BCD counter

[DTSFA]

hi

i have built a multiplex circuit ,

555 timer generates clock, into

http://www.datasheetcatalog.org/datasheet/on_semiconductor/MC14518B-D.PDF

BCD counter MC14518B-D,

this BCD output feeds into a ADG406 multiplex, each 'decimal' output feeds led,

LEDs clock nicely through, but, at does seems to only count up to decimal 8, LED 8 ?

any ideas, have I missed anything fundaemantal on the BCD chip ?

thanks

 

[BrianG]

Hi,

Looking at the datasheet you have attached for the MC14518B-D there is nothing you need to do to make it count as a BCD decade counter, i.e. no external feedback or reset decode as would be required using a binary counter. You don't say what kind of LED display device you are using, or why this is multiplexed, so I suggest you look carefully at how that should be driven and also look at the multiplexer device. You may be missing the most significant bit, which would then only count 0-7.

 

[DTSFA]

Hi Brian

we are building test box to test multicore cable connections

so the clocked BCD outputs to multiplexer, output from mux to one end of each core of cable, other cable end feeds LED, ( 24v individual LEDs )

if cable is wired correctly, pin to pin, we will see a nice scrolling effect to LED 14, ( 14 core cable under test)

what we have at mo, is scrolling nicely upto LED 8, then resets to LED 1, and so on,

think it may be that we need to use the MC14520 B, from timing diagram , this one seems to count to decimal 15

thanks

 

[benta]

Why are you using a BCD counter when you have 14 cores in your cable?

Benta.

 

[DTSFA]

MC14520 B gives me a binary 0-15 output, is ok, just case of using wrong IC

thanks for help

 

[waross]

It's been many years since I was into Boolean, but back in the day, A "Binary, Coded Decimal Counter" would only count 0 to 9. Although the counter was based on a 0-15 counter, it would reset at 9 for base 10 counting.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BrianG]

I understand your requirement now for the cable tester (always helps to give the full picture up front!) I would not recommend running your LEDs from a 24V supply for two reasons:
1)If you are also running the ADG406 multiplexer chip from 24V, this is close to the absolute maximum supply rating - not good design.
2) If you are running the ADG406 from a lower voltage supply, e.g. 12V then the higher LED supply voltage can cause leakage currents in "off" channnels to flow into the protection diodes of the multiplexer chip. As with most chips, this can cause unpredictable operation, random channels being energised etc.

Best plan is run the LED supply and ADG406 from the same supply rails (but less than 24V).

Brian

 

[IRstuff]

did you actually monitor the signals with an oscilloscope?

TTFN
faq731-376