# Measuring dc pulse width

Thread Starter

#### smokie

Joined Apr 15, 2009
15
Is there a way to display the width of a single dc pulse in fractions of a second on an a screen?
I want to know the actual width of a pulse from a 555 timer in monostable operation, not the calculated.

The pulse width is .1 sec to .5 sec.

#### iimagine

Joined Dec 20, 2010
511
oscilloscope

#### ScottWang

Joined Aug 23, 2012
7,397
If you have the oscilloscope then it is more easier, otherwise you will need :
1) 1 Khz frequency square wave generator.
2) An AND gate.
3) A square wave frequency counter, it would be 10 Khz or upper.

Connect 1) 1 Khz and your NE555 signal to the inputs of 2) AND gate.
Connect 3) frequency counter to the output of AND gate.
The above contents just a simple description, you will need the clear signal (RC differential circuit) from the ne555 pulse, and to clear the frequency counter to zero.

#### AlbertHall

Joined Jun 4, 2014
12,328
An arduino could do the job if you have one handy.

#### danadak

Joined Mar 10, 2018
4,057
Using Snap4Arduino this simple program will read pulse width on a pin and display
it in right hand window -

Note if you need to UART it out of Arduino board it is simple to add that. Or use
speech synthesis block to speak the pulse width value from your PC (Arduino
has to stay tethered to PC) that is easy as well.

The setup of Snap4Arduino a little involved in that Arduino board using Arduino
IDE has to have a specific version of firmata installed into it. This is a couple of
minutes task. Once thats done "normal" block programming proceeds and
upload to Arduino. Videos on this, not rocket science.

You want fractions of a second so a little more block programming needed to
format that.

Regards, Dana.

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Thread Starter

#### smokie

Joined Apr 15, 2009
15
Thank you all.

I thinking of going with a oscilloscope.

Will a oscilloscope display the pulse width of a one shot pulse? One pulse, i.e. hi then low, not a frequency.

#### KeithWalker

Joined Jul 10, 2017
3,034
Thank you all.

I thinking of going with a oscilloscope.

Will a oscilloscope display the pulse width of a one shot pulse? One pulse, i.e. hi then low, not a frequency.
A digital oscilloscope will display it in single shot mode. Play with the trigger level until you trigger on the leading edge of the pulse.

#### AnalogKid

Joined Aug 1, 2013
10,947
Will a oscilloscope display the pulse width of a one shot pulse? One pulse, i.e. hi then low, not a frequency.
Yes. Set the trigger mode to "Normal". Of course, to view the waveform after it is created you will need some form of storage.

ak

#### Danko

Joined Nov 22, 2017
1,823
You can do it so:
Connect C-E of NPN transistor in parallel with mouse button switch.
Send pulse from 555 to B-E of transistor in series with 10k resistor.
Write tiny computer program, and you will see pulse duration in numbers
on monitor screen.

#### ci139

Joined Jul 11, 2016
1,898
there's a lot of pre-tuning . . . but it's one possibility that gives you a number (quite precise if everything goes right)

BLUE LED-s (likely not the fastest but with suitable here voltage drop) I.discharge set to 100µA → Δt = ΔU·(C / I) determining the exact value for C might be a problem . . .

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#### vanderghast

Joined Jun 14, 2018
67
If you have a reliable clock (quartz cristal as example), you can AND the clock signal with your pulse and supply the output to a counter, such as a CD4020. Add red LED on the output pins to read the count, in binary. Ben Eater has a video showing how to use such a circuit at

#### SamR

Joined Mar 19, 2019
5,019
This might help ( videos on triggering and other features ) -
Thx for the link!

#### Plamen

Joined Mar 29, 2015
101
Is there a way to display the width of a single dc pulse in fractions of a second on an a screen?
I want to know the actual width of a pulse from a 555 timer in monostable operation, not the calculated.

The pulse width is .1 sec to .5 sec.
Petkan:
The most common way is to use an oscilloscope for direct measurement.
Another way is to use a digital frequency meter/counter in pulse duration mode(most accurate method).
Assuming you have no sophisticated gear - there is also an indirect way:
Trigger your 555 from a periodic signal with known frequency (like 50Hz or 60 Hz).
The period of your triggering signal should exceed your pulse width. Once you have a pulse train - use a DC voltage measurement Vaverage=Vcc*Tx/To, where Vcc is the power level of your 555, To is the period of the triggering signal. In another words your pulse duration is Vaverage*To/Vcc. This is indirect measurement i.e. the error is compounded by the errors of the arguments in the formula. If you have a variable frequency oscillator you can also use it for triggering and slowly increase the frequency. The average DC reading of the pulse train will increase with frequency up to a point where the triggering frequency period matches your pulse duration. Once you reach the point that the voltage no longer increases (close to Vcc) - your pulse width matches the triggering period.

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