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Raspberry Pi Zero W Power Abbilities

Posted: Wed Jul 17, 2019 8:11 am
by BRETT_No5
Hi All,

First time poster.

Not long ago I purchased my first Pi, a Zero W. Loaded Retropie and am enjoying so good old gaming.

I have now started constructing a barrio arcade to house this.

In doing so I will be using LED arcade buttons, approx 20. The button kit I was looking at had 3 pin encoders for the LEDs which are powered from the Pi and not a seperate power supply.

My question is, is this do-able with a Pi Zero W or will the power consumption be too great and case issues?

Would I be better to use 2 pin encoders and then powering the LEDs direct from a 12v power supply?

Sorry if the above is a stupid question as I am still learning here.

Thanks.

Re: Raspberry Pi Zero W Power Abbilities

Posted: Wed Jul 17, 2019 12:27 pm
by thagrol
The zero and zeroW(H) don't have any onboard protection or limitation on the 5v lines.

The 5v pins on both micro USB sockets and the GPIO header are tied directly together.

I'd expect availble power for the LEDs to be whatever you PSU provides less that used by the Pi.

Re: Raspberry Pi Zero W Power Abbilities

Posted: Thu Jul 18, 2019 3:20 am
by BRETT_No5
Pi is powered by a 2.4A USB. I don't know what that means for my LEDs but I am sure I'll find out.

Re: Raspberry Pi Zero W Power Abbilities

Posted: Thu Jul 18, 2019 4:17 am
by Imperf3kt
BRETT_No5 wrote:
Thu Jul 18, 2019 3:20 am
Pi is powered by a 2.4A USB. I don't know what that means for my LEDs but I am sure I'll find out.
It means you have 12W less resistances to power both a Pi0W (~150mA, ~0.75W) and your LEDs, assuming the power supply is accurately providing 2.4A at 5v

Re: Raspberry Pi Zero W Power Abbilities

Posted: Thu Jul 18, 2019 6:47 am
by BRETT_No5
Read somewhere that an LED button can draw 25mA, and with 20 buttons that's 500mA. Plus the 150mA from the Pi I should be good to go. Thanks for the help.

Re: Raspberry Pi Zero W Power Abbilities

Posted: Thu Jul 18, 2019 5:30 pm
by Burngate
BRETT_No5 wrote:
Thu Jul 18, 2019 6:47 am
Read somewhere that an LED button can draw 25mA, and with 20 buttons that's 500mA. Plus the 150mA from the Pi I should be good to go. Thanks for the help.
The current through an LED depends on how bright you want it, what colour it is (red ones have lower forward voltage than green ones, blue are higher again) and what resistor you put in series with it.

If you want it nice and bright, let it have as much current as it can take. The spec. sheets for many LEDs suggest 20mA as maximum, but you'll have to look it up for the ones you have.

Alternatively, you could reduce the current to almost nothing, and see if it's still visible - on a dark moonless night, less than a mA could make it as bright as Jupiter.

As for the switch bit - an LED button is just a switch with a built-in LED - a 10kΩ pull-up to 3v3 would take 1/3 mA when it's pressed.