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Author Topic: RC Battery voltages with ATTiny and nano  (Read 514 times)
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I was doing some research on reading voltages and found someone who suggested using ATTiny 45s for reading individual cell voltages.  Then pass the voltage reading onto a "master" meaning the nano on the right.  Would this work?



Thanks,

Loren


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You don't seem to have addressed the issue of the ATTinys running at voltages higher than the nano can connect to - have I missed something here? As it stands, I don't see that the ATTinys are giving you any benefit. The general approach might work if you used opto-isolators instead of direct connections.
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Sorry I didn't explain myself very well.  The batteries that I use are 3cell lypo batteries.  The sum of the cells is 11.1v

This is the diagram that helped me understand how the balance connector worked:

https://f47fb5b4-a-62cb3a1a-s-sites.googlegroups.com/site/tjinguytech/charging-how-tos/balance-connectors/rcheli-diagram-3s_lipo.png?attachauth=ANoY7crPH4yZMADK663EOJEZREBTu9DqXmRVV5T9ojjW0tujB1G-tZS3mb7ltL_e3Eg2hYc8YArvHATh_NP6vaeoqByCTCqK3aSQi0-P4ie0VXsQhR4OAPfoRHsX7elvjDV8YuO33Lo8e6P2Yf2OAO0qDF_ZZIo0DKnKnb3qd_qH3oTNLjJRNN9h11L5gavUOeIo556BJlPnEaXQvCP446wjN28dpwL8deQKrj-_VcdHUqm7T71coJ87bwbCcD8vCfk8zqNt3az95UU8S4021x4ytAvbvSGsmg%3D%3D&attredirects=1

The goal is to measure both the individual cells and the overall battery voltage.

Does that help?

Loren
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Does that help?

Yes, that's pretty much what I had assumed, but doesn't address my concern.

If you don't see what I mean, I suggest you imagine connecting this to a charged LiPo and follow the voltages through the system to see what voltages are applied to the Nano I/O pins. It seems to me that each ATTiny will be 'grounded' to a different voltage and the connections to the Nano will be outside the range that the Nano can tolerate. To use this approach, I think the ATTinys will need to be electrically isolated from the Nano.
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Ahh Now I see what you are saying.  What you are saying complicates things a bit...  Actually a lot.  Is there a simpler way to accomplish this?

Thanks so much for your help!
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What exactly are you trying to do?
Most LIPO battery chargers for more than one cell need some kind of balancing capability
to ensure that each cells voltage remains the same as the battery is charged.
This involves not only monitoring the individual cell voltage, but also controlling the current thru each cell.
Whilst this may sound easy to do its anything but easy, due to the multiple voltages and currents that have to be individually controlled.
As a result , there are dedicated LIPO battery balancing ICs, which do all the hard work for you.
Something like this
http://www.intersil.com/content/dam/Intersil/documents/fn82/fn8246.pdf

Texas Instruments and Maxim also make LIPO battery balancers.
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Is there a simpler way to accomplish this?

You could use a voltage divider to bring the voltage of each battery junction down into the range that the Nano can measure, but that would reduce the measurement resolution. I don't know whether that would matter, because you haven't said what resolution you need to achieve.

You could use optoisolators to pass data between the ATTinys and the Nano without electrically connecting them.

You could abandon the DIY approach and buy a component or product that does what you want - whatever that may be.
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