Rework wiring diagram for single-pole KCD11 switch
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@@ -4,8 +4,9 @@ This project uses one 18650 cell, a TP4056 charger module, an MT3608 boost
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converter, an Arduino Nano, and a ULN2003 driver board to power a 28BYJ-48
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stepper motor.
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A DPST switch controls the battery-to-boost path and independently disconnects
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the motor supply. The Arduino Nano clone used here has **no USB VBUS Schottky
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A single-pole KCD11 rocker switch turns the battery-to-boost path on and off.
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Turning the switch off removes the boost input, so the whole 5 V rail (Nano and
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motor) is unpowered. The Arduino Nano clone used here has **no USB VBUS Schottky
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diode**, so the USB and battery-powered 5 V supply must not be connected to the
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Nano at the same time.
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@@ -21,7 +22,7 @@ Nano at the same time.
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| 18650 Li-ion cell | Single cell, suitable holder or secure battery connection |
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| TP4056 charger module | Use a protected module with separate `B+`, `B−`, `OUT+`, and `OUT−` terminals |
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| MT3608 boost converter | Adjustable; set its output to 5.0 V before connecting the loads |
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| DPST on/off switch | Both poles operate together |
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| KCD11 rocker switch | Single pole, on/off; see the variant note below |
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| Arduino Nano clone | This clone has no VBUS Schottky diode |
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| 28BYJ-48 stepper motor | Use the 5 V version |
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| ULN2003 driver board | Matches the motor’s 5-pin plug |
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@@ -35,6 +36,23 @@ assume an unprotected TP4056 board provides battery over-discharge or
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over-current protection, and do not use its `B+`/`B−` pads as though they were
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protected `OUT+`/`OUT−` pads.
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### KCD11 switch variants
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The KCD11 family ships in several contact configurations and often shares one
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housing across them. Terminals labeled `1`, `1a`, and `1b` describe a single
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pole with two throws; the unused throw may be molded into the housing with no
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metal lug. This build needs only **one on/off pole with two usable terminals**.
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On the switch used here, `1` is the **center lug (common)** and `1b` is the
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populated throw; `1a` is an empty pocket and stays **unconnected**. Wire the two
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switch wires across `1` and `1b`. A mechanical contact has no polarity, so
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either wire may go to either lug.
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Confirm the switch with a multimeter before wiring: there should be continuity
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between `1` and `1b` when the rocker is on, and none when it is off. A single
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pole is sufficient because the motor has no independent supply of its own (see
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section 4).
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---
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## 2. Power flow
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@@ -42,9 +60,9 @@ protected `OUT+`/`OUT−` pads.
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```text
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18650 ──► TP4056 protected battery/load terminals
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│
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└── OUT+ ──► DPST Pole A ──► MT3608 ──► 5 V rail
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├── Nano 5V
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└── DPST Pole B ──► ULN2003 VCC
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└── OUT+ ──► KCD11 ──► MT3608 ──► 5 V rail
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├── Nano 5V
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└── ULN2003 VCC
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```
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The TP4056 is a **charger**, not a 5 V power supply. Its `IN+`/`IN−` terminals
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@@ -68,8 +86,9 @@ Charging input:
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USB GND ──► TP4056 IN−
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Battery-powered load path:
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TP4056 OUT+ ──[optional fuse]──► DPST Pole A common
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DPST Pole A switched terminal ──► MT3608 IN+
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TP4056 OUT+ ──[optional fuse]──► KCD11 terminal 1 (common, center lug)
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KCD11 terminal 1b ──► MT3608 IN+
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KCD11 terminal 1a (if present) ──► leave unconnected
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TP4056 OUT− ──► common system GND
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MT3608 IN− ──► common system GND
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@@ -79,8 +98,7 @@ Battery-powered load path:
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5 V and motor supply:
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MT3608 OUT+ ──► 5 V rail ──┬──► Arduino Nano 5V
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└──► DPST Pole B common
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DPST Pole B switched terminal ──► ULN2003 VCC
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└──► ULN2003 VCC
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Control and motor:
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Arduino Nano D9 ──► ULN2003 IN1
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@@ -103,29 +121,24 @@ load.
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---
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## 4. DPST switch operation
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## 4. KCD11 switch operation
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The DPST switch has two electrically separate poles operated by the same
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handle:
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The KCD11 is a single-pole on/off switch in the battery-to-boost path, wired
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across terminals `1` (center common) and `1b`:
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- **Pole A:** connects TP4056 `OUT+` to MT3608 `IN+`.
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- **Pole B:** connects the 5 V rail to ULN2003 `VCC`.
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- **ON (closed):** connects TP4056 `OUT+` to MT3608 `IN+`.
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- **OFF (open):** disconnects the battery from the boost input.
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| Switch state | Pole A | Pole B | Result |
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|---|---|---|---|
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| **ON** | Closed | Closed | Battery powers the MT3608; Nano and motor receive 5 V |
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| **OFF** | Open | Open | Battery is disconnected from the boost input; motor supply is disconnected |
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| Switch state | Contact | Result |
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|---|---|---|
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| **ON** | Closed | Battery powers the MT3608; the 5 V rail feeds the Nano and ULN2003 |
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| **OFF** | Open | Boost input is disconnected; the 5 V rail (and therefore the motor) is unpowered |
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With Pole B open, the motor’s supply is physically disconnected even if the
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Nano is powered separately. The Nano itself can still be powered by USB when
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the switch is off.
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Pole B disconnects only the ULN2003 `VCC`; it does not disconnect the driver’s
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`IN1`–`IN4` signal wires or its ground. If the Nano is powered over USB while
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Pole B is open, its outputs can still drive the ULN2003 inputs and draw input
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current. For USB debugging in this state, hold the Nano in reset or disconnect
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the `IN1`–`IN4` signal wires. The motor supply remains disconnected because
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ULN2003 `VCC` is open.
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The ULN2003 `VCC` is tied directly to the 5 V rail, so there is no separate
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motor cutoff. The motor is unpowered whenever the switch is off because the
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whole rail is dead. The Nano can still be powered over USB while the switch is
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off; in that case the rail—and therefore ULN2003 `VCC`—is fed from USB. See the
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debug mode in section 6.
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---
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@@ -133,7 +146,7 @@ ULN2003 `VCC` is open.
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The MT3608 is adjustable; it is not a fixed 5 V supply.
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1. Turn the DPST switch **OFF**.
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1. Turn the KCD11 switch **OFF**.
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2. Leave the Nano and ULN2003 disconnected.
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3. Connect the cell and measure MT3608 `OUT+` to `OUT−`.
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4. Adjust the module’s potentiometer until the output is **5.0 V**.
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@@ -150,7 +163,7 @@ can deliver 2 A at 5 V.
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### Run from battery
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- DPST: **ON**
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- KCD11: **ON**
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- Nano USB: **unplugged**
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- TP4056 charging USB: **unplugged**
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@@ -158,31 +171,29 @@ The Nano and motor are powered from the MT3608’s 5 V output.
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### Charge the battery
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- DPST: **OFF**
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- KCD11: **OFF**
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- TP4056 USB input: connected to a 5 V charger
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- Nano USB: **unplugged**
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With Pole A open, the battery-powered load path is disconnected. Keep the Nano
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USB unplugged during charging as the conservative procedure.
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With the switch open, the battery-powered load path is disconnected. Keep the
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Nano USB unplugged during charging as the conservative procedure.
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### Debug over USB serial
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- DPST: **OFF**
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- KCD11: **OFF**
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- TP4056 charging USB: **unplugged**
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- Nano USB: connected to the computer
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- Disconnect the MT3608 `OUT+` wire from the 5 V rail while debugging.
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The Nano clone has no VBUS Schottky diode. Disconnecting the boost output during
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USB debugging avoids applying USB 5 V to the MT3608 output. Pole B remains open,
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so the ULN2003 motor supply is isolated.
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USB debugging avoids applying USB 5 V to the MT3608 output. With the switch open
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the boost is off, but the ULN2003 `VCC` still follows the 5 V rail, which USB now
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powers through the Nano’s 5 V pin. Hold the Nano in reset (or do not run the
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sketch) so the driver does not drive the motor from USB.
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**Never connect Nano USB while the DPST is ON.** In that state, the MT3608
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**Never connect Nano USB while the KCD11 is ON.** In that state, the MT3608
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supplies the Nano’s 5 V pin, which could back-feed the computer’s USB port.
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With the DPST OFF during USB debugging, the signal pins remain connected to
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ULN2003 `IN1`–`IN4`; hold the Nano in reset or disconnect those wires, as
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described above.
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---
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## 7. First power-on checklist
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@@ -191,7 +202,7 @@ described above.
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2. Confirm the circuit ground goes to TP4056 `OUT−`; do not bridge `B−` to
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`OUT−`.
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3. With the switch OFF and loads disconnected, set the MT3608 output to 5.0 V.
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4. Recheck polarity and wiring.
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4. Recheck polarity and wiring, including the KCD11 continuity check.
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5. Connect the Nano and ULN2003.
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6. Run from battery only with the switch ON and Nano USB unplugged.
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@@ -209,9 +220,10 @@ described above.
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near the loads to help with supply dips. Observe its polarity.
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- Keep the Nano, MT3608, and ULN2003 grounds connected to the TP4056
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`OUT−`-referenced system ground.
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- Pole B isolates the ULN2003 motor supply only. It does not isolate the control
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inputs or ground, so it is not a complete electrical disconnection of the
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driver board.
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- The single KCD11 pole removes the whole 5 V rail when off, so there is no
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independent motor-supply cutoff. During USB debugging the rail and ULN2003
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`VCC` are fed from USB, so hold the Nano in reset and disconnect the MT3608
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`OUT+` wire.
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- Do not charge and run the load simultaneously with this simple TP4056
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arrangement. Supporting that requires a proper power-path/load-sharing
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design.
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