Logic Game

An interactive activity to demonstrate the function of logic gates.  What you see here is a functional prototype. In fact, it has been on the museum floor for years. I designed and built this display simply to demonstrate the possibilities of such an interactive to the powers that be.  Unfortunately, it works exactly as it is and therefore needed no update to be strictly functional.  As a result, this conspicuously raw plywood-and-construction-paper display remains stubbornly in situ.

From an exhibits design perspective, the challenge was how to convey to the visitor the simple Boolean algebra of AND, OR, and NOR gates.  From a technical perspective, the challenge is easy to sum up: wiring.

Other logic interactives I have seen have a major pedagogical flaw: the only aspects of the logic gates that can be manipulated by the visitor are the inputs.  Further, these activities rarely provide a way for the visitor to test themselves.  Rather, the visitor simply turns a couple of switches to one position or the other, and the display simply responds.  The display featured here addresses both of those problems.  Not only must the visitor provide the two inputs for each gate, she must also provide the correct output for that gate given the inputs she selected. This not only forces the visitor to choose three possibilities, rather than two, it further encourages the visitor to actually consider the situation, rather than merely turning switches and observing results.  The circuitry provides feedback for each of the eight permutations available when working with three tiles of two options each.

Logic gates

Logic gates

Here’s how it works: A set of logic gates are displayed on the console. The visitor can place wooden tiles that are labeled either 1 or 0 into each of three sockets for each gate.  (These tiles are shaped the way they are for a good reason: they have no radial symmetry and will fit into the socket only one way.  Why this is important will become clear.)





And gate with correct solution

AND gate with correct solution

Once the gate has been chosen, and the tiles have been selected, the visitor can press a button to ascertain whether or not they have a correct configuration.  Here we see that the tiles selected for this AND gate indeed render a true statement, so the test button energizes the “correct” light.






AND gate with incorrect solution

AND gate with incorrect solution

Here, the visitor has chosen tiles that do not render a true statement for an AND gate, and therefore the test button energizes the “incorrect” light.







After the visitor has completed the left side of the display – sort of a low-pressure logic tutorial – they can choose to solve the logic puzzle on the right side of the display.  This little puzzle requires the visitor to provide four inputs that will result in an output of 1 for the circuit as a whole.  Four inputs with two options each make for 16 possible permutations.  However, only 3 of those 16 permutations will result in an output of 1, so it is unlikely that the visitor will stumble on one of the correct answers by chance.

Logic gate puzzle

Logic gate puzzle

I started to wire this project with all manner of relays and switches, but I soon realized that it was getting pretty complicated pretty fast.  Then it occurred to me: just wire it up so that each of the eight permutations for each gate is represented in the circuit, and let the electrons – so to speak – go where they may.

The circuit is made aware of which tile is inserted into which socket by the presence of magnets in the tiles that activate magnetic reed switches behind the socket.  Each socket has two sets of reed switches, and each tile has a magnet in either of two positions: at the top of the tile, or at the bottom.  Which position the magnet occupies determines whether the tile is a 1 or a 0.  This is why the tiles must fit into the socket only one way: if the tiles did not have a mandated orientation, the circuit would have no way of knowing whether there was a 1 or a 0 in place.

The clusters of reed switches are arranged so that they account for every possible arrangement of tiles.  If a true arrangement is offered by the visitor, it picks up a relay that enables the “correct” light when the “test circuit” button is pressed.  If a false arrangement is offered, it picks up a relay that enables the “incorrect” light when the “test circuit” button is pressed.

It is to be hoped that one day some funding will magically appear, and I can build a new cabinet and get some professional graphics for this exhibit.  Just for fun, here is a picture of the jumble of wires responsible for the game’s electronic behavior.  This is what wiring looks like in the prototype stage.