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Double digit numeric displays

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 10 November, 2010 » Double digit numeric displays « Previous Next »

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michelleobrien
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Posted on Sunday, 31 October, 2010 - 10:31 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

If I buy a cheapo double digit numeric display -
for example this one -

http://www.maplin.co.uk/Module.aspx?ModuleNo=2166&OrderCode=BY66W#spec

- and connect the pins (a b c d e f g decimal
point common anode or cathode) up to a BCD ("1"
"2" "4" "8") generating device via a BCD-to-seven-
segment driver using appropriate resistors ...

... WILL THE DOUBLE DIGIT DISPLAY device then
happily be able to register a decimal count of
0 to 15 without more ado?

Or is more circuitry required to enable the
double digit display device to display accurately
the decimal readout when the count goes above 9,
ie 10 to 15?
Is smoke supposed to be coming out of that?
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joe
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Posted on Sunday, 31 October, 2010 - 11:40 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Probably not :-(

That display only has one set of segment drive pins (a-g) and two commons; one for each digit. It's possible, but probably more effort than it's worth. You would do better with two seperate 1 digit displays if your not going to be using a CPU or special display driver chip.
Have a read on multiplexed displays for more info.

As for what gets displayed when you reach 10, that depends on the BCD decoder used.
Its quite possible to display A - F on a standard 7 segment display, but most of the common decoders like the 7447 start displaying strange patterns from 10 onwards.

Joe
Read my ramblings - www.techbites.com/joe-farr
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michelleobrien
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Posted on Sunday, 31 October, 2010 - 01:00 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Joe. As I suspected - not so easy.

So at the risk of trying your patience, how would
one set about using two separate 1 digit displays
to handle a complete 0 to 15 decimal readout
from one single BCD "1" "2" "4" "8" input, for
example a simple 16-button keyboard encoder? (no
CPU or special display driver chip involved.)

Would it require the inclusion of some kind of
counter in the circuit in order to bring into
action the second seven-segment display (the one
assigned to display the figure 1 in counts above
9, ie. 10 to 15)?

Or is there a simpler solution?

(Message edited by MichelleOBrien on 31 October, 2010)
Is smoke supposed to be coming out of that thing?
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joe
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Posted on Sunday, 31 October, 2010 - 01:13 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Well... the million dollar question is:

Do you want to count in decimal from 00 to 99, or Hex from 00 to FF (255) ?

If you want to count in decimal then its a piece of cake.

2 x 7490's connected together to form a decimal counter will do the counting. Connect their outputs to 2 x 7447's and for each pulse applied to the counter, the display will increment.
I can find you a circuit for that.

If you want to count in HEX, AND you want to see 0-F then it gets a whole lot harder. Whilst the 7447 BCD decoders will count to 15, they display strange symbols for A to F. I'll have to have a look around to see what's available for A to F display.

Which do you need ?
Read my ramblings - www.techbites.com/joe-farr
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michelleobrien
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Posted on Sunday, 31 October, 2010 - 01:23 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The piece of cake option, please - count in decimal.
Is smoke supposed to be coming out of that thing?
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bruce
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Posted on Sunday, 31 October, 2010 - 02:11 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Decimal?
Count to ten.
For those who cant count to ten, count to five twice.

HTH
Bruce
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joe
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Posted on Sunday, 31 October, 2010 - 02:37 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Have a look at this:
http://www.angelfire.com/electronic/beausalector/7segmentcounter.html

This is a nice circuit (it's design, not how it's been drawn) because it only needs 1 IC per digit, and you could have from 1 to 1000 digits as needed.

The 4026 IC’s used are dirt cheap from Rapid as well.
Datasheet for the IC is here:
http://www.rapidonline.com/netalogue/specs/83-0359.pdf

As a side point, you “may” want to avoid Maplin when shopping for electronics parts. They can be rather expensive and often have stock issues when you go in-store.
Read my ramblings - www.techbites.com/joe-farr
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michelleobrien
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Posted on Sunday, 31 October, 2010 - 04:04 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks, Joe, but I think we're at cross-purposes.
I don't want to count. I know how to do build a
simple counting circuit and how to get a readout
of the result in decimal.

Do you remember the 40114 COS/MOS 64-Bit Random
Access Memory chip you were kind enough to help
me with in the thread "Basic Electronics from
Another Age - 64-Bit Memory."

The four lines of data output from the 40114 are
in BCD "1" "2" "4" "8" form. The output data from
the 40114 can be anything from 0000 to 1111.

It depends entirely on what code has been entered
on what address line of the 40114 and what address
line is selected at any one time to get a data
output reading on the four data output lines.

What I want to do is to display that 0000 0001
0010 0011 etc. output from the 40114 in decimal
form, feeding the four-line BCD code from the
40114 output into BCD-to-7-segment drivers and
then feeding the a b c d e f g output from the
drivers into two seven-segment displays.

It doesn't involve counting, simply display.

It works fine of course for 0000 to 1001 (0 to 9
in decimal) using just one driver and one seven-
segment display.

But what I can't work out is how to display in
decimal output data from the 40114 on counts
between 1010 to 1111 (10 to 15 in decimal) using
BCD-to-seven-segment drivers and two seven-
segment displays.

Can it be done?
Is smoke supposed to be coming out of that thing?
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joe
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Posted on Sunday, 31 October, 2010 - 04:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

ahhh ok, sorry... Now I see what your trying to do.

Can it be done... yes... simply, not that I'm aware of.

The problem is that all the IC's I'm familier with, display silly patterns when showing values 10 to 15 (or don't display anything at all).

The simplest approch would be to get hold of a couple of TIL311 displays. These are fantastic as they are proper LED displays, but accept BCD data (you don't have to supply the signals for the seven segments) and display the correct value (0 - F) automatically. Problem is they are discontinued and whilst Ebay has them:
http://cgi.ebay.co.uk/X1-USED-TIL311-Red-Hexadecimal-Display-Binary-Address-/230543183800?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item35ad71cfb8

they are rather expensive @ £8 each, but, they don't need any external components and they look fantastic when there running.

It would be possible to construct a digit decode matrix using diodes, but it would need rather a lot of them, or, you could do the work using logic gates, but that would probably be more complex than using diodes.

What's needed is a way of selecting one of 16 patterns; an EPROM / PROM / EEPROM would be ideal for this and whilst a bit overkill in many ways, and you would also need one per digit, would actually be quite cheap.

The common approch these days would be to use a CPU of some type or one of the dedicated display devices (ie from Maxim), but again, they need a CPU to drive them.

Off the top of my head, I can't think of a simple and elegent way of doing this would a fair amount of electronics being involved.

Assuming that you don't fancy spending money on those TIL311 displays, the best solution may be the diodes. Basically, you have a 1 of 16 decoder (74150 for example), and you feed it your 4 bit BCD and it enables one of it's 16 outputs. You then use that output to light the correct segments on the LED display using dioded. It was a very common way of doing things in the "good old days".

I'll have a think, but perhaps somebody else has some ideas ?

Joe
Read my ramblings - www.techbites.com/joe-farr
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poplar10
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Posted on Sunday, 31 October, 2010 - 06:16 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Joe, would a TDA4092 be of use ? It's a 5-bit input to 2-digit output.

data sheet here:http://www.datasheetcatalog.org/datasheets/228/378388_DS.pdf

Costs around £8 here: http://www.awatronic.co.uk/prod_11744.html

John
Nothing's impossible, I have found ...
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michelleobrien
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Posted on Sunday, 31 October, 2010 - 06:25 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Joe, thank you so much. You're marvelous.

My cursor finger is itching to hit that ebay link.
Will the housekeeping budget this week stand a
£16 hit for two TIL311s?

Mind you, I do already have a 1-of-16 decoder
(a 4514) ...

But those TIL311s are so very attractive ...

Oh, decisions, decisions ... !

Thank you again, Joe, for letting me pick your brains.
Is smoke supposed to be coming out of that thing?
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joe
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Posted on Sunday, 31 October, 2010 - 06:50 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@John,

Those IC's look interesting but I don't think they will do the job. They are designed to accept a 5 bit input and only count from 1 to 32; they can't display 0 which is a shame.

@Michelle, your welcome.
If you decide not to blow the house-keeping then diodes are going to be your best option, unless I or anybody else can think of something better.
Your be needing two of those 1 of 16 decoders; one for each digit by the way.
Read my ramblings - www.techbites.com/joe-farr
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ianjoh
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Posted on Sunday, 31 October, 2010 - 10:35 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hold fire.
I think I have some TIL311's in my stock box if you are still in need. They were used in a hand held intercom system controller from my service engineer days.
I will have a look when the sun returns tomorrow.
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alec_t
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Posted on Sunday, 31 October, 2010 - 10:57 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

There's talk above about BCD output from the 40114. Surely the output is straight binary, not BCD?
Or am I missing something?

Alec
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michelleobrien
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Posted on Sunday, 31 October, 2010 - 11:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Whoops, you're quite right, Alec. The output of the
40114 is straight binary.

My incorrectly calling it BCD is down to nothing
more than a learner's ignorance of the correct
terminology.
Is smoke supposed to be coming out of that thing?
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atferrari
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Posted on Sunday, 31 October, 2010 - 11:34 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I will have a look when the sun returns tomorrow

A poetic way of saying tomorrow, Ian! Or, it is that there is no electric light available?
Agustín Tomás - Buenos Aires - Argentina
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terrym
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Posted on Monday, 01 November, 2010 - 02:12 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It seems you are not the only one trying to do this.

Check this forum, about halfway down there's 2 different solutions (so you don't have to count them, there are 88 diodes in the first one).

http://cr4.globalspec.com/thread/58452/Binary-to-2-digit-seven-segment-display?from_rss=1

TM
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michelleobrien
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Posted on Monday, 01 November, 2010 - 06:31 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@terrym

88 fiddly diodes? 88? That decides it - the housekeeping takes the hit.
Is smoke supposed to be coming out of that thing?
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joe
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Posted on Monday, 01 November, 2010 - 07:58 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@Alec,

Yes... and No...

4 bit binary can of course can represent the decimal numbers 0 to 15. When it's used to represent just 0 to 9, then it's BCD, but what happens to the other 6 binary values.

Most chip designers decided to either ignore these >9 binary patterns (sensible I suppose but a shame), or output some other patterns (and there is a reason for it but I can't remember what it is); anyway, I've personally never found these patterns usefull.

Most people experimenting with electronics / computers would have prefered A to F for these patterns, but it appears that the chip designers don't agree; except for Texas who decided that a complete solution on a chip/display was a great idea and designed the TIL311.

The diodes solution is actually worse than 88 as unless you do some additional electronics, then you need 2 lots of 88, one set per digit. I hadnt realised that it would be so many.

It amazes me that nobody came up with a suitable and commonly available solution for this. Computer builders have been using and displaying HEX for years.

Hum... that gives me an idea... wheres my breadboard.
Read my ramblings - www.techbites.com/joe-farr
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ianjoh
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Posted on Monday, 01 November, 2010 - 08:56 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Good news! I have a couple.
It is much easier to go from house to various sheds in daylight!
If you still want them pm me your address & I will pop them in the post.
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epithumia
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Posted on Monday, 01 November, 2010 - 09:10 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

As Joe pointed out, the 74LS47 decoder is perfectly usable so long as you don't mind it displaying weird (but unique) characters from 10 to 15.

If you're just experimenting, that may be good enough. I've used it that way myself.

image

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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michelleobrien
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Posted on Monday, 01 November, 2010 - 10:23 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@ ianjoh

Will do, Ian. Thank you very much indeed for your kind offer.
Is smoke supposed to be coming out of that thing?
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terrym
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Posted on Monday, 01 November, 2010 - 12:34 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Joe, that was 88 diodes total for both digits.

Solution was a 74ls154 multiplexer plus those diodes. Don't forget, one of those displays will only ever display the number "1".

The other solution was 2 x 4008, 2 x 74ls47 and a couple of gates from another 2 ic's = 6 ic solution.

TM
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joe
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Posted on Monday, 01 November, 2010 - 12:54 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@TM,

I just wrote the text below, then went back over the posts and realised something; those memories Michelle's using, are of course FOUR bits, not eight. For some brain-fart of a reason, I'd assumed they were eight bit; probably because the memories I'm currently using are 8... or I'm getting old... or both.


--------
Original text:

But as it stands, the most that circuit can count to is 16 using two displays.

To display 8 bits you would either need two of those circuits (but that would be silly as it would actually need 4 digits and show 1515 for the value 255), or you would need to add additional diodes to correctly decode values 11 to 15, so that the one digit can display the characters A to F. I think that works out at 78 diodes per digit and you would need two digits to get to 255 (FF).

Joe
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bruce
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Posted on Monday, 01 November, 2010 - 12:59 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Wouldnt it be easier just to buy her a new mop?

Bruce


( I mentioned the war, once, but I think I got away with it )
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epithumia
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Posted on Monday, 01 November, 2010 - 01:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Not funny.

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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kevinbrunt
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Posted on Monday, 01 November, 2010 - 04:33 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I think Bruce has just been given a double digit display (and not the Churchill way round)....
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bruce
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Posted on Tuesday, 02 November, 2010 - 09:28 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello guys,
Now, I hate to judge before all the facts are in, but I think I may have scored an own goal.
It isnt true to say that the joke wasnt funny, or even that it was funny: it depends. Frankie Boyle ( who, IMO, should be canonised ) makes some outrageously cruel jokes, and they are very funny. But he's on a stage in front of an audience. By making said remark on an anonymous forum it risked crossing that fuzzy grey line between humour and abuse. It's all about context.
Now, while I dont mind a jot about upsetting religious believers ( except the Druids, BTW, I reckon they have the right idea ), the Pope, the Monarchy or Diane Abbot, all who richly deserve it, poor Michelle was what we call in the trade "collateral damage". Anyway, I have made my peace with the Lady and, like James Bond, I shall choose my next witticism with care.
I understand that I could get myself rudely ejected from this forum, which would be a pity, because you'll miss me when I'm gone.

Bruce
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alec_t
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Posted on Tuesday, 02 November, 2010 - 11:15 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The tricky bit seems to be getting the binary from the 40114 into BCD format. Once you've done that, going from BCD to 7-seg should be a doddle as chips for that are still available. Check out
http://answers.yahoo.com/question/index?qid=20090717043022AA6t1mC
Looks like others have had the same problem.

Regards, Alec
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joe
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Posted on Tuesday, 02 November, 2010 - 12:18 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Getting the data from true BCD into decimal is actually quite simple; just program an 8 bit PROM/EPROM/EEPROM to do the decoding.

The value out of the memory(s) provides the address into the PROM on the first 4(8) address lines, and the BCD value is presented on the 8 data pins; these 8 pins drive 1 or 2 x 7447 BCD to LED decoders for example.
It would just be a matter of working out the correct patterns to program.

Each PROM would then support decimal values 0 to 99

Farnell for example have 64K EEPROMS for 1.86 till they run out of stock. Rather overkill in size but they are cheap.

Problem is most people don't have the equipment to program the PROMS.
Read my ramblings - www.techbites.com/joe-farr
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kevinbrunt
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Posted on Tuesday, 02 November, 2010 - 01:07 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

If you're going for programmable, Farnell are selling one variety of the PIC16F54 for 57p.
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ianjoh
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Posted on Tuesday, 02 November, 2010 - 09:44 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Using an eprom or eeprom is a great idea, these are very much underated and underused as logic coders.
I have seen these used a few times in simple DTMF decoders and can make an AND gate as wide as the address lines.
These are simple to program manually if a programmer is not available by setting the address and data lines as required and then pulsing the program pin.
They can be erased in a uv exposure box?
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bruce
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Posted on Tuesday, 02 November, 2010 - 10:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Duh!
I had a look into using eeproms in the 1980s, IIRC.
It was technically possible to do it using a computer, but, of course, in those days you had to be able to program in DOS and God knows what else and build this circuit which had all the simplicity of a motherboard. The alternative was doing manually. It's like watching paint dry. For every location you program, you have to flick a load of switches, and, if you do drop a digit, you dont know until it's too late and have to start all over again. Maybe the technology has moved on
Still, rather you than me.
But dont let that put you off.
Was that a question about erasing?
If so, then that's the easy bit. Virtually any UV source will wipe it although some may take longer than others.

Bruce
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atferrari
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Posted on Tuesday, 02 November, 2010 - 10:42 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

They are for UV erasing is there is a window for it.

Otherwise they are, most probably, EEPROMs, electrically-erasable, isn't it?

If I am stating the obvious, sorry!
Agustín Tomás - Buenos Aires - Argentina
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bruce
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Posted on Tuesday, 02 November, 2010 - 11:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Yes, you can only use UV if they have a little window. I'd forgotten about the EEPROMs. Mind you, how can you tell if it's an EEPROM and not one of those OTP ones?

Bruce
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joe
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Posted on Wednesday, 03 November, 2010 - 06:49 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@Bruce,

Probably by the dirty great big part number stamped on it :-)
Read my ramblings - www.techbites.com/joe-farr
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azayles
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Posted on Wednesday, 03 November, 2010 - 02:52 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The data sheet shows that those dual displays have two common pins, one for each display. They're electrically the same as two single displays in that regard. A BCD to seven segment chip should work proving it's capable of driving two displays, unless you can use two chips and use a "carry out" pin, if the chip has one.
Actually you wouldn't even need the extra chip, just tie the carry out pin to the two segments of the leftmost display to make the "1"
Keeping the Magic Smoke in since 1978
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bruce
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Posted on Wednesday, 03 November, 2010 - 03:02 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Joe:
harsh, but fair!
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joe
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Posted on Wednesday, 03 November, 2010 - 03:19 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@azayles,

Using the carry out pins could be an interesting idea. Which BCD decoder were you thinking of ?

Joe
Read my ramblings - www.techbites.com/joe-farr
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azayles
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Posted on Wednesday, 03 November, 2010 - 03:25 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@joe

I wasn't thinking of any BCD decoder in particular, I've not used to them myself in quite a number of years, but I vaguely recall at least one chip having a carry in and carry out pin so that the appropriate segments for each display were lit for a given BCD/Binary digit grouping.
Keeping the Magic Smoke in since 1978
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joe
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Posted on Wednesday, 03 November, 2010 - 03:32 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@azayles,

I'd love to know which decoder you used... none of the standard ones I've played with have this feature; which would have been rather useful :-(

Joe
Read my ramblings - www.techbites.com/joe-farr
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azayles
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Posted on Wednesday, 03 November, 2010 - 03:56 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Probably a long obsolete one, unless I'm actually mistaken. I tried to find a reference to the chip in my old electronics book and came across the 7447, but no mention of a carry out feature. Maybe I was thinking of the Binary to seven segment decoder which decodes 0-9 and A-F. But I don't know if this has a carry out, either.
Keeping the Magic Smoke in since 1978
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joe
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Posted on Wednesday, 03 November, 2010 - 04:02 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@azayles,

Probably not much point with a carry out on a binary to HEX decoder as you need all 4 bits to get from 0 to F. The 7447 would have been an ideal candicate for a carry out but I guess the chaps at Texas etc, knew best :-(
Read my ramblings - www.techbites.com/joe-farr
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azayles
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Posted on Wednesday, 03 November, 2010 - 04:15 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@joe

Oh oops! Good point!
And indeed. Seems odd they'd leave out a carry out pin. Can't have saved them THAT much money not implementing it?
Keeping the Magic Smoke in since 1978
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kevinbrunt
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Posted on Wednesday, 03 November, 2010 - 04:16 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

What a BCD-to-7segment decoder *would* have is not carry pins, but ripple-blanking pins, to suppress leading zeroes.
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azayles
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Posted on Wednesday, 03 November, 2010 - 04:20 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I saw the ripple blanking input/output pins on the 7447 chip diagram in my book (Digital Electronics - A Practical Approach. Third Edition by William Kleitz. ISBN 0-13-210287-0) so this may have been the source of my confusion.
Keeping the Magic Smoke in since 1978
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alec_t
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Posted on Saturday, 06 November, 2010 - 12:33 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

If the source data is 4-bit, it can represent 0-15 in binary but only 0-9 in BCD format: we need 5 bits to represent 0-15 in BCD.
So, to convert a number in binary to BCD to meet Michelle's display requirements we start with old bits b3,b2,b1,b0 and we need new bits nb4,nb3,nb2,nb1,nb0. The logic is:-

nb4 = b3 AND (b2 OR b1).
IF nb4 = 1 [i.e the number is > 9] THEN (nb3=0, nb2=b2 AND b1, nb1= NOT b1, nb0=b0).

Forget about 88 diodes; this logic can be done using just 1 OR gate, 2 AND gates and 1 inverter. In practice, the OR/AND/inverter functions could be implemented using 2 quad NAND chips.
b3...b0 provide one set of input bits to a quad 2-input multiplexer (74157); nb3...nb0 provide the other set.
nb4 is used to control the MPX to select either set and to drive two segments of the 'tens' digit directly to display '1' for numbers > 9. MPX output bits 3...0 drive a BCD-to-7-seg decoder for the 'units' digit.

HTH,
Regards, Alec
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magnum4
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Posted on Saturday, 06 November, 2010 - 01:17 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Guys,
Why wouldnt this work?

"BCD" is input lower 3 bits to IC2 and upper bit to Ic1. I have not tried this Michelle, But I think it would work? Open to the table :-)
BCD2DEC
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Jim
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joe
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Posted on Saturday, 06 November, 2010 - 01:25 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@Jim,

Your only supplying 3 bits (A, B & C) to IC2 (which is the Units digit). The maximum value that could be displayed on that display is seven.

What about digits 8 and 9 ?

I think you've managed to create an Octal display :-)
Read my ramblings - www.techbites.com/joe-farr
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magnum4
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Posted on Saturday, 06 November, 2010 - 01:25 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Scrap that. The 3 bits Of course will only display 0to 8 . Should think before opening mouth Lol Sorry
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Jim
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magnum4
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Posted on Saturday, 06 November, 2010 - 01:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Lol Beat me to it Joe :-)
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Jim
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epithumia
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Posted on Saturday, 06 November, 2010 - 02:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Here's another way of implementing Alec's suggestion.

Instead of using logic to calculate the new bits, I've used an adder. Add 6 is the same as subtract 10 if you ignore the carry.

7483 was my first thought, but I couldn't find any for sale so substituted 74HC283.

Epi


(Message edited by Epithumia on 06 November, 2010)
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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epithumia
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Posted on Saturday, 06 November, 2010 - 02:24 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hmm, it didn't prompt me for the upload. Try again..

myimage

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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alec_t
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Posted on Saturday, 06 November, 2010 - 05:00 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Yup. That's tidier (1 chip less). I see you've used NORs instead of NANDs to implement the 'tens' logic. I like the use of the adder for the 'units' part.

Alec
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alec_t
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Posted on Saturday, 06 November, 2010 - 09:24 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

....unfortunately the 74HC283 adder also seems to be obsolete. I've Googled around and can't find it listed by the usual suppliers (Farnell, Maplins, Rapid etc).

Alec
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azayles
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Posted on Saturday, 06 November, 2010 - 11:08 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I've had a good hunt around, and there doesn't seem to be a good single chip (or even two chip) solution anywhere on the whole internetweb.

Could you burn off a cheap FPGA or EPROM with your 4 bytes of data feeding the address lines, and the data lines feeding the display segments?
Keeping the Magic Smoke in since 1978
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ianjoh
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Posted on Saturday, 06 November, 2010 - 11:26 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

You are all making this too complicated
I am going to stick with the sheer simplicity of using a 2716 eprom to convert the data and drive two cd4511 diplay drivers, I have chosen these as ICs as I have them to hand to try.

Address a0 to a3 hex data
Data lines d0 to d3 drives the 1's digits
Data lines d4 to d7 drives the 10's digits
I will program the eprom with the following

adr data
00 f0
01 f1
02 f2
03 f3
04 f4
05 f5
06 f6
07 f7
08 f8
09 f9
0a 10
0b 11
0c 12
0d 13
0e 14
0d 15

the 'f' in the data will cause the 10s display to blank up to the value 9 (according to the data sheet).
Just need a little time to do a circuit diagram and build it....
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epithumia
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Posted on Sunday, 07 November, 2010 - 09:36 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Alec, 74HC283 is available at Farnell:

Order code 1750337, 17 in stock, 36p.

http://uk.farnell.com/texas-instruments/cd74hc283e/logic-4bit-binary-full-adder-16dip/dp/1750337

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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joe
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Posted on Sunday, 07 November, 2010 - 10:00 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@ianjon,

Whilst using a PROM of sometype has already been discussed, I'm not sure how using an EPROM makes this simpler than say, Alec's or Epi's solution.

For one thing, your EPROM is going to need to be programmed, something that many constructors don't have the equipment for, and EPROMS's ain't cheap, well, not as cheap as a couple of 74's, anyway.

However, if you did want to use an PROM, then why do you need the 4511's ?

If you use EPROM data bits 0 to 6, to drive segments "a" to "f" direct on the units digit, and data bit 7 drives both segments "b" and "c" on the tens digit, wouldn't that work ?

If you wanted to save a complete LED digit, you could re-program your PROM to display HEX on the one display.
Read my ramblings - www.techbites.com/joe-farr
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alec_t
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Posted on Sunday, 07 November, 2010 - 10:38 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@Epi
I stand corrected. I thought Google would have picked up that. Should have checked the Farnell site directly.

@Joe
Agreed. And as a simple alternative (but not so pretty), use a single digit display for the units, with its decimal point representing 'ten'.

Alec
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epithumia
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Posted on Sunday, 07 November, 2010 - 01:50 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Of course, the sad thing is that these days it's easier for many to use a PIC... decoding, driving and these days even the oscillator on one chip.

I have an EEPROM programmer somewhere, but I doubt it works with my current PC. If I wanted to use an EEPROM, the first things I'd have to do would be build an EEPROM programmer.

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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azayles
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Posted on Sunday, 07 November, 2010 - 02:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

And of course then you'll need a programmed EEPROM for your EEPROM programmer.
So begineth the vicious circle of woe.
Keeping the Magic Smoke in since 1978
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azayles
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Posted on Sunday, 07 November, 2010 - 06:05 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Seems I can't edit my last post, so I'll have to double-post. Sorry :-(

But I found this set of TIL311's listed on ebay for cheaper than two of the originally posted ones.

http://cgi.ebay.co.uk/Set-2-TIL311-Hex-LED-Display-COSMAC-Elf-Xlnt-Pulls-/330487880944?pt=LH_DefaultDomain_0&hash=item4cf29cdcf0
Keeping the Magic Smoke in since 1978
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ianjoh
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Posted on Tuesday, 09 November, 2010 - 10:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@ Joe
Apologies for the rather slow response.
Yes, you could use the prom to drive the display directly but it would need to be buffered to provide the current drive, therefore you are still no better off on the chip count.
I dont think the OP was particularly concerned for the cost to be absolute minimum.
As there are only 16 line of code to program I dont think a programmer is necessary as a one off, a couple of resistor networks, 2 banks of dip switches and a push-to-make would do as a programmer.
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joe
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Posted on Wednesday, 10 November, 2010 - 07:17 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

"a couple of resistor networks, 2 banks of dip switches and a push-to-make would do as a programmer."

aka... a PROM programmer.

Of course, you've neglected to mention the trickier bits of EPROM programming.
Depening on the IC make, you need 25v from somewhere as well as the 5v.
Also, there’s a minimum and maximum program pulse width (45 to 55ms) to be supplied else you risk damaging the EPROM.

As for driving LED's directly from EPROMS, I personally never had any problems and my first Christmas flasher (which by any standards was rather pathetic with only 16 red LEDs) did rather well for the two years I used it on my tiny 6” tree in my bedroom.

If you felt the need to add buffering I would go with a 74245; cheaper, and one less IC.

But that’s just me.
Read my ramblings - www.techbites.com/joe-farr
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michelleobrien
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Posted on Wednesday, 10 November, 2010 - 10:10 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

As a humble hobbyist with only a basic grasp of
electronics I am genuinely astounded ...

... all this ingenuity to get the tens digit 1 to
show in a double-digit numeric display in decimal
on counts 10 to 15 when translated from a four-bit
straight binary original in systems where no
counting is involved?

It's amazing. It feels like I've opened a
Pandora's Box.
Is smoke supposed to be coming out of it like that?
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joe
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Posted on Wednesday, 10 November, 2010 - 11:22 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Michelle,

I think this is the nature of electronics. Everybody has their own way of doing things, prefered technology they are comfortable with etc especially when there is no simple, single chip solution.

For example, few people would argue against using a MAX232 or one of it's relatives for serial to TTL conversion. It's an industry standard.

However, in reality, whilst this BCD problem "should" be such a simple thing todo, it's actually quite complex.

We count in decimal (frequency counters, clocks) etc and there are chips available that will do that. But to display random data in decimal dosnt seem to be as common.

Engineers connecting your 4-bit memory to a dipslay for example, would almost always opt for hexadecimal as it saves a display digit and so cost. Older systems would have used octal but that's still a single digit. Even with HEX, there are few solutions available that will do that in an appealing way unless you start looking at dedicated display drivers or CPUs.

For me, it's all part of the fun, and anyway, it's kept people amused on the CZ :-)
Read my ramblings - www.techbites.com/joe-farr

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