Please look over this circuit

Discussion in 'The Projects Forum' started by wannaBinventor, May 22, 2010.

  1. wannaBinventor

    Thread Starter Active Member

    Apr 8, 2010

    I was fiddling around and I made this circuit. It's one of the first one's I've made without following some one else's design, so I'm asking that you look it over and point out any things that are just ridiculous/pointless/inefficient. The circuit does in fact work, though not as cleanly as I'd like.

    It essentially works like this:

    When the circuit is turned on, LED1 is on. When the LDR is shadowed, LED 2 will shine and the low voltage buzzer will buzz. If you replace Q2 with a 2N5062 SCR, the buzzer will stay on until a pushbutton on its gate (not shown) that is linked to ground is pushed to turn off the SCR.

    If you swap the LDR (R1 in the schematic) with R2, the buzzer and lights will now respond to quick flashes of light.

    Problems and issues:
    The buzzer response doesn't seem to be instantaneous. It seems like the LDR has to detect some change in light - then back again to set off the buzzer. IE: When in "flash detector" configuration (LDR in r2 position instead of r1 position), it will go off and latch (if SCR installed) when a camera flashes anywhere nearby. However, if I light a lighter and move it right above the LDR, it will switch the LEDs but will not set off the buzzer until I shut the flame off. Why?

    I don't really think the 6k resistors at r3 and r4 are best, I just picked those.

    Last edited: May 22, 2010
  2. Wendy


    Mar 24, 2008
    I don't have anything to look at that file. You need to use a standard format, such as .PNG, to allow people to see it.
  3. wannaBinventor

    Thread Starter Active Member

    Apr 8, 2010
    Sorry about that. I've figured out how to do it.

    A few things: I haven't quite figured out LTSPICE so it may look a little sloppy. Also, as you are looking from left to right you will see the first voltage divider has the LDR on it. It should not show as being connected to the second voltage divider - that is something LTSPICE did that I don't know how to correct. I just threw in a resistance for the LDR. It seems to be around 1900-2200 ohms at just regular room lighting, but obviously changes.