How to measure sub-audio time delays with a PC

Discussion in 'The Projects Forum' started by SinewaveMan, Dec 20, 2013.

  1. SinewaveMan

    Thread Starter New Member

    Apr 21, 2013
    16
    3
    A description of how to do this is in the attached PDF. Please accept apologies for submitting it like this, but I do not know how to do it otherwise.

    Since writing this document I came across a post that told about "Phantom power" from the sound card mic input connector. That is something I never knew about so I did some extra "snooping" at the mic input of my Compaq laptop. I use a DT830D DMM for my measurements. When there is no recording device active on the PC, there is no output from the mic connector. When a recording device is active then 3.6 volts (no load) is measured. The short circuit current is 800uA (800 micro amps). This can be used to monitor relay contacts without connecting anything to the electronics. A 33K resistor across the relay contacts and a 100K resistor in series with the signal to the PC gives me suitable differential pulses. There is a little noise and contact bounce, but not bad enough to affect my time measurements.

    I am pretty keen on writing the application to measure delays similar to a lap timing stop watch. It would measure times between the same polarity pulses, or (eg) between a positive and a subsequent negative pulse. The display would be a table of successive readings so that the observer can see changes in times while adjusting for calibration.

    Please can someone tell me how to trap those pulses as events in a VB or VBA application? With that information I will write the application and make it public to anyone interested.

    Kind regards and best wishes to all over the festive season.
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Interesting idea, but if you just want to measure elapsed times (stopwatch type stuff) then I would use the USB port and a $3 TTLserial->USB adapter module.

    The USB port gives you access to a lot more power for your device and its sensors, and you can get the data from the USB virtual serial port and disply or log it in hyperterminal or any free serial program.
     
  3. SinewaveMan

    Thread Starter New Member

    Apr 21, 2013
    16
    3
    Yes, I will probably do that eventually. The way this all started was when I used a 4536 chip and had to calibrate the oscillator. That was easy using the "Visual Analyser", looking at frequencies from 40Hz to 500Hz. Then I needed some monostables for turning on lights and releasing the shutter. That required sub-audio measurements (I never entirely trust the calculated times). Most of the components come from my scrap box and I try to resist purchasing unless I will be using the item often or essentially. So - that Serial/USB adapter is becoming essential [​IMG]. Thanks for the response and the hint.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,777
    1,103
    Another way would be to use audio recording software such as Audacity to monitor the interval between the input clicks at the mic socket.
     
  5. SinewaveMan

    Thread Starter New Member

    Apr 21, 2013
    16
    3
    Yes, exactly - thanks Alec_t.
     
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