Newbie and son needs help

Discussion in 'The Projects Forum' started by IFish, Jun 1, 2013.

  1. IFish

    Thread Starter New Member

    Jun 1, 2013
    I am trying to help my 7 year old son design and build a compact circuit that turns on a bright LED light with a mercury switch where the LED remains on (or blinking) for a specific amount of time after the switch has been closed (even if the switch becomes open after initially turning the LED on and starting the timer). The finished product should be small enough to fit into the opening of a 2 liter plastic soda bottle if possible. I am brand new to this and really do not know the terminology to research many of the necessary components that may be needed to complete this project or what may be available within the needed small size requirements for this project. Any help or information will be greatly appreciated.

    Thanks in Advance.
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    You could use a latching "one shot" like I designed to run my scope calibrator. When I hit the button, it provides power for ten minutes then goes off. The ON time can be varied by changing the value of the timing capacitor (the 47uF/10V Tantalum). Your mercury switch would connect between the SW terminal and ground. This runs off a 9V battery (connect to +BAT node). The VCC node is the power to the other circuitry controlled by the one shot which goes off after it times out.

    As to making all this small enough to fit into the ed of a soda bottle: I doubt it.
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
    This should be doable: A 555 one shot, a LED or a blinking LED. Question: does power need to be cut at time out?
  4. sheldons

    Well-Known Member

    Oct 26, 2011
    can be made ultra small using 2 transistors and a few resistors and a couple of capacitors ......heres the schematic....can be made even smaller if using surface mount components
  5. edwardholmes91

    Active Member

    Feb 25, 2013
    As people have posted it can be done using a couple of 555 timers, one as an astable to flash the LED and a monostable to keep it on for an amount of time. Or you can use an already flashing LED and just a monostable. This will fit inside a soda bottle, but you may struggle to get it to fit through the opening. Surface mount is an option but this does make soldering very difficult for a beginner, I'd recommend sticking to through hole components if possible.

    I can draw up a circuit for you and I can work out a PCB pattern, but I would need to know the max sizes of the board you want to make. I can have a play and see if I can fit it on the board. My personal thoughts judging by the size requirements is to use a flashing LED and a monostable, this will limit component count and reduce the size of the overall board.
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Just for fun, here's how it would look with a microcontroller:

    That's the battery, mercury switch, and the LED, plus a resistor, cap, and a 50 cent chip. The circles are just connector points so it can be programmed in the same board it lives.

    I'm not suggesting you try to build it this way, I'm just playing "Build that Circuit."

    I can built THAT circuit in 6 parts... and I wouldn't stop until I saw if it really needs that cap.
  7. bance


    Aug 11, 2012
    Sounds like a candidate for dead bug style assembly.....