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open-ephys / acquisition-board

Hardware interface for streaming up to 512 channels of neural data via USB
https://open-ephys.github.io/acq-board-docs/
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400Hz noise in DAC #2

Closed jvoigts closed 10 years ago

jvoigts commented 10 years ago

There seems to be some bleeding from the status LEDs to the DAC out, we're not completely clear on why this happens yet.

jvoigts commented 10 years ago

For now, the issue can be solved by removing the status LED function by using the bit file variant without LED output. The bitfile doesn't initialize the LEDs to zero though, so expect some random lights on each new boot up cycle of the board.

jvoigts commented 10 years ago

It turns out that the noise is not caused by the LED control signal, but seems to come directly from the LED pwm circuit, so if you are seeing the noise, and using the modified firmware to avoid the issue, make sure that all LEDs are off.

I'm pretty optimistic that bigger decoupling caps can solve the problem, ill test it in the next few days.

jvoigts commented 10 years ago

Think this is solved now by powering the LEDs directly from the 5V jack which puts the injected noise upstream of all the regulators. We should still test if we're getting radiated noise. If so , we could move the LEDs to a separate board that sits on .1inch headers above the main pcb.

open-ephys commented 10 years ago

Powering the LEDs directly from the 5V power supply solves the problem completely. For acquisition boards with version number 2.2.1 and higher, using LEDs and DACs simultaneously won't be an issue.