Stirling Blue - BBC micro:bit LCD - Blog 6

10 Jun 2018

One of the PCBs I designed for the BBC micro:bit arrived and I wanted to see if it worked, so here is a short blog about it.

This PCB is one of the two PCBs that will make up the micro:bit TXTR introduced in Blog 3.

Here is what the PCB looks like on both sides:

This PCB primarily connects the micro:bit to an SPI 5110 LCD, but it also has connections for external power, I2C, 3 analog inputs, and an SPI QWERTY keyboard. It includes a power switch and a backlight switch for the LCD. There is a footprint for a FRAM chip to augment the memory in the micro:bit, since LCD graphics and fonts will require more than what is available in the stock micro:bit.

Here is what the initial build looks like - the micro:bit is located beside the LCD, leaving room for the keyboard below:

Here is a short video of the micro:bit and LCD in action:

This is a nice milestone - the first circuitry and micro:bit software for the final design that is actually working.

The software is going to change significantly because right now the LCD font takes up most of the memory. This will be off-loaded either to the keyboard module (PSoC4) or the FRAM chip, hopefully leaving sufficient room for Bluetooth communications software.

Here is an illustration of what the micro:bit TXTR will look like, in case you missed Blog 3. The area between the displays and the keyboard will be occupied by the keyboard microcontroller (a PSoC 4). In the final design this area is minimized by overlapping the two circuit boards:

The keyboard PCB was manufactured about a month ago but is still making its way around the globe. Hopefully it gets here soon as I want to see the whole device working.

Other aspects of the project are undergoing quite a struggle. The deeper I get into the PSoC6, the more I need to learn. I'm still doing a lot of wheel spinning and head scratching, but there is minor progress - very minor.

Upcoming blogs:

how Stirling engines work
start connecting some sensors to the PSoC6
designing the sensor interface PCB
the micro:bit keyboard

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balearicdynamics over 6 years ago

Doug, this project is incredibly nice. I love also the aesthetics you decided for the entire system. The rounded screen display remember me a 50's B/W televisions. As the keyboard is on a separate board, did you considered the option to have a device folding like a super-mini laptop?

Enrico
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balearicdynamics over 6 years ago

Doug, this project is incredibly nice. I love also the aesthetics you decided for the entire system. The rounded screen display remember me a 50's B/W televisions. As the keyboard is on a separate board, did you considered the option to have a device folding like a super-mini laptop?

Enrico
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dougw over 6 years ago in reply to balearicdynamics

Cool idea - flip communicator, but it never crossed my mind. In any case, I can't handle the cost of flex PCBs and my designs always try to minimize cabling.
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balearicdynamics over 6 years ago in reply to dougw

Where do you make the flex pcb ? Very curious...
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dougw over 6 years ago in reply to balearicdynamics

I don't make flex PCBs (yet). I would have them manufactured by a PCB shop - but can't afford it.
Even for regular PCBs, I have them manufactured, but the price is much lower.
Here are some shops I've used with good results:
https://www.apcircuits.com/home.aspx
https://www.itead.cc/open-pcb/pcb-prototyping.html
https://www.seeedstudio.io/fusion_pcb.html

Here is one I'm looking at:
https://jlcpcb.com/?gclid=EAIaIQobChMIpZfGpPTJ2wIVF57ACh34oQJ8EAAYAiAAEgIvXPD_BwE

I have used some flex PCB shops at work, but don't have any to recommend.
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balearicdynamics over 6 years ago in reply to dougw

By about one year Electrocircuits has a couple of very interesting options in PCB making for prototyping. One is they will make PCB prototypes (five units max) without the finished (green) part for a very very reasonable price. These are just for prototyping purposes and have the advantage that if something is wrong you can curt and jump the design without trashing the entire project. The second option are - also at a reasonable price - semi-flexible PCB. I think it is the worth to take a look at.

Enrico
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