FrSky Amp/Current Sensor.

All mods related to the frsky telemetry series of the firmware
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jhsa
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Re: FrSky Amp/Current Sensor.

Post by jhsa » Mon Jan 28, 2013 12:14 pm

I think he might be using er9x. If so, there is no offset.
I wanted to use once a temperature sensor that reads negative values, the TMP36, and as far as I know, I couldn't because of the offset..
Had to use a TMP37 (harder to get) that only reads positive temps, also better for what I need it for.

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Re: FrSky Amp/Current Sensor.

Post by Trieste » Mon Jan 28, 2013 4:09 pm

Thank you very much!

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Re: FrSky Amp/Current Sensor.

Post by MikeB » Mon Jan 28, 2013 7:35 pm

Actually, there is an offset available for the current. It works like the altitude offset, it isn't stored in the EEPROM.
In one of the fixed telemetry views, altitude is displayed. LONG MENU sets this to zero.
In another of the fixed telemetry views, both A1 and A2 are displayed. If either of these is set to 'A' (current), then LONG MENU zeroes this value.

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Re: FrSky Amp/Current Sensor.

Post by jhsa » Mon Jan 28, 2013 8:06 pm

oh, didn't know about that ;)
The little secrets our developers keep hidding from us :P :mrgreen:
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Re: FrSky Amp/Current Sensor.

Post by Trieste » Tue Jan 29, 2013 8:17 pm

rainer wrote:Wouldn´t it be sufficient to specify 400 as the range of that channel with an offset of -200A
I don´t have my transmitter handy, but if it´s possible to set the range to 400 that should work.
like that 0v would equal -200A 1.60v = 0A and 3.2v=200A

Rainer

Perhaps with open9x. But for whatever reason open9x won't run properly on my TelemetreZ+th9x. I also don't mind getting dirty in the code. I was meaning to take a look anyway.

Also - Mike - Thanks again. I've been able to compile my own version and run with it. The math is a little weird - I was trying to find where you're setting the limit of 65 - any pointers? If not no biggie - I can make it work with additional hard coding. I am also going to pre-set the offset for my needs so I don't have to set it each time.


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Re: FrSky Amp/Current Sensor.

Post by MikeB » Tue Jan 29, 2013 11:09 pm

The 65 is not a set limit, it just happens.
8-bit analog value and 8-bit ratio multiplied by each other gives 65535 maximum,
This is divided by 100, and the result treated as 10th of amps, so 65.5 Amps max.

BTW, I'm about to commit an update, where I've moved several procedures to different files, where they should be. So procedures to do with telemetry are being moved to frsly.cpp. This includes scale_telem_value().

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Re: FrSky Amp/Current Sensor.

Post by Trieste » Wed Jan 30, 2013 5:44 pm

Sweet. I'll check out again. Knowing the math helps a ton.

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Sat Feb 09, 2013 6:19 pm

Another current meter but this time 50A (but for same price you can get 100A version) and more simpler!

http://www.ebay.com/itm/390341332320

in this version it's only needed 2x1.5kohm resistor and 10uF capacitor:
IMG_0451.JPG
End result:
IMG_0454.JPG

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Re: FrSky Amp/Current Sensor.

Post by kaos » Mon Feb 11, 2013 9:53 pm

For 100A version would the resistor and capacitor the same as the 50A?

by the way, this is really nice, small, light, simple without the digital sensor hub. especially for trouble shooting/set up new plane it is great.

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Mon Feb 11, 2013 9:59 pm

kaos wrote:For 100A version would the resistor and capacitor the same as the 50A?
Yes, 100A only lacks resolution, output voltages are same.

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Re: FrSky Amp/Current Sensor.

Post by kaos » Mon Feb 11, 2013 10:06 pm

How much less resolution we are looking at between 50A and 100A?

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Mon Feb 11, 2013 10:12 pm

1/2

20mV/A vs 40mV/A

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Re: FrSky Amp/Current Sensor.

Post by kaos » Mon Feb 11, 2013 10:17 pm

Is there a way to mod the 100A version with same resolution as 50A?
I have plane/heli is running just above 50-60 amp but under 100 amp

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Mon Feb 11, 2013 10:34 pm

not in simple way, it involves opamp and subtracting 2,5V from start voltage so you don't need to divide voltage.

My suggestion: http://www.rctimer.com/index.php?gOo=go ... oodsid=861 , clean, simple and plug&play

But my opinion is if you have something that runs on 60A, +/-1A off is not big deal (by my calculation you will have resolution of 1,2A)

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Re: FrSky Amp/Current Sensor.

Post by kaos » Mon Feb 11, 2013 10:52 pm

Thank you Isvedic.
I think I am going to make the 50A version. for a couple of the planes i have may just resort to the Frysky amp sensor which cost abou the same as the RC timer version, while needing the hub. but for the model needs 100A is large enough to carry/arrange the hub too. ;)
The greatest part of your design is simple small, easy to be used on smaller planes without a hub.
Thx again. Once I get the part, if I run into problem, I will come up here again. ;)

Oh, what happens if I use the 50A on a plane that may have a burst of 55-60 A in the rare extreme situation, the sensor just burn out and just won't read the amp any more or if burns out it will cut off the power as well?

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Mon Feb 11, 2013 11:00 pm

"The thickness of the copper conductor allows survival of the device at up to 5x over-current conditions." So you won't go down because of that, but if you get reading of 60A from 50A sensor let me know I'm curious too :)

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Re: FrSky Amp/Current Sensor.

Post by kaos » Mon Feb 11, 2013 11:11 pm

who wants to be the 1st tester on that? :lol:
I think I will be the 1st, my heli uses 45A esc and some times they got really hot, I suspect it some times goes to 60A bursts and it will puff a 2200mah 20C lipo. ;)

order the ebay chip now. one spare for tester. ;)

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Mon Feb 11, 2013 11:47 pm

from their docs:"When the current flowing through the copper conduction path (between the IP+ and IP- pins) exceeds this threshold, the open drain overcurrent fault pin will transition to a logic low state"

So in theory over 50A it should show 0A

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Re: FrSky Amp/Current Sensor.

Post by kaos » Tue Feb 12, 2013 12:11 am

Great, thx for the info, at least I don't need to worry about crashing the plane. ;)
by the way, can't order the chip yet (pay now). It is Chinese New Year, it does not matter order it today or a wk from now, nobody is going to process/ship it till a wk later. ;)

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Re: FrSky Amp/Current Sensor.

Post by jhsa » Tue Feb 12, 2013 9:03 am

The seller doesn't sell to Germany..
Will this one work? I think this one is unidirectional with 60mV resolution

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... ink:top:en

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Tue Feb 12, 2013 10:57 am

jhsa wrote:The seller doesn't sell to Germany..
Will this one work? I think this one is unidirectional with 60mV resolution

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... ink:top:en

Thanks

João
It should, just be careful in what direction you put current.

Unidirectional have 50% better resolution (60mV/A vs 40mV), end voltage is higher than bidirectional but still lower than 3.3v after 1:2 voltage divider

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Re: FrSky Amp/Current Sensor.

Post by jhsa » Tue Feb 12, 2013 11:42 am

But I think that with the biderectional sensor you would have to set an offset on the radio as the zero amps would not be equal to zero volts on the output, right?
Also why a divider? If you look at the specs on the ebay page, it says that output is 2.5V. I don't know how they calculate that as 0.06V (60mV) X 50 = 3V, not 2,5V

Or maybe I'm missing something..

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Tue Feb 12, 2013 12:04 pm

UPDATED!
jhsa wrote:But I think that with the biderectional sensor you would have to set an offset on the radio as the zero amps would not be equal to zero volts on the output, right?
Right, offset is 0.6V
jhsa wrote:Also why a divider? If you look at the specs on the ebay page, it says that output is 2.5V. I don't know how they calculate that as 0.06V (60mV) X 50 = 3V, not 2,5V

Or maybe I'm missing something..

João
when is 0A output is 0.6V and on 50A is 0.6V+3V(60mV x 50)=3.6V

still over frsky 3.3v A1/2 input limit
Last edited by isvedic on Tue Feb 12, 2013 12:19 pm, edited 1 time in total.

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Re: FrSky Amp/Current Sensor.

Post by jhsa » Tue Feb 12, 2013 12:07 pm

But because this one is unidirectional I thought it would be 0V at 0Amps....
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Re: FrSky Amp/Current Sensor.

Post by isvedic » Tue Feb 12, 2013 12:28 pm

but with unidirectional 100A you can measure 65A with no voltage divider and still preserve good resolution!

offset=0.6V and resoulution=40mV/A

so 0.6V+(40mV/A x 65A) 2.6V = 3.2V <-- bingo!

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Re: FrSky Amp/Current Sensor.

Post by jhsa » Tue Feb 12, 2013 12:50 pm

so, with the 100A sensor and not exceeding 65A We get the best possible resolution, right?
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Re: FrSky Amp/Current Sensor.

Post by isvedic » Tue Feb 12, 2013 12:57 pm

Yes, resolution in that case would be 0.3A

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Re: FrSky Amp/Current Sensor.

Post by jhsa » Tue Feb 12, 2013 1:24 pm

Is there a link for the unidirectional 100A sensor?

Thanks

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Re: FrSky Amp/Current Sensor.

Post by isvedic » Tue Feb 12, 2013 1:38 pm


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Re: FrSky Amp/Current Sensor.

Post by kaos » Tue Feb 12, 2013 8:31 pm

sounds like I should get a 100A chip too. glad did not order it yesterday. ;) 65A would cover most of my needs.

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