help with timing circuit

Discussion in 'General Electronics Chat' started by craigza, Sep 26, 2006.

  1. craigza

    Thread Starter New Member

    Sep 26, 2006
    4
    0
    Hi all, im new to forums and was wondering...

    [​IMG]

    wanted to know your comments on wheather this would work..
    and also ive been told to find out what the 0.10M stands for ( 10-100k )
    any other usefull comments would be much appreciated :)
     
  2. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Well, if you change the transistor to an NPN and if the output device is a self contained buzzer, it'll work.


    0.1 MegaOhm = 0.1 millions Ohm = 100 kOhm = 100,000 Ohm.


    If you don't need to boil another egg right after the first one, 2 of the diodes are a waste and the diode on the buzzer is a waste no matter.
     
  3. craigza

    Thread Starter New Member

    Sep 26, 2006
    4
    0
    thanks for that alot of help, but im actualy making a steak timer. 3 buttons ( meaning 3 of those circuits ) each button will start a timer for a different rarity of steak.
     
  4. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    No point in 3 separate and almost identical circuits.
    You could use a 3-position switch to select the time used when the button is pressed.
    I could draw you a schematic. What are the times approximately ?
     
  5. craigza

    Thread Starter New Member

    Sep 26, 2006
    4
    0
    yes please :D , times are ....
    3mins - Rare steak
    4mins - Medium rare
    6mins - well done
    and yes i did cook steak to test these :p thanks for this. :D
     
  6. craigza

    Thread Starter New Member

    Sep 26, 2006
    4
    0
    found a decent switch.. think a 4 way rotary switch would be good enough to use?
     
  7. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Absolutely and then you could add: 15 minutes = "incinerated" :D

    [​IMG]
    Don't mind the odd look of the rotary switch, a single deck will do fine, but this was the only one I had in my CAD libraries and so it looks more tidy than if all the wires were crammed to a single deck.

    When power is applied (put a switch in the +9V line), it will use the time allready selected by SW1.

    You MUST use a CMOS version of the 555 - like ICM7555 or LMC555 - or it won't work with such long times.
     
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