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help with timed night light

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pape21

New Member
hi guys.

im a new member here and have just started on some very simple circuits.

at the moment i am trying to make a circuit that acts as a night light that turns on a set of LEDS for a set period of time (e.g. 3 minutes) when either a motion sensor is triggered or i move my hand through a directed beam of light.

i havent got to understanding programing microcontrollers yet so if there is a way that doesnt require any programming please could you advise me

thanks
Pape21
 

Andy1845c

Active Member
Do some reading on the 555 timer IC. Here is just one of many sites on it.

LM555 Timer Circuits

A micro controller would work, but isn't really needed. Spend an hour or so reading up on the 555, its very common and very versatile.
 

pape21

New Member
thanks for the advice.

from what i have managed to understand, i need to make a monostable oneshot 555 circuit and use a 2200uf capactor and a 100k resistor ( for the light to come on for 3 minutes then go off untill the circuit is triggered again)

could someone confirm this for me please :)
 
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Hero999

Banned
Nice try, unfortunately the leakage will probably be too high.

Use a 220:mu:F tantalum and a 1M, a CMOS 7555 is probably also a good idea.
 

solis365

New Member
thanks for the advice.

from what i have managed to understand, i need to make a monostable oneshot 555 circuit and use a 2200uf capactor and a 100k resistor ( for the light to come on for 3 minutes then go off untill the circuit is triggered again)

could someone confirm this for me please :)
I worked on a similar project where my circuit had to wait exactly 1 minute from turn-on time. at the end of 1 minute a motor was turned on. long story short, I used a big capacitor to get my big time constant--big mistake. try to make the cap smaller. in non-technical language, the 555 couldnt supply enough current fast enough to charge the big caps, or so i suspect... smaller caps, bigger resistor.
 

pape21

New Member
thanks for all your help guys.

i have finished my project now and made a box for it and i will post a picture of it when i get my camera charged
 
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