ALFAT OEM sd-reader doesn't connect


How is it possible that the ALFAT OEM only sends only a small voltage (under 1V) toggle to the PC over DP2 and DM2?

I’m working on a project where my custom circuitboard controls an ALFAT OEM board. My handheld device logs data to the SD card. Then when the user connects to a PC, the device switches ALFAT to sd-reader. I have one alfat on a breadboard which works perfectly. I can change modes, then connect to the PC as external storage device. My oscilloscope shows that DP2 and DM2 toggle high to 4-5V. great!
However… on my prototype circuitboard, when I send the command to initialize sd-reader mode, the DP2 & DM2 lines toggle but the voltage is very weak (under 1V).

So how did I mess up? I’m wondering if I somehow fried something on my alfat accidentally? But it can still write to the sd card ok. Originally I screwed up and had the USB data lines connected in parallel to an FT232 uart converter. That was dumb, but I removed the connecting wires. Could doing that damage the ALFAT or the FUSB2805?

you might need to show your actual PCB schematic to get more depth in responses. I’d expect that this is a more likely area you’ll hit an issue…

@ solara.kane -

  • Looks like there is no connection on Pin 18 where input 5V for USB?
  • Did you modified hardware on ALFAT OEM? seems to be that C1 is removed.