Frsky A1 voltage divider calibration setting .

[Matt]

Hi,

I have just flashed my TX with the Frsky version of ER9x and have been trying to follow the guides to setting up the TX with the calibration for the voltage divider for the battery monitor on a1. I have made the suggested divider of 3.3k and 22k but when I get to the part were I set up the telemetry details for the Model in receiver I see a voltage were I believe I should be entering a number??? I can see i can change this field from a raw number, to an Amps etc but how do I enter the scaling factor. Is this a recent change. Is there a document which outlines the correct setup details for the current firmware??

Matt

[Kilrah]

The receiver's input (D8R) can measure 3.3V max. So for example if you use a divider that divides by 4, you'll be able to measure 3.3*4 = 13.2V. That's what you'd enter in the telemtery screen for the full scale value.

[MikeB]

So for 3K3 and 22k, at full scale you will have 3.3V across the 3K3 and 22V across the 22k, a total of 25.3volts, so enter 25.3 as the voltage for the A1 ratio.

Mike.

[ShowMaster]

I found this link very usefull. It was posted when I asked for divider help.

jhsa wrote:
Hi showmaster.. here, try this. It's a voltage divider calculator.. I found it usefull to calculate my resistors

http://www.linuxfocus.org/~katja/toolbo ... lator.html

João

This is the link I've been using but today it's not working on my ipod but hopefully not for good?
http://www.linuxfocus.org/~katja/toolbo ... lator.html

I did a screen capture with my iPod do I'll post that since it shows the divider circuit and math to do it your self. Worked great when it worked? I haven't found a way to attatch pix's to posts withy iPod so I'll need to fire up my w7 comp and wait.... and wait...
You have to pick 1 resistor as a constant, an output voltage, and an input voltage I use 3.3k for R2 and 3.3v for U2, and 14 v for U1(3 cell Lipo with headroom)
Lately for 13.6v I've used 3.3k and 10k. I sometimes make the 10k a pot do I have some "wiggle room".
I just got a few Frsky dividers to try and I see I can select a range by selecting a differant input resistor. Never used them, made my own. I have some year old ones that may be a differant divider ratio. Comments from everyone making their own, or the Frsky versions I'm sure would be appreciated.
If known, what Frsky RX's have what input divider ratios for A1 and A2? I have many versions over the last year and thought Frsky had decided but even my newer d8r ll seems to be differant form d8r. I have a new d8r ll plus to try among with the newest 4ch. I plan to make up a list as I go along for each model rx using a er9x menu setting and a new Frsky divider, and the newest d8r ll plus and 4 ch as the standard and work backwards to see what readings the RX's give.
I think it'll be if use?
SM

[gohsthb]

A simple formula for figuring this out:

Value to enter in the telemetry screen = [3.3*(R1+R2)]/R2

R2 is the resistor that goes to ground, R1 is the resistor that connects to your battery+
3.3 is the highest voltage that the receiver can have as an input.
It is also recommended to add a small capacitor in parallel with R2. Something like 0.1uF or 1uF would be fine.

-Gohst

[purcilas]

If i have the frsky voltage sensor and i only want to measure rx battery voltage. Do i need to swap the cable on the sensor from 3s to 2s?

Its just a bit cobfusing how this all works.

Sent from my SAMSUNG-SGH-I777 using Tapatalk

[Kilrah]

What receiver do you have? As some have a 2.5V reference instead of the 3.3V one...

[gohsthb]

Some of the receivers have a built in divider that is connected to the battery voltage already. If that is the case I think it is normally a 4:1 ratio, and so you would set the voltage to 13.2.
-Gohst

[purcilas]

I am using d8r iis and d8rv2 and d8rsp

Sent from my SGH-I777 using Tapatalk 2

[purcilas]

And d8rii plus

Sent from my SGH-I777 using Tapatalk 2

[Hexperience]

I've been looking for this info... thanks!

Can I add another question in... so if I have the "stock" frsky voltage sensor using the higher ratio (6:1) I would set A1 to 19.8v right? I have found that 5.9:1 works better so I could use 19.4?

Thanks
Dave

[gohsthb]

Dave,
That looks correct. The 5.9:1 ratio comes out at 19.47 though. So you might have to put in 19.5 instead of 19.4. Just test with a meter and see which setting matches.

If you know the resistor divider ratio, then use this formula. 3.3*(ratio)=telemetry value
the ratio is found by (R1+R2)/R2
-Gohst

[Crucial]

The link to the calculator above is dead. This looks to be a second source.

http://tuxgraphics.org/toolbox/circuit- ... lator.html

[jhsa]

That's the one I use

[skelator]

nice post i have been looking for this, making my own sensor but after I have my TX modded with telemetry

[ShowMaster]

That's the one I use

In fact you're the one that sent the first link to me sorry I didn't give you the credit it deserves. I use it a lot since doing the math makes me have to think. Thank you.
SM

[jhsa]

Don't worry about that.. I don't care about credits.. It's a good thing so it has to be shared