Laptop hangs on Post and boot with external K/B. I need a 5v delay switch on.

Jan 03, 2007 4 Replies
M

I need a 5V delay switch on to the external RF transceiver of my wireless K/B. The delay will take the 5V in from the USB and then supply 5 volts to the keyboard about 20 secs later(variable).



Laptop has no BIOS updates and I cannot afford another external keyboard. So the keyboard works ok, once the laptop is booted, but posting and resuming XP stalls the laptop for some unknown reason.



Laptop is being used as a media center you see, under the TV, and it's own keyboard is busted anyway!



Thanks.



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O

A slow charging capacitor feeding a schmitt trigger gate, itself controlling a mosfet that controls the +5v.

Figure out the value of the resistor and you should be done.

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M

The mosfet has a very low on resistance doesn't it. cos that was my next q. How do I make sure that 5V is at the output end of the transistor, to save me using a relay.

I am too long outta this game to remember anything anymore!

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O

RdsOn is usually a few ohms, some of them even have less than one ohm. And considering this is USB, you only need to have one that supports 5V and 500mA, which they pretty much all do... And 4.9v will most often be accepted by devices, after all the losses in a USB cable could actually amount to this sort of deviation if not more.

Cheers

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M

I did a cct out which has a 74132 and a pnp transistor and it looks good. Doesn't look to be any voltage drop on the emitter (load side) of the transistor. Now, just have to get my hands on a 74132!

Thanks.

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