how to make simplest pulse generator that is controlled by laptop

Discussion in 'General Electronics Chat' started by JJoll, Dec 15, 2015.

  1. JJoll

    Thread Starter Member

    May 7, 2013
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    Hi,

    I need to make a pulse generator so that whenever it is called, it has to produce one pulse of 150ms. I need to control this pulse generator with a laptop, because I am automating a system of circuits and I need to trigger one specific circuit by sending a 150ms pulse to it. How can I approach this? Any suggestions? I was thinking of using a 555 pulse generating circuit, something like this: http://www.electroschematics.com/5834/pulse-generator-with-555/

    But this seems a little bit of overkill. I just need to send only 1 pulse. I am currently writing the code to control connect and integrate my system with some devices using a GPIB-USB adaptor and any recommendation on the pulse generating circuit and way of connecting it to a laptop would be greatly appreciated.

    Thanks
     
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    This will be a far from "simple" project. You will most likely need a mcu. Is that in your skillset?
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The big problem with modern laptops is that they lack parallel or serial ports of old... With those, this was easy.

    A USB to Serial Port Dongle can be used by toggling one of the control pins, like DTR. This gives you a signal you can control via any programming environment.

    I assume you want the PC program to determine when you want the pulse. You need the external timer to determine how long the pulse is, once triggered.

    Either the rising-edge or the falling-edge of DTR can be used to trigger your timer. I would add an opto-isolator between the DTR signal and your circuitry, to protect the laptop. Use a real power supply instead of trying to power your circuit via the USB from the laptop...

    Try this:

    163.gif
     
    Last edited: Dec 15, 2015
  4. Brownout

    Well-Known Member

    Jan 10, 2012
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    It is, as this is a free-running pulse gen (astable mulitvibrator) What you want is a one-shot or monostable multivibrator. Also can be made with a 555. There are lost of schematics available via google. Trigger from your computer using a USB-to-Serial adapter as described above. Or, you can use a USB to parallel (FTDI) adapter and trigger your one-shot by directly writing the IO register.
     
  5. cmartinez

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    Yup... I'd definitely go with an MCU too. I can show you how to do it with an AT89LP4052 (or 8051), and a simple MAX232 driver.
    You'd need a USB to RS232 adapter, though. Which btw are not expensive and easy to come by.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    In the category of overkill, you could also use data acquisition hardware - connected to your computer via USB - to accomplish this. Such hardware could also take over a lot of your automation chores. I like the LabJack devices but Dataq is another choice. $50-120 or so, depending on which model.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Couldn't the USB to Serial Port Dongle that Mike talks about in post #3 drive the output signal directly? If you can turn DTR on and off to trigger a 555, why not turn it on and off with a 150 ms software time and ship it out?

    ak
     
  8. crutschow

    Expert

    Mar 14, 2008
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    If the 150ms time is not particularly critical then AK's approach should work.
    But a USB to parallel adapter might allow easier control of the time period of the pulse.
     
  9. MikeML

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    When I tried to time events from a Visual Basic program running in Windoz, it seems I could get about +- 10ms...
     
  10. BReeves

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    Nov 24, 2012
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    I wrote a C++ Windows program that does what you need to test trigger a thrill ride photo system. Used the parallel port as a poor mans DIO interface and a 3rd party game timer library for accuracy. You can find older laptops with a parallel port on eBay for less that what a DIO adaptor would cost. The Parallel port will give you a 5 volt pulse which could be used to do almost anything with a few added components. The app isn't very large and I wouldn't mind sending it to you if interested.

    Just keep in mind it is a test app with no documentation and will require Windows XP or the 32bit version of Windows 7.
     
  11. GopherT

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    Nov 23, 2012
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    @JJoll

    You could go low tech as well, depending how accurate your timing requirement is.

    You could program a black screen on your laptop and have it flash white for 150 mSec. Then build a simple phototransistor trigger circuit. Place the phototransistor in front of your screen and poof, done. No risk of a bad circuit design or execution blowing out a USB port and all is done. .
     
    Last edited: Dec 16, 2015
  12. spinnaker

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    Hey Rube, can't you do better? Maybe add a golf ball and a toy airplane into the mix??? :)
     
  13. GopherT

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    Piss off man! My answer is easier than any of the others. The rest all required copper wire and connectors. Even a suggestion of finding an old PC with a parallel port.

    On the other hand, a glass ball and a spiral wire track could make this fun...

    Never mind, no way to interface the hamster wheel to the trigger circuit.

     
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