555 timer project help

Thread Starter

mecj5

Joined Jul 9, 2008
5
I have searched the Internet for days trying to find a circuit to do what I want it to do, so if this has been asked before I apologies.:D

So with that being said on to with what I'm trying to do, what I'm trying to do is use a 555 timer to delay the off by 30 sec of an led after the lights go off in the room (so i don't stub my toe on the wall:() and remain off even if the lights come on(only be on after the lights have just been turned off).
is this possable with a 555 timer of would i have to go with a micro?

any input or feedback is greatly appreciated
thanks
 

tracecom

Joined Apr 16, 2010
3,944
Step by step.

LED is on.
Lights are on.
Lights go off.
30 minutes pass. Lights may turn on and off repeatedly, but have no effect.
LED goes off.

Is that what you want?
 

Wendy

Joined Mar 24, 2008
22,155
If not you are describing a really basic monostable, the simplest of the configurations. You just need to make the sensor go from high to low when the lights go out. So it is the light sensor you are needing help with, do you want to use a phototransistor or a LDR?

555 Monostable



Use 2 555s with this, one for the sensor, one for the timer. Swap the CDS (LDR) and resistors.
 
Last edited:

Thread Starter

mecj5

Joined Jul 9, 2008
5
Step by step.

LED is on.
Lights are on.
Lights go off.
30 minutes pass. Lights may turn on and off repeatedly, but have no effect.
LED goes off.

Is that what you want?
no that is not quite what i want

step by step
Room lights are turned off
LED is on for 30 secs
LED goes off
Room lights come on
Led stays off
(only on when lights have just been turned off no other time)

that is what i'm trying to accomplish
 

tracecom

Joined Apr 16, 2010
3,944
no that is not quite what i want

step by step
Room lights are turned off
LED is on for 30 secs
LED goes off
Room lights come on
Led stays off
(only on when lights have just been turned off no other time)

that is what i'm trying to accomplish
Okay, my mistake about the 30 minutes. I see that you said 30 seconds.

I think I have a schematic somewhere; I'll look.
 

CoHPhasor

Joined May 13, 2013
13
no that is not quite what i want

step by step
Room lights are turned off
LED is on for 30 secs
LED goes off
Room lights come on
Led stays off

(only on when lights have just been turned off no other time)

that is what i'm trying to accomplish

I'm confused by what you are trying to do.
So what is going to ever make the LED back on, will it be switched to reset?
 

Thread Starter

mecj5

Joined Jul 9, 2008
5
If not you are describing a really basic monostable, the simplest of the configurations. You just need to make the sensor go from high to low when the lights go out. So it is the light sensor you are needing help with, do you want to use a phototransistor or a LDR?

555 Monostable



Use 2 555s with this, one for the sensor, one for the timer. Swap the CDS (LDR) and resistors.
i'm having a hard time picturing what your telling me with the two 555 timer do you happen to have a circuit?

i would like to use a cds because they seem to be more sensitive, but it doesn't really matter to much to me.
 

Thread Starter

mecj5

Joined Jul 9, 2008
5
I'm confused by what you are trying to do.
So what is going to ever make the LED back on, will it be switched to reset?
no i am hoping to get the timing ramp to reset when the lights go out but have the led stay off when the room lights are on.
 

pprakash

Joined May 10, 2013
1
If I understand it right below is the pattern you are looking for.

1. Room Light is switched ON (Should also act as a trigger to activate the circuit) - LED stays Off
2. Room Light is switched Off - LED should be ON for 30 Secs


This can be achieved with slight modification to tracecom's circuit by having the RESET pin of 555 as well controlled thru an LDR which will hold it High until the light goes Off. So you will have 2 LDRs, One to sense Light ON and other to sense Light Off.
 

Bernard

Joined Aug 7, 2008
5,601
A contination of Bill's ckt. Sampling of several LDR's gives at least a 10-1 resistance change from subdued light to subdued dark.
20k 470k
5k 100k
10k 150k
100k 1M
R1 assumed the 20k, which gives 2V or 10V on pins 2&6 with R1 =100k- better if a pot. U1-3 is either lo or if light is on goes lo at turn off, triggering U2. If LED[ bright white?] affects LDR, then D1-R4 clamps U1-2 hi, preventing interaction. R5 depends on LED selected.
 

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Thread Starter

mecj5

Joined Jul 9, 2008
5
A contination of Bill's ckt. Sampling of several
LDR's gives at least a 10-1 resistance change from subdued light to subdued dark.
20k 470k
5k 100k
10k 150k
100k 1M
R1 assumed the 20k, which gives 2V or 10V on pins 2&6 with R1 =100k- better if a pot. U1-3 is either lo or if light is on goes lo at turn off, triggering U2. If LED[ bright white?] affects LDR, then D1-R4 clamps U1-2 hi, preventing interaction. R5 depends on LED selected.
that is excatly what I want it to do, thank you so much

and thanks to everybody for you help and feedback
i knew it was possible but couldn't figure it out
 
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