KrystaLED (First PCB Project Help,Comments,Suggestions please) ATTiny&WS2812b

[calli]

Hi,

I am still not sure where to put it. It is just a hobby thing no commercial intents, will be OSHW for sure. But as it is my first project with a PCB I need many suggestions, critics and comments for sure.

I made a little platform (3D printed) which (as for now) includes a digi stumb (Attiny USB plug) a WS2812b and a 9V Battery. See the image.

As little project I decided to try Easy EDA and made "proper" version of it.  Link (tell me if it is not working):https://easyeda.com/carsten.wartmann/KrytaLED-c606fd6f46d342eaa2b26589556419c8

So far I think it could work.  Some more thoughts/questions:

- I made a single and a double sided pcb. The double sided will be more easy to mount.
- mounting is so far thought to be with hot snod. Fast and easy. Screws are a bit delicate at the position on the top of the case
- double sided pcb can be smaller
- the connector is so big so that it is easy to use for flashing and dev, I want to annote the pins, but not sure how to do in Easy EDA, named the pins in schematic but that does not show in board?
- as power source I want to use/salvage some of these cheap 18650 2600mAh USB "Power Bank"s gives me 5V a protection, charger and a cell. It ca even power other toys
- forgot a button and maybe a switch

So you see it is still a bit in a flow.

Please have a look and tell me if you see big errors or other quirks.

Cheers,
Carsten

[calli]

Oh:

- I choose a SOIC package as I think it is nice to solder at home, however I have no clue how the avaibility for such parts is today?
- EasyEDA: Every time I use the "Hand" tool the part in the schematic to select the part hangs on the mouse. Is this a preference or do I miss another select tool?!7
- I did not found WS2812b for soldering? Do I need to salvage them from stripes?!

Carsten

[calli]

Better share Link:

https://easyeda.com/carsten.wartmann/KrytaLED-c606fd6f46d342eaa2b26589556419c8

So did I something wrong? I had the impression that this topic could bring up some discussion?

Carsten

[cowana]

For a first board design, that looks pretty good!

A few points:

• Decoupling capacitors. For removing noise from the power rails, you need decoupling capacitors. Recommended is 100nF by each of the microcontroller and LED.
• Series resistor between microcontroller and LED. Highly recommended to prevent blowing up the LED, which is very sensitive.
• Availability of base WS2812b LEDs: very common on either ebay or Aliexpresss. Try adding '10pcs' to your search.
• Mounting holes: It's always worth thinking about mounting before you order PCBs - adding mounting holes for screws can make your life significantly easier than trying to clamp/glue them into place!
• Pin naming: you'll have to add text manually to the silkscreen layer of the PCB if you want the PCB labelled.
• USB connector: if you're looking to power the thing from a powerbank, it would make sense to put a (micro?) USB connector on the board, so you can use a common lead. That would also let you easily power it from a normal phone charger if required.

[calli]

For a first board design, that looks pretty good!

A few points:
...

Thanks! (it is of course not a very complicated design ;-)

I just showed it someone  on twitter and he came up with similar comments.

- Decoupling caps CHECK
- series resistors. Cant hurt. I experimented quite a much so far with the ws-leds without trashing one.
- mounting holes. Idea to consider, but due to mechanical reasons I cant't use screws very easy. I will look into my cas construction. (the LED needs to be quite flush with the top I think for best effect. I will experiment a bit)
- PIN Naming. I feared this. A bit sad...
- USB: no the salvaged USB Power Bank/boost/charger will provide these ports...

Big one: I swapped VDD and VSS on the WS LED... Doh!

Back to drawing board.

Thanks a bunch!
Carsten

[cowana]

Big one: I swapped VDD and VSS on the WS LED... Doh!

I'm not sure if the original link is still the latest circuit, but what I'm seeing at the moment seems to be reversed for the WS2802 LED.

On the schematic, VDD should go to 5v, and VSS to GND (which is the opposite of the current wiring).

When you look at the PCB, remember that components on the bottom layer are mirrored - it's as if you are looking *through* the board.

[calli]

VDD/VSS... Well than my first reviewer made a mistake :-) I should have checked myself... I trusted him blindly because of his experience.

Thanks for the hint!

Carsten

[calli]

VDD/VSS I had it right in the first try, then due to a misunderstanding I swapped it...

Worked a bit in the project. Now to Check all.

Carsten

[calli]

I made up my mind and did a version with 9V power:

https://easyeda.com/carsten.wartmann/KrystaLED_V2-482deda29a354482b808f5eb867bdf80

This time handrouted PCB.

Carsten

PS: Yes Version 1 is already ordered, will make a nice experiment PCB with all the headers exposed.

[calli]

Hey forgot to keep this thread up to date!

I made a second design and the PCBs for version 1 arrived, then I ordered version 2.1. First took 4 weeks (cheep ass airmail non tracking) and second 3 weeks. I am quite happy with the PCBs. Soldered both versions and they work well!

Comments welcome.
Carsten

[Hextejas]

That's a really clean design. I hope my 1st one looks so nice.

[Photon939]

Your board looks nice, as for the design I'm wondering why you went with the addressable LED instead of a regular RGB LED driven by the ATTINY output pins?

[cowana]

With the exception of the top pads on C2 (which is lacking a fillet), that looks like excellent soldering for a first PCB. Good job!

[calli]

The solder of C2 is only looking so bad in the image, in fact it looks nicer from the side and the better looking C3 is worse. Weird reflections I guess.

The switch I plan to get actuated with a flexible latch printed on the top side of the case. Cross fingers that it works :-)

Carsten

[phil from seattle]

Your board looks nice, as for the design I'm wondering why you went with the addressable LED instead of a regular RGB LED driven by the ATTINY output pins?

I can't answer for him but I, too, have been using WS2812Bs.  There is a lot to like. They are very cheap off ebay ($10 USD for 100). Single pin control, quite bright, easy brightness control (no need for PWM), fairly low processor overhead to drive them, once set there is no need to maintain them. They aren't perfect - the Green LED is much brighter than the others, 5V only, need translation for 3.3V control and the protocol is a weird, time based NRZ thing that basically requires bit-banging so a microcontroller is needed. But given that micros like the tiny85 are around $1.00 USD, cost is quite reasonable. You can add a large number of LEDs to the string and still only need 1 pin to control. Each LED in the string needs 30 uS to set its color and brightness. So you can control a LOT of LEDs with out overburdening the CPU.   

I've also used Cree RGB LEDs and prefer the WS2812Bs. Directly driving an RGB LED to arbitrary color/brightness takes more processor resources than WS281x LEDs. If you want to drive more than one LED, the WS281x is hands down the better way to go.

[calli]

Ah the WS2812b. Yes, it is cheap, easy to control, easy exapandable to high numbers of LEDs and almost no external components, just one pin. And all Phil says. ;°)

Carsten

[phil from seattle]

Good point about fewer components.  No current limiting resistors needed, no CC supply either.