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Ripple Blanking 74LS47N

Ripple Blanking 74LS47N



I have just finished a 4 digit counter circuit. However, i am having difficulty getting the ripple blanking to work. I have used 74LS160N synchronous 4-bit counters feeding 74LS47N BCD to 7 segment display drivers and then to 7 segment displays with common anode. I have tried connecting the ripple blanking between each 74LS47N but with no joy!  I have tried what is supposed to be connected and when this didn't work i tried every other configuration but i cant seem to get it.

The RBO of the MSB 74LS47N feeds the RBI of the next one down and so on. The RBI of the MSB 74LS47N is tied to earth and the RBO of the LSB is left open. With all the RBO's and RBI's tied high the circuit works perfectly and all displays show zero or a relevant number.

I have attatched the circuit file, please excuse the mess of it, there's connections everywhere !!!

Can anyone help me with this please? Any input would be very much appreciated as it is an aspect of the circuit i would really like to get working.


Many Thanks



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Message 1 of 8

Re: Ripple Blanking 74LS47N


Is this what you are trying to achieve?

The last OR Gate U28b could have been eliminated and the output could have been taken directly from U27b output, but I left it so the circuit could  be continued with more digits. I also included a reset button. 

Please let me know.

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Message 2 of 8

Re: Ripple Blanking 74LS47N

Hi again,

One minor change is a push button switch could have been used instead of the spdt reset switch.

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Message 3 of 8

Re: Ripple Blanking 74LS47N

Hi Kudos


Thats a superb circuit you've put together. It just shows even simple things like mounting the IC's 90 degrees round can neaten up the circuit no endSmiley Happy

Thats exactly what i was after but unfortunately i dont have the time or the parts( the gates) to incorporate it into my device.

The circuit you've built is exactly what i was after but i didn't know if it could be done by simply adjusting a few of the connections to the IC's to get the ripple blanking working. The ripple blanking connections on the 74LS47N's made me believe it could be done with some alterrations. maybe thats not the case.

If the only way it can be done is to use the external gates then i won't be able to use it. The circuit i have is fine but the ripple blanking would have just neatened up the display a bit and possibly saved a bit of battery life. Its not essential that i get it working but thankyou very much for the input, its very appreciated.

I also noted that you have tied the ABCD inputs to the 74LS160n's high, does this a make a difference at all as i have just left mine open?






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Message 4 of 8

Re: Ripple Blanking 74LS47N

Hi again


Just another quick point. i see your clk arrangement is slightly different to mine. My RCO feeds the ENP of the next IC but yours is connected to the CLK of the next IC. Can you tell me if there is any difference between the two?


Thanks Again



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Message 5 of 8

Re: Ripple Blanking 74LS47N

Hi Rob, 

As to concerning your questions, by tying my RCO to the ClLK created a ripple triggering circuit. This method would cause the display to the right to be the Least Significant Digit. It also insured that the count would almost always start at zero instead of the random starts, and could eliminate having to add additional components to insure the counter starts at zero, an economical approach. 

As for tying the ABCD pins together to high, in this case it could have tied to GND also, but thinking about it tying to GND is better. However, the reason is, when working with digital circuits, it is a good practice to never leave the unused inputs on counter IC's with serial and parallel input open to prevent false triggering. A circuit with ungrounded inputs may work fine in your home but if it is placed in an environment with high static discharge, like under the hood of a car with leaky plug wires, you may not get the same results. 

I will fiddle around with your circuit to see if the same result can be achieved without additional parts.

Gerald.Smiley Happy 

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Message 6 of 8

Re: Ripple Blanking 74LS47N

Ok. Thanks for that input. Its good to try and pick up new things.Obviously i'm still a beginner as far as electronics is concerned. Thats good advice about  the connections being left open. I'll be sure to connect them to either ground or +voltage. I'll have a play around with it.


Thanks again



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Message 7 of 8

Re: Ripple Blanking 74LS47N

Hi again, I actually built your circuit because experiece has taught me always build the circuit. After doing so, I discovered a counting error existed in the practical circuit. Simulators are good but they are not perfect. 

Here is the circiut with the new changes, it includes your approach of clocking all the counters at once. I hope you receive this post. I was unable to blank the other unused digit without the additional circuit as you mention. 

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Message 8 of 8