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Rework wiring diagram for single-pole KCD11 switch

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rafael
2026-09-29 16:54:54 +08:00
parent 9508f6a81d
commit 2cf732d65b
1 changed files with 58 additions and 46 deletions
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WIRING-DIAGRAM.md
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@@ -4,8 +4,9 @@ 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 converter, an Arduino Nano, and a ULN2003 driver board to power a 28BYJ-48
stepper motor. stepper motor.
A DPST switch controls the battery-to-boost path and independently disconnects A single-pole KCD11 rocker switch turns the battery-to-boost path on and off.
the motor supply. The Arduino Nano clone used here has **no USB VBUS Schottky 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 diode**, so the USB and battery-powered 5 V supply must not be connected to the
Nano at the same time. Nano at the same time.
@@ -21,7 +22,7 @@ Nano at the same time.
| 18650 Li-ion cell | Single cell, suitable holder or secure battery connection | | 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 | | 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 | | MT3608 boost converter | Adjustable; set its output to 5.0 V before connecting the loads |
| DPST on/off switch | Both poles operate together | | KCD11 rocker switch | Single pole, on/off; see the variant note below |
| Arduino Nano clone | This clone has no VBUS Schottky diode | | Arduino Nano clone | This clone has no VBUS Schottky diode |
| 28BYJ-48 stepper motor | Use the 5 V version | | 28BYJ-48 stepper motor | Use the 5 V version |
| ULN2003 driver board | Matches the motor’s 5-pin plug | | ULN2003 driver board | Matches the motor’s 5-pin plug |
@@ -35,6 +36,23 @@ 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 over-current protection, and do not use its `B+`/`B−` pads as though they were
protected `OUT+`/`OUT−` pads. 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 ## 2. Power flow
@@ -42,9 +60,9 @@ protected `OUT+`/`OUT−` pads.
```text ```text
18650 ──► TP4056 protected battery/load terminals 18650 ──► TP4056 protected battery/load terminals
│ │
└── OUT+ ──► DPST Pole A ──► MT3608 ──► 5 V rail └── OUT+ ──► KCD11 ──► MT3608 ──► 5 V rail
├── Nano 5V ├── Nano 5V
└── DPST Pole B ──► ULN2003 VCC └── ULN2003 VCC
``` ```
The TP4056 is a **charger**, not a 5 V power supply. Its `IN+`/`IN−` terminals The TP4056 is a **charger**, not a 5 V power supply. Its `IN+`/`IN−` terminals
@@ -68,8 +86,9 @@ Charging input:
USB GND ──► TP4056 IN− USB GND ──► TP4056 IN−
Battery-powered load path: Battery-powered load path:
TP4056 OUT+ ──[optional fuse]──► DPST Pole A common TP4056 OUT+ ──[optional fuse]──► KCD11 terminal 1 (common, center lug)
DPST Pole A switched terminal ──► MT3608 IN+ KCD11 terminal 1b ──► MT3608 IN+
KCD11 terminal 1a (if present) ──► leave unconnected
TP4056 OUT− ──► common system GND TP4056 OUT− ──► common system GND
MT3608 IN− ──► common system GND MT3608 IN− ──► common system GND
@@ -79,8 +98,7 @@ Battery-powered load path:
5 V and motor supply: 5 V and motor supply:
MT3608 OUT+ ──► 5 V rail ──┬──► Arduino Nano 5V MT3608 OUT+ ──► 5 V rail ──┬──► Arduino Nano 5V
└──► DPST Pole B common └──► ULN2003 VCC
DPST Pole B switched terminal ──► ULN2003 VCC
Control and motor: Control and motor:
Arduino Nano D9 ──► ULN2003 IN1 Arduino Nano D9 ──► ULN2003 IN1
@@ -103,29 +121,24 @@ load.
--- ---
## 4. DPST switch operation ## 4. KCD11 switch operation
The DPST switch has two electrically separate poles operated by the same The KCD11 is a single-pole on/off switch in the battery-to-boost path, wired
handle: across terminals `1` (center common) and `1b`:
- **Pole A:** connects TP4056 `OUT+` to MT3608 `IN+`. - **ON (closed):** connects TP4056 `OUT+` to MT3608 `IN+`.
- **Pole B:** connects the 5 V rail to ULN2003 `VCC`. - **OFF (open):** disconnects the battery from the boost input.
| Switch state | Pole A | Pole B | Result | | Switch state | Contact | Result |
|---|---|---|---| |---|---|---|
| **ON** | Closed | Closed | Battery powers the MT3608; Nano and motor receive 5 V | | **ON** | Closed | Battery powers the MT3608; the 5 V rail feeds the Nano and ULN2003 |
| **OFF** | Open | Open | Battery is disconnected from the boost input; motor supply is disconnected | | **OFF** | Open | Boost input is disconnected; the 5 V rail (and therefore the motor) is unpowered |
With Pole B open, the motor’s supply is physically disconnected even if the The ULN2003 `VCC` is tied directly to the 5 V rail, so there is no separate
Nano is powered separately. The Nano itself can still be powered by USB when motor cutoff. The motor is unpowered whenever the switch is off because the
the switch is off. 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
Pole B disconnects only the ULN2003 `VCC`; it does not disconnect the driver’s debug mode in section 6.
`IN1`–`IN4` signal wires or its ground. If the Nano is powered over USB while
Pole B is open, its outputs can still drive the ULN2003 inputs and draw input
current. For USB debugging in this state, hold the Nano in reset or disconnect
the `IN1`–`IN4` signal wires. The motor supply remains disconnected because
ULN2003 `VCC` is open.
--- ---
@@ -133,7 +146,7 @@ ULN2003 `VCC` is open.
The MT3608 is adjustable; it is not a fixed 5 V supply. The MT3608 is adjustable; it is not a fixed 5 V supply.
1. Turn the DPST switch **OFF**. 1. Turn the KCD11 switch **OFF**.
2. Leave the Nano and ULN2003 disconnected. 2. Leave the Nano and ULN2003 disconnected.
3. Connect the cell and measure MT3608 `OUT+` to `OUT−`. 3. Connect the cell and measure MT3608 `OUT+` to `OUT−`.
4. Adjust the module’s potentiometer until the output is **5.0 V**. 4. Adjust the module’s potentiometer until the output is **5.0 V**.
@@ -150,7 +163,7 @@ can deliver 2 A at 5 V.
### Run from battery ### Run from battery
- DPST: **ON** - KCD11: **ON**
- Nano USB: **unplugged** - Nano USB: **unplugged**
- TP4056 charging USB: **unplugged** - TP4056 charging USB: **unplugged**
@@ -158,31 +171,29 @@ The Nano and motor are powered from the MT3608’s 5 V output.
### Charge the battery ### Charge the battery
- DPST: **OFF** - KCD11: **OFF**
- TP4056 USB input: connected to a 5 V charger - TP4056 USB input: connected to a 5 V charger
- Nano USB: **unplugged** - Nano USB: **unplugged**
With Pole A open, the battery-powered load path is disconnected. Keep the Nano With the switch open, the battery-powered load path is disconnected. Keep the
USB unplugged during charging as the conservative procedure. Nano USB unplugged during charging as the conservative procedure.
### Debug over USB serial ### Debug over USB serial
- DPST: **OFF** - KCD11: **OFF**
- TP4056 charging USB: **unplugged** - TP4056 charging USB: **unplugged**
- Nano USB: connected to the computer - Nano USB: connected to the computer
- Disconnect the MT3608 `OUT+` wire from the 5 V rail while debugging. - 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 The Nano clone has no VBUS Schottky diode. Disconnecting the boost output during
USB debugging avoids applying USB 5 V to the MT3608 output. Pole B remains open, USB debugging avoids applying USB 5 V to the MT3608 output. With the switch open
so the ULN2003 motor supply is isolated. 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 DPST is ON.** In that state, the MT3608 **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. supplies the Nano’s 5 V pin, which could back-feed the computer’s USB port.
With the DPST OFF during USB debugging, the signal pins remain connected to
ULN2003 `IN1`–`IN4`; hold the Nano in reset or disconnect those wires, as
described above.
--- ---
## 7. First power-on checklist ## 7. First power-on checklist
@@ -191,7 +202,7 @@ described above.
2. Confirm the circuit ground goes to TP4056 `OUT−`; do not bridge `B−` to 2. Confirm the circuit ground goes to TP4056 `OUT−`; do not bridge `B−` to
`OUT−`. `OUT−`.
3. With the switch OFF and loads disconnected, set the MT3608 output to 5.0 V. 3. With the switch OFF and loads disconnected, set the MT3608 output to 5.0 V.
4. Recheck polarity and wiring. 4. Recheck polarity and wiring, including the KCD11 continuity check.
5. Connect the Nano and ULN2003. 5. Connect the Nano and ULN2003.
6. Run from battery only with the switch ON and Nano USB unplugged. 6. Run from battery only with the switch ON and Nano USB unplugged.
@@ -209,9 +220,10 @@ described above.
near the loads to help with supply dips. Observe its polarity. near the loads to help with supply dips. Observe its polarity.
- Keep the Nano, MT3608, and ULN2003 grounds connected to the TP4056 - Keep the Nano, MT3608, and ULN2003 grounds connected to the TP4056
`OUT−`-referenced system ground. `OUT−`-referenced system ground.
- Pole B isolates the ULN2003 motor supply only. It does not isolate the control - The single KCD11 pole removes the whole 5 V rail when off, so there is no
inputs or ground, so it is not a complete electrical disconnection of the independent motor-supply cutoff. During USB debugging the rail and ULN2003
driver board. `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 - Do not charge and run the load simultaneously with this simple TP4056
arrangement. Supporting that requires a proper power-path/load-sharing arrangement. Supporting that requires a proper power-path/load-sharing
design. design.