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simple 3 digit, large 7 segment LED display

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tgator

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I am wanting to make a 3 digit LED display board for use on a drag car to display an ET in bracket racing. The display should be 3" tall x 12" or less in length. Te display only has to display whatever numbers that I manually input. No processing or other functions are needed. The input should be done from a small control box that can be mounted inside the drivers compartment and numbers input by using individual dials for each digit, a keypad or up/down pushbuttons. Similar productions units are sold but I cannot afford and I really would like to work on my own little electronics project. The following is a classified website that has one of these displays for sale:
https://www.racingjunk.com/exec/ca/view/338556/Digital-LED-Dial-Board.html

I mostly need help with a circuit to input the numbers for the seven segment displays. Any help is greatly appreciated and needed- it been several years since I have done any electronics work.
 

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It appears that they use a thumbwheel switch to input the numbers displayed, does anyone know if the thumbwheel switch can control the seven segment driver directly?
 
Hi,

If those thumbwheel switches are like the ones i've seen,
then they only have tiddley little contacts in them.
I would not think they could drive the lights directly.

There are various contact arrangements available within those
thumb wheel switches, you can get ones with a binary output,
done by the little contacts inside.

I would imagine you could also get them with seven-segment output
lines, but i haven't seen any.

If you can get them with 7-seg outlets, that makes your circuitwork
pretty straight-forward, just a follower on each line.

Best of luck with it, John :)
 
tgator said:
... does anyone know if the thumbwheel switch can control the seven segment driver directly?
The thumbwheel switches (BCD output type) should have no problem connecting to and controlling the seven-segment driver chips. The thing is, since the digit segments will likely require more current than the decoder-driver chip can handle, transistors to handle the current for each segment will probably be required. Although, the datasheet for the 74ls47 states that it's outputs can sink 24mA per segment at up to 15V. Here's a link:
**broken link removed**
JB
 
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