Voltage Display Changing - Observation

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scottyp
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Voltage Display Changing - Observation

Post by scottyp »

I am back getting to know er9x on my 9x's, I have ver 818. I have calibrated the voltage to display what the battery actually measures and all is good until I change models. Then the displayed voltage drops a couple of tenths of a volt. If I cycle the power, then the voltage reading is back to where it should be. That being said, the value in the DiagAna menu is 0598 and that is calibrated to show 10.0V . After I change models, I still get the 0598 reading, but is showing 9.8V until I cycle the power, then it is back to the 10.0V . Measuring the battery with a good meter, I get 10.0V in all cases. Is this a known condition? I am using a LiFe battery, which I am new to, and getting to know their characteristics as well. Not a huge deal as I am aware of it and will cycle the power as needed.

Thanks,
Scott

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MikeB
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Re: Voltage Display Changing - Observation

Post by MikeB »

Not known, but I can see it happening. Is your BG reading (BandGap) on the diagana screen changing when you load a different model?

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MikeB
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Re: Voltage Display Changing - Observation

Post by MikeB »

I have some averaging on the BandGap value, which is used to help measure the battery voltage. This averaging doesn't work as well as it might. If the result was a bit higher, due to the 5V dropping, the BandGap value didn't drop back down when it should, resulting in a lower measurement of the battery voltage.
On the radio I just used for testing, the BandGap seems quite stable without any averaging, so I think I'll remove the averaging and save the flash space (36 bytes).
For information: The BandGap is used to monitor the 5V supply. The 5V supply is used as the reference for measuring the battery voltage. There is a problem that when the battery voltage drops below about 7 volts, the 5V supply also drops, causing the measured battery voltage to report as increasing when it is actually reducing! The BandGap value is used to correct this.

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jhsa
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Re: Voltage Display Changing - Observation

Post by jhsa »

Now I know that what sometimes I thought it was a bad switch is probably what you've just described. :)
I used to turn the radio ON, and after a while the voltage would drop a bit. Good that I always calibrate the battery when it is near the alarm voltage to reduce errors, and after the radio is ON for a little while.
What are the side effects of removing the averaging?
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MikeB
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Re: Voltage Display Changing - Observation

Post by MikeB »

None, as long as the BandGap value is stable.

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andrewju
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Re: Voltage Display Changing - Observation

Post by andrewju »

But this will lead to incorrect readings if the battery is at about 7V, right?
I used to power my radio from about 6.5V (not for flying though - just some testing at home)...
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MikeB
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Re: Voltage Display Changing - Observation

Post by MikeB »

No, it will continue as before, the BandGap is still being used, unless you disable it in the menu. That option is present in case the BandGap doesn't work on a particular processor, which has been seen on a very small number of processors.

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scottyp
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Re: Voltage Display Changing - Observation

Post by scottyp »

Thanks for the replies. The bandgap is changing from 243 to 249 after changing models and then goes back to 243 after a power cycle.
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MikeB
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Re: Voltage Display Changing - Observation

Post by MikeB »

That is the reason for the voltage changing then, I'll post a test version with a fix in soon then.

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Re: Voltage Display Changing - Observation

Post by andrewju »

MikeB wrote:No, it will continue as before, the BandGap is still being used, unless you disable it in the menu.
Ah, I got it!

Thanks a lot!!!
scottyp
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Re: Voltage Display Changing - Observation

Post by scottyp »

Wow, nice.

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