While I’m reading up on the PIC32MZ, I thought it would be good to knock out a quick mod card for Callisto, and the new MZ based board. I wanted the mod to incorporate lots of connections for sensors and servos while also fitting within the profile of Callisto.
The Callisto Pin-Map
Callisto interfaces with the real-world through its pin-map. The schematic shown here identifies the pins along with their special functions. D# are the basic pin numbers for the digital GPIO functions of Callisto. Pins with “AN” denote analog input capable pins, and pins labeled “P#” denote pins that can be PWM outputs.
There are 3 power rails on Callisto: VBUS is the +5V from the USB port, VBAT is the voltage from the battery, and the 3.3V output from the on-board regulator. There is also an enable pin (ENA) that allows the output of the 3.3V regulator to be disabled when the signal is grounded.
Design of a Mod
For the Explorer Mod, I decided to setup every GPIO pin with a servo style connection. Each GPIO maps to a 3-pin male connector where the middle pin is power, and the pin opposite the GPIO pin is ground. This enables any servo to be connected to the 3-pin interface directly. Also, I took the opportunity to duplicate the GPIO headers as an inner row of interconnection so that they can be used as test-points, wiring positions or to interface other sensor boards. There is 0.2” center-to-center between the inner rows of contacts which leaves room down the center channel for routing wires or connecting components.
About the Other Interfaces
Other than the servo connections, I added an interface for a HC-SR04 ultrasonic module. The contacts behind it are to connect the trig and echo IO to the GPIO of Callisto. There is also a supply selection jumper for picking the supply for the ultrasound module. The supply rail can be selected as either VBUS or VBAT.
Lastly, I added a handy reset button to reset the main board from the expansion mod.
The only thing left to do now is to wait for the boards to arrive from the manufacturer.