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Thread: conjunction of projects - OHMS LAW help?

  1. #1
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    conjunction of projects - OHMS LAW help?

    Hello,

    Help Required.

    Briefly, I recently purchased a Mean Well 70W 5V 14A Power Supply and have acquired an unsafe amount of knowledge from the internet and forums. When testing voltage across the main terminals of the power supply, I shorted the terminals with the multi-meter lead and there was fireworks. It is a timely reminder that this can be a dangerous hobby. Luckily neither the electrical components nor myself was damaged. Consequently, I have decided to double check every step. 14A is a decent amount of current. Do you hesitate to think of the damage possible?

    To the point of this post, I wish to join some projects together.

    One project is a drum machine based around teensy 3.6. It has 18 buttons and 19 Ws2812 leds and a couple of 10k linear pots. The teensy will powered from the new power supply and the leds to be powered in parallel from the same power supply and the earths tied together. It is working well from the desktop power supply at present. Current draw for this component is not so large. No more than 1A?.

    I have another project created a few months ago still sitting on the breadboard. It is a sound visualizer using components of a msgeq7 chip and a teensy 3.6. This runs 7 arrays of 25 ws2812b leds (175 leds) wired in parallel with the teensy and the "equaliser" chip. It works perfectly creating a nice rainbow visualisation based upon different sound frequencies. I want to take this off the breadboard and power it with the same new power supply, in parallel with the teensy drum machine circuit. The current drawn from this circuit could be quite large.
    175 leds x 0.06 Amps maximum each = about 10 amps?
    Multimeter readings come nowhere near this however.

    So my long-winded question is, in joining these two projects into one box so that I can have led visualisations of the drum machine sounds, DO i need to do some OHMS law calculations for current, and employ different resistors to control the current flow to each component of the circuit? Do I need to include capacitors to smooth out the flow to both of the drum machine and visualiser circuits? What can i do to prevent ground loops and switching noises that will be inherent when the LEDS in the visualizer circuit draw a huge amount of current then nothing in a split second?

    Apologies as I am not really sure of the words to ask the question accurately.

    How do i join these projects together and do it safely?

  2. #2
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    There are a bunch of potential issues as you note having LEDs doing PWM on the same system as audio. One useful element here is that both Teensies are actually running at 3.3V from internal regulators, so as long as the 5V does not ripple down below about 3.6V the Teenzy and Audio stuff should be seeing pretty low noise. So the basic idea is to run everything off the 5V, and use secondary regulators to 3.3V for the audio elements. From the sounds of it the power supply has plenty of filtering caps internally, but one tweak if you have trouble is to put 100-500uf capacitors on the start of each strip to minimise noise propagation though quite likely your strip already has caps space along it for this reason. Another design item is to avoid running the LED conductors close to the audio element, and ideally have the power and ground for the audio sub section only join the LED power at the output from the power supply itself, keeping the LED current flow separate from the audio one as much as possible.

    With your measured current draw, did you have them at full white? Measuring during light shows will get you the average, not peak or worst case current draw.

  3. #3
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    Thanks for sharing your expertise GremlinWrangler. It's nice to have peace of mind.
    With your measured current draw, did you have them at full white? Measuring during light shows will get you the average, not peak or worst case current draw.
    I had considered it but I'm only doing the predictable rainbow effect there, leds are only roygbiv colors, 25 on each. The rgb's are not even mixed for the most part, with only one element illuminating. Current was an average 2.5A, certainly not exceeding 3.

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