My dataaqusition system using USB interface to computer. I am using 18F4550to do that.

My device has separate power ,I need a LED to glow in hardware and the software needs to detect System when plugged.
My hardware needs to be clean from the SMPS noise or ripple or whatever from computer power supply.

What is the best and effective filer mechanism to use on USB connectivity?

Thanks

 

did you need the LED to glow when you plugin your device into the computer Or glows when pulggin into the power supply ???

 

if you need the LED glows when putting the device to the USB ,you simply connect a limitted resistor to the LED and connect it to the VCC,GND of the USB connector in the device board.

 

Do we need to connect the ground of USB connector to my board ground. Also I need to connect the Vcc of the USB connector to MCU So that firmware can detect host plugged.
In this case Gnd needs to be conected.
Any filetr mechanism here?

regards

 

You need to connect the ground together, there's no avoiding that. Otherwise there would be no common reference point for voltage on both systems.

If you have separate power supply, there's no need to connect the Vcc. USB detection does not depend on the Vcc sensing, but on pulling D+ and D- lines to a certain voltage.

Just make sure that the PIC is separated from the data acquisition system (ground and Vcc), to avoid interference.

 

If you have separate power supply, there's no need to connect the Vcc. USB detection does not depend on the Vcc sensing, but on pulling D+ and D- lines to a certain voltage.

My system connects to PC only at the time of data uploading. If a pin is used to detect the USB connector Vcc, the USB engine needs to be started only at the time of plugin to start enumeration.
Microchip's FUSB board has such a mechanism. They use two inductors to couple and Vcc lines to board. But I cant find out the value of inductor.

Thanks again

 

Right, so you are actually sensing the Vc at the micro side. There's no problem with that, and you don't need to worry about any filtering at all. Just use a resistor to an input pin.

 

Right, so you are actually sensing the Vc at the micro side. There's no problem with that, and you don't need to worry about any filtering at all. Just use a resistor to an input pin.

Thanks for the help.