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Dotstar power management
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Please be positive and constructive with your questions and comments.

Dotstar power management

by ss023459 on Wed Jan 09, 2019 1:58 am

Hello,

I have 4 dotstar 8x8 tiles purchased from Adafruit configured into a single 16x16 grid. Driven by an arduino mkr1010 wifi.

I am working to power limit the grid to 1.5A in total as this is for a school STEM class project and they can get very very hot to the touch and could hurt someones eyes with all 256 leds at peak white. At 1.5A they look great are more than bright enough for what the kids need to do.

I have made some power limit guarantees in software by limiting allowable brightness and doing some on the fly math to assess the approx power each display configuration will take before writing it out to the 16x16 grid.

But I would like to build in some hardware protection to in order to be super safe as its a school project with many kids helping.

Issues I have yet to fully resolve are:
-- on power up all the dostar leds flash a very bright color for a fraction of a second.
-- on reset/re-prog of the arduino a random pattern can appear on the 16x16 and sometimes can be very bright/hot and draw such high power that lowers the supply voltage and freezes the processor leaving the offending pattern persisted on the LEDs still drawing power.

My current plan is to place a 500mA polyfuse on each 5v supply to the 8x8 tiles and to gate the total 5v supply to all 4 tiles with n channel mossfet and have the arduino turn on power to the led grid once it is booted. This I think in conjunction with the software protections will work well enough.

This should work I think by removing the power from from the 16x16 led grid when reset/re-prog occurs as the mkr1010 digital output are confirmed to go/stay low on reset and power on.

However, when then turning on the power to the dotstars via software control of the mosfet am I just defering the problem?

Hopefully this makes some sense.

Any suggestions or comments or experiences to share?

I will of course post the final solution when its safely working.

Thanks.

ss023459
 
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Joined: Sat May 19, 2018 1:54 am

Please be positive and constructive with your questions and comments.