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Lm3914 and a couple of 4014s

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Gary Templeman

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It's not practical I know, but I thought it would be fun. A 200 LED oscilloscope as a good soldering project for low speed, simple projects etc, ie: 555 projects. Easy I thought, use the LM3914 to drive the ten vertical 10 LEDS while the two 4017s to handle the twenty horizontal LEDS in a 10x20 matrix. But it's not so easy!. Can any one suggest a sensible way to convince two 4017s to step through twenty LEDS horizontally clocked by an adjustable 555 as the time base. Since 4017 count decades I wanted them to both count on the same clock input but #1 4017 to display the first ten LEDS while #2 4017 ran the second ten LEDS. Each 4017 needed to blank the other 4017. Some one with greater logic skills I'm sure could sort this. I tried #1 4017 holding reset the 4017 #2. I've tried #1 4017 blanking the #2 4017 by killing it's ground, I've even tried powering off each 4017 alternately. None of these attempts really work. Any ideas out there from minds much brighter than mine?
 

atferrari

Well-Known Member
Killing the ground? Isn't it any enable signal to use? Or even controlling the clock?
 

fezder

Well-Known Member
So you want to scan it like matrix? Can you try 74595? If you insist of usinf 4017, place flip-flop to control which of 4017 listens to clock signals, and when it's time to switch ic, other 4017 clock inhibit and reset are both tinkered, but I can't recall will reset blank leds or not....

And yeah, like ferrari suggested, killing ground works also. (using n-fet or transistor as low-side switch)
 

schmitt trigger

Well-Known Member
If I understand correctly............ what you want to do is to strobe the outputs but keep on counting, then I'm afraid you will have to use external gates to do so.

Since you have 20 outputs, you'll require a total of 5 CD4081 quad AND gates to do so.
 

fezder

Well-Known Member
projects like these really makes one wonder how handy microcontrollers really are :) Don't get me wrong, I'll tend to think first if something can be done easily without micro...
 

dr pepper

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Most Helpful Member
 

atferrari

Well-Known Member
And yeah, like ferrari suggested, killing ground works also. (using n-fet or transistor as low-side switch)
Well fezder, it is the opposite; I was not actually suggesting that but commenting his OP which I quoted but now does not show up.

In fact, I recall some distant past experience where disconnecting the ground allowed some "spurious" feeding through I/O pins so I discarded it in my mind forever.

BTW, straight from the datasheet, here is how they suggest to cascade some. Probably the base for a solution to his request.

Cascading 4017s.png
 

fezder

Well-Known Member
Well fezder, it is the opposite; I was not actually suggesting
Hehe, true, it's not wise to disable ground....I suggested it and you thinked out loud? :D And now I read starting message of OP and indeed mentions of killing ground, my bad, sorry ferrari!
In fact, I recall some distant past experience where disconnecting the ground allowed some "spurious" feeding through I/O pins so I discarded it in my mind forever.
Hmm, now that you mentioned, I too have encountered this behavior when using arduino and "forgot" to supply vcc for IC's
That circuit is handy for freguency division. Phew, I remember my first major problem in this site when I was doig knight-rider with 40192, d-flip flop, and some other ic's. IIRC eecribs or similar named member here helped bunch with it :).
 
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