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# Digit Display for Child Toy

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#### bxmas13

##### Newbie level 2
I am trying to build a toy for my kid and I would like to add a digital display that he can adjust(make numbers change) with a rotary switch.
How would I accomplish this? I am a beginner, my only electronic experience is from my high school electronics class 15 years ago. I am willing to get my hands dirty and learn.

If this is too in depth for a beginner please feel free to let me know.

Here is the display I am talking about.

Thanks so much!

Added after 5 hours 34 minutes:

I think I found the answer. Get a 10 position rotary switch. On each position wire it so that it completes the circuit for each specific segment on the 7 segment display.

So in other words: position 1 gets wired to pins 'b' and 'c' to make the number 1.
position 2 gets wired to a, b, g, e, d and so on.

That sound right?

Almost, but you'll need to include some diodes to stop cross-linking of segment combinations... The schematics below show what happens in a simplified case, where we have a 2-position switch and 3 LEDs - a, b and c. With the switch in the left hand position we want LEDs a and b to be lit, and with the switch in the right hand position we want LEDs b and c to be lit.

Note here that, because LED b is common to both switch positions, it forms a link between both sides of the switch, and so even though the switch is in the left-hand position we will get unwanted current flow through the common link (as depicted by the red arrow) and across to LED c which will then also be lit.

If we now include diodes in series with the connections between both sides of the switch and LED b, this cross-link is broken - these series diodes prevent current flow from one side of the switch to the other.

For this example, the series diodes on LEDs a and c aren't necessary, because neither of these LEDs are shared between switch positions, however for the full circuit you're intending to build, you'll find that all of the segments are shared between at least two of your switch positions, and so you will need these series diodes on each LED.

HTH
Chris

Oh yes that makes sense. Thank you so much!

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