'drift' you refer to is probably due to the scaling sometimes having more than one setting resulting in the same displayed value.
Suppose you have a 4:1 divder, this means the maximum voltage you can measure is 13.2 volts (4*3.3), so the scaling factor would be set to 132.
Now, suppose the voltage you are measuring is 5.0 volts. This is divided by 4 to give 1.25 volts. This is a proportion of 1.25/3.3 of the analog to digital converter that gives an output of 0 to 255. This will give a conversion value of 96 (its rounded down). When scaled using the 132 above, this results in a reading of 4.9 volts, which is actually correct given the rounding down (4.969 is the floating point calculated value). You most likely then change the scaling to 133, which gives a reading of 5.0 (5.007 if floating point calc). You could also change to 134 or 135, and both these will also give a display of 5.0 (5.045 and 5.082). From one measurement to another there is some variation, and if you are actually close to 5.000, the display will probably drop to 4.9 frequently, while if you are close to 5.099 the display will flick to 5.1 frequently. All this is more noticeable if the measured voltage is a lot less than the maximum for the scaling allowed.
You also have a delay for the screen update, to prevent the display from becoming unreadable due to frequent changes, so the measured value may have changed, but it has not yet been displayed.

BTW, 'v' goes up to 25.5 volts, and 'V' goes up to 51.0 volts (twice).

Mike.
Hi Mike.
Your description exactly matches the characteristics of what happened during my calibration. Thanks for your clear and precise explanation.
Mutchy


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