Noraiz963/DC-Motor-ControllerA 555-timer-based DC motor speed controller designed in KiCad — uses a variable-duty-cycle PWM signal driven through a power transistor to control motor speed with a single potentiometer.
DC motor speed controller is an open-source printed circuit board by Noraiz963, from the Noraiz963/DC-Motor-Controller repository on GitHub. It is a 2-layer board of 50.4 × 33.3 mm with 21 parts on 11 nets, routed with 68 tracks and 0 vias.
It is built around the NE555P and TIP122. Its parts include 4 diodes, 3 capacitors, 3 resistors, 2 connectors and 1 IC. It belongs with the robots and motor control boards of this library.
A simple, low-cost DC motor speed controller built around the classic NE555P timer IC. The 555 runs in astable mode with an asymmetric charge/discharge network to generate a variable duty-cycle PWM signal, which drives a TIP122 Darlington transistor to switch the motor. A single potentiometer gives smooth control over motor speed.
The circuit is built around four functional blocks:
Power enters through a 3.5mm terminal (J2). A 1000µF capacitor (C1) smooths the supply rail so switching transients from the motor don't disturb the 555's timing. A 2.2k resistor (R1) drives an LED (D4) as a power-on indicator.
The NE555P (U1) is configured as an astable oscillator. Instead of a single resistor, the charge and discharge paths are separated using two steering diodes (D1, D2) around a 100k potentiometer (RV1). This lets the charge time and discharge time be adjusted independently, producing a duty cycle that can be swept across a wide range — from mostly off to mostly on — rather than being stuck above 50% like a standard 555 astable. R2 (1k) limits current into the 555's internal discharge transistor. C2 (100nF) is the timing capacitor. C3 (100nF) bypasses the CONTROL pin per the 555 datasheet recommendation, keeping the internal reference stable.
The 555's OUT pin drives the base of Q1 (TIP122) through a 1k base resistor (R3). The TIP122 is a Darlington transistor capable of switching several amps, acting as the actual power switch for the motor while the 555 only supplies the low-current control signal. As RV1 is adjusted, the PWM duty cycle changes, which changes the average voltage delivered to the motor — and therefore its speed.
Because a DC motor is an inductive load, switching it off abruptly causes a voltage spike as the motor's magnetic field collapses. A flyback diode (D3, 1N4007) is placed across the motor output to safely clamp this spike and protect Q1 from damage.
J2 (DC in) → C1 filter → 555 astable (RV1 sets duty cycle)
→ 555 OUT → R3 → Q1 (TIP122) base
→ Q1 switches motor at J1, PWM-style
→ D3 clamps inductive kickback on every switch-off| Ref | Value | Description |
|---|---|---|
| U1 | NE555P | Timer IC, astable PWM generator |
| Q1 | TIP122 | NPN Darlington transistor, motor switch |
| RV1 | 100k | Potentiometer, speed/duty-cycle control |
| R1 | 2.2k | LED current limiting resistor |
| R2 | 1k | 555 discharge current limiting resistor |
| R3 | 1k | Q1 base resistor |
| C1 | 1000µF | Input filter / bulk capacitor |
| C2 | 100nF | Timing capacitor |
| C3 | 100nF | 555 CONTROL pin bypass capacitor |
| D1, D2 | 1N4007 | Charge/discharge steering diodes |
| D3 | 1N4007 | Flyback protection diode |
| D4 | LED | Power-on indicator |
| J1 | 3.5mm terminal | Motor output |
| J2 | 3.5mm terminal | DC power input |
Designed by MAKER.
| Qty | Value | Footprint | References |
|---|---|---|---|
| 3 | 1N4007 | Diode_THT:D_DO-41_SOD81_P10.16mm_Horizontal | D1, D2, D3 |
| 2 | 100nf | Capacitor_THT:C_Disc_D4.7mm_W2.5mm_P5.00mm | C2, C3 |
| 2 | 1k | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R2, R3 |
| 2 | 3.5mm | TerminalBlock:TerminalBlock_MaiXu_MX126-5.0-02P_1x02_P5.00mm | J1, J2 |
| 1 | 1000uF | Capacitor_THT:CP_Radial_D10.0mm_P5.00mm_P7.50mm | C1 |
| 1 | 100k | Potentiometer_THT:Potentiometer_Alps_RK163_Single_Horizontal | RV1 |
| 1 | 2.2k | Resistor_THT:R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | R1 |
| 1 | LED | LED_THT:LED_D5.0mm | D4 |
| 1 | NE555P | Package_DIP:DIP-8_W7.62mm | U1 |
| 1 | TIP122 | Package_TO_SOT_THT:TO-220-3_Vertical | Q1 |
The 15 most common of 21 parts.
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It measures 50.4 × 33.3 mm and has 2 copper layers, 1.6 mm thick.
21 parts, built around the NE555P and TIP122. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
From the Noraiz963/DC-Motor-Controller repository on GitHub, at the commit this page was made from: the board is PCB layout/DC motor speed controller.kicad_pcb and its schematic Schematic/DC motor speed controller.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Its repository states no licence, so its author keeps all rights: ask Noraiz963 before reusing the design.