Perhaps make each square out of bulk resistive material with electrodes on two edges. Place a circle of conductive material on the bottom of each piece. The size of the circle will determine the effect that piece will have on the measured resistance of the square when the piece is placed on it. Orientation of the pieces on the squares will not matter because you are using a circular shaped conductor. You would need to be able to discriminate 12 different sizes of circles. Bob Ammerman RAm Systems ----- Original Message ----- From: "Robert Rolf" To: Sent: Tuesday, March 09, 2004 3:05 AM Subject: Re: [OT:] Chessboard (sensor) 0xDEADBEEF wrote: > > Am Dienstag, 9. Mdrz 2004 05:46 schrieben Sie: > > So how would you handle the confusion of capturing apiece. For example > > you move a white bishop across the board to capture a black rook. You > > remove the > > black rook and set the white bishop in its place. > > > > Being a chess players and computer nut for years an engineering friend > > and I thought this out back in the days of the Commodore PET. For it to > > go beyond having > > entering the data manually. you would have to as a minimum have 12 > > unique peices identified. for the white side: pawn, rook, knight, > > bishop, queen & king. and the > > same for black side. We did some experiments with the resister idea but > > had some problems with the resistance of the conection. > > Well it's still the easiest and cheapest solution!!! If you choose the > resistance of each resistor the way that even with small mistakes in the > connection resistance the controller could still detect it reliable! > I think about building a potential divider with the chess figures as a par of > it. The controler then detects the potentials and dicides what figure is on > the scanned field (therefore the potential must be within a given range, that > could surely be achieved even with these connection resistance problems!) > > > > > What about these micro ID chips they inject into dogs and other pets to > > ID them? > > > > This might be the most elegant solution, but the most expensive, too. What Jinx suggested, a resonant coil under each square whose frequency is changed by the loading of the piece, is elegant and inexpensive. If you used RFID you'd have the coils and multiplexer anyway. You could drill the bases of existing pieces and insert a varying length of iron rod to get N discrete frequencies corresponding to the type of piece. Or possibly various types of metals in a couple of thicknesses. Their eddy current decay profiles are all different (hence metal detectors that can discriminate between brass and iron). And the idea of using hall effect and having different field strengths for the pieces is also cheap and simple. Black would be one polarity. White the other. This avoids the problem of contact resistance and oxidation. One could also use an IR transparent base and a reflective patch with discrete reflectances (not bar code although a varying duty cycle grid (halftone) would give you something that is easy to print). What I don't understand is why you need to know the 'starting position'. I thought all chess games start with the pieces in the same position, so all you need to detect is which squares have activity, assuming that the humans know the movement rules for the pieces. Do let us know what you discover works best. My bet is hall effect with enough variance in the magnet strengths that position error is within the 12 quantizing levels you'd need. Or IR. Robert -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.