Hardware Reference
In-Depth Information
Designing the BeagleBridge circuit
The following Fritzing diagram shows the schematic for this project.
The potentiometer is connected via BBB's
Analog-to-Digital Converter
(
ADC
) pins.
BBB's analog inputs can only tolerate a max of 1.8V; so, it's very important to use the ded-
icated analog voltage pin, pin P9_32 (pin number 32 of the connector P9), which provides
this voltage. Do
not
connect the potentiometer to the normal 3.3V or 5V power rails, as this
will damage the processor. We'll arbitrarily pick the analog input AIN5 on pin P9_36 as our
input pin, and connect that to the middle lead or output of the potentiometer. Lastly, con-
nect the last lead of the potentiometer to the dedicated analog ground pin, P9_34.
The LED and LCD both use 3.3V and the common ground. We need a serial transmit pin
for the LCD, so we'll arbitrarily pick P9_13, which is the transmit for UART4. UART1
transmit on P9_24 or UART2 on P9_21 will also work fine.
Lastly, we need a GPIO to control the LED. Again, any will do, but I've picked pin P9_15.
You'll need a resistor to limit the current to the LED. Sizing a resistor is straightforward us-
ing Ohm's Law; we just need to know the forward voltage drop and the max current of the
LED. This information is found in the datasheet. If you are using SparkFun's 5mm Green
LED, its max current is 20mA and has a forward voltage drop of 2.2V.
