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Circular Circuitry

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This problem involves circuits which feed back into themselves: The output of a gate can be traced through the circuit back into the input of the same gate! This can lead to all sorts of interesting behaviour, which will be explored in this problem. Please note that the gates here are not interactive: they are thought experiments .

What will happen when you switch on these circuits?

What will happen if you change the gates to different types?






The following two circuits have the same gates. Look carefully at the wires which are switched on. What do you notice? What do you think will happen when the switches are flicked on and then flicked off?





Can you create your own feedback circuits? Investigate their properties.


Click here for a poster of this problem.



NOTES AND BACKGROUND

A key concept in computing is that of random access memory : whilst computers logically process commands they are also able to store user inputs whilst a procedure is being followed. Memory is built using logic gate circuits which feed back into themselves. The most simple of these is the 'flip-flop' which you can read about in the Wikipedia article . The flip-flop is a device which has two different stable states, and can thus 'remember' if a switch has previously been flipped.


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The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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