Hi:

I am thinking about building a frequency counter. The display would use the CD4511 chip. I read that instead of using a current-limiting resistor on each cathode, you could slave all the CD4511's.

"After looking at the datasheet, it appears that you can slave all the CD4511 chips to a pulsing source to modulate the LED current. This basically eliminated all the resistors we were talking about, since you can use a variable duty cycle square wave that'll just be enough to turn the elements on without burning them." Quoted from a thread on this site.

What exactly would this look like? Note: I have not designed the frequency counter circuit yet.

TY
E

 

Before worrying about saving a few resistors, you want to be looking at the overall design.

First criteria would have to be the maximum frequency you would like to count.
Next criteria would be the desired resolution, and hence the number digits you would like to display.
Then you have to choose the time base, the counting period, and the accuracy and stability.

If you decide to go with 4000 series digital logic, you need to look up the maximum clock frequency.
Having looked at all of that, I would not be bothered at all at installing current-limiting resistors for each segment. Another option would be to go with LCD display modules instead of LED displays.

 

Before worrying about saving a few resistors, you want to be looking at the overall design.

First criteria would have to be the maximum frequency you would like to count.
Next criteria would be the desired resolution, and hence the number digits you would like to display.
Then you have to choose the time base, the counting period, and the accuracy and stability.

If you decide to go with 4000 series digital logic, you need to look up the maximum clock frequency.
Having looked at all of that, I would not be bothered at all at installing current-limiting resistors for each segment. Another option would be to go with LCD display modules instead of LED displays.

How be you just answer my question.

 

Hi:

I am thinking about building a frequency counter. The display would use the CD4511 chip. I read that instead of using a current-limiting resistor on each cathode, you could slave all the CD4511's.

"After looking at the datasheet, it appears that you can slave all the CD4511 chips to a pulsing source to modulate the LED current. This basically eliminated all the resistors we were talking about, since you can use a variable duty cycle square wave that'll just be enough to turn the elements on without burning them." Quoted from a thread on this site.

What exactly would this look like? Note: I have not designed the frequency counter circuit yet.

TY
E

It would require a current sensing circuit, as the current would vary with both the temperature of the LEDs and the temperature of the 4511, especially as it has a bipolar emitter follower on each output, and that is likely to cost more than 42 resistors.
If you don't use current limiting resistors, you will find the pcb rather more difficult to track.
You could save most of the resistors by multiplexing the displays.

 

Thanks IanO. What would the circuit look like if I did multiplex the displays?

E

 

Thanks IanO. What would the circuit look like if I did multiplex the displays?

E

There would be a single 4511 driving the anodes each via a resistor (7 resistors in total), and a darlington driver or similar driving the cathodes.
Then you would need a multiplexer to get the data inputs to the 4511 at the right time, and counter (4017) to generate the multiplexing signals for the cathodes.
I seem to remember there being an IC that did it all for you. Look up 74C925.

 

You might be thinking of Intersil ICM7216.

https://www.epanorama.net/sff/Test_equipment/Counters/Benchtop Frequency Counter.pdf

 

You might be thinking of Intersil ICM7216.

Actually I probably was, but it is many years since I last came across it. I did a quick google search and found 74C925 which does a similar job. The first one that came to mind was the ICL7106 which is not the right thing at all.

 

Hi:

I am thinking about building a frequency counter. The display would use the CD4511 chip. I read that instead of using a current-limiting resistor on each cathode, you could slave all the CD4511's.

"After looking at the datasheet, it appears that you can slave all the CD4511 chips to a pulsing source to modulate the LED current. This basically eliminated all the resistors we were talking about, since you can use a variable duty cycle square wave that'll just be enough to turn the elements on without burning them." Quoted from a thread on this site.

What exactly would this look like? Note: I have not designed the frequency counter circuit yet.

TY
E

The circuit they show in the datasheet isn't slaving many CD4511's together, it's using one 4511 in a multiplexed system to sequentially drive each LED digit in turn, controlled by the CD4555, and getting correspondingly phased input data supplied to it.

 

How be you just answer my question.

How about you ask a better question.

ak

 

Your question is lacking so much information that it is impossible to answer to whatever your satisfaction is.

For starters, don't keep the source of your information a secret. Please post a link to the thread you are quoting.

a) without the context surrounding the quote, its applicability cannot be evaluated.

b) Not everything posted on this forum is golden.

ak

 

How about you ask a better question.

ak

Your reputation as a smart-mouth sob preceeds you. No wonder
no one respects you!

 

Your reputation as a smart-mouth sob preceeds you. No wonder
no one respects you!

Are you sure?

I feel respect to member AnalogKid based on my own experience and not on what unidentified "no ones" could say.

 

I am closing this thread for a while to allow people a cool off time out.

 

I have unlocked this thread any more Ad hominem attacks will result in this thread being locked permanently.

 

For 7 segment displays, the easy and convenient approach is to employ a 7-resistor array in DIP14 or SOIC4 format. These arrays were designed precisely for that purpose

 

Without a link to the original thread, it is impossible to say for sure, BUT - the idea quoted in post #1 sounds like a very bad idea. Blasting an uncontrolled, high current through an LED, even for brief periods of time, will cause component failure way ahead of any reasonable expected lifetime.

The 4511 output stage has a non-zero output impedance, and this will limit the LED current even if there are no external current-limiting resistors. But all that does is transfer the power that would be dissipated in resistors to being dissipated in the output stage, a power level way above its ratings. Again, *not* a good strategy for long-term reliability.

Note that the CD4511 datasheet has a sample schematic for multiplexing. Also, both of the LED display example schematics have external current limiting resistors. This is a clear and unambiguous indication that the output stage needs over-current protection.

Consider the CD4553B. This is a three-decade counter with display multiplexing built-in. The datasheet has a complete schematic for a 6-digit display subsystem that should work with whatever is the output of your frequency counter front end.

ak

 

Without a link to the original thread, it is impossible to say for sure, BUT - the idea quoted in post #1 sounds like a very bad idea. Blasting an uncontrolled, high current through an LED, even for brief periods of time, will cause component failure way ahead of any reasonable expected lifetime.

Automotive lighting uses a similar - but not quite so extreme - idea. The LEDs are correctly ballasted for 12V, and then PWM is used to reduce the on-time when the voltage increases to battery charging voltage.

 

Completely agree. My point to the TS is that

The LEDs are correctly ballasted

and

This basically eliminated all the resistors

are not Not NOT the same thing.

ak

 

If there were a 4000-series 7-segment decoder (with outputs like a 4026/4033) then it could probably be used without resistors, for a small range of supply voltages.