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Topic: LC Studio Card Reader - BAD PCB (Read 4 times) previous topic - next topic

Arctic_Eddie

I recently received an SD card reader made by LC Studios. The reader did not work on my Mega 2560 but the GPS logging shield was OK. The scope showed very noisy signals from the reader and poor 3V3 on the card. The reader did work if connected directly to the Mega 3V3 line. Closer examination of the card and the sellers schematic shows pin 1 of the regulator chip, one end of C3, and one end of C4 are connected. However, they are floating with no connection to ground as it should be. When I ground this line, the reader works from the Mega 5V0 line, as it should.

There are two easy fixes for this problem. First, feed 3V3 from the Arduino to the 3V3 pin on the reader. This alone will solve the operational problem. A better solution is to ground the floating line, as it should be. Scrape some paint from the top ground plane just under the 'O' in Studio to expose some copper. Connect a short jumper wire from pin 1 of the regulator, pin closest to back of card socket, to the exposed copper.

Surprisingly, the sellers schematic shows a missing ground symbol along the bottom of the regulator, C3, and C4. The circuit and board designer is the culprit in this case.


SoundreameR

Hello. I am using the same garbage... mine works, for now (with little magic)

Check out this post from fat16lib in my thread: http://arduino.cc/forum/index.php/topic,122098.msg923701.html#msg923701

I am getting really frustrated from all the problems with cheap chinese hardware...

Arctic_Eddie

I've also had some bad hardware other than this one. They're not doing a very good job of QC or keeping up with the latest Arduino IDE, especially in LCD backpacks. I found this reader is also sensitive to the level shifter values. I'm using the 74x125 taken from my GPS logger shield and duplicating some of the circuitry. I'll be switching to the Adafruit Micro-SD reader as it should be a simple wire-to-pin plug-in job. I'm using mine on a Mega 2560.

The problem goes back to the schematic designer. They left out the ground connection to the regulator and it's two filter caps. The board layout just followed the schematic so it's also bad. Apparently, nobody bothered to see if the thing worked. Using a 3V3 supply, it's fine, but using 5V0, it won't work. By adding a short jumper wire from pin 1 of the regulator to a scraped off ground area under the logo, the reader works OK.

PaulS

Quote
I've also had some bad hardware other than this one. They're not doing a very good job of QC or keeping up with the latest Arduino IDE, especially in LCD backpacks.

But, you did save a few pennies, right?

Arctic_Eddie

After the addition of a 6mm piece of bare wire, yes, about 75%.

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