Does Glowbit need a pull up or pull down resistor?

1

I am using a Glowbit Matrix with a Rpi Pico W running Micropython. When the Pico starts to boot some of the Glowbit leds flicker momentarily. I assume that the GPIO output to DIN is initially configured as an input until the Glowbit module runs so the voltage level is undefined and fluctuates. Would a pull up or pull down resistor help to prevent this?

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2

Hi John,

A diode in line with the signal would be the best way to stop the fluctuations, (a weak pull down after if the issue is still present).

Have you tried other pins? Would it be possible to send through a photo of your setup?

3

Thanks Liam

I’m away from home for a few days, but I’ll try a diode when I get back. At present I have DIN connected directly to the GPIO on the Pico.

4

Hi Liam, John
A diode will drop the voltage by about 0.6V (depending on diode type) which doesn’t leave much out of 3.3V. One down side of a 3.3V system versus 5V. Also as the GPIO pin cannot pull down to ground with a diode present there would be a real chance the “DIN” point would stay high. In this case a pull down resistor would be required.
Cheers Bob

5

My Glowbit Vcc is 4.5v. I wonder if a level shifter with a 10k pull down on the Pico side would work. Has anyone else noticed a startup flicker with the Glowbit? It’s not a big problem but just looks a bit dodgy.

6

Hi John
That GlowBit VCC has nothing to do with the logic level. That is the LED supply.
If you start mucking around with the commonly available simple logic level converters they already have pull up resistors and you can’t use a pull down. If you do you will just finish up with a voltage divider and probably nothing will work.
You could try a pull down of about 10k on the GPIO pin. I don’t think it will do any harm and just might fix your problem.
Don’t use any diodes. I just looked at Core product text and it says the GlowBit logic is 2.7 to 5V so if you use a diode you are down to 2.7V and nothing might work. Would be unreliable at best.
Cheers Bob

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I agree with @Robert93820 - a 10k pull-down ought to suffice.

Anything else eg. logic level shifter will introduce complexity and problems. Bi-directional logic level shifters are known to have data-rate issues with WS2812B LEDs.