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Battery-Powered 28BYJ-48 Stepper Controller

This project uses one 18650 cell, a TP4056 charger module, an MT3608 boost converter, an Arduino Nano, and a ULN2003 driver board to power a 28BYJ-48 stepper motor.

A single-pole KCD11 rocker switch turns the battery-to-boost path on and off. Turning the switch off removes the boost input, so the whole 5 V rail (Nano and motor) is unpowered. The Arduino Nano clone used here has no USB VBUS Schottky diode, so the USB and battery-powered 5 V supply must not be connected to the Nano at the same time.

This document describes wiring and power only. It does not include Arduino code.

1. Components

Component Notes
18650 Li-ion cell Single cell, suitable holder or secure battery connection
TP4056 charger module Use a protected module with separate B+, B−, OUT+, and OUT− terminals
MT3608 boost converter Adjustable; set its output to 5.0 V before connecting the loads
KCD11 rocker switch Single pole, on/off; see the variant note below
Arduino Nano clone This clone has no VBUS Schottky diode
28BYJ-48 stepper motor Use the 5 V version
ULN2003 driver board Matches the motor’s 5-pin plug
Optional fuse Near TP4056 OUT+; rated above normal load current and below safe limits of the cell, protection board, and wiring
Optional capacitor 100–470 µF across the 5 V rail; observe capacitor polarity and voltage rating

Check the labels on the actual modules: board layouts and terminal names vary. Some TP4056 boards do not have a protection circuit or separate OUT terminals. This diagram requires a protected module with separate load terminals. Do not assume an unprotected TP4056 board provides battery over-discharge or over-current protection, and do not use its B+/B− pads as though they were protected OUT+/OUT− pads.

KCD11 switch variants

The KCD11 family ships in several contact configurations and often shares one housing across them. Terminals labeled 1, 1a, and 1b describe a single pole with two throws; the unused throw may be molded into the housing with no metal lug. This build needs only one on/off pole with two usable terminals.

On the switch used here, 1 is the center lug (common) and 1b is the populated throw; 1a is an empty pocket and stays unconnected. Wire the two switch wires across 1 and 1b. A mechanical contact has no polarity, so either wire may go to either lug.

Confirm the switch with a multimeter before wiring: there should be continuity between 1 and 1b when the rocker is on, and none when it is off. A single pole is sufficient because the motor has no independent supply of its own (see section 4).

2. Power flow

18650 ──► TP4056 protected battery/load terminals
                     │
                     └── OUT+ ──► KCD11 ──► MT3608 ──► 5 V rail
                                                          ├── Nano 5V
                                                          └── ULN2003 VCC

The TP4056 is a charger, not a 5 V power supply. Its IN+/IN− terminals are the USB charging input. The B+/B− terminals connect to the battery. The protected module’s OUT+/OUT− terminals provide the battery-voltage load connection.

The MT3608 boosts the cell voltage (approximately 3.0–4.2 V) to 5.0 V.

3. Wiring schematic

Battery:
  18650 (+) ──► TP4056 B+
  18650 (−) ──► TP4056 B−

Charging input:
  USB 5 V (+) ──► TP4056 IN+
  USB GND     ──► TP4056 IN−

Battery-powered load path:
  TP4056 OUT+ ──[optional fuse]──► KCD11 terminal 1 (common, center lug)
  KCD11 terminal 1b ──► MT3608 IN+
  KCD11 terminal 1a (if present) ──► leave unconnected

  TP4056 OUT− ──► common system GND
  MT3608 IN−   ──► common system GND
  MT3608 OUT−  ──► common system GND
  Nano GND     ──► common system GND
  ULN2003 GND  ──► common system GND

5 V and motor supply:
  MT3608 OUT+ ──► 5 V rail ──┬──► Arduino Nano 5V
                              └──► ULN2003 VCC

Control and motor:
  Arduino Nano D9  ──► ULN2003 IN1
  Arduino Nano D10 ──► ULN2003 IN2
  Arduino Nano D11 ──► ULN2003 IN3
  Arduino Nano D12 ──► ULN2003 IN4

  28BYJ-48 5-pin plug ──► ULN2003 motor connector

Important TP4056 ground detail

Connect the cell’s negative terminal to B− only. Connect system ground to OUT−. Do not add an external wire directly joining B− to OUT−; that can bypass the protection circuit on a protected TP4056 module.

The battery negative and system ground may be connected internally through the module’s protection circuitry. Use the module’s labeled load terminals for the load.

4. KCD11 switch operation

The KCD11 is a single-pole on/off switch in the battery-to-boost path, wired across terminals 1 (center common) and 1b:

  • ON (closed): connects TP4056 OUT+ to MT3608 IN+.
  • OFF (open): disconnects the battery from the boost input.
Switch state Contact Result
ON Closed Battery powers the MT3608; the 5 V rail feeds the Nano and ULN2003
OFF Open Boost input is disconnected; the 5 V rail (and therefore the motor) is unpowered

The ULN2003 VCC is tied directly to the 5 V rail, so there is no separate motor cutoff. The motor is unpowered whenever the switch is off because the whole rail is dead. The Nano can still be powered over USB while the switch is off; in that case the rail—and therefore ULN2003 VCC—is fed from USB. See the debug mode in section 6.

5. MT3608 setup

The MT3608 is adjustable; it is not a fixed 5 V supply.

  1. Turn the KCD11 switch OFF.
  2. Leave the Nano and ULN2003 disconnected.
  3. Connect the cell and measure MT3608 OUT+ to OUT−.
  4. Adjust the module’s potentiometer until the output is 5.0 V.
  5. Power-cycle and recheck the output.
  6. Connect the Nano and ULN2003 only after confirming the voltage.

The module’s current capability depends on its components, input voltage, and cooling. The MT3608 IC’s “2 A” switch-current rating does not mean every module can deliver 2 A at 5 V.

6. Operating modes

Run from battery

  • KCD11: ON
  • Nano USB: unplugged
  • TP4056 charging USB: unplugged

The Nano and motor are powered from the MT3608’s 5 V output.

Charge the battery

  • KCD11: OFF
  • TP4056 USB input: connected to a 5 V charger
  • Nano USB: unplugged

With the switch open, the battery-powered load path is disconnected. Keep the Nano USB unplugged during charging as the conservative procedure.

Debug over USB serial

  • KCD11: OFF
  • TP4056 charging USB: unplugged
  • Nano USB: connected to the computer
  • Disconnect the MT3608 OUT+ wire from the 5 V rail while debugging.

The Nano clone has no VBUS Schottky diode. Disconnecting the boost output during USB debugging avoids applying USB 5 V to the MT3608 output. With the switch open the boost is off, but the ULN2003 VCC still follows the 5 V rail, which USB now powers through the Nano’s 5 V pin. Hold the Nano in reset (or do not run the sketch) so the driver does not drive the motor from USB.

Never connect Nano USB while the KCD11 is ON. In that state, the MT3608 supplies the Nano’s 5 V pin, which could back-feed the computer’s USB port.

7. First power-on checklist

  1. Confirm the cell goes to TP4056 B+ and B−.
  2. Confirm the circuit ground goes to TP4056 OUT−; do not bridge B− to OUT−.
  3. With the switch OFF and loads disconnected, set the MT3608 output to 5.0 V.
  4. Recheck polarity and wiring, including the KCD11 continuity check.
  5. Connect the Nano and ULN2003.
  6. Run from battery only with the switch ON and Nano USB unplugged.

8. Design notes

  • Use the Nano’s 5V pin for the regulated 5 V rail. Do not use VIN for this 5 V supply.
  • The 28BYJ-48 plugs directly into the ULN2003 board; individual coil wires should not need to be jumpered.
  • Standard 28BYJ-48 ULN2003 boards do not have a current-adjustment trimmer. Leave their bypass capacitors installed.
  • An optional 100–470 µF capacitor can be placed across the 5 V rail and GND near the loads to help with supply dips. Observe its polarity.
  • Keep the Nano, MT3608, and ULN2003 grounds connected to the TP4056 OUT−-referenced system ground.
  • The single KCD11 pole removes the whole 5 V rail when off, so there is no independent motor-supply cutoff. During USB debugging the rail and ULN2003 VCC are fed from USB, so hold the Nano in reset and disconnect the MT3608 OUT+ wire.
  • Do not charge and run the load simultaneously with this simple TP4056 arrangement. Supporting that requires a proper power-path/load-sharing design.

9. References

These tutorials cover the stepper/driver portion of the project:

TP4056 load-sharing background:

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