BCD counter for seconds????

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Hi all,

I want to make a clock timer for a basketball scoreboard that counts down.

I was thinking of using a BCD counter such as the CMOS 4510 but I notice
that the "carry out" pin goes high only on the ninth number.

I want to count down in minutes, so I need a way to trigger the next BCD
after 60 seconds, not 99 seconds. Know what I mean?

For instance when there is five minutes left, it counts down to 4 minutes
and 59 seconds, and so on...... The 4510 would incorrectly show 4 minutes
and 99 seconds....

Is there a better alternative to the 4510 that is designed to count down in
the 60 seconds "time" format?


Re: BCD counter for seconds????

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look for a programmable counter and use he carry (and underflow) events to
load it with 5

or just use a microcontroller...

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Re: BCD counter for seconds????

I would suggest using a microcontroller as well.  Something like a
Stamp, AVR or PIC.

Then you may be able to add features like score keeping, pause, add
time etc..

Have a look in the Jaycar or Dick Smith catelog.  Some micros can be
programmed in Basic like the stamp.  It is quite easy to use.

Good luck,


jasen wrote:
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Re: BCD counter for seconds????

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74C927 - (If you can get one) - will give you X:XX.X   i.e. one digit of
minutes (which can be cascaded to other Minute Counters) Seconds and Tenths
of seconds

Or simply use a diode AND on Bits B (Pin 11) and C (Pin 14) to reset the
4510 and provide a minutes Pulse - two 1n4148's and a Resistor.
http://www.play-hookey.com/digital/electronics/dl_gates.html - Circuit on
the right of the page is the diode AND gate - pretty simple eh and requires
no more ICs.

In fact http://www.doctronics.co.uk/4510.htm gives the logic Diagram (under
'shortening the count' - it also gives the Diode version) this resets the
counter when it reaches 6 so a Seconds counter using this for the Tens digit
will give you a count from 00 to 59 Seconds.

You may find the pulse is a bit short for the next stage in this case feed
the output from the AND gate directly to the next stage however feed the
reset pin (pin 9) of the 4510 via a resistor (say 10K) and try a small cap
from the reset pin to GND (you may need to try a couple of values start
around 10nF) - this will delay the reset of the 4510 slightly which in turn
will effectively lengthen the pulse to the next stage so the display will
actually show 6 but only for a very brief period (in other words it is
unlikely to be visible to the naked eye).

Unless you are familiar with using embedded Controllers (and I am presuming
if you are asking this question you are not) then the learning curve,
Investment in Programmer etc would make this project somewhat complicated.

Richard Freeman

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