Acrylic Display Sign

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parkview
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Acrylic Display Sign

Post by parkview » Sat Mar 06, 2021 2:53 pm

In 2020, Stephen showed me a USB power Acrylic display sign that he had quickly made up for an event. Months later I was at a monthly Robotics meeting meeting and it occurred to me that it would be handy to a battery powered sign that could have removable Acrylic signs that can be swapped out for the different meetings or events I attend. The WS2812/Neopixel RGB LEDs could act as a battery charge indicator and they would be recharged via a USB cable.

I had a go at designing up a two layer PCB, but was struggling to fit all the components and tracks onto a 45mm wide PCB. I then restarted laying it out as my first 4 layer PCB. The PCB was a complete failure, with all the layers shorted together. I had misunderstood the production capabilities of JLCPCB and sent them a PCB designed around using blind/buried via's. They came back as a through-hole construction.

This is the next version of the PCB and I have taken the opportunity to upgrade the DC-DC Boost converter to be a higher 3A capacity. I also added a capability to switch on the battery voltage measurement, take a reading and then switch it off again. This will prevent the resistive voltage divider from draining the battery.

The PCB will be in blue, but should look something like this:
Acrylic_Sign_PCB_Front_V0.7.jpg
Acrylic_Sign_PCB_Front_V0.7.jpg (122.58 KiB) Viewed 763 times

parkview
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Posts: 522
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Location: Busselton
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Re: Acrylic Display Sign

Post by parkview » Sat Apr 24, 2021 5:21 pm

While I was waiting for the new Acrylic Sign PCB to arrive, I had a go at making a prototype display based on a bunch of individual boards: A TP4056 Li-ion battery charger, a 3.0-4.2V battery voltage to 5V boost DC-Dc converter, my ESP8266 LED controller and a small MOSFET isolator hand soldered board. I had a go at designing up a MDF based container for it all:
Acrylic SignV1.1.jpg
Acrylic SignV1.1.jpg (41.86 KiB) Viewed 707 times

Even using a 4-layer PCB, I couldn't design the board as small as I wanted, so I will have to design up a new version of the MDF sign container.

parkview
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Re: Acrylic Display Sign

Post by parkview » Sat Apr 24, 2021 5:33 pm

The Acrylic Sign PCB turned out really well or at least so far. It has condensed all these small boards:
Acrylic Sign V1.jpg
Acrylic Sign V1.jpg (33.29 KiB) Viewed 707 times
all onto one PCB with added functionality (only 20 LEDs where programmed to turn on):
Acrylic Sign V2.jpg
Acrylic Sign V2.jpg (55.6 KiB) Viewed 707 times
It can host two runs of WS2812 (Neopixel) LEDs. In theory the DC-DC boost IC can pump out 3Amps, but I think 2Amps should be enough for a couple of small strings of LEDs. I have also have some indicator LEDs, provision for two capacitance touch plates and switches. In theory, I should be able to run this powered by two 18650 batteries in parallel.

The GPIOs are all based from this project: viewtopic.php?f=9&t=2449, so it didn't take much to get a basic LED rainbow wave happening.

parkview
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Posts: 522
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Re: Acrylic Display Sign

Post by parkview » Sun Apr 25, 2021 10:21 am

On the first version of the PCB to boost the Li-ion 3.0V-4.1V battery voltage up to 5V I used the SX1308 DC-DC converter IC. With this, I had to also add a SS34 schottky diode to the circuit. After the first version design, I spent some time researching DC-DC boost and buck converters and finally settled on using the SY7088 for all new designs.

I swapped out the SX1308 IC for the SY7088. It's much smaller AND incorporates a charge pump diode inside the IC - extra bonus! This IC is tiny (2mmx3mm) and runs cool to the touch at 1A:
small-dc-dc.jpg
small-dc-dc.jpg (47.34 KiB) Viewed 702 times
Above, I have added some reference sizes. Also, the SOT-23 MOSFET body is around 1.3mm x 3mm wide (not including the metal contacts). Note: you can just about make out the solder balls in the solder paste

Since designing the second (above) version of the PCB, I have found the DMC2400UV, a tiny 1.6mm x 1.6mm dual P-MOS & N-MOS MOSFET. This will replace both of the above SOT-23 MOSFETs in the next version of the PCB.

I am in love!

parkview
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Posts: 522
Joined: Tue Jun 24, 2014 8:25 pm
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Re: Acrylic Display Sign

Post by parkview » Fri Apr 30, 2021 5:45 pm

Just finished logging battery voltage measurement while 25 LEDs (WS2812 - Neopixel) where lit up at 50% brightness. My PCB will automatically turn off when the battery voltage reaches 2.5V. I found that my seven year old Ultra-fire (what a name!) cheap Chinese Li-ion battery ran for 8 hours 36 minutes:
LED-runtime.jpg
LED-runtime.jpg (31.09 KiB) Viewed 682 times
I have arrowed three periods where I paused the lights for a while and that the battery recovered a bit. As per all Li-ion batteries, there is a steep voltage drop once the battery voltage hits 3V. In my case it might have only lasted around 6-7 minutes at approximately 450mA load at 5V.

I am sure that a new good name brand Li-ion battery (eg: LG, Samsung) will last a lot longer than my old light weight battery.

parkview
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Posts: 522
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Re: Acrylic Display Sign

Post by parkview » Sun Jul 11, 2021 12:34 pm

The blue acrylic sign PCB works really well and I am very happy with it. It is however around 44mm wide, so it won't fit into the initial MDF housing I made, so I designed up a new wider and a bit taller housing. It's made from stacked up layers of MDF and included provision of a USB Micro extension cable at one end and a power switch at the other. The Li-ion 18650 battery is mounted in a 3D printed battery holder. The bottom of the housing is screwed into place via M3 bolts inside 3D printed nijaflex feet. The M3 bolts screw into brass heatset nuts that are press fitted into laser cut holes into MDF and reinforced with epoxy glue.
sw-maker-sign.jpg
sw-maker-sign.jpg (23.73 KiB) Viewed 462 times
A bit of sanding and a few layers of matt black paint the housing is completed:
acrylic-sign.1.jpg
acrylic-sign.1.jpg (36.85 KiB) Viewed 462 times
The Acrylic sign is replaceable and just sit's in place via gravity. It can be swapped around depending on what meeting of event it's being used at. Below I have tested spraying the acrylic with mat black paint leaving the text masked out with masking tape. It's kind of ok, but makes for a very dark sign, maybe ok for use at a dimly lit event?

Overall, I am very happy with the way this turned out. I had nearly finished designing a new smaller compact version of the PCB, but this one is working so well, I don't think I really need too.

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