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greeeg

ledClock - dual colour led matrix

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Hey Guys,

 

Exam times again, so I feel like I have a tonne of time for my projects.

This is a project I started in February 2014. I found a very nice 8x8 dual colour LED display. I designed a PCB for them when I ordered them, instead of when I actually had them.

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I had built a PCB up with a G2542 8kb / 512b (Mem/RAM) but didn't manage to get it working.

 

Over the last few weeks I got back into this project, and low and behold it did actually work!!

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I built up a new PCB because it was designed as a common cathode driver, but the displays were common anode.... -_- (on the first board, I had bridged the common mosfets.)

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of course using 0402 parts. (this display need 64 of these O_O)

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back of PCB contains clock, half a DCDC stepup and a BMA222 accelerometer.

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Front & back

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Now I needed a case, this is my first project I decided to actually make use of a cheap chinesse laser cutter I now own.

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The piece with all the slits in it create a "living hinge" which creates a cool organic looking case. as opposed to a rectangle.

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I'm still working on improving code. Basic clock functionality is in.

 

lastly I'll leave you with my dud designs. which while not very practical. are actually 100% useful. A failed design can teach you alot!

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I will be making this open source, I would like to make more in the future, which may involve buying more displays from china (if there is interest maybe even a group buy?? ;))

 

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I have designed and ordered a new PCB. I will be moving the brains off the display board. This increases the unit cost slightly. But enables me to fix some bugs that were present in the current version.

  • No Reset or Output enable lines (display will sometimes show garbage on screen when powered up) (No easy, PWM, brightness control)
  • Limited MCU resource (512b or RAM is not enough to support a double buffered [64b per frame] display driver)
  • Double sided load (I want to make use of my reflow oven. Double sided loads need more complex stencil applying techniques aswell as 2 thermal cycles. Hand soldering the back is very time consuming)

I did a quick video showing the schematic and PCB layout in KiCad

 

Love it :)

Feel free to start one!

I have a new PCB in the pipeline. I'll wait until that's arrived before I start up a group buy.

 

Nice. A great to see you getting on well with the laser too.

 

I think you need the laser badge on your profile. (I see it's now been added)

Thanks! I've been mainly cutting out other peoples designs, seeing how they fit together. 

I think you have a very similar laser cutter.

Overall I am very impressed with everything it does for the price. The stock fume extractor is probably the worst part. Also the A4 cutting space is a little small sometimes.

 

Thanks for the badge BH :lol:

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I would absolutely buy one of those - would go great with my other DIY clocks on my desk. Holy crap those 0402s are small though. A kit with even 0603 or 0805 would be much easier to assemble though.

I really need to polish up and add features to the code. I'm leaning toward making it solely USB powered, one less thing to worry about.

 

Logistically it's about the same time for me to assemble them with a stencil + solder paste + re-flow. Unfortunately I doubt I can fit 0603 let alone 0804 sized parts :(

If I were selling it as kit it would be more of an assemble the case, slot in the electronics module kind of deal.

 

I know this isn't as fun, I could potentially whip up a kit if you were feeling game enough? Dust off that magnifier glass ;)

 

BTW - how much did the laser cutter set you back?

 

It set me back just short of $500AUD inc postage. I bought it from a local "box mover" off ebay. They buy in a whole shipping crates worth of stuff like this from china.

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You can cut Mylar solder paste stencils with the laser by the way. I converted my laser to run from Mach3 so only really does vector cutting. With the rapid head movement and tiny pads I end up with fairly misshapen rectangles but it works well enough. Raster engraving might work better.

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You can cut Mylar solder paste stencils with the laser by the way. I converted my laser to run from Mach3 so only really does vector cutting. With the rapid head movement and tiny pads I end up with fairly misshapen rectangles but it works well enough. Raster engraving might work better.

Ohh! I actually never thought of that. I've tried cutting out air brushing stencils from various thin plastics. they generally curl a little too much near the cuts..maybe I'm not cutting fast enough. I reduce the power as much as I can without the laser cutting out.

 

The software that came with my cutter isn't terrible. it acts as a plugin for coreldraw. I have not worked out how to align raster and vector cuts, But I'm generally only doing vectors.

All my design work I do in rhino and import dxf into corel for cutting

 

 

When I order PCBs I've been adding metal stencils. The new revision of this clocks PCB will have one of them.

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I use 75 micron Mylar with masking tape on both sides, cut at 2000mm/min 5mA. 0805 pads are fine. I just used one long pad each side for LQFP and QFN as the soldermask should sort that out when reflowed. 0402 might not work well when vector cut.

 

I'll try to write the process up if I can. Obviously not close to a metal stencil, but I was home etching boards so made sense. Fun to try if nothing else.

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@@greeeg - I'm game - I'd prefer a kit I can make :)  But I'll take one either way to be honest.  You could always consider doing a partial kit as well - put the resistors on and let them solder the chips.  Looking at the picture it doesn't actually look too bad and I've done 0402 before.  

 

I'll have to look into the laser cutter when I eventually get a garage.  It's top on my list of tools to get.  I could definitely swing around $500.

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@@Fred I need to try the masking tape trick, this is to avoid the "melted" edges? I used HPGL-output from KiCad which I converted to G-code before feeding it to Mach3, but could not use the stencil due to the edges beeing slightly raised from the melted plastic.

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@@Fred @terjeio  Every kapton stencil I have received from OSH Stencils has been laser cut, and they have perfect edges, even down on 0402 parts. Maybe kapton cuts easier than mylar? or they might use some backing materials? like how waste board is used when drilling/milling to avoid chip-out on the back edges.

Of course they probably use a much more advanced laser cutter.

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The masking tape sorts out the melted edges on the mylar. I've not tried kapton myself, but I believe it should cut well.

 

The slightly misshaped holes are entirely down to the fact that I'm cutting small rectangles at very high speed. Asking the head to turn a fast sharp 90 degree corner means there's some overshoot and vibration. You'd never really notice if the shape wasn't so small.

 

Raster engraving might solve this completely. I've not looked into this as it's certainly good enough for my current needs. LQFP and QFN worked fine last night, despite using crusty old paste that I thinned out with flux and stirred with a screwdriver! I'll try taking some photos.

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