Drifting calibration of A1 FrSky telemetry voltage ErSky9x

[Mutchy]

I have an ErSky 9x Tx with FrSky Telemetry. In one electric model I have an FrSky FSH-01 sensor hub connected to the FrSky D8II Rx at the digital input port on the side of the Rx. It is used for two temperature measurement inputs only. It is powered from the Rx. In addition I have a home crafted voltage divider connected into the A2 port. It's output is just under 3 volts when the main power pack 10s LiPo shows 40.2 Volts.

My problem is that the Rx voltage displayed on the ErSky 9x screen drifts ie changes over time from the calibrated value. Also until the 10s pack is connected and A2 voltage display becomes active, the A1 displays a voltage about half of the actual Rx voltage. The 10s LiPo voltage does not drift: it is rock solid.

Because the 10s LiPo voltage does not drift I assume the Tx firmware and the screen display are OK and that my technique for adjustment of the divider when calibrating the display to match my multimeter is also OK. I suspect that the information sent from the Rx varies and that the Tx hardware and firmware are following what the Rx is telling it.

I use a separate 3s LiPo battery pack for the Rx power through a voltage regulator which gives a constant 5.2 Volts. The actual voltage at the input to the Rx ie from the voltage regulator and at either of the aileron outputs is exactly the same and does not drift. This voltage powers the hub via a lead connected from the receiver to the hub. The hub, Rx, VR and Rx battery are on the same earth. The main 10s LiPo pack and hence the voltage divider are directly connected and provide a second earth reference which is connected to the first earth via the side of the Rx.

Could this dual earth circuit be the problem? How do I fix it? Connect the two batteries earth leads with a jumper wire?

All suggestions very welcome
Mutchy

[Mutchy]

I took a new D8R - II plus Rx with the A1 shorting plug installed for Rx Voltage telemetry using the inbuilt circuit. ie new Rx and no hub connected and no voltage divider connected. The Rx voltage does not drift.

More tests tomorrow. It's bedtime.

Mutchy

[MikeB]

What is your "hand crafted" divider like? Could it simply be a resistor warming up and changing resistance? You are dropping nearly 40 volts across it. If you are using a pot, these can have a large drift in voltage with temperature, much more than "standard" resistors.
How much drift are you getting?

Mike.

[gohsthb]

You should have only one ground. Check your wiring very carefully.
-Gohst

Sent from my LG-P999 using Tapatalk 2

[Mutchy]

The scale factor for the Rx voltage is 11.5 v. The source of the voltage information in the original configuration is a FrSky FSH-01 telemetry hub. The scale factor for the 10s pack divider is 45.0 and the ratio of the divider is 2.98/40.2 = 0.074. The voltage divider is merely three 1 Watt resistors on a piece of Veroboard. I am using ErSky version R122 V1375 Mike Mod Rev B 17-10-2012.

This problem is associated with another, here: viewtopic.php?f=7&t=1295&p=31193#p31193 where with voice annunciation active on the ErSky 9x, the voltage announced for the A1 port is in error by a factor of ten for voltages below 6 Volts. So I have been doing lots of experiments with another receiver and different circuits for powering the Rx. NB The 10s pack voltage is rock steady with no drift and is announced perfectly.

I changed the Rx to a DR8-II PLUS (replacing the original DR8-II) which has the feature that a shorting jumper across the A1 to x pins forces the Rx internal voltage circuit to supply the telemetry data in preference to the FSH-01 telemetry hub. When the shorting jumper is in place on the new DR8-PLUS Rx, there is no drift in Rx voltage and no jump when the main pack is connected (and the announcement is correct for voltages in the 4 to 5 Volts range) so the source of the drift appears to be the FSH-01 hub. When the jumper is removed the voltage display drifts 2 to 3 Volts and the announcement is incorrect by x 10.

To confirm that the data from the hub is the source of the problem I connected the hub to another model's D8R-II Rx and had the telemetry announced. The announcement of voltages below 6 Volts was x 10. I connected the main pack voltage divider and the main pack. The Rx display jumped by about 2 times and drifted about 2 Volts over 5 minutes.

I conclude that the FSH-01 hub telemetry data (RS232 serial protocol?) when used with a D8R-II Receiver results in voltage display drift and jump in A1 and diplayed values less than 6 Volts being announced at 10 times the displayed value. The drift and jump does not happen with the jumper across A1 to x on a D8R-II PLUS Receiver but when the jumper is removed the announcement below 6 Volts is out by 10 times and the display drifts.

I hope that helps.
Steve

[MikeB]

What value are your three 1 watt resistors, and what type of resistor are they?

If you hae a chance, can you look at the displayed value for the receiver voltage and see how many decimal places are displayed? In particular, is the voice announcement OK with 1 decimal place, and out by a factor of 10 when 2 decimal places are displayed?

Mike.

[Mutchy]

I have just tested the system and can confirm that when the display has two decimal places the voice announcement is out by a factor of 10. ie 6.13 V was announced as 61.3 V whjle 6.2 V was announced as 6.2 V.

I connected the earth (negative) lead of the main pack to the negative lead of the Rx pack. The drift and jump persisted as before with no change in the characteristics of the system.

I conclude that the use of the FSH-01 FrSky telemetry sensor hub is unreliable for Rx Voltage telemetry when used with either the D8R-II receiver or the D8R-II PLUS receiver without the jumper inserted in the A1 port.

I guess this is why FrSky upgraded to the "plus" version and now recommend the jumper for Rx voltage telemetry. They even provide the shorting jumper with the Rx.

Steve

[Kilrah]

I conclude that the use of the FSH-01 FrSky telemetry sensor hub is unreliable for Rx Voltage telemetry when used with either the D8R-II receiver or the D8R-II PLUS receiver without the jumper inserted in the A1 port.

Wait a sec. The sensor hub does NOT measure RX voltage.

If I understand well, your D8R-II has your divider for the flight pack on A2, the hub on the data port, and nothing on A1, right?
Then it's perfectly to have some strange drifting voltage on the A1 channel. A1 is A1 whether the hub is there or not, it doesn't magically replace the value.

So, if you want to measure RX voltage with A1, you need to connect the RX voltage there. With a D8RII-Plus it's easy, as the receiver has an internal voltage divider connected to the supply voltage and providing 1/4th of the supply voltage to the middle pins of the A1 and A2 ports. So all you have to do is put a jumper between the middle and signal pins on either A1 or A2, and you'll have receiver voltage on the corresponding channel. With a D8R-II this internal divider doesn't exist, so if you want to measure receiver operating voltage you have to put an external 1:4 divider on the receiver's supply and connect it to the A1 or A2 pin, just like you did for your flight pack. The hub doesn't change anything to this, it's completely independent.