555-based button-press simulator circuit

Discussion in 'The Projects Forum' started by JimHung, Apr 22, 2013.

  1. JimHung

    Thread Starter New Member

    Apr 21, 2013
    4
    0
    Hey everyone,

    I'd like to design a simple circuit that will emulate a physical button-press on an off-the-shelf toy voice recorder. My goal is to turn a little 10-second recordable voice module into a tailor-made (and re-recordable) annoy-a-tron.

    Here's the module that I have lying around: http://www.amazon.com/Message-Recor...06582&sr=8-2&keywords=recordable+voice+module

    There is a little conductive pad push-to-make switch that is used to trigger the sound or hold to record a new sample.

    My idea is to automate the sound playing by using a transistor as a switch to mimic the press of the button.

    So here's my issue - I'm trying to figure out what is the best design for the delay timer which will a) be able to be in the "off" state for a number of minutes, and b) be "on" for a similar period of time to a natural human press (I'm guessing about 1/3-1/2 a second?).

    After doing some research into ways I can pull this off, I found a few websites suggesting a 555 as an astable oscillator - this one in particular caught my eye: http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

    The "Improved 555 Oscillator Duty Cycle" in particular seems like it fits the bill. I'm just having problems understanding how to select the right resistor/capacitor values that would give me an on/off cycle of something like 0.5s/420s (7 mins). There are a few calculators floating around, but they seem to expect you to know what R/C values you want to try - I haven't got a clue where to even start. Also, none seem to reflect the circuit in the link with the diode jumping R2.

    If anyone can give me some advice, I'd really appreciate it.

    Thanks in advance!

    Jim
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
  3. JimHung

    Thread Starter New Member

    Apr 21, 2013
    4
    0
    This looks like PRECISELY what I was after!

    I've just done the math and I'm comfortable I can switch up the numbers to make any reasonable delay I want - this is really great, much appreciated.

    Out of interest, is there any particular reason you chose such a cap? I'm assuming the line of thinking is that you'd pick a roughly reasonable sounding cap size and then do the calculation to find the required resistance, using the closest resistor you have - and if the required resistor is a ridiculous value, change the cap and try again?

    Thanks again for the help,

    Jim
     
  4. JimHung

    Thread Starter New Member

    Apr 21, 2013
    4
    0
    Hey - just wanted to post a quick update to again say thanks, the project turned out really well and your suggestion works great.

    Here's a picture of the final product.

    Jim
     
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