Quad Motor Driver & 5 V Power Board

Drive four brushed DC motors, power your microcontroller from a clean 5 V rail, and read your battery voltage — all from one 1S lithium cell, on one board.

Designed and built by Navi3D for small robots, rovers, walkers and micro drone frames.

What This Board Does

Connect a single lithium cell and the board gives you three things at once:

**Four independent motor channels.** Each one takes a PWM signal straight from your microcontroller and switches a motor on, off, or anywhere in between.

**A regulated 5 V supply.** Your MCU, servos and sensors get a steady 5 V even though the battery sits below 4.2 V — and it stays at 5 V as the cell drains toward 3.0 V.

**Live battery monitoring.** A dedicated `b+` pad feeds your ADC a scaled copy of the battery voltage, so your firmware always knows the charge state.

Specifications


Battery input	1S lithium, 3.0 V – 4.2 V
Motor channels	4, independently controlled
Continuous current per channel	1 A
Peak current per channel	2 A (short bursts)
Regulated output	5.0 V
5 V rail current	up to 800 mA
Control signal levels	3.3 V or 5 V logic
PWM frequency range	1 kHz – 20 kHz
Battery sense output	half of battery voltage
Idle current draw	approx. 1.2 mA
Mounting	2.54 mm through-hole pads throughout

Pinout

Every label below is printed on the board silkscreen next to its pad.

Power in

Pad	What to connect
BAT+	Battery positive
GND	Battery negative

Motor connectors — one at each corner

Four 2-pin connectors, marked M+ and M−. Motor leads go here. Swapping the two leads reverses which way the motor spins.

Connector	Controlled by
Top-left corner	M3 signal pad
Top-right corner	M4 signal pad
Bottom-left corner	M1 signal pad
Bottom-right corner	M2 signal pad

Motor signal pads

Four single pads labelled M1, M2, M3, M4. Each takes one GPIO or PWM output from your microcontroller and controls its matching motor connector.

Rails and monitoring

Pad	What it gives you
b+	Battery voltage sense — connect to an ADC pin
5V	Four regulated 5 V pins, all connected together
GND bus	Five ground pins along the top edge, all connected together

The four 5V pins and five GND pins exist so you can power several devices — MCU, servo, sensor, LED strip — without splicing wires or building a separate distribution block.

The b+ Battery Monitor

b+ outputs exactly half the battery voltage. Wire it to any analog input — no extra resistors, no external divider board.

javascript

Battery voltage = b+ reading × 2

Reading it in firmware

For a 12-bit ADC running on a 3.3 V reference:

cpp

int   raw    = analogRead(BATT_SENSE_PIN);   // 0 .. 4095
float v_adc  = (raw * 3.3f) / 4095.0f;       // volts measured at b+
float v_batt = v_adc * 2.0f;                 // actual battery voltage

What the numbers mean

Battery state	Battery voltage	Voltage at b+
Fully charged	4.20 V	2.10 V
Healthy / nominal	3.70 V	1.85 V
Time to land or park	3.30 V	1.65 V
Stop immediately	3.00 V	1.50 V

Running a lithium cell below 3.0 V shortens its life and can damage it permanently. Set your low-voltage warning in firmware at 3.3 V and a hard stop at 3.0 V.

Input range

Because the output is half the battery voltage, a 3.3 V ADC has plenty of headroom on a 1S cell — the reading tops out around 2.1 V on a full charge, so there is no risk of clipping.

Driving the Motors

Send a logic high to a signal pad and the motor runs. Send a logic low, or leave the pin as an input, and it stops. PWM the pad for speed control.

cpp

// Simple on/off
digitalWrite(M1_PIN, HIGH);   // motor 1 full speed
digitalWrite(M1_PIN, LOW);    // motor 1 off

// Speed control
analogWrite(M1_PIN, 180);     // roughly 70% speed

Choosing a PWM frequency

Anything between 1 kHz and 20 kHz works. Below about 18 kHz you will hear the motors whine at the switching frequency — pick 18 – 20 kHz if you want the build to run quietly.

Direction

Each channel is a single-direction speed control. Motors spin one way only, set by how you wire the two leads into the connector. There is no reverse and no active braking — cutting the signal lets the motor coast to a stop.

Current

Each channel handles 1 A continuously. Short bursts to 2 A are fine, which covers the startup surge of most small geared motors. If a motor draws more than 1 A while running steadily, give the board some airflow or move to a lower-current motor.

Quick Start

Step	Do this
1	Battery + to BAT+, battery − to GND. Check twice.
2	Motor leads into the corner connectors, M+ and M−.
3	Any 5V pad to your MCU's 5 V input; any GND bus pin to MCU ground.
4	Four MCU PWM pins to the M1 M2 M3 M4 signal pads.
5	One MCU analog pin to b+.

Your microcontroller and this board must share ground. Without that shared connection the motor signals have nothing to reference and the channels will behave unpredictably.

What Makes This Board Different

**The 5 V rail does not sag with the battery.** Most small boards tap 5 V through a linear regulator, which simply cannot produce 5 V from a 3.7 V cell. This board steps the voltage *up*, so your MCU and servos see a full 5 V from a fresh cell right down to a nearly empty one. No brownout resets halfway through a run.

**Motors stay off until you tell them otherwise.** Every channel is held off by default. During MCU reset, firmware upload, or a momentarily floating pin, the motors do not twitch or run away.

**Inductive kickback is handled on-board.** Each channel has its own protection across the motor terminals. You do not need to add flyback diodes to your motors — that work is already done.

**Battery telemetry with zero extra parts.** The `b+` pad is ready for an ADC pin. No divider to calculate, no resistors to solder, no separate sense module.

**Real power distribution.** Four 5 V pins and five ground pins mean a servo, an MCU, a sensor and an indicator can all be fed from the board directly.

**Everything is labelled.** Every pad is named on the silkscreen — `BAT+`, `GND`, `5V`, `b+`, `M1` through `M4`, and `M+` / `M−` on each connector.

Important Safety Notes

**Check battery polarity every single time.** Connecting the battery backwards will damage the board immediately and permanently. If you are plugging and unplugging often, fit a keyed connector so it can only go in one way.

**1S batteries only — 3.0 V to 4.2 V.** Do not connect a 2S pack, a 7.4 V pack, or a 9 V battery. Higher input voltage will push the 5 V rail above 5 V and damage whatever is plugged into it.

**There is no overcurrent protection.** A jammed or stalled motor will keep drawing current until something overheats. Detect stalls in firmware, and fit an inline fuse on the battery lead if your build can physically jam.

**Add a fuse for anything that moves fast or carries weight.** A 5 A inline fuse on the battery lead is cheap protection for the whole system.

**The board draws a small current whenever a battery is attached.** Roughly 1.2 mA at idle. Unplug the battery during storage — leaving a small cell connected for weeks will discharge it below its safe floor.

**Motor terminals are live whenever the battery is connected.** One side of each motor connector sits at battery voltage even when the motor is stopped. Disconnect the battery before rewiring anything.

Troubleshooting

Symptom	Likely cause
Motor does not run at all	MCU ground not connected to board ground
Motor runs but ignores PWM	Signal on the wrong pad — check the corner-to-pad map above
Motor runs backwards	Swap the two motor leads in the connector
5 V rail reads low	More than 800 mA being drawn, or the battery is nearly flat
b+ reads zero	ADC pin not configured as an analog input
b+ reads half what you expect	The pad outputs half the battery voltage — multiply by two
Motors stutter under load	Battery sagging; try a cell with a higher discharge rating
MCU resets when motors start	Use a battery with lower internal resistance, or add a capacitor across BAT+ and GND

Support

Questions about this board, or something not behaving as described here — get in touch through navi3d.in.