# Single 7 segment display for 0-9 and hexidecimal from 4 bit input

#### Jack Bourne

Joined Apr 30, 2008
39
Hi, I have been trying to get to the most simplest version of the logic gates for a 7segment display and I wondered if you have he most simplified version.

#### Wendy

Joined Mar 24, 2008
22,155
Just for clarification, you want 0-9,A-F. Right?

I've done a quick search, and couldn't find anything but BCD versions, which is 0-9. I may be mistaken, but if you want the extra digits you'll probably have to come up with a wired decoder. If I am wrong I'd like to see the chip used myself.

This might be a good application for one of 16 multiplexers, 7 of them, one for each segment.

#### hgmjr

Joined Jan 28, 2005
9,029
You could use an EPROM programmed to produce the 7-segment output of your choosing based on the 4-bits at the input.

hgmjr

#### hgmjr

Joined Jan 28, 2005
9,029
Or a PAL if you like.

hgmjr

#### Wendy

Joined Mar 24, 2008
22,155
Dang, can't find those chips either, although it could be done with 2 1to8 multiplexers in pairs. That would be a bad chip count, I figure around 15 chips total.

Another way is a 1 to 16 decoder and a diode matrix, one chip and many diodes, with drivers.

#### Wendy

Joined Mar 24, 2008
22,155
The PROM or EEPROM would be the more elegant solution though a lot harder to implement unless you have the hardware, or a friend to has the hardware. The diode matrix is an older method, a trade off between parts count and work.

The other method is to use an existing BCD decoder, and add the extra 6 decoded outputs, but I suspect this could get rather hairy quick.

#### bertus

Joined Apr 5, 2008
20,650
Hello,

The only things I could find are the 74C917, a 6 digit hex decoder.
Or a TIL311, this is a hex decoder with buildin display.

Greetings,
Bertus

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#### Wendy

Joined Mar 24, 2008
22,155
I like it. Works for me.

#### beenthere

Joined Apr 20, 2004
15,819
Wit until you see the price for a TIL3xx chip.

#### milkisgood

Joined May 4, 2008
6
Just get a 7-segment decoder and a few logic gates for the input.

Draw a truth table, create an equivalent boolean expression (multisim will do this for you if you have it) and convert to simple and inexpensive NAND gate equivalent circuit.

#### Wendy

Joined Mar 24, 2008
22,155
$20 at JameCo for the TIL311, what did you find? Still haven't found the 74C917 yet, which is the better option if it exists. #### SgtWookie Joined Jul 17, 2007 22,210 I had no idea the TIL311's were that expensive. I think one of my local suppliers has a number of them in a bargain bin. Might have to take a look tomorrow. #### Wendy Joined Mar 24, 2008 22,155 Well, while I was factually truthful, they do have some quantity discounts. Not sure I would want to buy them though. One thing is for sure, whatever the end result is if it is a decoder circuit you'll probably want to multiplex to reduce parts count. Last edited: #### SgtWookie Joined Jul 17, 2007 22,210 Yeah, that's better.$4.25 @ Jameco.
Kind of overkill to drive a single display though.
Seems like an ideal application for a uC, perhaps a PIC.

#### Jack Bourne

Joined Apr 30, 2008
39
Just get a 7-segment decoder and a few logic gates for the input.

Draw a truth table, create an equivalent boolean expression (multisim will do this for you if you have it) and convert to simple and inexpensive NAND gate equivalent circuit.
Sorry If I didnt describe it but I wanted to create the 0-9 A-F driver with logic gates.

What feature is it called on multisim? I have got version 10 professional today as I neeeded simultor.

#### Wendy

Joined Mar 24, 2008
22,155
If you want to use logic gates there really isn't a minimum number. One of the reasons everyone was looking for a decoder is this was the kind of job chips were designed for. You'll just have to create a truth table for each segment and work it through. I can guarantee the count will be high though. really high.

#### SgtWookie

Joined Jul 17, 2007
22,210
If you want a head start on it, look up a datasheet for a Texas Instruments' SN74L47, a BCD to Seven Segment Decoder/Driver. There are actually several other IC's described in there which perform basically the same function.

There are 31 gates and 10 inverters in that IC. That's just for BCD. You'll still have to go A through F.

That TIL311 looks better all the time

#### Wendy

Joined Mar 24, 2008
22,155
Actually I liked the Maxum decoder. Might seem a waste, but it is relatively cheap and does the job in one chip, what more could you ask? I could see the need for a Hex display chip very easily. I learned a long time ago that you never use all the functions, just what you need.

#### Papabravo

Joined Feb 24, 2006
14,205
It should be straight forward to use seven 16:1 multiplexers to do the job.