How to Discuss the Important Things With Your Kids

With my youngest about to turn 7, I found it an important time to discuss with her the most important question of all:

How do 7-segment LCD displays work?


7-segment LCD displays are the sort you see on old-fashioned digital watches, microwave ovens, time-traveling deloreans and other common household appliances.

First I drew 10 sets of the 7 cells, all inactivated. I described to her how the 7 cells are switched on or off to make the numbers. Together we colored in the right cells to make up each digit.

7 segment display

We talked about how the digits from 0 to 9 can be described by 7 switches. I drew up a blank truth table and filled out the first row, to show which switches were on or off for the '0' digit.

She got it immediately and set about filling out a lot more of it. She soon optimized filling out the truth table by doing a single segment at a time across all numbers (rather than getting a single digit done at a time). i.e. she would fill in one column at a time instead of one row at a time. I found that a surprising optimization, and it was definitely a faster way to do it.

I described a bit about how you could make a circuit that does this. (She's made simple analog circuits with roominate and snap circuits). I talked about the use of a decoder and an oscillator; I doubt she absorbed much of that... digital circuit design can wait, this was more of a way to spark her own thinking.

Later that day I asked the kids what their favorite part of the day was. My youngest replied that her favorite was the bit where we drew the 7 segment displays. I was happily surprised so set about writing this "bragpost". I think it means this is an activity that kids might enjoy more than you'd initially expect.


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