greeeg

ledClock - dual colour led matrix

23 posts in this topic

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!!

post-274-0-98367500-1447748263_thumb.jpg

 

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.

post-274-0-94654200-1447748306_thumb.jpg

 

Front & back

post-274-0-48148800-1447748320_thumb.jpg

post-274-0-95346600-1447748333_thumb.jpg

 

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.

post-274-0-96335900-1447748350_thumb.jpg

 

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

post-274-0-16422600-1447748363_thumb.jpg

 

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!

post-274-0-55753700-1447748383_thumb.jpg

 

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?? ;))

 

abecedarian, pine, bluehash and 3 others like this

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Love it :)

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?? ;))

Feel free to start one!

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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)

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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.

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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.

terjeio likes this

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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.

Yes, I have never tried to run mine that fast yet.

 

I've done more work on the code. Not worrying about code size. ( It is around 7kb, basically maxing out the poor G2452. )

post-274-0-08364500-1447944604_thumb.jpg

 

 

And the forward voltage diode drop voltages for anyone interested.

post-274-0-90164000-1447944587_thumb.jpgpost-274-0-93408100-1447944595_thumb.jpg

cubeberg, terjeio and bluehash like this

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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.

Just tested, the masking tape works fine. Now I need to buy some solder paste... I ran my laser at 500mm/min with 1200PPI so I did not get any deformation - I think pulsing the laser while cutting allows me more freedom in selecting the speed as the power delivered to the cut remains more or less constant even when the head is accelelerating/decelerating.

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@@terjeio Glad you got it working. My setup is just on/off, so I needed to turn the current to minimum and the speed to maximum.

 

Perhaps if we've got any more discussion on lasers and stencils we could start another thread rather than taking this one further off topic.

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Received the new display PCBs

 

This is the first time I've done a proper panelised design. Managed to wrangle kicad into doing that without any major issues. The boards are routed between and v-scored along each end.

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Nice fit for the LEDs. The old PCB the spacing was a tad tight.

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I wanted to have the soldermask removed on one of the PCBs. I even specifically mentioned it in the panel file along with describing the V-score lines, that I wanted no soldermask on the bottom PCB. However they put it on anyway. I guess it's to reduce costs (due to more gold plating). But I did pay extra for the ENIG plating. Seeed's custom service for PCB errors is pretty flaky, I doubt I can get any refund/replacement. (It could also be to do with seeed's rules on panelisation and different designs)

post-274-0-81134900-1448417568_thumb.png

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Did not have enough parts to assemble an entire panel. I've done 2 boards.

 

Seems to work as expected! I am currently adjusting the brightness by a PWM into Output enable.

post-274-0-28850200-1448454435_thumb.jpg

 

The new PCB does not feature a MCU. It has a breakout for the major signals the display needs

  • Serial IN
  • Serial Clock
  • Data Latch
  • Output Enable
  • Reset
  • Vcc
  • Gnd

This means to complete this clock I will need a second daughter board. I deferred getting it fabbed because I had not designed it. This is the next step. I also need to decide if I want a dedicated RTC. Or maybe a GPS?! (I like the idea of not needing to set time..

 

Having the controller board separate means I can potentially make a more advanced control PCB, maybe an ESP8266? Pulls down internet time.

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The first boards I assembled used wire links across the MOSFETS because I did not have any in stock. I designed the PCB to use SC70. (SOT323) does anyone know why there are SC and SOT part numbers?

 

Turns out I tried using some SC59 (SOT 23) P channel's This did not work, at all. Turn out I wired the Source and the Drain the wrong way around. Because I hardly ever use P channels, and basically everything about them is inverted from N-channels.

post-274-0-85932300-1453454006.png

The way I have wired it in my original circuit, the current will always flow though the body diode!!

 

So I've re-designed the PCB and sent it for fabrication. :P

 

I still have not decided on a control board for this yet. I felt that I was reaching the limits of the G2542 after adding a date display to the software RTC with automatic day of the week calculation. the old board also did not feature a proper buzzer. limiting it's function for an alarm clock.

 

Exploring the ESP8266 space is interesting, due to it's ultra low cost. If this desk clock is wall powered using wifi could yield some cool features, Notifications/ internet counters. The trouble is programming/coordinating cloud services to perform the task.

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MAX7219's are interesting parts, however if I want to avoid the grey market. these parts are VERY expensive. digikey stock them at $14 AUD a piece.

 

Also the displays I'm using are smaller 1.9mm leds, vs 3mm. and the SOIC package sadly would not fit :(

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