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[Group Buy-19][O] TMS0803/5 Emulating Calculator With Bubble Display

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Got an interesting problem with my second kit.

Turn on. No display. randomly mash buttons. displays 0000000 for split second, then blank.

Check power and pin voltages... 

1- 3V

2-7 1.3V

8-13 0.3V

14-15 1.3V

16 3V

17-18 0V

19 0.3V

20 0V


I assume I did something wrong like insert LEDs wrong way. Start cutting leads off (hate de-soldering)

Bingo. LEDs light up missing a couple segments. LED installed correctly.


Faulty/fried bubble module?

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Would this be of interest?   I have a bag of them (80, all pictured). In various stages of pin bending(i don't think any are broken though). I didn't really have any plan for them, totally forgot I

@@amstan @@bluehash   Thanks for amstan, I am (we are) getting these bubble leds.    I will do a version of PCB for them, try a prototype, and will discuss how we can utilize the donation properly

All the ones I made were w/ white buttons. Just matches well w/ the white silkscreen on the green PCB. As long as they are two pin 6.5mm spaced they are good.   I pick the green PCB as when I starte

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Faulty/fried bubble module?


Those led modules are pretty good. I never had any problem w/ the 20+ units I handled.


The circuit is a bit tricky as to save IO pins I had used the same pins to scan for tactile keys. There are "stolen" cycles during the led multiplexing to switch them pins as input to scan the keys. During which if the code detects a key being pressed, it will wait for it to be release and the leds will be blank during such period.


If you have (obviously not in your case) a bad or short tactile switch. The initialization code will think that you have a key pressed and will wait (forever) for it to be release. This is the "hold+switch" mode selection logic for the slow-cpu, secret message, sinclair rom start-ups.


Although I never had problem w/ this issue after the 1st prototype. But it may cause problem if you use some cheaper IC sockets (those that does not have round machined pins) as they can introduce stray capacitance to the set-up and introduce false key-press reads. This design does not have regulated power and the direct LED driving will drop the voltage quite a bit and it's not that good when switching the pin to read keys. I don't have a scope to understand it completely, but I would assume when this happens, we could introduce may be a 25-47uF capacitor to the power to make the supply more stable. Or the software timing for reading keys may also be adjusted to counter that.

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Is there going to be another GB of this kit now that YouTube's Arduinoversusevil did a piece on this project and got me all twitterpated?


@@Hankus , I understand @@bluehash will be making a few kits available for sell in the store. Not sure about the timing though


Arduinoversusevil's (?? @@swampdonkeykami ??) video is awesome, the PIN 1 is the lone square pad on dip components, I will update the build thread and emphasis that.


p.s. Is it true that the engineers' rings are made from a broken bridge in Quebec?

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As for @@amstan LED donation, which I mentioned in an earlier post that I managed to blow one of them, it turned out that (I believe) it was bad before I tried them. I finally got time to check all the 80 LED modules and it turned out most has some problems. There are 23 units that are good, the rest all have either missing digits or segments. And some of them has one or two "weak" segments, etc. I recall buying from ebay that had similar problem. Guess this is what happen when they sat in a bag for 20+ years.


Sorry to hear that.

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Sorry to hear that.




The yield rate is not at all bad! Compare w/ my ebay purchases, I order a batch of 4 modules (9 digits) and NONE of them are good, each have some digits / segments missing. Before that another order I received a funny relay instead of the led bar.


I am still very thankful for the pieces. You can fetch quite a bit from them on ebay these days. I haven't really work on them (special edition DataMath calcs) lately as I am busy w/ a HP calculator emulator. But will get to it in a few weeks time. The set will cover a few units for future POTM prizes.


I was trying to order some more bubble leds from Sparkfun and found that they are all gone. Re-stock dates come and go, I hope I can still get some from them as those are likely old-new stocks and can be exhausted.

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Not sure this is the right thread but feel free to move it / suggest a new one :-)



Well ... I'm not a huge fan of Doctor Who but my mum (in her 70s) is! I just happened to be walking past her enjoying this episode:
right at the 26 minute mark, and *what* do I see but a Sinclair Scientific repurposed no less to convert 2 dimensional entities into 3 dimensional entities - a device that goes on to save the whole planet ...
and these images with the re-branded 2Dis (Two Dis) logo conveniently covering the old Sinclair Scientific logo
... and in these you can clearly see the distinctive 1.4:2 LED display format 
I can see the headline now ... device with 320 eleven bit words saves Earth
and some people just think it was another calculator
I wonder if their props guy (or gal) was inspired by Ken's blog
Phil M




Via Ed

The BBC has published some artwork of the device - apparently it is even a working calculator:
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