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Night light ckt diagram..... help please

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madmikejt12

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hi, i was wondering if you could help me on this circuit please??

I am unsure about the relay, what relay should i use please? and what are the contacts? (e.g NO, NC, COM ect)
 

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As load on the relay is bulb and I assume that you don't have any timing constraints so you can use any general purpose relay.

When relay is in off state NC gets connected to COM and when relay is in on state NO gets connected to COM.

Expansion of these terms is:

NC = Normally Closed
NO = Normally Open
COM = Common
 
dipal_z said:
As load on the relay is bulb and I assume that you don't have any timing constraints so you can use any general purpose relay.

When relay is in off state NC gets connected to COM and when relay is in on state NO gets connected to COM.

Expansion of these terms is:

NC = Normally Closed
NO = Normally Open
COM = Common

ok, thanks :)

audioguru said:
Those batteries won't last very long.

Which ones, 9v 3v or both? can you recomend something please?
 
recommend doing away with the relay.
recommend changing the filament lamp for a white LED.

That should extend battery life considerably.

John :)
 
would this circuit be ok?
D1- White LED
R3- Cds cell (couldnt find a Cds on CircuitMaker)
 

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Use NPN transistors with the LED and battery in that polarity.
If you want to use PNP transistors then reverse the polarity of the LED and battery.
The LED will burn out without a current limiting resistor in series with it. Its max is only 3.5V but you have a 9V battery.
You are using a ground symbol instead of an arrow for the slider of the pot.
 
ok, thanks for that :D oops, 4got about the resistor.

About the ground symbol, Circuit maker said i didnt have a groung (as it always does :evil: so i put it there :D lol
 
Hi Mike,

That sort of arrangement would be much more economical on batteries,
however any current through the LED also flows through the limiting
resistor, so to keep this fairly low, how about making the supply
voltage 4.5 volts, three cells, that means the limiting resistor
would be using less power than the LED rather than more with 9 volts.

Also if you cross couple between the collector of the second transistor
with a high value resistor back to the first transistor, then you get
a slight "schmitt" effect and the LED should switch on rather than
wind up gradually. This could save a little on batteries too as it
would only come on when needed.

Best of luck with it, John :)
 
thanks John, i was actualy wondering about that, i didnt know weather to have it come on instantly or gradualy. I am making it for a 1 year old (its obviously going to be in a case and im having a a winnie the poo design on the front (drawn by my sister because i can't draw and cut out by me because she can't saw lol).. pity i can't use a 12v AC supply, i could have plugged it into the mains then and used my transformer:D lol
 
I hope it turns out ok mike.

John :)
 
thanks John, so do i lol :lol:
 
ive just thaught (1st time for everything :lol: ) i ordered a 3 AA battery holder (4.5v) don't ask why!! (i ordered it with the rest of my stuff thinking "oh, i might need one one day") i could have chosen the more common ones (2 and 4 battery holders) what a co-incidence :p

Instead of the Cds, i could put a control knob just to test couldn't i? my Cds cell is buisy in a temporary circuit to wind my mum up when she turns the light on :twisted:
 
Think also about alkaline battery life if the nightlight operated at only 10mA for 12 hours each night:
A 9V battery would last 5 nights (very expensive).
AAA cells would last 10 nights (they are also expensive).
AA cells would last 25 nights.
C cells would last a lot longer.
D cells nearly forever.
A car battery would self-discharge long before the LED would drain it. :lol:
 
thanks audioguru, I think i will go for the AA batteries, i will also place a switch to turn the whole thing off if it's not needed/wanted.
Thanks everyone for all your help :)
 
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