This pico is great! Now I have a question

#1

All,

I received my Pico board a few days ago and was able to play with it last night. Initially it wouldn’t light up. I did some basic trouble shooting to find the the pads on the led strip are not typical with the pads on the Pico board. The data and clock are reversed. I simply reversed the pins on the connector and it works great.
The question I have is, can I wire three strings in parallel on one Pico board? Obviously I would need a larger power supply.
Or, would I need to connect the Pico board to an expansion board?

Thanks.

Don.

#2

You normally add strings end to end, so you end up with one long string. You need to feed power every 200 pixels or so.

As to the data and clock being reversed, this is a common thing, there is no real standard for LED strips, so depending on where you get the strip from, you can find the wiring is different, even if the connector is the same.

I have had strips with power reversed, clock and data reversed, clock, data and power reversed (that’s easy,you just reverse the whole connector).

It’s actually easy to pull the pins out of a jst connector using a paper clip. I just pull the pins on the strip, and match them to the connector I put on the PB, when I get a strip with an odd wiring set up.

See JST connector disassembly / assembly - YouTube

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#3

For parallel connection (as opposed to serial, one after the other), where all 3 strips will display the same thing, you just need to connect to all 3 strips. With the Pico being so small, you might find it easier to not try to connect them directly, but add wires and just join all 4 of each type (so all 4 data, all 4 control, all 4 ground, and all four voltage.) Technically, depending on how many amps you need, you might separate the voltage into multiple supplies, if you need more than one power supply, but the GROUNDs still need to be connected, I believe.

#4

Thank you for the info. I was able to use a straight pin and release the two middle connectors and swap them.

#5

That’s good to know. I’m curious if you will degrade the clock and data signals after x number of parallel strips.
I didn’t realize how much power these strings will consume.
I’ve been using the 12 v 6803 led strings for the last few years with an off the shelf controller. With a 12v12ah Lifepo4 battery I can run them for around 2.5 hours depending upon what pattern. Looks like I will need to add more power if I run 3 5 meter strips of Sk9822. It may not be a good portable solution for a pedal car.

#6

Batteries: Depends on the brightness and pattern (how many lights you light at once). I’d say that 12v is going be more more energy efficient than 5V, for example.

Re the clock and data lines and number ofconnections. Unsure about those with clock lines, but ws2812s regenerate their data, so pixel 0 gets it from the controller, but then the data going to pixel 1 comes from pixel 0, so having multiple lines doesn’t matter.

#7

Oh that’s interesting. So, would you need to have a repeater in place for the data line if you are running 300 pixels?

#8

No, powering (voltage/amperage) is usually the concern after 300 pixels, not data.
The concern for data tends to come when you just can’t push data fast enough for the number of pixels, to maintain the frame rate you want. Usually way more than 300 though. And that’s when an output expander is useful, it takes the data and basically parses it into multiple pieces, so multiple strings each get their chunk. (so say you wanted 2000 pixels, but the frame rate is too slow, but 4 strings of 500 are fine… so you can still work with 2000, but then the output expander sends 0-499 to the first string, 500-999 to the second (which sees it as it’s own 0-499), and so on.

#9

No,

If you are using APA102’s (or similar) data and clock signals are regenerated by each pixel. ws2812s don’t use a clock signal, but do regenerate the data every pixel - so no repeaters required.

What you will find is that the length of cable between the PB and first pixel is important - too long, and you will have to reduce the clock speed to compensate. ‘Too long’ is measured in meters though, so on a pedal car, you should be fine.

As to power - the power used by 5V LED strips is the same as 12V strips - what’s different is the current draw. At 5V you will pull 2 1/2 times more current than at 12V, and as losses are equivalent to the square of the current, a 5V system is less efficient than a 12V system.

Most 5V LED strips will run from a 3.7V LiPo just fine (with reduced brightness), so a large capacity 3.7V LiPo battery is usually good enough to run everything. PB runs at 3.3V, so 3.7V is enough for it to work.

So get yourself a large 3.7V LiPo, and some chunky power wiring, and you are good to go. Keep an eye on the amps though, they add up quickly.

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#10

That’s great news thank you for the reply.

#11

At what point does this actually have an effect? I’m trying to plan my first project but I think it’ll only have somewhere around 50-60 pixels. should I be concerned about amperage at that size?

#12

Each led draws about 20mA, and there are three per pixel - total of 60mA if they are all full on (bright white).

60mA X 60 pixels = 3.6A

So 60 RGB pixels on full white draws 3.6 Amps, which is a lot. More than you should be pulling from a LiPo, anyway.

If you run them at reduced brightness, or not white (white is worst case), you will pull less current.

#13

okay gotcha, what can be done to solve this issue? Is the solution use a different type of battery or configure the LEDs differently?

#14

Just don’t run the pixels at maximum, or don’t run them all white.

The pixelblaze has a “max brightness” setting, which you can use to limit the maximum power draw.

Most patterns won’t set all the pixels to maximum white, so 3.6A is the worst case condition.

Mostly you’ll only draw a couple of Amps, and you’ll be fine.

You just need to be aware of what you are likely to pull. Do the math so you don’t accidentally set fire to something.

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#15

It depends on the lipo. Often in C ratings, a multiplier of the total capacity as a current draw rating. So a 500mAH battery with a 1C rating should be run at 500mA or less.

Some lipos are rated for 20C or more. For example a tiny 500mAH battery designed for quadcopters with a 10C rating would be ok with 5A (just won’t last long), and a big 4000mAH battery with a 1C rating will have no problem with 3.6A.

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