SPI voltage level 0v ?

General Discussion
1

https://forum.beagleboard.org/t/how-to-control-fine-pwm-on-ai64/35539

An extension of the above post

I am controlling the WS2813 via SPI D0(P9_21).

The default voltage of the SPI is specified as 0.72V, and I was wondering how I can get it down to 0V.

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In the picture above, it outputs 0.72V, but when I give a command, it goes down to 0V, and then it goes HIGH and LOW to 3.3V.
I think only the first LED of the WS2813 is malfunctioning because of the 0.72V there.

Is there any way to reduce the default voltage of SPI D0 port to 0V? There is nothing in the DeviceTree about this.

2

I would say that the line is maybe floating when not being actively driven although I think it unlikely.

Have you tried adding a pull down resistor ?

I would also use a level shifter on the output as the led strips are designed for 5V use, and while you may get it to work using a 3.3v signal you may find it is not consistent.

1 Like
3

thanks reply.
I was wondering if it could be handled S/W before adding the pull down resistor. I will install the pull down resistor tomorrow and share the results after the install.