Cape Debug - Pin Voltage?


Still having trouble getting the Raspberry Pi to communicate with the Cape, but I have finally narrowed things down a bit.

I am using an Arduino Uno to debug the Cape's UART (running the Serial Monitor on the Arduino IDE). When I touch a jumper to the pin on the atmega328 chip itself, I get the proper readings that the cape should be sending over UART. However, when I connect to the pins (it's supposed to be either 24 or 26, but I tried just about 8 - 46 just in case) I get nothing. Additionally, tests with a voltmeter show that the atmega is putting out slightly under 5 volts, whereas none of the pins are putting out anything.

Looking at the cape schematic, there is a line under the voltage translator that says a pull-up resistor is required if either the atmega or BeagleBone are in hi-z mode. Is it possible that I just need a pull-up resistor?


check your connections vs the Alamode board, these use a similar translator as the cape:


I did some comparison, and it looks like the cape requires 3V3 from the BeagleBone to power the lower-voltage side of the translator. However, plugging the Pi's 3V3 into the appropriate pin on the cape does nothing and, curiously, causes LED3 to go out. Is it possible that the 3V3 must be provided on both pins that the BeagleBone usually uses, and not just the one labeled "VDD_3V3EXT from BeagleBone PMIC" on the schematic?


Your 3.3V seems to be in the right location. you can confirm with a ohm-meter between the two pins that it is the same point.

but you will also need 12V provided to the cape so it generates the 5V for the arduino and the 5V side of the translator.

its also important that the Pi and cape shares the same common ground.

i dont have any explanation for the Led3...