Alternatives

• PCB design alternative
• LiPo charger from Adafruit

Power distribution boards

• Matek PDB-XT60 w/ BEC 5V & 12V
• Matek Systems PDB Supports 3S Battery for FPV Racing Drone HUB5V12V

Power source

Motors normally require higher voltage (6V, 12V, 24V) and current, and it's a good practice to keep motors, LEDs (like very long strips of LEDs), switches electronically seperated from the logic (3.3V). But how do you decouple it when the whole project should work from the battery?

Do you use two batteries? Just imagine what a headache is to keep two separate batteries charged. I can only think about sophisticated system where there is an assumption that motors can kill the battery often, but at the same time the main brain must continue operating, therefore it remains only one option: to send a signal about help to other robots. But I've never seen such design.

So what normal people use instead?

Power supply needs to be protected from Back EMF when motors abruptly stop or reverse the rotation direction. But rechargeable battery only wins from this effect. The only concern will be values above maximum ratings especially for li-poly batteries that are very sensitive.

Read more: Operating an Arduino for a Year from Batteries

Battery charger

Let's design our custom board for powering the robot from one lithium polymer battery, say 3.7V and 2500mAh.

First of all, even before using the battery in any way, we should think about charging it. Here's a battery charger from Adafruit based on MCP73833 (evaluation board doc). For a second I thought that I found cheaper option - MCP73831 on Digi-Key in a 5-lead SOT-23 package, but it consumes 4x times less current during charging which means that it's going to charge much slower and has less indication signals. The datasheet provides PCB layout example.

Old alternative for these chips is MAX1555 and TP4056.

Additional components:

• 3x indicator LEDs: 2x yellow and 1x white
• 2x capacitors 4.7uF - Voltage Rating 10VDC
• 3x resistors 470 Ohms - for LEDs, so for 20mA the Power Rating would be >100mW
• 1x resistor (to set maximum charging current) 1K - for 25mA current (?), therefore the Power Rating >125mW
• 1x resistor (to skip temperature control) 10K - for 50uA and 1.25V = 62.5uW

Step up voltage regulator

We need to boost 3.7V voltage from our battery to 5V level where Arduino and motors can work. Preferably we should supply 3.3V to logic board and separate 5V or 6V or even more to motors. But we must keep the first version simple.

Again we start with a popular at this time breakout board and look at the main chip (TPS61030). For logic board AND motors I found 1.8A TPS613222 and 3.6A TPS61032 switch current boost converters from Texas Instruments. The datasheet provides PCB layout example.

Old alternative for these chips is TPS6109.

Additional components:

• 1x coil (inductor) 2.2uH (max DC current > 1.18A)
• 1x schottky diode (alt) (required for >250mA loads) - find average and peak current from the inductor (1.8A, 2.4A)
• 1x resistor 5 Ohms (for RC snubber) - power dissipation of the snubber is calculated as CV^2f = 150pF x (5V)^2 x 1MHz = 3.75mW (frequency of the circuit is calculated by the formula in datasheet with values V_in = 4V, V_out = 5V, n = 0.9, L = 2.2uH, I_lh = 0.5A)
• 1x capacitor 150pF (for RC snubber) - x3 of schottky diode capacitance (45pF x 3 = 135pF) and voltage rating 10V
• 3x capacitors 10uF - voltage Rating 6.3VDC

Connectors

• Arduino uses barrel jack connector, and more precisely 2.10mm ID (0.083"), 5.50mm OD (0.217")
• Power for Arduino or Raspberry Pi (1/2 - in theory) - Micro USB Type B Male Vertical - connector is perpendicular to the board's surface thus it connects to Arduino or Raspberry Pi perpendicular as well. Raspberry Pi 1/2 where lower power consumption. Some components not rated for the current greater than 1A, so with Raspberry Pi 4 it can fry them)
• Battery to the board - JST PH Connector
• For charging USB cable let's be modern and use type C - USB Type C Female

Q&A

• Do you know that batteries can have multiple cells. One cell is 3.7V. 2 cells (2S) - 7.4V. 3 cells (3S) - 11.1V

• Why capacitors are basically everywhere?