Anyone knowing electronics please help me..

[infra_red_dude]

that circuit is designed to behave like that. imagine what will happen if the time is reduced? the device will switch off and hence the whole circuit becomes useless. we need a pulse for a very short duration (in the order of milliseconds) for the system to boot up. that circuit can't be used unless the computer doesn't haf any problem while the poweron pins are kept shorted. now the question is how can we test if this causes any probs or not?

 

[iMav]

Yeah this will do the trick u can make use of that voltage coming to the buzzer, u only need a small amplifier to increase the current to drive a relay.This will make a cheap timer clock with good accuracy.

exactly what i had in mind instead of the buzzer we connect the power wire of the cabinet power switch

 

[ajaybc]

Does any one know whether there is any problem in keeping the poweron button in the CPU pressed?

 

[ranjan2001]

I dont think so................why not try it on a old comp if u have any.
Power button is to short the circuit & ones its short & remain shorted nothing would happen, re shorting it would shut down.

 

[iMav]

@ajay: there are circuits for what u said but i cant remmber which 1s but there are various ways for that ....il see if i can dig 1 up .... for now i think we could use a gate even if it is high it will generate a single pulse and wont be affected of what happens next

 

[infra_red_dude]

how will a gate convert a cont. high to a pulse, imav??? output duration will be like the input duration. we need to generate a pulse at a specific interval to trigger a relay which in turn shorts the power terminals momentarily to turn on the system. there are circuits. lemme also try to search for them.

 

[iMav]

arre 1 0 wala gate ... hai yaar waisa circuit padha hai par abhi yaad nahi ...

current is coming and it will stay high that is at logic 1 so the cpu will only get a continuous 1

 

[infra_red_dude]

1 0 wala gate? not gate? hey bhai.. no gate will generate pulses.. rather a latch (single input flip flop made of not gates) will hold the value for long. and thats exactly opposite to what we want. yeah i know there are pulse generating circuits but they are too complex to build. keep searching imav... i too will.. hope we stumble upon something simple...

 

[iMav]

arre sorry flip flop

 

[Pathik]

@ajay
i went thru the circuit and it'll work. but i haf one doubt regarding the relay. in that circuit the relay will remain on for the entire period till the circuit is manually switched off. when connected to the computer this means that the two pins will be shorted untill its turned off. however the method applied to power on modern system is that there's a momentary short of the two pins on the mobo. as soon as it powers on the switch is released and they are no longer shorted. will there be any harm to the system if the two pins are shorted for long? that is my question now.

Afaik in most systems the system boots up only wen the power button is pressed and then released.. Not if the power button is kept pressed.. Btw aint there any ic wich can communicate with the cmos??

 

[infra_red_dude]

^^^ communicating wid cmos is not an easy task!

 

[iMav]

infra yaar ... and gate kaam karega na ... 11=1

 

[infra_red_dude]

yeah bhai, but the output will stay at 1 (high or low) meaning that the power pins will be shorted continuously. thats not what we want. thats the whole problem!

 

[iMav]

haan toh buzzer ka timer toh adjust ho hi sakta hai ...

 

[infra_red_dude]

hmmm... we'll need two counters for this circuit then. the first one is for setting the trigger time and the second one is to turn the circuit off after say about 500ms (which is approx to a pulse). but it'll not be that easy to build!

 

[iMav]

how about this ... i think this is perfect for a project

*img403.imageshack.us/img403/4820/monostablewc0.jpg

 

[infra_red_dude]

thats a good start imav some things which need to be taken care of. after the trigger is pressed the the cicuit turns on. but here we want the circuit to trigger say after 1 hour of pressing the switch and that too only for half a second. so we'll need to modify this circuit. but good thinking, imav

 

[ajaybc]

Thanks Imav and infra red dude for trying ur best to help me.
Keep posting in this thread if u come up with some thing.

Still nobody cud come with a solution and I had wake up at 2AM today also.

Still nobody cud come with a solution and I had wake up at 2AM today also.

 

[infra_red_dude]

sorry pal... cudn't look into this matter. been busy wid my GRE classes

 

[ajaybc]

Had to wake up at 2AM 2day also