Decimal to seven segment conversion...

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Externet
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Decimal to seven segment conversion...

Post by Externet » Fri Oct 12, 2012 8:36 am

Hi fellows.
I was after this elusive chip a long time ago, and the need resurfaced again.
Originally, I wanted the ten output lines of a LM3914 bar display to show instead, numerically on a seven segment display.

It is NOT about binary converted to decimal. Am looking for a chip with TEN inputs to seven segment outputs.
Like from a rotary ten position switch producing the digits 0 to 9 on a seven segment led display.

Edited: The known alternative is to use a 10 position switch with BCD output into a 4511 IC to the display,
or take the long route :sad: from ten position switch to a 40147 IC to a 4511 IC to the display.
Miguel
- Abolish the deciBel ! -

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haklesup
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Re: Decimal to seven segment conversion...

Post by haklesup » Fri Oct 12, 2012 12:31 pm

it can be done with multiple chips, first you need a 16 to 4 line decoder (you can ignore some of the inputs) and then a binary to 7 segment decoder chip. Do you need features like reset, clear, clock or counter like functions?, you may need to add some flip flops to handle that.

I don't recall ever seeing a single chip solution for this unless you want to program a microcontroller, they could handle it, you just need one with 17 or more I/O pins and not much memory, that would be the modern solution

Alternatively you can design the whole thing with only nand gates using standard logic design techniques.

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Re: Decimal to seven segment conversion...

Post by Lenp » Mon Oct 22, 2012 8:21 am

If you just want to to display 0-9 on a 7 segment display from a 10 input source, like a rotary switch, or buffered logic, why not consider a diode matrix?
10 inputs to 7 outputs and the diodes map the coding. 0=a,b,c,d,e,f ... 1=e,f ... 2=a,b,d,e,g /.... 8=a,b,c,d,e,f,g
The diode polarity depends on if its a common anode or cathode display, and, don't forget dropping resistors for the segments.
It's not elegant or high tech, but it does work!
Len
Len

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Externet
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Re: Decimal to seven segment conversion...

Post by Externet » Mon Oct 22, 2012 8:30 am

Of course, Len, that is correct... When you have to build one, not several dozens.

I wonder if such diode matrix already exists in a chip form, capable of 50-100+ mA
Miguel
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Lenp
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Re: Decimal to seven segment conversion...

Post by Lenp » Mon Oct 22, 2012 8:47 am

I guess if you don't want to use the 16x4 then 4x7 setup with 2 chips and the matrix is too cumbersome then a processor is what's left.
Can you bundle other functions into the processor to make it more cost effective?
Len
Len

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Re: Decimal to seven segment conversion...

Post by Dean Huster » Fri Oct 26, 2012 6:14 pm

The 74154 essentially does what a diode matrix would do and in the same amount of space even though it is a 24-pin chip on 0.6 row centers. I don't know if there's a CMOS version and if so, is probably small so you'd have to cascade a couple. Another option that might take up even more space is to program a couple of EPROMs to do more expensively and with more hassle that the '154 16-4 demux would do.
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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Lenp
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Re: Decimal to seven segment conversion...

Post by Lenp » Sat Oct 27, 2012 9:32 am

Hi Dean,

Isn't the 74154 a BCD encoder? I have the impression the OP wants 10 inputs translated to 7 segment coded outputs?
Should that have been a 74147, a DEC to BIN encoder?

The lash up could be the 74147 feeding the 7446 7 segment drive to the display

If I missed it, let me know!

Len
Len

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Re: Decimal to seven segment conversion...

Post by Robert Reed » Sat Oct 27, 2012 5:15 pm

Exter

Take a look at the CD4026 and see if that will work in your plan.

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Externet
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Re: Decimal to seven segment conversion...

Post by Externet » Sat Oct 27, 2012 6:27 pm

Very good suggestion, Robert. That chip opens up other perhaps better ways to do it !

Thanks !
Miguel
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Re: Decimal to seven segment conversion...

Post by Gorgon » Tue Oct 30, 2012 6:02 am

If you have found your solution, good.
If not, I will come back with my old idea of using some old eproms if you got them. A 2716 2k eprom would do what you need if programmed correctly. The address lines are the inputs(10(11)) and the data lines the outputs(8). So if you have some 2716 or higher laying around, use them as programmable logic. :mrgreen:
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

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