unable to enable GPIO output

Louis Bouchard

Hi,

I am trying to output from GPIO0, but even after reading the documentation and a few forum posts, I still can't make it work.

The forum posts in question are these:

https://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/advanced_light_control/f/924/p/349595/1695961

https://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/advanced_light_control/f/924/t/389999

The pin numbering described in the second link is wrong. I found the correct ones in the following document:
www.ti.com/.../tidr157.pdf (page 5, and the pins are mirrored since it is from a pandaboard's point of view)

So here is the connection layout I thought would work:

I connected J3 pin 1 (EXT_1v8) to a 1.8v source on J10. I bridged it to J3 pin 4 (SYS_MASTER_MUX_SEL) to enable level shifting.

I connected pins 18(gpio0) and 8(gnd) of connector J6 to a voltmeter hoping to see the voltage vary according to the changes I make in the peripheral control section lightcrafter control software.

I have found that connecting any voltage source to J3 pin 1 (EXT_1v8) disables USB communication to the computer. The device litteraly disappears from the list if I do 'lsusb' on linux, and of course the Lightcrafter control software cannot connect either.

Where have I gone wrong? Should I do something with J3 pin 22 SYS_USB_SEL? It is left unconnected, so I assume it is set to low and therefore the usb should not be routed to the non-existing pandabord.

Any insight would be appreciated.

thank you,

Louis Bouchard

over 8 years ago

0 Paul Goedeke over 8 years ago

TI__Mastermind 30600 points

Hi Louis,

Thanks for the detailed question. If you would give us a little time to take a look at this, that would be much appreciated. We'll get back to you once we try what you've done on a unit that we have here.

Best,
Paul

0 Danny White over 8 years ago

TI__Expert 3240 points

Hi there Louis,

After some research and looking at the schematic it looks like the set up might be pulling more current than the 1.8V regulator can supply (TPS79718DCKT datasheet here). You might try hooking up a separate DC power supply to act as the 1.8V source. If the issue continues we can try to replicate your setup early next week.

Best,

~Danny White

0 Louis Bouchard over 8 years ago in reply to Danny White

Prodigy 140 points

Thank you, I will try an external power supply this afternoon and report back with the results.

In the meantime, I have a related question: would it be possible to supply it with 3.3v or 5v without damaging the lightcrafter?

thank you

Louis Bouchard

0 Paul Goedeke over 8 years ago in reply to Louis Bouchard

TI__Mastermind 30600 points

Are you referring to the system power supply for the Lightcrafter? Using 3.3V or 5V instead of 12V?

In that case, I don't think you would damage the Lightcrafter but it won't work properly either.

-Paul

0 Louis Bouchard over 8 years ago in reply to Louis Bouchard

Prodigy 140 points

Ok, so we just tried the external power supply. We connected 1.8v to pin 1 (EXT_1v8) and 4(SYS_MASTER_MUX_SEL) of J3.

It still doesn't work, but we might be homing in to the problem: the lightcrafter actually loses usb connectivity when both EXT_1v8 and SYS_MASTER_MUX_SEL are connected to the 1.8v psu, but not if only EXT_1v8 is connected.

hopefully this might help you diagnose theproblem,

Louis

0 Louis Bouchard over 8 years ago in reply to Paul Goedeke

Prodigy 140 points

Paul Goedeke said:
Are you referring to the system power supply for the Lightcrafter? Using 3.3V or 5V instead of 12V?

No, I am talking about supplying 3.3v or 5v to pin 1 (EXT_1v8) of J3 (so that the GPIO pin's 'high' voltage can drive a relay)

0 Paul Goedeke over 8 years ago in reply to Louis Bouchard

TI__Mastermind 30600 points

EXT_1V8 should only take 1.8V. There is a risk of damaging components.

We were able to get the GPIO working by doing the following:
1. Tying SYS_USB_SEL (Pin 22 on J3) to ground.
2. Tying SYS_MSTR_MUX_SEL (Pin 4 on J3) to 1.8V.
3. Pin 1 on J3 to an external 1.8V

Please try that and let us know if that solves the problem. We recommend supplying 1.8V from an external supply because the on-board 1.8V supply is only capable of 50mA. It is also important to make sure you hit the "set" button on the GUI before you check the state of the pin.

Thanks,
Paul

0 Louis Bouchard over 8 years ago in reply to Paul Goedeke

Prodigy 140 points

It works!

thank you again for your help!

Louis

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unable to enable GPIO output