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By mandress
#200310
Hello:

I am a super newb on these forums so I apologize if this sucks.

I have a project where I have 9 Nexus 7 tablets each connected to their own IOIO-OTG with each IOIO driving an RFID module.

I also have another Nexus 7 tablet that drives a IOIO-OTG over BT and this too has an RFID reader module attached to it.

I am observing a situation where the RFID reading range is greater and more reliable when reading over the BT tablet whereas the tablets that are tethered over USB are driving the IOIO and also taking a charge.

Question: Is it possible that the charging tablets could draw away from the 5v supply to the RFID module?

I do know that if I run the BT setup on it's own power I can get away with a 9v 300mA no problem.

But, perhaps obviously, if I use that supply on one of the tethered setups the PSU gets really hot and I am not sure of RFID performance.

To power the IOIOs in the deployed architecture I use 2 9v 9.5A PSU. So one PSU powers half and one PSU powers the other half.

This might be a bit vague but can anyone tell me if it is likely that the draw from the Nexus 7s charging over USB would be messing with the consistent driving of the RFID module? Or is it more likely something else? If it is that, is it simply a matter of lowering my voltage or making more amps available? Even a third PSU and then each tablet would have over 3A available versus the 1.9A I have now.

ASIDE: yesterday I nuked my 5th or 6th IOIO board. I keep getting caught by that pain in the butt problem of using a 12v supply with a long cord in my test environments. From now on < 9v only.

Thanks for any advice you may have.

Mark