New poker card design

After spending hours last night updating and re-writing their printing routines, Nick from Custom Stuff emailed over some print previews of playing cards with coloured boxes in each corner, according to our latest ideas.
In short, some of them looked horrible.

With the correct photo, with the correct border, on the correct coloured background, sometimes it doesn't look ghastly (Queen of spades in the example photo) but mostly, the garish coloured blocks just distract from the images on the card and look awful (9 of spades).
Yes, we could make playing cards with "regular" card faces, pips and spades and diamonds and the like. But even then, each suit would have three picture cards with a jack, queen and king on them. So they'll still look terrible!

This morning, Nick showed us some left-over offcuts from a deck made overnight.
The customer had asked for a different coloured border around each of the cards, to signify which suit the card was (they were for teaching games to adults with learning difficulties). Apparently, thanks to the rise in internet poker and in particular, tiny graphics in mobile poker games, it's not uncommon for poker cards to use different colours for different suits - black = spades, red = hearts, blue = diamonds, green = clubs. This makes identifying your cards easier on a small-screen device (apparently).

My guess is that the programmers chose "primary" colours (let's not get into yellow being a primary colour and green a mixture of blue and yellow - we're dealing with lights, not pigments here!) to make each suit easily distinguishable from the others. Whatever the reasoning, this is quite fortuitous for us!

Having explained our card-reading idea, Nick suggested an alternative card layout:

The entire border of the card could be coloured to match the suit on the card (this was a quick mock-up, my guess is that clubs would probably be green, not blue). The numerical value of the card could be shown via a series of 4 black and white dots. Nick explained that these dots are much less conspicuous than large multi-coloured blocks, and we have to agree!

Of course, a 4-bit value gives us a range of values 0-15 (or 1-16 if you prefer).
Which is perfect: we can determine the suit of the card by detecting the colour of border, then read off the black/white dots to get the value. It does mean that we'll need 5 LDRs instead of four (the fifth will be under the border of the card, immediately to the outer edge of the dots) but the symmetrical layout of a playing card means we can just put all five in a line and the orientation of the card will make no difference.

We're quite excited by this new development.
The cards look great (we've yet to see a physical card, as Nick has a lot of work to do getting her programmer(s) to re-code their website for us!) and how it works should be quite simple.

By using black and white dots, our LDRs should be able to read a white dot value, irrespective of the colour being reflected off the face of the card - we can use this as a double-check; if we flash a red light and read back two white dots, we would expect the same response when we flash it blue and green.

Exciting stuff. We're already building prototype boards (using black tubes over the LDRs like we did with our invisible instrument last year) for reading the black/white dots, and we're pretty confident we'll have this working quite quickly. The only bit we haven't yet tried is the colour detection. More posts coming soon!

Poker table - without RFID

Here's an idea we had quite some time ago, while proposing ideas for the HackLlan show-and-tell session in November last year. It was for a poker table which could read cards without using expensive RFID hardware.

Well, at BuildBrighton we're talking about holding our first poker night - so it'd be really cool if we could broadcast it live - complete with overlay graphics, just like they use on the telly!
The original idea for identifying cards was to use "intensities of light" and non-primary colours to determine which grid pattern was showing over a single exposure. After a bit of trial and error, we found it difficult to tell when one, two or three squares of the same colour were showing in a pattern and the card detection device failed.

That's not to say we're giving up!
Nick at Custom Stuff has arranged to create some decks of customised playing cards, entirely to our own design rather than through their online editor, so we're now thinking about a different layout. The latest idea is this:

Each card will have "index" numbers in all four corners (this is an option you can set in the custom stuff online editor) BUT we're going to put each index into a different coloured square.
We'll have an LDR under each corner of the playing card (which sits on a black plate with holes cut in the corners, so only the colour in each corner is displayed from underneath) and then flash an RGB LED through red, green and blue.

By measuring the reflected light from each corner, we should be able to work out which colour is at which corner (and thus, which card is face down on the detector)

We've come up with this pattern sequence for our playing cards. The idea is to find which corner contains the black or white square (if black, the LDR under this corner will always return zero, if white, it should always return full brightness) and then read the colour pattern off the card.
If every card has only one black or white square, then we can convert a sequence of colours into a card value and it won't matter which way around the card is placed on the detecting plate.

The beauty of this design is that we don't have to work out intensities of colour - simply set a threshold value and if that value is met, we can detect the presence of a particular colour; it turns the result into a binary operation once more.

For example, let's say we've put the six of diamonds onto our detector (for the sake of example, let's assume it's the same way around as the blocks in the diagram above).
We flash the RGB red and read the values, clockwise, from each LDR at each corner of the card (the LDRs are inside black tubes, so are only reading reflected light, not direct or ambient light from the LDR).

The first LDR (top left) reads 190 which is above our threshold value of 100.
The second LDR (top right) reads 180 which is above our threshold value.
The third LDR (bottom right) reads 30 which is below our threshold value.
The fourth LDR (bottom left) reads 54 which is below our threshold value.

We need to allow for a little bit of leeway in our threshold, in case any ambient light creeps in, or if the blue, for example, is not an exact blue with absolutely no red pigment in the ink. This is where our "intensity" approach failed last time - the inks were not perfectly exact colours and the range for error was greater than our range for detecting colour. This time, we're simply saying "is this corner red, green or blue?"

Now let's flash the RGB blue and read the values again.

The first LDR (top left) reads 43 which is below our threshold value of 100.
The second LDR (top right) reads 176 which is above our threshold value.
The third LDR (bottom right) reads 156 which is above our threshold value.
The fourth LDR (bottom left) reads 78 which is below our threshold value.

Lastly, flash the RGB green and read the values once more:

The first LDR (top left) reads 57 which is below our threshold value of 100.
The second LDR (top right) reads 185 which is above our threshold value.
The third LDR (bottom right) reads 41 which is below our threshold value.
The fourth LDR (bottom left) reads 158 which is above our threshold value.


Now collating these results, we can see that the first LDR (top left) responded only to the red light. So let's say that is red. The second LDR (top right) responded to all colours, so that must be our white square (if it was black, it would be the only one to respond to none of the RGB flashes). The third LDR (bottom right) only responded when the RGB was flashed blue and the fourth (bottom left) only responded to green light.

So we have red, white, blue, green. In our look up table, this corresponds to only one card in the deck - the six of diamonds. To look up the card in our microcontroller, we'll probably cycle the colours until we either start with black or white - so our sequence would be white, blue, green, red. This means we don't have to store all possible permutations of each colour sequence to be able to perform an accurate look-up
(we don't want to try to look up red, white, blue, green and have no matches because the microcontroller is comparing against white, blue, green red!)