4-Digit LED without Arduino

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skarkowtsky

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Can a 4-digit 7 segment display be driven by a thumbwheel switch and bcd decoder without Arduino or any other code-based circuit?
 

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What? You mean you think the ONLY way you can drive a 4-digit 7 segment display is with a microprocessor? What, exactly are you trying to do?
 

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That’s what I was hoping to hear!

In the past, I’ve driven 4 single 7 segment LEDs with a 4 digit thumb wheel going into 4 4511 decoders (one per digit).

How would I do this with the same thumb wheel, but into 1 4-digit display??
 

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Hi,

It depends on the used display.
If all the 4 digits can be controlled individually, then just use 4 thumb wheels.

If you have done this before ... and it worked ... then tell us where you now see the difficulty.

Klaus
 

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skarkowtsky said:
How would I do this with the same thumb wheel, but into 1 4-digit display??
Click to expand...

Multiplexing is how. Each digit has its own common wire. Turn on each digit one at a time rapidly in sequence.
Outputs from 4511 go to the 7 segments.

At the same time a digit is activated, choose 4 bits from a corresponding thumbwheel. Apply these to the 4511 inputs. This requires something equivalent to four 1-of-4 selectors.
 

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I have limited knowledge. Does multiplexing require an Arduino or something similar, or can it be achieved with analog components too?

I want to use 1 4 digit thumb wheel to set the 4 digits on the 4 digit display.
 

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Hi,

wait: 1 thumb wheel and a 4 digit display???
What is your idea? I don´t ask about a solution or a schematic. I ask for a description how you want to input your 4 digits with 1 wheel.

Klaus
 

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Hi Klaus,

I want to be able to spin any digit on a 4-digit thumb wheel, and have that number display on any of the corresponding 4 digits of a 4-digit 7 segment display.

A few years ago, and with BeTwixt’s help, I achieved something similar with analog components and 4 single 7 segment displays. But as you can imagine, there were hundreds of components involved.

I want to know if I can achieve the same using a 4-digit display, to reduce the number of components needed.

The wild card: I don’t want to use an Arduino or the like. I’m curious if this could be achieved with just nuts and bolts components.
 

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Hi,

Ah, now I see it´s a "four digit" thumb wheel.
..then I´m back at post#4.

***
Hopefully you did not use (much) analog parts.
I´d try to use as much as possible digital logic parts.

.. you say "hundreds" .. wow, much effort...

Klaus
 

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Referring to post 4, how would I decode into. 4-digit display? Those appear to have less pins than a single digit display.

In the past I used a 4511 per digit. Is there a chip that would be better?
 

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Hi,

again: we do not know what display you use.
If it was my job I´d look for it´s exact part number, look for a datasheet and find out what the pins are for and how to use them.

Again: it depends on your display and your thumb wheel. I have no clue about them.

Klaus
 

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I think we’re getting into the weeds here. I just want to know if there is a chip or series of chips that will decode the 4 digit thumb wheel specifically for a 4 digit display. Can it be done, or does it also require something like an Arduino?

I can look into part numbers and data sheets when that time comes.
 

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Hi,

Interesting way to create/solve problems.
I have no experience with this way. I´m curious how others can help. I hope they can help better than me.

Klaus
 

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i assume your thumb wheel puts out BCD
i also assume your display is a 7 segment type
so thumb wheel to BCD to 7 segment decoder to display

one thumb wheel to one BCD to 7 segment decoder to one display
repeat 3 more times

it would help if you specified the thumb wheel and display you want to use
 

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skarkowtsky said:
Ok, so it can’t be done with a 4 digit 7 segment. Thanks for confirming!
Click to expand...
NOBODY SAID THAT!!

people keep asking you to provide specifics about what devices you’re using, and you keep not providing that information.

“Hundreds of components”??
 
Last edited:

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Holy Christ.

I started the aforementioned one, which was to be 48 individual 7 segments in 12 groups of 4.

So yeah, it would’ve been hundreds of components. It worked wonderfully, but I gave up after the second set of digits, because of how time consuming it was.

Where is BeTwixt when you need him?
 

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Needless to say with a processor this is a single chip solution.
One could use a single thumbwheel switch, a button to select
digit, and a muxed 4 digit 7 segment display.

Keep this in mind for future possibilities.

Something like this -



This is one chip except for R's and NPN transistors, those are external. I think you can
get those in a single array chip with the base resistors included in chip.

The debouncer is to debounce the digit select switch, again debouncer onchip.

So solution, being muxed, minimal wiring so much more reliable.

Code maybe 20 - 25 lines of code. Board size of your thumb. 4 digit display size your
choice. After debug and coding finished you snap off right side of board and
use left side in solution.

Board is ~ $ 15.

As you can see in right hand windows most of chis resources left for other tasks, eg.
they are available for other functionality.

Ignore values of R's in image, base Rs ~ 1K and collector probably around 200 ohms would do.

To power you could use a 5V wall adapter with USB cable out and plug into board.


Regards, Dana.
 
Last edited:

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The missing link here is the exact display type.
If it has four independent digits with connections to each segment of each digit, you can treat it as four identical circuits. The switch outputs going to the segments, through decoders if necessary.

If the display is multiplexed, meaning the segments of all the digits are wired in parallel, you have to send the segment information for each digit in a sequence, only allowing current to flow through the common pin of the digit at the same time as that digit's segments are being driven. It needs far fewer connections but the driver circuit is a little more complicated. It is still fairly easy to do without an MCU.

Brian.
 
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Hey Brian, been a long time!

“If the display is multiplexed, meaning the segments of all the digits are wired in parallel, you have to send the segment information for each digit in a sequence, only allowing current to flow through the common pin of the digit at the same time as that digit's segments are being driven. It needs far fewer connections but the driver circuit is a little more complicated. It is still fairly easy to do without an MCU.”


This is how I want to do it-without an MCU.

What components would I need in between the thumb wheel switch and display? Can I incorporate the 4511, or is a different decoder required?
 

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