Following on from Thursdays meet-up, as often happens I started looking at toys. The Early Learning Centre has a selection of phonics (keyword, not necessarily actually phonics) related educational items, including a few electronic ones. Goodie.
I was upset and distressed to find that the Peppa Pig's Fun Phonics was not in stock. They did however have an exciting looking Phonics owl which appeared to contain quite a few similarities to what we were talking about on the Thursday meet-up. It also had a little toy owl on it!
The box had pictures of the cards that came with it which appeared to be all time same shape, size and colour with no visible contacts. Score.... something with contact-less ID's. Lets see how other people approached this commercially.
So anyway.... here's the Phonics owl thing:
It was also avialable with a little bear.... but owl's are way cooler. Here's the back of the box:
So this thing has 2 modes, and comes with 17 pairs of cards. Not sure yet if the pairs are the same, or unique (is the Apple card the same as the A card - or are they unique?)
On with the action, lets get it out and start playing:
First thing I noticed is the cards are actually card (sounds a little silly I know). They all have light blue backs and are indeed all the same shape. Putting some screws on the back , they do not stick. So if there are any magnets in there, they are very week. The base of the recess for the cards in the base unit is also made of card, ooo, probably a reason for that not being made out of plastic. More than likely a plastic base would have been too thick for doing whatever is going on here.
Les have a play:
Quite nice. When you pop in the cards the base reads out either the letter "The Letter A", or the word "Apple". When you put in a matching pair you get a nice little jingle and a "Correct". When it misreads a card (which happens if you only half insert the card it tells you to remove the card, insert a card or something else. The message it gives seems a little random between cards. No doubt related to the mechanism behind the card reading.
I was also happy to see there is no problem with putting the cards in the other way round (Apple in the first slot, A in the second).
So, there is a minimum of 34 unique cards (17 * 2, as it knows the difference between letters and words). So at lease 6 bit assuming there is some kind of digital reading going on. It could still be analogue, but that seems unlikely.
Here's a little video of it in action:
Nice, the unit seems to work pretty well. The cards a a little tricky to get out though. Again, possibly related to the reading system.
So then... how is it reading these cards. Before opening it up I decided to have a bit more of a play with it. Look what happens when you put on more than one card at once on the same space...
Interesting.... if you put more than one card on the unit at once, it reads something that's not either of the cards. And you can place the correct answer in the second slot and it tells you it's the correct answer. Further to this, it doesn't work with all cards. Some cards will read off just one of the cards you put down. Using more than one card, you can place one of the cards in the wrong way round and still get a valid read (something you cannot do normally).
So, now I'm figuring we are looking at some kind of capacitive reading system. As there are 34 possible cards (6 bit) and the system knows if a card is the wrong way round... a system that can be fooled SOMETIMES, by having one the correct way, and one the incorrect way... We must surely be looking at 7 bit, EITHER where the 7th bit is used for orientation checking, OR the capacitive sensors are positioned so that they do not line up when in the wrong way. I'm putting my money on the first option, as the system will give the different reads with cards the wrong way in.
Just before I started to open up the thing, I accidentally knocked some stuff off a shelf and on to the reader. What a spot of luck, it started saying stuff. So we have discovered you can cause reads to happen by placing something metallic on the reader in certain positions. See below.
By moving the knife blade around I was able to generate a few dufferent cards (both letters and words). Before opening up the device I decided to open up a card and see what makes it tick.
Just as expected, there some conductive material in the cards. This card no longer works as some of the black conductor got ripped off and there is no longer any connection in parts. Where there is a connection the material seems to have a resistance of 2k/mm. Don't have a conductive pen so can't play with making my own cards quite yet. But this does confirm some of the operation of the cards and readers. And why it works when you stack cards on top of each other.
Anyway... lets get this thing open.
First thing to note is the large number of inductors on the top side of the board. There are 8 of the larger through hole ones, 8 transistors, 8 diodes, and 8 pairs of wires going to the board attached to the reading area. There are also a couple of 22u caps and 4 more inductors on this side. They don't appear to be connected directly to the sensor part of the device.
The mode is also set through the power switch. The mode of operation is configured through the green and orange wires marked P23 & J1-2 on the PCB.
Also notable in the above picture is the leads going to the sensor board on the left. They are short, but covered in sleeving and heatshrink. May well be that these leads are shielded to prevent interference.
Lets crack on...
Looking at the bottom of the board we can see the speaker. Following the traces we can see that some of those extra inductors are used as part of the audio output system. Other than a couple of passives, the speaker is connected to the larger chip marked U3.
The smaller blob on the back which is unmarked has traces leading from the power input, and has the other inductors connected to it. Some kind of switch-mode supply one would assume (the device runs on 3x AA's).
There are also 2 LM324 Quad op-amp's in the surface mount packages. There are some connections to the 8 leads going from the sensor board to these chips. So these must be used to amplify the output from the sensor board.
And there we go. Each redder has 8 pads on it. Looking at the card we took apart earlier, and testing a few more connections using foil, the centre is common and connected (via the cards) to each of the outer pads. Each of the outer pads is connected between the two readers.
One interesting thing here is lower middle left and right pads. These are the only 2 that are not symmetrical. Instead the 2 inner pads are connected. Perhaps it is this that stops cards being inserted in the wrong way round (via means of a calculate-able checksum perhaps). The card we took apart earlier does have a connection to one of these pads. If you replicate the other connection on this card on the left hand reader (where the other pad would not be used), it works file. However when you do the same on the right hand reader it will not work. Interesting....
What ELC have done here is very interesting. It appears to be very reliable. Cards are very easy and cheap to create. There is not too much hardware involved in reading the input cards. And it's all kept well away from the user.
Might have a play with getting something like this up and running.