Power Supply

Using a single power source needs further knowledge about Zumo power supply. Fortunately, I find out from the schematics. However, this is still the most challenging but fun part of the project.

Power Supply in Zumo

It's quite different how Zumo Shield (aka Zumo for Arduino) and Zumo 32U4 handle the power. I focused on Zumo Shield because I will use it to build zpi1.

Zumo Shield

Zumo Shield simply splits the battery power (VBAT) into following paths:

• VM input of the motor controller (no regulation, to drive motors)
• Regulated 7.45v to VIN pin in Arduino connector, to power Arduino
• One of the blue LEDs (the other two red and one blue LEDs are powered by VIN)

It's clear Zumo Shield only connect VBAT to motors and one of the blue LED. The rest goes to Arduino through VIN pin. As Arduino may possibly access external power from its own power jack, that's why there's an alert in Zumo Shield Manual:

Warning: When powering the Arduino from the Zumo Shield, you must never connect a different power supply to the Arduino’s VIN pin or plug a power supply into the Arduino’s power jack, as doing so will create a short between the shield’s power supply and the Arduino’s power supply that could permanently damage both the Arduino and the Zumo Shield.

Arduino is powered by 7.45v VIN from Zumo Shield, and it generates regulated 3.3v and 5v power back to Zumo Shield for all the peripheral, like buzzer, sensors, and motor controller (the control logic), etc.

Simply speaking, Zumo Shield doesn't power peripherals on PCB, but powers Arduino and uses Arduino's output 3.3v and 5v to power the peripherals. Only motors are directly powered from batteries.

Zumo 32U4

Zumo 32U4 handles the power in a completely different way, because micro controller ATmega32U4 is integrated onboard.

Zumo 32U4 utilizes a power selector which allow power to be supplied both from batteries and USB at the same time. It selects one automatically.

It may simplify the way integrating Raspberry Pi. As I'm not using Zumo 32U4 for zpi1, I'm not digging the details here. I may come back when I start customizing Zumo 32U4.

Power Raspberry Pi

Connect with Arduberry

Arduberry is actually an Arduino (with ATmega328 onboard). By connecting it to Raspberry Pi, it allows Raspberry Pi easily access the Arduino and the peripherals connected.

It provides a simple solution to put in Raspberry Pi where an Arduino is expected.

I'm very happy with Arduberry as it plugs Raspberry Pi to Zumo Shield so easily.

However I was confused with one question:

Raspberry Pi is powered externally, and Zumo Shield provides VIN to the connected Arduino, why it doesn't cause short?

I googled the projects plugin Raspberry Pi via Arduberry, none of them mentioned the power issue. All worked out-of-box.

According to the schematics of Arduberry, VIN is not connected to Arduberry. That means, with Arduberry, the power supply from Zumo Shield is completely ignored. That answers my question, and I no longer worry about short. Though I have to find out a new path to wire the power from batteries to Raspberry Pi.

The VBAT and GND pins on Zumo Shield

I was so excited when I found VBAT and GND pins on Zumo Shield PCB:

It's a considerate design. I can wire VBAT to another step-up/step-down regulator to generate 5v power for Raspberry Pi.

I soldered two pins to connect wires to VBAT and GND:

The Step-up/down Regulator

The reason choosing Step-up/down regulator, not step-up, because I want to keep the possibility of using 4 AA alkaline batteries which provides 6v power and has to step-down to 5v.

I ordered VERTER 5v boost/buck from Adafruit. Not sure if it can provide enough current. I can replace it if it's not enough.

The good thing about VERTER is it provides 2 outputs, one to USB, the other to the pins. I need exactly 2 outputs of regulated 5v, one for Raspberry Pi and the other for Servo HAT.

It also provides a standard USB female port. I can use standard USB-A to micro USB cable to connect Pi. However I customized the cable because it was difficult to hide the standard cable.

To verify the power supply, connect the micro USB to a USB breakout board, and use a multimeter to check the voltage.

The assembled pictures:

Next

The rest of the work is much simpler. I need to customize some acrylic plates to stack things up. Read Stacking for details.