# i need help urgently on a project

#### ghanashree

Joined Oct 6, 2009
6
i'm working on a college project that needs to use 555timer n relays for room automation. can anyone plz suggest me the simple circuit that i can develop in 3 to 4 days? please it's really urgent....

#### Wendy

Joined Mar 24, 2008
22,701
Not much to go on there. What kind of automation, how is it triggered? Powered? What is it controlling? Why is it needed?

A 2 line sentence like that is impossible to work with.

#### StayatHomeElectronics

Joined Sep 25, 2008
1,073
What exactly are you trying to control?

#### ghanashree

Joined Oct 6, 2009
6
it's for controlling the classroom circuit. we r told to set the timer such that for recess time n after thr colg is over..the lights n fans should be automatically turned off n we r not supposed to use microcontroller as we have not studied it yet.

#### ghanashree

Joined Oct 6, 2009
6
i'm really confused. our teacher hasn't told us anything that will help us out.

#### ghanashree

Joined Oct 6, 2009
6
i'm very new in electronic world n very confused about designing circuits. plz help me out guys

Last edited by a moderator:

#### onlyvinod56

Joined Oct 14, 2008
363
hello ghanasree,

r u really want to use 555 timer?
i dont think that a 555 can be set for a long time period (almost all morning 9:00am to evening 4:00pm).
u just find out with ur lecturer about the compulsory of 555......

instead, u can do this by other ICs

#### Wendy

Joined Mar 24, 2008
22,701
Problem is, you still haven't told us what you want. Defining the job is always the first step. So let me guess.

You want to turn on an AC high voltage line for 8 hours at the push of a button? If this is wrong, or if there are other bells and whistles that are required now is the time to state them. I'm going to assume a 9V battery is OK.

#### ghanashree

Joined Oct 6, 2009
6
if not 555, then which ic can b used? and will it b possible to construct it so early?is a p.c.b.required?may b i'm asking questions like a non-technical person, but i'm so desperate because we are told to submit it in 3 days. n our lecturers seem to b in no mood to help us.we are supposed to construct a very simple circuit. we are also told to use occupancy sensors

#### ghanashree

Joined Oct 6, 2009
6
u r partly right bill sir. bt i also need to set a time gap of 45 mins. from 12.30pm to 1.15pm for which supply will b off(recess)

#### RiJoRI

Joined Aug 15, 2007
536
The heart of it could be a 555 clocking a series of shift registers every 15 minutes, moving a bit along. The register outputs would be wired to the light controller. Then you'd need to figure out an occupant detector. A switch on the door? This would start the 555 running, and probably load the first S-Reg.

For the 1st 14 clocks the power would be on, for the next 3 it would be off (disconnected), and the final 11 would be on.

Of course, this all assumes that the room is entered precisely at 9 AM.

--Rich

Personally, I'd go get a multi-setting timer. and use the 555 as a support for it.

Rich (BB code):
+------+
|       |
| Timer |----+
|       |    |  <== Plug
|       |----+
|       |
|       |
|       ||=   <=== IC to keep bottom of unit from banging against the wall.
|       ||=
+------+

#### StayatHomeElectronics

Joined Sep 25, 2008
1,073
That is a truly innovative use of a 555.

#### Wendy

Joined Mar 24, 2008
22,701
You could use a series of long time monostables, each triggering the one after it.

From what you've said the 555 is manditory, does it have to be just one? I doubt it.

Check the application notes for a 558 to see what I mean. This could easily be modified for a 555.

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#### t06afre

Joined May 11, 2009
5,934
This is perhaps in the alley that already has been suggested. It seams like you may use a resolution equal to 15 minutes. So you split the day up in 96 time segment. That will be a 7 bit counter counting up to 95 then resetting to zero. Then you decode all functions from the 7 bit counter. A very simple solution would be to feed the 7 bit counter to a ROM circuit

#### Wendy

Joined Mar 24, 2008
22,701
The data sheet says a 555 can go for hours, I suspect that a lot of folks limit this little chippie. It will work with large capacitors and resistors, you just have to understand that some older caps will give you problems.

#### Bernard

Joined Aug 7, 2008
5,788
Longest 555 time for me was about 3.5 hours.This seems a little rediculus but here goes: As suggested by t06afre, a counter, 4040 12 stage binary,driven by a free-running 555 with a period of 28.125 sec will output a 15 min period @ Q6. Operation starts with a 24 h timer or switch etc, setting a flip-flop[FF B ]which releases 4040 to start counting & sets FF L, enabling Relay Driver to turn on lights if there is activity in room.Activity is detected by passive infra-red detector J [PIR ] which triggers 555 K and shorts timing cap on every activation so that if there is no activity for 15 min. ,lights go out. Lights enabled at start, 1:15, & by cleaning crew. Lights disabled at 12:30 , 4 PM, & lack of activity. Wish you luck.

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