Connect with us

Need Thought on Slot Switch

Discussion in 'Electronic Basics' started by Razzel, Aug 11, 2005.

Scroll to continue with content
  1. Razzel

    Razzel Guest

    Built a slot switch to feed into the soundcard. It is intended to
    calculate the period of a pendulum. 1) IT WORKS. but not well enough.
    When the beam is blocked by a 1/4 in. wide barrier (in the 1 in slot) my
    returned values are a couple in the low 120's, then jump to a run of 4-5
    130's then back to 119 or 122 before jumping again to 130's. The
    unblocked values are all over the place. 94, 61, 140, 210, 190, 88, 60,
    60, 138, 218, ...
    Nothing is hot. Its running off of a wall wart which is 9.12v unloaded.
    I would expect if it is the wall wart problem then both sets of values
    would vary similarly.
    Both the LED (super bright) and the photoreceiver transistor (R/S
    276-145) are fed from this source.
    Any ideas why the values are out of whack???
    I can show the circuit if needed but hopefully someone has a similar
    experience. I think it must be CJD !
  2. Bob Masta

    Bob Masta Guest

    I'm not sure I understand exactly what you are
    doing, but if you are using a steady-on LED to
    feed the sensor, then the sensor output will
    be mostly DC with transients only on the edges.
    Sound cards are AC-only devices, with blocking
    capacitors cutting out everything below 20 Hz
    or so (maybe as low as a few Hz on some cards
    but definitely not DC). So the trick here is
    to modulate the LED with a high frequency,
    something in the 1 to 10 kHz range, say. Then
    your sensor signal will be easily detected by the
    sound card. The only hitch is that the time
    resolution is limited by the square wave frequency.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day