Battery telemetry on new ACCESS PLUS receivers

[DavidMc]

I've always used the FBVS01 module to give me lipo voltage readings. They were cheap and easy to use. Now as I get ready to order some new receivers, I see this module is no longer listed. I read the instruction manual for the PLUS 6 and PLUS 8 and see that no mention is made of how this is accomplished. Someone please tell me how to get onboard battery voltage telemetry from these RXs. I use 3,4 and 6 cell LIPos.

Thanks
David

 

[HENNY]

I've always used the FBVS01 module to give me lipo voltage readings. They were cheap and easy to use. Now as I get ready to order some new receivers, I see this module is no longer listed. I read the instruction manual for the PLUS 6 and PLUS 8 and see that no mention is made of how this is accomplished. Someone please tell me how to get onboard battery voltage telemetry from these RXs. I use 3,4 and 6 cell LIPos.

Thanks
David

Hi David.
Some of the Archer Plus receivers now have a 10-1 voltage divider fitted to the Ain2 input on board the receiver so you no longer need the cheap external voltage divider. Be careful and check the manual the wording will say " Voltage Measurement Range via AIN2 (External device): 0-35V (Battery Voltage Divider Ratio: 1:10)"

FRsky making thinks easier.
Henny

 

[DavidMc]

So does that mean that I can just run a wire from the battery/esc positive side directly to the AIN2 pin? What does "Voltage Divider Ratio 1:10" mean? Will it handle up 35 volts?
Sorry to be such a doofus but I don't want to fry anything. Also, could not find anything at all about it in the manual.
Thanks for answers
David

 

[HENNY]

May I have the full receiver type number before progressing. For example the Archer Plus GR8, in the specification section in the voltage measurement line it quotes 0-35 volts.

https://www.frsky-rc.com/wp-content/uploads/Downloads/Amanual/ARCHER%20PLUS%20R8%20GR8%20Manual.pdf

So as a bit of back ground, all RC receivers internal electronics runs off 3.3 volt even though you connect it to 5 volts, these receives have their own small bec just to power the receiver electronics.
The Ain2 line used to be connected to FRsky analog sensors (Way back in time) The Ain2 line needed an input voltage of 0-3.3 volts, anything higher would cause damage to the receiver, certainly 35 volts would kill it. The FBVS01 module would voltage divide your lipo voltage for measurement from say 3S or 4S to a voltage range of 0-3.3 volts. So the FBVS01 was a simple resister voltage divider, you could easily make one with 2 resistors.

So someone asked FRsky to make the Ain2 to have its own internal voltage divider, and some of the Plus series receivers actual now have this, however, best to check the manual for the Ain2 measurement range. So if the receiver does support this simply connect the battery positive to the Ain2 wire ( sometimes the green wire) and the battery negative to the black wire. You may need to adjust the ratio control in the Telemetry page so that the indicated TX voltage matches the battery measured voltage.

Hope this helps
Henny

 

[DavidMc]

OK, maybe I'm beginning to understand. So if the manual says "voltage measurement range via Ain2 0-35 volts" then that means it's okay to wire the Ain2 pin directly to lipo voltage up to a maximum of 35 v, then calibrate on the telemetry page, right? So what does the "battery voltage division ratio 1:10" mean? Does this mean that the device internal to the receiver automatically splits the voltage by 1/10th, example 20 volts input to Ain2 would be read by the Rx as 2 volts? By the way, I would probably be using the Plus R6 and Plus R8 mostly, maybe an occasional G or S series.

Many thanks. I don't understand why FrSky doesn't make things like this clear in their manuals.
David

 

[Miami Mike]

The FBVS01 has 3 division ratio options, which are 2:1, 4:1, and 6:1. Using OpenTX, the "ratio" setting on the Telemetry page means the voltage that should be displayed when the voltage at the AIN2 input is at its upper limit of 3.3 volts.

If you choose the "1S" option for a divider ratio of 2:1 then the correct "ratio" setting on the Telemetry page would be 2 x 3.3 = 6.6.
If you choose the "2S" option for a divider ratio of 4:1 then the correct "ratio" setting on the Telemetry page would be 4 x 3.3 = 13.2.
If you choose the "3S" option for a divider ratio of 6:1 then the correct "ratio" setting on the Telemetry page would be 6 x 3.3 = 19.8.

If a receiver has a built-in voltage divider with a 10:1 ratio then I'd assume that the correct "ratio" setting would be 33.0 and the upper limit that the receiver could handle at its A2 input would be 33 volts, so I'm not sure why 35 volts is acceptable.

 

[HENNY]

OK, maybe I'm beginning to understand. So if the manual says "voltage measurement range via Ain2 0-35 volts" then that means it's okay to wire the Ain2 pin directly to lipo voltage up to a maximum of 35 v, then calibrate on the telemetry page, right? So what does the "battery voltage division ratio 1:10" mean? Does this mean that the device internal to the receiver automatically splits the voltage by 1/10th, example 20 volts input to Ain2 would be read by the Rx as 2 volts? By the way, I would probably be using the Plus R6 and Plus R8 mostly, maybe an occasional G or S series.

Many thanks. I don't understand why FrSky doesn't make things like this clear in their manuals.
David

I tried to make it as clear as possible. In any case what ever receiver you are using check the manual for that exact receiver, some receivers can only work with Ain2 of up to 0-3.3 volt.

 

[HENNY]

The FBVS01 has 3 division ratio options, which are 2:1, 4:1, and 6:1. Using OpenTX, the "ratio" setting on the Telemetry page means the voltage that should be displayed when the voltage at the AIN2 input is at its upper limit of 3.3 volts.

If you choose the "1S" option for a divider ratio of 2:1 then the correct "ratio" setting on the Telemetry page would be 2 x 3.3 = 6.6.
If you choose the "2S" option for a divider ratio of 4:1 then the correct "ratio" setting on the Telemetry page would be 4 x 3.3 = 13.2.
If you choose the "3S" option for a divider ratio of 6:1 then the correct "ratio" setting on the Telemetry page would be 6 x 3.3 = 19.8.

If a receiver has a built-in voltage divider with a 10:1 ratio then I'd assume that the correct "ratio" setting would be 33.0 and the upper limit that the receiver could handle at its A2 input would be 33 volts, so I'm not sure why 35 volts is acceptable.

35 volts is the maximum that the ratio control can accommodate. So a maximum of Battery size S8.

 

[Miami Mike]

It seems to me that with a built-in 10:1 voltage divider some accuracy is lost when using lower voltage packs. I feel that the highest accuracy is achieved with a divider configured such that a fully-charged pack produces the limit of 3.3 volts at the A2 input.

For example, I use 3S LiPo packs, which output 12.6 volts at full charge, so for use with my Uni-RX X8R receiver I assembled a divider with a ratio of 12.6 to 3.3, using values comparable to the resistors in the FBVS01. I wired it to the battery input of my ESC and connected the output to the X8R's A2 input (which was RSSI before I upgraded to Uni-RX). And on my radio, I set my A2 sensor to a "ratio" of 12.6.

A fully-charged 12.6 volt pack feeding a 10:1 voltage divider would output only 1.26 volts to the A2 input, which is only about 38% of the range it's capable of measuring. The built-in divider in these new receivers may sound like a nice convenience but I believe it can cost you some accuracy.

 

[HENNY]

It seems to me that with a built-in 10:1 voltage divider some accuracy is lost when using lower voltage packs. I feel that the highest accuracy is achieved with a divider configured such that a fully-charged pack produces the limit of 3.3 volts at the A2 input.

For example, I use 3S LiPo packs, which output 12.6 volts at full charge, so for use with my Uni-RX X8R receiver I assembled a divider with a ratio of 12.6 to 3.3, using values comparable to the resistors in the FBVS01. I wired it to the battery input of my ESC and connected the output to the X8R's A2 input (which was RSSI before I upgraded to Uni-RX). And on my radio, I set my A2 sensor to a "ratio" of 12.6.

A fully-charged 12.6 volt pack feeding a 10:1 voltage divider would output only 1.26 volts to the A2 input, which is only about 38% of the range it's capable of measuring. The built-in divider in these new receivers may sound like a nice convenience but I believe it can cost you some accuracy.

The accuracy remains at .05 volts even with 10:1 divider. This is because the digital resolution has significant digital bits to describe the required voltage. However you can continue to use the previous FBVS01 if you can find it anywhere.

 

[MikeB]

While the built in divider is specified as 10:1, I believe it is actually 11:1. 10:1 would only allow input voltages to 33.3V.
I just did a test and connected a 3.0V battery to the AIN2 input of an Archer R10plus. Looking at the raw telemetry data on the Tx, the value received is 21. The A2 value on telemetry actually originated on the D8 receivers and is sent as a value from 0 to 255, where 255 represents 3.3V.
So a value of 21 represents a voltage of 21/255 *3.3V = 0.2718V. 3.0V divided by 11 is 0.2727V.
The measurement resolution is 1/255 *3.3V *11 = 0.142V. Regardless of the input voltage, the measurement "step" is this 0.142V.
If you measure a 3S LiPo, nominally 11.1V the raw telemetry value is 11.1/11/3.3*255 = 77.
77 is actually 77/255*3.3*11 = 10.961V
78 is 78/255*3.3*11 = 11.103V (0.142V higher).

Mike

 

[Wayne]

With the abuse we put on our batteries, this is actually accurate enough.

Aloft still offers the good old FBVS.

FrSky Battery Voltage Sensor (FBVS-01) - (No wires)

The FrSKY Battery Voltage Sensor is used with the FrSKY sensor hub and telemetry system.

alofthobbies.com

We used to sell over 100 a month, these days I'd guess it is less than 10.

 

[Miami Mike]

While the built in divider is specified as 10:1, I believe it is actually 11:1. 10:1 would only allow input voltages to 33.3V.

Hmm... I got curious about what "voltage divider ratio" really means so I did some research. I found that it's not the ratio of the two resistor values, it's defined as the the ratio of voltage of the output to the input voltage, so we really should be talking about expressions of the form 1:10 or 1:11. Here's a Voltage Divider Calculator with more info.

A voltage divider with a 1:10 ratio would have a resistor of N ohms on the negative side and 9N ohms on the positive side, and with 33.3 volts applied would produce an output of 3.33 volts, which would be more than what's allowed. But with 33.0 volts applied a 1:10 ratio would produce an output of 3.3 volts, which would represent the upper limit of the A2 sensor.

A voltage divider with a 1:11 ratio would have a resistor of N ohms on the negative side and 10N ohms on the positive side, and with 36.3 volts applied would have an output of 3.3 volts, so it looks like if the divider actually has a 1:11 ratio then up to 36.3 volts would be allowed.

 

[HENNY]

Hmm... I got curious about what "voltage divider ratio" really means so I did some research. I found that it's not the ratio of the two resistor values, it's defined as the the ratio of voltage of the output to the input voltage, so we really should be talking about expressions of the form 1:10 or 1:11. Here's a Voltage Divider Calculator with more info.

A voltage divider with a 1:10 ratio would have a resistor of N ohms on the negative side and 9N ohms on the positive side, and with 33.3 volts applied would produce an output of 3.33 volts, which would be more than what's allowed. But with 33.0 volts applied a 1:10 ratio would produce an output of 3.3 volts, which would represent the upper limit of the A2 sensor.

A voltage divider with a 1:11 ratio would have a resistor of N ohms on the negative side and 10N ohms on the positive side, and with 36.3 volts applied would have an output of 3.3 volts, so it looks like if the divider actually has a 1:11 ratio then up to 36.3 volts would be allowed.

Yes a 1:10 would have a tenth of the voltage and an 1:11 would have an 11th of the voltage. Max adjustable voltage is 35 volts in the Telemetry Ain2 menu.

 

[HENNY]

While the built in divider is specified as 10:1, I believe it is actually 11:1. 10:1 would only allow input voltages to 33.3V.
I just did a test and connected a 3.0V battery to the AIN2 input of an Archer R10plus. Looking at the raw telemetry data on the Tx, the value received is 21. The A2 value on telemetry actually originated on the D8 receivers and is sent as a value from 0 to 255, where 255 represents 3.3V.
So a value of 21 represents a voltage of 21/255 *3.3V = 0.2718V. 3.0V divided by 11 is 0.2727V.
The measurement resolution is 1/255 *3.3V *11 = 0.142V. Regardless of the input voltage, the measurement "step" is this 0.142V.
If you measure a 3S LiPo, nominally 11.1V the raw telemetry value is 11.1/11/3.3*255 = 77.
77 is actually 77/255*3.3*11 = 10.961V
78 is 78/255*3.3*11 = 11.103V (0.142V higher).

Mike

Hi Mike. Just performed some Ain2 resolution tests. While the D8 had a resolution of 8 bits (256) my tests with a GR8 confirms I can see changes of 10mili volts at the Ain2 pin and reflected at the receiver telemetry monitoring side. So am wondering if the 2k resolution of the sticks has also been allowed at the A/D side of the Ain2. I am using a precision adjustable power supply and a digital volt meter at the RX Ain2 side and monitoring what the Ain2 telemetry shows me at the TX side.
Henny

 

[jure]

as a reference , this is part of the data sheet for the FBVS01,
and a sketch showing the resistor network and the nominal 1% resistor values.

 

[MikeB]

My testing was with an Archer R10 plus, HW: 1.1.0, FW: 1.0.8.
TX is a X20 running ACCESS on TD-ISRM HW: 1.4.0, FW: 2.2.4(EU-LBT).
External voltage applied to the AIN2 signal on the small, 4-pin connector.
At the Tx side, I logged the raw data sent by the TD-ISRM, so no, possible scaling applied to this.
There were only 4 telemetry values, RSSI, RxBatt, AIN2 and VFR.

The AIN2 value was just 21 (decimal) to represent 3.0 volts.

What hardware and firmware versions did you use?

Mike

 

[HENNY]

My testing was with an Archer R10 plus, HW: 1.1.0, FW: 1.0.8.
TX is a X20 running ACCESS on TD-ISRM HW: 1.4.0, FW: 2.2.4(EU-LBT).
External voltage applied to the AIN2 signal on the small, 4-pin connector.
At the Tx side, I logged the raw data sent by the TD-ISRM, so no, possible scaling applied to this.
There were only 4 telemetry values, RSSI, RxBatt, AIN2 and VFR.

The AIN2 value was just 21 (decimal) to represent 3.0 volts.

What hardware and firmware versions did you use?

Mike

Hi Mike
X20S running FW Ethos running ACCESS FCC 1.5.9, running 8 channel mode. Receiver GR6 V2.1.12
External voltage applied to Ain2 directly, ( no voltage dividers) voltage was around 2 volts from the power supply. Confirmed this voltage at Ain2 with a DVM.
The receiver had RSSI, VFR, Rxbatt, Alt, Ain2 set the receiver accuracy to 3 decimal points for monitoring. I set up a screen display to see the Ain2 results.

Henny

 

[MikeB]

What firmware revision on the TD-ISRM (Settings|Info)?
Also what firmware on the GR6+? The FrSky site only shows firmware versions up to 1.0.10.

Mike

 

[HENNY]

What firmware revision on the TD-ISRM (Settings|Info)?
Also what firmware on the GR6+? The FrSky site only shows firmware versions up to 1.0.10.

Mike

The X20S ISRM FW is version HW 1.4.0FW: 2.2.6 (FCC) The receiver is the Archer GR6 not the plus version with V2.1.12
Henny