Teaching Guide Binary Device Example


In one of the ‘Teaching Tips’ sections there is an example student response where the binary question is, “Do we have a quiz or a test today?” and to send ‘quiz’ the device method is ‘one quick tug of the string’ and to send ‘test’ it is two quick tugs of the string.

I’m just wondering if people on the forum are viewing the device (string) as binary or not. Here is my thinking and I would love someone to correct me:

The device could be binary if the resting state (the neutral position the kids tend to return the string to) and the element of time was taken into account. However, the method described in the example is more of a ‘tally’ system (not binary).

Any thoughts?


I agree with your thoughts that related to the endgame the lesson is going after it isn’t strictly binary, but I feel the students have followed the instructions and defined a device that by their definition only has 2 states and since initial direction doesn’t include any timing element, they really don’t have a way to distinguish a tug vs do nothing until later in lesson when timing is introduced.

My 2 cents…


Thanks Jim! The lesson plan says,
“Students will often create devices that have a third “neutral” state or do-nothing state. Challenge students on whether their device really only has two states and encourage them to improve their devices accordingly.”

I find that all my students create binary devices to begin with (until they have to send 4 and 8 bit messages), but they don’t all use them in that way and the only way we could get them to do so is to introduce the element of time.

This year I have found it very powerful to just let them make/use their devices as they want, and then as the wrap-up discuss how their original devices could have been kept unmodified but still send more than 2 bits. I do this with a paper that is colored green on one side and red on the other. I first show them 2 different messages, A & B. Then I show them 4 different messages: AB, BA, AA, BB. The last two 4 bit messages are where they begin to understand the necessity of a time element to keep their devices binary. (One other note: I do this physical demo after a discussion about how to formulate 2 bit, 4 bit, and n bit messages, using only 2 symbols, and we write out all the combinations on the board. Since all the kids have had Algebra with some probability/combinations work, they get it).