Issues with breadboard SD Card Reader - Page 1
Forum section: electronics / beginners

author: dtfgator
author_rank: Newbie
timestamp: September 22, 2012, 05:05:48 am
content: Hi,A few weeks ago I asked about SD Card Reader circuits, and someone pointed me to the Genesys Logic GL823 (datasheet here:http://www.docin.com/p-167108114.html).I got a few samples and just started prototyping with them... It doesn't want to seem to work at all. I've got it all on a breadboard with a normal SD card (pins soldered to 22awg wire), and the unit appears to boot (status LED blinks a little) and then it goes solid. Windows recognizes a device, but says it failed to install drivers properly and won't show the card. Mac doesn't do anything.I've attached my schematic as I've got it now, which includes the 680ohm USB ref resistor as required in the data sheet. I didn't see anything in the datasheet that my schematic is missing (unless the chips aren't pre-programmed or something ridiculous like that, but I doubt thats it). I know other designs call for pull-up resistors on the data lines to prevent floating, but I'm starting with an SD card inserted so I don't think it should be a problem, and others have gotten away without them.Am I just being an idiot or could there be a bigger problem here? Thanks for any advice you guys have.Edit: In the picture, the connector on the left is a USB male with correct pin numbers. Center is the GL823 IC, and right is the SD connect (pins based on assigned number, not location). I am trying to run in x4 mode.

author: Balaur
author_rank: Unknown
timestamp: September 22, 2012, 08:52:52 am
content: I would be very careful about signal integrity issues on the breadboard wires, especially on the SD wires. Try to make them as short as possible.I have used the SMSC USB222x series of Flash Media controllers and SD cards were no longer accessible after some 5 cm of wires.The (slightly non-trivial) requirements for the routing of critical analog signals (especially SD CMD, CLK, DATx, USB+/-) were described in an application note.Good luck,Dan

author: amyk
author_rank: Super Contributor
timestamp: September 22, 2012, 12:20:03 pm
content: Even ignoring how you managed to get a QFN or SSOP on it, a breadboard is definitely not ideal for prototyping a USB 2.0 device. The DM/DP lines are very sensitive to small variations in length, and the stray inductance and capacitance introduced by a breadboard is going to have a huge effect on the signal. If you can, try forcing the port to operate in full speed mode and see if it works. Regular SD has a clock frequency of 25MHz, far below the USB 2.0 480MHz, so I think the problem lies in the USB end.

author: dtfgator
author_rank: Newbie
timestamp: September 22, 2012, 04:12:02 pm
content: All of that is probably true. I used a SSOP breakout board that I reflow soldered in my oven -- all the pins are good with no shorts. I'll try decreasing the length of all the wires and see if it changes anything.If that doesn't work, does anyone see any flaws in my schematic? If not, I might just go straight to having real PCB's made.

author: amyk
author_rank: Super Contributor
timestamp: September 23, 2012, 09:03:38 am
content: Quote from: dtfgator on September 22, 2012, 04:12:02 pmWith the USB pair it's not as much a matter of how long they are (USB cables can be up to 5m in length) but whether their lengths match, although the longer the cable, the more pronounced the effect is. Does your breakout board keep the same trace length for DM/DP? The cable pair should also be twisted together up until the short stub of track leading to the IC pins.

author: euchrideucrow
author_rank: Newbie
timestamp: February 20, 2017, 05:39:27 pm
content: I know this is a super old thread. But i'm currently in the process of working with the same IC. Did you ever get this to work or did you move on to a different IC?