120 LED Ring Clock

[jondaddio 1]

Greg,

 

I forgot to give you an update on the delivery of the completed controller board - received it on 18 April (one week ago...time has gotten away from me!).  Thanks so much!

 

Jon

[greeeg 460]

I didn't use enough catalyst for the amount of resin I had, and it was very cold.

 

long story short, after 2 days outside, and 2 days under a halogen lamp the resin set.

 

I'm using those solder in standoffs to power the thing. and I have a 0.5"? 4 pin programming header soldered on. (TI standard)

 

In a few days I'll have time to route out the resin from the wood.

[dpharris 13]

Hey -- just received my LedRing controller segment (Canada).  Thanks.  Is there code installed in the mpu?  Did you make a programming fixture?  

... soldering iron, here I come :-)

[greeeg 460]

Yes, there is a small test program on then MCU. it should show accelerometer data with one moving pixel over 6 of the LEDs and then the other 6 show a rainbow.

 

this was the programming jig I made.

 

But then later just soldered a connector, it's not a perfect fit unfortunately. It was hard to find a small connector that wouldn't obscure parts on the other-side of the PCB.

 

Maybe a future revision could use tagConnect? ;P

 

I finally mounted the clock, I think it's looking quite fine.

 

And I made a write up here, included lots of photos from the physical side of the project.

http://www.instructables.com/id/Rainbow-Ring-Wall-Clock/

[bluehash 1,581]

Awesome!

[greeeg 460]

Thanks Bluehash,

 

dpharris asked for the schematic for the ledRing controller board.

 

I had thought I uploaded it, but I was mistaken. Also my altium license has expired, and I can't open the schematic. Tomorrow I'll be at uni, so I'll open it up there and export as a pdf for you guys.

 

For now here is the code that I have developed. The capSense library takes up a fair bit of ram, static and stack space, ~120bytes so tweaking would be required to reduce this to fit with a full 120 LED framebuffer, I'm sure it can be done. I somehow managed to damage one of the LED on the inner ring, so my clock is only running with 60 LEDs.

 

Warning, it's not very pretty.

ledRing_Code.zip

[Fred 453]

I see your write up on Instructables got featured, and you made it onto Hackaday!

[dpharris 13]

Nice write-up!  Thanks in advance for the schematic.  

[greeeg 460]

@@dpharris Here is the schematic in pdf form.

The uni has an older version of altium, so the schematic title block thing didn't work :/

 

ledRing_controller.pdf

[jrychter 14]

Hey, some quick notes having taken a look at the schematic:

 

The caps around MMA8453Q should probably be larger (a mistake in the value in the schematic?): C15 is normally 100nF, while C16 at least 1

[greeeg 460]

Hey, some quick notes having taken a look at the schematic:

...

And I am really impressed with the final result!

Thanks for the feedback, Always appreciated.

 

I tend to rush on the schematics a bit, because I know that board layout takes along time. and then its about 2-3 weeks before the boards even come.

So this was a mistake on my part, I populated C16 with 2.2uF and C15 with a 1uF all the other decoupling capacitors were 100nF.

 

It is a habit of mine to place crystal load capacitors. because even though the value line MSP's have built-in capacitors other MSP430's do not. But they are not populated, I enabled the internal ones in software.

I'll have to keep in mind to write things like DNP on my schematics.

 

If you have a closer look, the dual mosfet is not in a push-pull configuration.

R3 is just a good design practice, it is as you say to ensure that if the microcontroller hasn't configured it's pins that the gate will stay LOW.

 

R7 shouldn't actually be that low, that was another schematic error that I made but never corrected. Keep in mind that these are 0402 parts, rated at 1/16 W. R7 is needed to pull the output LOW when the P-channel is turned off. But R7 is actually discharging the gate capacitance of the first LED. So I wanted R7 to be as small as possible, but after some back of the envelope calculations I settled on ~500 ohms, this means the part is dissipating 1/20 W, and won't burn up.

 

The mosfets couldn't be arranged in push pull because a HIGH from the microcontroller (3v) wouldn't create a large enough Vgs (5-3 = 2v) to turn off the P-channel. Data sheet specifies threshold voltage for P-channel as 0.5 - 1.5volts.

 

 

 

I would use the dedicated buffer/level shifter. You avoid this entire mess. I tried it because I want to use these mosfet in another project I have in the works.

[jrychter 14]

Greg, thanks for the answers! I suspected you populate the actual boards differently from the schematic.

 

As for the push-pull, when I wrote "push-pull" I meant the microcontroller output (e.g. what is inside the micro, driving the pin). And the MOSFET pair you found is actually quite nice, I'll save this for future projects.

 

My approach is different, because I'm designing a battery-powered device, where every mW counts (I generate 5V for WS2812 from a Li-Ion battery). This is why the low-valued resistor caught my eye immediately.

[dpharris 13]

Fantastic project, and well executed. Small changes could be made. Thx for advice re caps. The resistor to ground is a good safety measure for mosfets. The level shifter could have been a single mosfet, see http://www.nxp.com/documents/application_note/AN10441.pdf -- but we are micromanaging here. Still, all food for thought :-).

[Lord anubis 1]

Wow, just finding this great project.

 

Stil possible to order some parts?

[greeeg 460]

Wow, just finding this great project.

 

Stil possible to order some parts?

Thanks

 

Unfortunately you won't be able to order anything from me, I've run out of parts for this project. But all the Gerber's are avaliable, please note that currently these contain a few supificial errors.