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Topic: New 8x8 matrix toy (Read 5164 times) previous topic - next topic

New 8x8 matrix toy

Hey again,

So it was awhile ago when I posted about my old 8x8 matrix toy. I've finally got around to creating a new version which incorporated an 8x8 bi-colour 3mm LED matrix module. and a controller board the size of the LED module itself. Here is a sped up soldering video.
http://http://www.youtube.com/watch?v=1MkQzpkjcxQ

Basically using the larger LED display enabled me to fit a coin cell batter on the back. the underside of the PCB houses a MSP430 2kb micro controller, 3x 74hct595's and 16 cathode sinking n-channel mosfets.

I would really like idea as to what to do with this. I've already got it displaying sprites and going into a 0.4µA sleep mode when the button is pressed. I like the idea of creating a variable sided dice (d4,d6,d10,d20), and there are examples of generating random numbers from the uncertainty/difference between the two internal clock sources.

The designs will be open source on my blog eventually.

Re: New 8x8 matrix toy

Reply #1
Nice soldering video!
Got a question? Please ask in the forum for the fastest answers.

Re: New 8x8 matrix toy

Reply #2
NIce soldering (and fast ;))

Are the FET needed? IIRC the 595 can sink about 15-20mA.

Re: New 8x8 matrix toy

Reply #3
with row or column scanning the total current per row could reach 480mA easily. a burnt fet is much cheaper to replace than a micro or 595, (3 colors x 20mA ea x 8 per row) assuming 20mA leds

it looks very well thought out, great job. this would make a great kit:)

Re: New 8x8 matrix toy

Reply #4
I don't think a 2032 battery can supply 480mA :)

Re: New 8x8 matrix toy

Reply #5
[quote author="Sjaak"]I don't think a 2032 battery can supply 480mA :)[/quote] that is just a arbitrary # with all thee colors on max and the entire row lit up.

i'm sure under normal use it will not be that high, always engineer for worst case.

i think the average cr2032 is about 225mAH, i don't want to even try to start to calculate theoretical real use conditions, but i guess you could get an hour or 2 use out of a single battery with a dancing stick figure, maybe an average consumption of about 20-50mA and a peak of 150mA

(contest idea) guess the battery life.

Re: New 8x8 matrix toy

Reply #6
I did solder up one board without the mosfets, using small pieces of solder shorting the Gate and Drain pins. The LEDs aren't as bright when you have an entire row lit up. The ON Semi 74HC595 parts I'm using state 35mA/pin and 75mA total. so the mosfets do help to sink some extra current. I would have used mosfet packs (2+ mosfet's per IC) but these sot23 devices came up the cheapest (~0.09c each).

The display module is bi-coloured so the current consumption would be less. In practice it maxes at around 80mA due to the current sourcing limitations of the high side 595.

From some initial testing when the devices goes to sleep it uses 0.15µA total. Using this figure a standard energizer battery (datasheet) of 240mA/h the device would last for 700 years in sleep, the batteries shelf life would likely be shorter than this figure.

Re: New 8x8 matrix toy

Reply #7
I just tested a TianQiu CR2032 straight out of the packaging.  Dead-short on an HP 3435A amp meter, initial current was 250-300mA, falling to ~100mA within 5 seconds.  This implies an internal resistance of the coin cell on the order of 12-30 ohms.

Considering it's multiplexed, I also hypothesize that you may have gotten away without the FETs.

Quote
I did solder up one board without the mosfets, using small pieces of solder shorting the Gate and Drain pins. The LEDs aren't as bright when you have an entire row lit up.

Of course, if I hadn't missed your last post, I may not have bothered...

Re: New 8x8 matrix toy

Reply #8
[quote author="phirephly"]This implies an internal resistance of the coin cell on the order of 12-30 ohms.[/quote]
That backs up the data in the energizer datasheet for the CR2032. it's stated a typical IR of 10-40 Ohms.

[quote author="phirephly"]
Considering it's multiplexed, I also hypothesize that you may have gotten away without the FETs.
[/quote]
I possibly may have gotten away without then on a fresh Battery. But I think the FETs help out more when the battery runs down a bit.

[quote author="phirephly"]
Of course, if I hadn't missed your last post, I may not have bothered...[/quote]
It's always good to experiment. A fun and informative way to spend time :)

Of course I could use a Li-ion 2032. they have much higher discharge rates than standard CR2032 cells. And they run at 3.6v and are rechargeable. But I'm scared of shorting them out with the cheap battery holsters I have, so I haven't bought any. :/

Re: New 8x8 matrix toy

Reply #9
@ Greeeg

i really like your idea ! your mini board can become something that nerds want to have on their desk :o)

idea,  im sure u already thought of a desk clock  and some "wearable " adaptation.
the rf option could have been interestion too !

:o)

 

Re: New 8x8 matrix toy

Reply #10
Ok So I've finished off most of the code for this guy. I made a post about it on my blog. http://http://blog.greg.so/2012/01/8bi8-overview.html

Here is a short youtube video I made showing off the main features. http://http://www.youtube.com/watch?v=sXVhfoKJW7E

1 button really restricts what this device can do. Next revision I might add another button or maybe an accelerometer, I do have a pile of MMA7455's they are dirt cheap. :D