USB Host Shield for Arduino UNO MEGA 2560 Support with Google Android ADK HUB

My objective was simply to use a very inexpensive (<$20) Logitech USB Keyboard as a "remote control" of one MAX7219 board with 64 LEDs (8x8 matrix) on an Arduino UNO - 5v at about 3mA per LED at max intensity of "15." This could easily be made to control 256 LEDs with 4 x 7219's, right? I have not tried that yet. Range is over 30 feet - never tested longest range; whatever max wireless keyboard capability is. HOWEVER, there were a couple curious QUIRKS I have yet to work out. Seems I MUST POWER the combo of UNO/HOST SHLD from the UNO USB from a PC or a power cube in an outlet; will typically not work using only DC Power Input Socket on UNO - i.e. will not work dependably with no power to the USB port... it tries to... and will sometimes if it WAS just powered from the USB and unplug it with power to the VDC port, but will not initiate on reset with DC power alone. I've tried fooling the UNO USB port into thinking it was powered from a cube... injecting 5v/3.3v to the USB, but that is not working just yet. I've scoured the schematics of both UNO and HOST SHLD, but still confused what is special about the USB power on the UNO versus the 5 VDC input power - appear to be the same difference. Also, HOST SHLD is supposed to pass I/O through but digital pins that worked to control 7219 from the UNO alone, no longer worked out of the HOST SHLD header. I moved them to A0, A1 & A2, (as shown in the photo) and it works fine. Still have to investigate what happened to those digital I/O. ALSO, there are MANY online videos about using this HOST SHLD card and the 7219, but I found I had to watch quite a few to get all the info I needed to make this work as I wanted - any single ASCII keyboard code can be assigned to any single LED - and that's all I was after. Thanks for reading!

Arrived with pins bent very badly. More importantly, Arduino UNO (and others) is completely unresponsive when this board is attached. Will not even blink an LED. You can't upload any sketches nor get anything from the serial port. Arduino works fine once you remove this piece of junk. A visual inspection did not reveal anything obvious and a quick check with an Ohm meter did not show any shorts or similar. Would give it zero stars if I could.

Works well. Get it

The shield is good and operates properly after all the jumpers are connected. However, the long connector pins are not sturdy so they could bend inward or outward if not perfectly aligned. I bought 3 of them and had to ohm out all the pins on each one, after inserting to ensure that a pin was not inadvertently bend inward where you can't visually spot it from the outside. This is a pain. t would be much better if they used normal strength connector pins.

works good

Didn't work out of the box but was able to modify it a bit to make it work. TLDR add resistors (1k ohm should be fine) in between the arduino and this shield for these pins: MOSI and SCK on the ICSP header, and pin 10 used for SS. Connect the rest of the pins with jumper wires (should only need 5V, 3.3V, GND, pin 9, then MISO and RESET on the ICSP header).Explanation: as many others have stated, the 74hc125 chips they use are not supposed to be used for level shifting - they're tri state buffers. This board has two of them, since the MAX2431E usb chip runs at 3.3V: one to shift arduino signals down to the MAX, and one to shift MAX signals up to the arduino. The level shifting up seems to work fine, as the 74hc125 considers the 3.3V signal from the MAX as logical high, even when its own VCC is 5V. The level shift down is the issue though. The manufacturer is powering that 74hc125 with 3.3V, so that the 5V input signal from the arduino gets output as a 3.3V signal. However, the 74hc125 has clamp diodes to the power rails! So applying 5V to the input will cause a large amount of current to flow into its 3.3V vcc through the clamp diodes. This is what causes the 3.3V bus to rise as another reviewer pointed out, which results in the MAX chip being overvolted and not working. The easy solution is to add a resistor before any of the downshifting 74hc125's inputs - that is, SS, MOSI, SCK, and RESET. However, the RESET pin isn't directly connected to 5V anyway, it has a pullup resistor already, so we don't need to change it. Adding the other 3 resistors limits the current sink of the 74hc125 so the 3.3V bus doesn't rise as much. After that it worked fine.Reverse-engineered schematic attached

Got this shield to add a PC USB keyboard to an Arduino Mega2560 project. Used the library listed in the product description on Amazon. This library is also available in the Arduino IDE library manager. Found the manual for the shield at the site listed in the product description. To set up the board for a PC keyboard, the 5 volt USB power jumper was soldered, and the power to the shield 3.3v and 5v jumpers were soldered. Everything worked fine using the library's example "USBHIDBootKbd" Arduino sketch.

sold me broken hardware. the last thing I need is spend a bunch of time troubleshooting defective hardware. After soldering the thing to work and wasting hours troubleshooting its clear that this component never worked. no power from plugged in usb. safe yourself the huge headache and buy elsewhere.