Thread: uSDC20D computer on sense details

Originally Posted by Hark

I have the uSDC20D for my laptop. Is it possible to use a modified USB cable in order to provide the computer on sense signal? Is there a better, more recommended approach for getting this to work with a laptop?

From the instructions:
The Computer On Sense cable consists of a signal Diode that connects from the controller to a 4-pin Molex computer Hard Drive or CD-Rom Power connector connecting to +12 volts. This is how the controller detects the computer is on so that is doesn’t inadvertently turn on/off the computer when it is already on or off. It also allows “Power Down Mode” to be very short. The diode’s polarity points away from the uSDC.

Can I get more details about the specifics of this diode and how it's supposed to be hooked up? I've learned a lot in my trials/tribulations in my install, but this one has me vexed.

The diode just prevents 12 volts from going into the uSDC and damaging it if you can only use the 12 volt line. If you are connecting it up to 5 volts, you don't need the diode.

What happens, is when the Computer Power supply is off, the 5 volts that is connected to onsense, is pulled to ground by the power supply being off. (No voltage on the 5 volt rail) The diode just lets you use the 12 volt rail too. But because people will try everything under the sun, I just allways reccomend the diode.

Any diode will work. Signal, schottky, 4148, etc..






-Jeff

Thanks Jeff - so if I pull apart a USB cable, isolate the + and - wires, and put a jumper connection on the end that goes go the uSDC20D, I should be ok? Is it correct that USB is only 5V?

Originally Posted by Hark

Can I get more details about the specifics of this diode and how it's supposed to be hooked up? I've learned a lot in my trials/tribulations in my install, but this one has me vexed.

Here you can see when the power supply is on, no current goes through the diode.

When the power supply is off, the uSDC sees a diode drop above 5 volts which it knows is off. The uSDC20D always has a 5 volt power supply.

The diode allows the power supply 5 volts to be 5 or 12 volts.

-Jeff

Originally Posted by Hark

Thanks Jeff - so if I pull apart a USB cable, isolate the + and - wires, and put a jumper connection on the end that goes go the uSDC20D, I should be ok? Is it correct that USB is only 5V?

Yup if you do this, you don't need the diode. Just connect it right to the onsense pin.