Help with down counter

Hi guys, I was wondering if anyone could help me with a project I was planning on trying. I've had a look in some threads and I think some of the ways described could work for me...but so far all I know about electronics is from doing a gcse and AS level course, and what I do know is confined to very specific ways. So I'm hoping I can do this using parts I'm familiar with even if it's a roundabout way of working.
Right the project; I want to build a circuit that will count down and display the numbers on 3 seven segment displays. The only way I know how to count down is by using D-type flip-flops connected together, but I'm not sure how to set the number they count down from, can it be done by "entering" the number you want using the set pins? The largest number I would want to count down from would be 300, so I think I would need 9 D-types. The part I'm not sure about is using these to drive a seven segment display, we have been told about a 4511 IC although I think this can only drive one display and I can't figure out how to connect them together. I don't think connecting several D-types to each 4511 will work? This seems a lot more complicated than it needs to be but if I don't want to get confused with new parts.
Thanks for any help.

You can use an UP/DOWN counter (4510) **broken link removed**
coupled with a BCD to 7 seg (4511)

Thanks thats a good site. So 3x (4510), 3x (4511) and 3x 7 segment displays will do it? Thats great, thanks very much

Still haven't got around to making this circuit, but I have drawn the counting bit out. Just realised that I've missed out the UP/DN pin connections, should be shown connected to 0V. I'm not sure about how to set the number it should be counting down from, could someone explain it please? I presume the intputs on the 4510 are used. Also its not essential but is there an easy way to quickly switch between different numbers to count down from?

My circuit (basicly copied from that site so hopefully its ok): **broken link removed**

use the load inputs (in BCD) to set a number you want to count down from, you will also have to use the load input , maybe connected to the reset line haven't checked the specs

For a down count, pin 10 (U/D) of the 4510 must be held low, according to the data sheet.

AllVol

Yup, I missed out pin 10 to 0V.
Ok thanks, and is there an easy way of entering BCD to the inputs in a way that could be changed quickly? Doesn't matter if there isn't. I'm guessing this would all be a lot easier with a PIC but I haven't learned anything at all about those yet.

Much easier, less hardware, provided you can write the software and program it into the chip. Plenty of pins left over for 'set' switches and for the "down count" switch input.

Good luck. Have fun. Regards, Mike

<added>

The 1-chip Charlieplexed solution is more a 'novelty'. The 2-chip multiplexed solution, or 1-chip with segment driver transistors, uses more PIC pins but provides a much brighter display.

yup it could be done easy with a PIC and a LED driver from maxim. Anything up to the PIC12XXX serie would be enough depending how many i/o you need.

Could also be a bigger PIC without any extra Driver, no multiplexing and plah plah.

MikeK8LH:

Charlieplexed? I like it .. I have done that, just did not know Charlie beat me to the naming rights.


A pic 12F509, does maxim have a serial LED driver?

max6955 is commonly use by me. I2C bus, pretty straightforward to use, can even scan a Keypad for you. Really nice

Maxim have plenty of those LED drivers, the one i suggested is probably too big for this application...
**broken link removed**

Even if doing multiplexing is not a big tedious job, those driver make life simple, no worries to have about the refresh, and so on

mramos1 said:

A pic 12F509, does maxim have a serial LED driver?

Click to expand...

They've got a whole bunch of 3-pin and 4-pin serial interface LED drivers. A popular old 8-digit 7-segment display driver in a 24-pin package was the MAX7219/MAX7221.

Probably more to the point of this thread would be some of their (Maxim) 4-digit up/down counter chips with built-in 4-digit 7-segment display drivers.

Mike

Those are pretty nice. If he ends up with a pic, the 16F628A would have enough IO line to not need the Maxim chip though. Going to check the Maxim chips out.

Mike said:

Probably more to the point of this thread would be some of their (Maxim) 4-digit up/down counter chips with built-in 4-digit 7-segment display drivers.

Click to expand...

Are these ones still a type of PIC? I would have no idea how to program one, even if it is an easier way.

Hi Psycho',

Sorry for the late reply. The Maxim ICM7217A is not a PIC but kind of a hybrid of four 4510s and four 4511s all in a single package. It directly drives the display segments (no resistors) and common cathodes (no trasistors). Here's one of the application examples from the Data Sheet which shows Thumbwheel switches to load the counter as well as an Up/Down switch, a Load Counter switch, etc. Pretty much a single chip solution.

Have fun. Kind regards, Mike

Yes, I used one of these in my Amiga days as a floppy drive track display, so I could see where the "problem" tracks were. Very easy to use but not what the initial request was intimating at.

Paul Obrien said:

Yes, I used one of these in my Amiga days as a floppy drive track display, so I could see where the "problem" tracks were. Very easy to use but not what the initial request was intimating at.

Click to expand...

Paul,

He asked about them (the Maxim 4-digit counter chips) just a couple posts back Sir.

Regards, Mike

So sorry, you get used to these posts being about home work that when someone really does want a simple circuit.......

Mike said:

Hi Psycho',

Sorry for the late reply. The Maxim ICM7217A is not a PIC but kind of a hybrid of four 4510s and four 4511s all in a single package. It directly drives the display segments (no resistors) and common cathodes (no trasistors). Here's one of the application examples from the Data Sheet which shows Thumbwheel switches to load the counter as well as an Up/Down switch, a Load Counter switch, etc. Pretty much a single chip solution.

Have fun. Kind regards, Mike

Click to expand...

Thanks that looks great! Yeh its not what I asked about originally but I didn't think I would be able to cope with much more lol, this should be ok for me. Not actually homework in this case, I didn't know about this forum when I was doing my AS ...less than a month until results day, hope I did good in electronics, want to take it next year too.
Anyway thanks again for all the help guys

EDIT: Ok, I was just having a look on that link to the Maxim site, I can't see a "M7217A" listed on that page? Also I typed "M7217A" and "MAX7217A" in the search bar but got 0 results. Am I using the wrong name for it?

Psycho_Raptor said:

Thanks that looks great! Yeh its not what I asked about originally but I didn't think I would be able to cope with much more lol, this should be ok for me. Not actually homework in this case, I didn't know about this forum when I was doing my AS ...less than a month until results day, hope I did good in electronics, want to take it next year too.
Anyway thanks again for all the help guys

EDIT: Ok, I was just having a look on that link to the Maxim site, I can't see a "M7217A" listed on that page? Also I typed "M7217A" and "MAX7217A" in the search bar but got 0 results. Am I using the wrong name for it?

Click to expand...

The part number is ICM7217A. The datasheet is here.