need to measure duty cycle of DC pulse

Hi Folks.

I need to measure the duty cycle of a DC pulse. I'm in a spot of difficulty because the pulse width is around 0.1s. Which is too fast to measure manually... and I don't have an oscilloscope. A sampling rate of 20Hz would be sufficient, and I need only the pulse widths, not the actual voltage. Can anybody recommend a cheap (and simple) solution to get the measurement?
I was thinking of using the soundcard, because I've seen some soundcard oscilloscope software. But the soundcard is AC coupled and besides, I'm not sure how to wire it without killing my soundcard.

Any advice or suggestions would be appreciated.

Don't know if there's any really low cost way to do it.

A Google search turned up numerous adapters that connect to a PC to give an oscilloscope function. For example Parallax has a two channel unit for $140 **broken link removed**.

You could buy a Pickit 2 programmer from Microchip. They have a simple 3 channel logic analyzer built in that may fit your needs?

**broken link removed**
3 channel software pwm.

Do you know the "on" voltage? Does the voltage drop to zero during "off" part of the cycle? What is the source of the pulse and how much might it be affected by the measurement process? My thought would be to construct a resistor capacitor combination as a filter of sorts and measure the resulting DC voltage. You'd have to do some math to determine the right combinations - and to work backward from the resulting DC voltage.

Dwell was the term used when auto ignition systems were point contact type - and a dwell measurement function was common on automotive type measuring instruments. If I am not mistaken, duty cycle is part of some DMMs today.

Seems like you should be able to do what you want but cheap and simple probably requires some work.

Thanks for your replies. I ended up using the soundcard to measure the cycle, as I could clearly see the rising and falling edges. I got the peak voltage by using an old analog multimeter which isn't limited by low sample rate of most digital multimeters.

Not an ideal solution...... But it did the trick.....

I am wondering if the response of the meter isn't doing some averaging - so you may think you are getting a peak reading. With 0.1s pulse width - can your meter respond that fast?

stevez said:

I am wondering if the response of the meter isn't doing some averaging - so you may think you are getting a peak reading. With 0.1s pulse width - can your meter respond that fast?

Click to expand...

good point. the reading was lower than i expected. that would be why...

hi,
If you download audacity free, from the web, it will work with your PC's sound card, you can use the cursor to measure the period.