A question about ISP interference

Hi all,

I’m building a modular led light, that consists of wooden blocks. Each block connects to the next one using a magnet attached in the centre of a 3x3 PCB. Around it are 3 concentric copper circles that carry Data, GND and Vin across the blocks, powering the SK6812 strip inside them. Length of LED strip can be anything from 16cm(if one block is used) up to 5 metres if all blocks are used. Should I expect any interference in the ISP signal caused by either the magnets or current? Does it matter which circle I use for Data, inner, middle or outer?

Hi Petros,
What do you mean by ISP? I’m either not familiar with the term in this context or perhaps my coffee is lacking this morning :slight_smile:

I’m guessing you mean electromagnetic interference (EMI/EMF)?

Static magnetic fields don’t usually interfere with electrical signals. Also, the magnetic fields created by powering 5 meters of LEDs will still be quite weak, and won’t interfere with your magnet holding things together.

From a power standpoint having a solid ground reference is very important for LED data, so if the rings represent connection area, I would swap GND and Vin so that GND has more of a connection area and hopefully less resistance.

I know you didn’t ask about this, but I wanted to say that with any kind of connector, getting a solid connection is key, especially for power connections carrying significant current. A little resistance between the connection can turn it into a very effective heater, and I’ve seen that kind of thing start fires.

If you think copper bands touching with a magnetic mount to hold it in place is going to work reliably, good luck with that.

I’ve seen some Tetris-y blocks that did a simple 2 wire connection (power only) via touching pads…

And you’ll see how fussy that is. Now try adding a data line, which BTW, you can’t fork with normal WS2812s, without losing individual addressablilty. (Yes, you can use the mystery LEDs which will handle this, see my post re that).

Good luck with it. It’s not going to be easy to make it so good that it’s not frustrating and perhaps even a danger as above.

Keep in mind that NanoLeaf etc all use tabs not merely magnetics so they depending on friction fits, and they don’t design them to be moved around a lot.

Thanks for your replies. I meant SPI, not ISP, which (I guess?) is the protocol used in addressable leds?

I’m using pogo pins in the male side of the blocks that touch the concentric rings in the other, plus guides in all 4 corners so the blocks stay in place and are held together with the magnet in the middle. I’ll be testing everything next week once I have all parts in my hands.

I’ll keep GND in the outer circle, Vin in the middle and Data in the inner.

Hi @Petros,
Oooh, gotcha. I tend to think of SPI (serial peripheral interface) as the 2+ line stuff that has data + clock.

Technically the one wire LED stuff is a serial protocol, but I wouldn’t call it SPI™ unless it comes from the silicon valley of France, otherwise it’s just sparkling LED data. :rofl:

Cool, I was going to suggest pogo pins! Having something spring-loaded and gold coated will go a long way. I’ve seem some pogo pins advertised as fairly high power, and a few of them spaced around the ring could do the trick!

I’m curious, are you plating the copper rings? Using ENIG or hard gold type processes?

I can’t help but look at my old Mac’s MagSafe connectors (not the new iPhone wireless ones). These were also basically a pogo pin type setup with a magnet to hold it all together. They did have some issues when dirt and grime got on them, and most of my old power adapters had small scorch marks where the resistance increased enough to make them tiny hotspots.

1 Like

@wizard I realised only two days ago that the pogo pins I ordered might not be enough to carry the current needed for these strips(I’m looking at 18amps@5v if all blocks are connected. My main issue is space, as I want the two PCBs to “sandwich” together and can’t seem to find any low profile pogo pins that are high current. The ones I got are these: https://www.amazon.de/gp/product/B07FPFBDF9/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

There are no specs and I wonder what will happen if I place 4 of them per circle, if it will be enough. If you have any suggestions, please share, I could go for say 4-5mm instead of 2mm but don’t know where to look and frankly I hate ordering from amazon. I’m trying to see what other options exist that can be of use, like the metal connectors inside rotary switches(I don’t even know how they are called in English) that might simplify the design and lower the cost that is piling up.

Do bear in mind that I’m neither a coder nor engineer, my knowledge when it comes to circuits is substantially bigger than coding, but all of it comes from experience after having built various things in the past that required some kind of a circuit in them, so please don’t laugh:).
So when you ask whether I’m plating the rings, I have no clue what is that, I will google it for sure, but if you have suggestions on how to make it more safe(and actually operational), please do so.

That is the style of pojo pin I had in mind. You can find a ton, perhaps too many options, with datasheets and specs and rated currents via the big distributors.

Check https://www.digikey.com/ and https://www.mouser.com/

Maybe here

There are also PCB mountable springs that look pretty low profile:

Only 1.5A though. And you’d need a whole lot of pressure to make sure several of these made good connection.

Copper oxidizes and corrodes easily, and quickly becomes a poor conductor on its surface. For PCBs that are intended to act as a connection point, copper is often coated in gold (or nickel then gold). The connector for a PCIE card is a good example, those are “hard gold fingers” and are intended to stand up to some wear.

You can get PCBs with ENIG, a very thin gold plating over nickel, but it scratches off easily.

Likewise with those connectors, many will be gold plated.

@Petros You may want to look at this guy’s project, I know its not for flashy blinky lights but the connector idea he has might be something you could use or something similar.

As regards the addressability you might be able to use a few of the GP pins to work out how many LEDs are connected, I think you would need a master block and work from there.
Or what happens if you just connect the second block up in parallel , won’t it just repeat the pattern of the first block. As long as the LED number and type are the same it should work, or am I missing something.
Have you seen those magnetic USB charging cables?

I’m back to the drawing board as they say:)

Pogo pins are out of the equation, I will never reach the desired amps successfully and safely given the small footprint(connecting PCBs can be 3x3cm max) and low profile needed.

As much as I love the idea of keeping the pieces together magnetically, I’ll have to go for something else, most probably the classic pins used for LED strips anyway. Now I’m thinking of having 3 pins in the male side, and 6 holes in the female(3 plus 3 inverted, so the blocks can be connected in two ways, “normal” or 180 degrees inverted).

Here’s a video of one block:

That one in particular is 20x3x3 with 12 leds inside, final blocks will be 16x3x3 with 10.

As mentioned in another thread, this is meant to be a birthday present to my girlfriend which is on May 21st, so I don’t have an awful lot of time to solve all issues. The good thing is that everything concerning wood, plexiglass or leds is solved, and I’m getting to know a bit more on how to code everyday. What remains is the connector-which of course is the most important part:)

I don’t mind losing addressability whenever the strip is split, I think you can still do beautiful things even if blocks running in parallel are the same. I bought the expander as well and will have a few outputs available. I’ll make a few cables that end with a connecting cube(3x3x3) so she will be able to do all sorts of combinations.

If time permits, I’ll make angled connecting blocks so that she can make a sphere as well.

Anything magnetic I’ve seen so far(including that great linux computer that you linked) just can’t handle the 18Amps of max theoretical load if all blocks(30 x 10 leds) are used.

1 Like

18A is a huge amount of current for any connector. Connectors designed to handle this kind or current will be large.

The thing to bear in mind it that 18A is the maximum current draw for all pixels white at maximum brightness (which is very bright - too bright to look at directly). You can reduce the current draw by limiting the maximum brightness. Pixelblaze has a “maximum brightness” setting for exactly this reason.

The other thing you could do is separate the data from the power. Clock/data uses no current, so could be a separate connector to power.

The third thing you can do (and this is what I do) is recognize that voltage is inversely proportional to current. So as you increase the voltage, the current drops in proportion.

What I do is supply 24VDC, for each strip of pixels, you include a small DC to DC converter like this https://www.amazon.ca/Adapter-Converter-Regulator-Waterproof-Converters/dp/B07H7YGCMB/ref=sr_1_11?dchild=1&keywords=24V+DC+to+5V+DC&qid=1617480554&sr=8-11 , connected to each strip. The DC to DC converter only feeds the local pixels (inside each box). The worst case current draw at 24V DC is now about 3.6A, which is well within the range of most small connectors.

24V is also safe, and easy to generate at 4A. Like this https://www.amazon.ca/SHNITPWR-100V-240V-Converter-Transformer-5-5x2-5mm/dp/B08DKR5KV4/ref=sr_1_1_sspa?dchild=1&keywords=24v+4a+dc+plus&qid=1617480823&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVEhMOTVVMEpCTzE4JmVuY3J5cHRlZElkPUEwOTk1ODI4MU1QTk9DTUlES04wViZlbmNyeXB0ZWRBZElkPUEwMDYwODA5M1VITEhUV0E4RktQQyZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

You may even be able to use your original magnetic connector idea with the increased voltage strategy.

Best of luck!


Would this type of Connector work for you?

@Nick_W and @TechDoctor, thanks for your replies.

Going for downconverters is a nightmare, as I’d have to fit 1 in every block(25 in total). Apart from the space issues, it would raise the cost well above my budget.

I went for these guys:

They come in 5A varieties but I’m doing the PCBs in JLCPCB and unfortunately they only have 2A versions in their inventory, so I’m using 4 in a star formation to get 13A total, with a magnet in the middle to hold the 2 PCBs together. I’ll have 250 leds max, so that would cover my needs.

I’ll post build pics along the way.

If you are making a PCB for each strip, you could include a buck converter on each PCB to drop the voltage. They cost a few cents each.


You should know that making or breaking high currents is not a good idea in 5V circuitry, you can induce high voltage transients that will damage the strips. I would include transient suppression and local fusing components as part of your design (I use thermal resettable fuses and TVS diodes). See An Introduction to Transient Voltage Suppressors (TVS) - Technical Articles

Having said that, the chances of you actually drawing anything near 18A is small, in most cases the current will be much less, and you would probably have no problems. The maximum current will be flowing in the first connector, all subsequent connectors will have significantly lower current flow.

How are you powering this project? 20A 5V PSU’s are not cheap or small.

I will be interested to see what you actually build. For what it’s worth I am an electronics engineer.

1 Like

@Nick_W I was about to ask if hot plugging would be an issue(as this is part of the fun of the project), and you just answered it. I’m already way over my knowledge spectrum when it comes to electronics though. The way I’m doing it, I think I’ll max at around 10-12A, not 18, and that would be only if the LEDs are at full brightness which I might as well restrict through Pixelblaze’s global settings. Are you suggesting a simple placement of a diode between Vin and the strip in every block?

@Petros Sounfs like you’ve found your spring connectors. But, I just ran across a pogo pin connector rated at 20 amp. It might come in handy in the future. 2 Pcs Test Probe 20 Amps Pogo Pin Connector Low Voltage 12V Spring Loaded outside Center Pin 20A High Current Thimble M3228|Connectors| - AliExpress
AliExpress has a wide range of very affordable parts if you can plan for the long shipping times.

Looking forward to seeing more pictures of your project in the future.

Impressive! This project is unfortunately time-constrained, so certain compromises have to be made(though the connectors I will be going for seem to be ok, if only they came in higher amps).

Thanks for the link:)

I would include a 5V Transient Suppression Diode across the power lines on each module - not just a regular diode.

They are cheap, and will prevent transients from blowing up a strip.

A 100 ohm resistor in line with clock and data might be a good idea as well, to prevent any ESD issues on the data/clock lines.