Hi all,

does anyone know of a particular unit, or otherwise, where I can find the circuitry to build a digital duty cycle display?

The circuit runs on 12 volts, 1KHz max' and it could include a frequency counter.

I know I could use an Arduino, but was wondering if anyone had any other ideas.

Many thanks in advance.

 

A little more explanation of what you are trying to measure. "Duty cycle" is a ratio of time periods, not something you count.

Ken

 

With a variable frequency, you'll need a microcontroller.

 

Point taken about it not being a counter....

The circuit runs a stable frequency from between 200 to 1Khz (it is an experiment), yet needs to maintain a 50% duty cycle.
To that end, I already have an adjustable, working system, however it would be nice to be able to read the duty cycle without having to connect
a meter each time.

We can buy off-the-shelf digital displays for amps, volts and temperature etc. so I was wondering if anyone knew of a display/circuit to read the duty cycle, as shown in the image below, only without using an Arduino?

 

With a variable frequency, you'll need a microcontroller.

Like an Arduino...?

 

RC integrate the PWM output, scale the averaged voltage to 0v-Xv = 0-100%, and read on a meter.

Ken

 

Here's one but I doubt you'll be happy with the price.
Otherwise, if you want to build your own, the Arduino is likely your best bet.

 

The circuit runs a stable frequency from between 200 to 1Khz (it is an experiment), yet needs to maintain a 50% duty cycle.

If you double the frequency and use a flip flop, you'll always have a 50% duty cycle.

 

Like an Arduino...?

Is it a microcontroller or microcomputer? A microcomputer would need a real time OS.

 

If you double the frequency and use a flip flop, you'll always have a 50% duty cycle.

The frequency cannot be above 1Khz but thanks for the suggestion

 

Here's one but I doubt you'll be happy with the price.
Otherwise, if you want to build your own, the Arduino is likely your best bet.

Thanks for the input.

You're right... I don't like the price

It is looking like a cheap xxxuino is the best option.

 

The frequency cannot be above 1Khz but thanks for the suggestion

The frequency would be doubled on the input of the flip flop and halved on the output.

400-2000 Hz in, 200-1000 Hz out. Using a toggle flip flop is a common solution for obtaining a 50% duty cycle.

 

Yes, a FF will guarantee as near perfect 50% duty-cycle independent of frequency.

 

Do you mean something like a 4013 connected to the 555 output?

I had thought about using an IR2151 and therefore having no need to read the output...

 

Mimicking one form of a 555 astable, the 2151 comes close to 50%duty cycle. However, it will not be exact. First, the 555 section output impedance is not symmetrical, so the equivalent timing resistance is different for the up and down half-cycles. Second, the 555 section output voltage is not truly rail-to-rail, again affecting the capacitor charge and discharge times. The datasheet says the range is 48% to 52%.

ak

 

Mimicking one form of a 555 astable, the 2151 comes close to 50%duty cycle. However, it will not be exact. First, the 555 section output impedance is not symmetrical, so the equivalent timing resistance is different for the up and down half-cycles. Second, the 555 section output voltage is not truly rail-to-rail, again affecting the capacitor charge and discharge times. The datasheet says the range is 48% to 52%.

ak

I think I'll try the 2151 anyway and see how close I can get

 

Hi all,

does anyone know of a particular unit, or otherwise, where I can find the circuitry to build a digital duty cycle display?

The circuit runs on 12 volts, 1KHz max' and it could include a frequency counter.

I know I could use an Arduino, but was wondering if anyone had any other ideas.

Many thanks in advance.

Count the number of microseconds the signal is high. Count the number of microseconds the signal is low, and divide. Most frequency counters will do this I think. If the question is about a signal you are creating the solution is in the design. Can you post a schematic of the design? Do you have an oscilloscope so you can view the signal?

 

Count the number of microseconds the signal is high. Count the number of microseconds the signal is low, and divide. Most frequency counters will do this I think. If the question is about a signal you are creating the solution is in the design. Can you post a schematic of the design? Do you have an oscilloscope so you can view the signal?

Hi, I have no circuit diagram. I am making this up as I go along... Although I do have a scope.

The desired output is two channels 180° out of phase from each other (hence the 50% duty cycle request) whilst both channels run at the same frequency which I wanted to keep below 1 Khz. I want to switch two opto-couplers (4N25), flip - flopping, if you like?

So far, I have been experimenting having a 555 as the signal generator. That part is not the problem.

As I write this, I have a 555 triggering a HEF4013 but output 2 (pin 13) is half the frequency of output 1 - so this is no good....

It failed with aa relay, yet seemed to work using an NPN and PNP back-to-back on the 555 output, until I connected 2 opto's in parallel to the PNP. ?!!!??!!!???

Surely it must be a doddle to have a circuit run at a fixed low frequency whilst flipping and flopping in perfect division?

 

As I write this, I have a 555 triggering a HEF4013 but output 2 (pin 13) is half the frequency of output 1 - so this is no good....

That should work perfectly if wired correctly, which is why we always need a schematic before we can have an informative conversation.

ak

 

That should work perfectly if wired correctly, which is why we always need a schematic before we can have an informative conversation.

ak

Good point.

I have been working to schematics, however they are what I have drawn in my notepad and not easily transferred onto a webpage.

The circuit I used earlier for the 555/4013, I lifted from a site and it was this...

It is not the circuit I am looking for, as it clearly states 1/2 a 1/4 frequency.

It does indeed flip and flop, only F/4 is half the frequency of F/2... as mentioned