I use the
uln2003a to switch a device (with use of a MCU) that is capable doing several things, like fm-radio, bluetooth, playing MP3's etc. It also provides an USB function when it is connected to a computer, it provides an usb soundcard and a SD-card interface. The function is only enabled/started when selected on the device.
The switch works okay, however, when connected to a computer the device is recognized but the computer is unable to communicate with the devices. In Windows there is an exclamation mark present with the comment "Device doesn't start, code 10".
When I bypass the
uln2003a switch with a wire, connect ground directly so the
uln2003a has no function, all of the devices operates just fine. I tried the following experiment:
- Start the device,
- Connect point
Bwith a wire (see schematic below) to bypass switch,
- Select USB mode and working fine.
As soon as I disconnect this wire (ground still connected via uln2003a), devices starts to malfunction in Windows.
The uln2003a switch the same ground and I don't understand why USB is not working. Can somebody explain what's going on?
Simple schematic to give some idea what's going on:
ULN2003A datasheet: http://www.ti.com/lit/ds/symlink/uln2003a.pdf