The CD4511 Chip

Thread Starter

elec_newbie

Joined Oct 19, 2023
21
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
 
Last edited:

MrChips

Joined Oct 2, 2009
30,488
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.
 

Thread Starter

elec_newbie

Joined Oct 19, 2023
21
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.
 

Ian0

Joined Aug 7, 2020
9,502
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.
 

Ian0

Joined Aug 7, 2020
9,502
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.
 

sarahMCML

Joined May 11, 2019
353
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.
 

AnalogKid

Joined Aug 1, 2013
10,944
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
 
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
 

AnalogKid

Joined Aug 1, 2013
10,944
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
 

Ian0

Joined Aug 7, 2020
9,502
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.
 

Ian0

Joined Aug 7, 2020
9,502
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.
 
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