The SpeedPulser converts digital speed pulses from a gearbox hall sensor (or a Can2Cluster signal) into a 10 kHz PWM signal that drives a BLDC motor — giving life back to an OEM analog speedometer without a mechanical cable. It is fully open-source, WiFi-configurable, and calibrated per cluster type so the needle reads accurately across the available speed range of the motor.
It is based on a LOLIN C3 Mini (ESP32-C3) and uses a TY3816B BLDC motor driven via a native LEDC hardware PWM channel.
| Feature | Detail |
|---|---|
| Speed input | 5V / 12V square-wave (hall sensor or Can2Cluster) |
| Motor output | 10 kHz hardware PWM, 12-bit resolution |
| Closed-loop feedback | PID trims duty from the motor feedback pin (optional) |
| Calibration profiles | 18 built-in (VW, Ford, Fiat, Merc, Smiths, Opel, VW Bay) |
| Custom calibration | Calibration Builder — capture, generate, save, export/import |
| Calibration Curve | Live duty-vs-speed curve with the current operating point on the Dashboard |
| Status Monitor | Live measured speed, PID trim and actual motor speed (Hz) |
| WiFi UI | Web app type interface |
| Needle sweep | Configurable on power-up |
| Speed offset | Global fixed offset or 5-point speed-dependent curve |
| OTA updates | Firmware upload from the browser |
| Power management | Auto WiFi-off + CPU scaling after 1 min idle |
| Remembers settings | All settings stored to ESP32 Preferences (NVS/EEPROM) |
| Cluster | Range | Calibration by |
|---|---|---|
| VW MK1 / MK2 Golf | 120 mph | Martin Springell |
| VW MK1 / MK2 Golf | 120 mph | Forbes Automotive |
| VW MK1 / MK2 Golf | 120 mph | Tara |
| VW MK1 / MK2 Golf | 140 mph | Forbes Automotive |
| VW MK1 / MK2 Golf | 160 mph | Forbes Automotive |
| VW MK1 / MK2 Golf | 300 kph (1.8T) | Forbes Automotive |
| VW Bay VDO | 90 mph | Community |
| Ford Escort | 120 mph (var. 1) | Forbes Automotive |
| Ford Escort | 120 mph (var. 2 — Darren) | Community |
| FIAT Uno | 40–160 mph | Forbes Automotive |
| FIAT Uno | 20–110 mph | Forbes Automotive |
| Mercedes W123 | 120 mph | Forbes Automotive |
| Smiths 5/8" | 70 mph | Forbes Automotive |
| Smiths 5/8" | 90 mph | Forbes Automotive |
| Smiths 5/8" | 150 mph | Forbes Automotive |
| Opel Manta A-72 | 200 km/h | Forbes Automotive |
Users are actively encouraged to submit new models, calibrations, or corrections via GitHub or Discord.
Pre-assembled SpeedPulser units are available here: SpeedPulser — Forbes Automotive
The PDF Installation Guide on GitHub provides full step-by-step hardware fitting instructions.
The pre-assembled PCB:
The three-pin Input connector on the bottom edge of the PCB accepts 12V battery power and the speed signal:
| Pin | Signal | Notes |
|---|---|---|
| 1 | PWR_IN (12 V) | Closest to board edge; connect to ignition-switched 12 V |
| 2 | GND | Common ground |
| 3 | Speed Signal | 5 V or 12 V square wave from hall sensor or Can2Cluster |
Pull-up / Pull-down jumper: Different hall sensors require either a pull-up or pull-down resistor. A 2-way jumper header on the PCB selects this. If the SpeedPulser is not registering incoming pulses, swap the jumper position. Sensors with an internal resistor can have the jumper removed entirely.
An on-board adjustable LM2596S buck converter steps the 12V supply down to approximately 9V to power the motor, keeping the motor's operating range and torque within spec across the full speed scale.
The five-pin Motor connector on the top edge of the PCB:
| Pin | Signal | Notes |
|---|---|---|
| 1 | Motor Power | Black — 5–9 V (set via on-board trimmer) |
| 2 | Motor Feedback | White — BLDC feedback pulse; read on GPIO 4 for closed-loop PID (optional) |
| 3 | Motor Direction | Green — LOW (normal); enable Reverse to flip needle direction — HIGH (reversed) |
| 4 | Motor Ground | White — motor ground |
| 5 | Motor PWM | 10 kHz PWM from ESP32 (via NPN level-shifter to 4V) |
Motors are supplied with the coupler pre-fitted; the final drive pin and securing pins are included separately.
- Remove the motor from the coupler housing.
- Align the drive pin into the coupler recess and press home — a few light taps should seat it fully.
- A spare coupler is supplied. Couplers are 3D printed; slight alignment variation is normal. A brief gentle heat application (≤ 100 °C) can encourage a true run.
- If excessive vibration causes the coupler to loosen, a small drop of super-glue will fix it permanently — confirm it runs true before the glue sets.
Drive shafts are supplied longer than required. Trim to suit your cluster, typically flush with the motor housing. Confirm the shaft does not bottom out in the cluster before tightening.
Once the motor is assembled, slide it over the OEM cluster shaft. Check:
- The drive pin engages cleanly
- The motor spins freely by hand
- The pin length is sufficient to engage the cluster but does not prevent the housing from seating fully
Take time here — good fitment minimises noise and extends coupler life.
Couplers are 3D printed and every motor / housing / cluster pairing wears in slightly differently. Expect to revisit the on-board potentiometer once after a few hours of running so the top-end reading still hits full-scale cleanly.
Connect to the SpeedPulser WiFi access point and navigate to 192.168.1.1 in a browser.
The interface is a single-page app served from the ESP32's LittleFS flash partition. Settings are applied in real time and saved to EEPROM automatically every 2 seconds.
Live read-outs updated automatically:
| Field | Description |
|---|---|
| Incoming Speed | Speed value calculated from incoming hall-sensor pulses (km/h or mph) |
| Motor Duty | PWM duty cycle currently applied to the motor |
| Measured Speed | Speed derived from the motor fedback pin when feedback is enabled |
| PID Trim | Duty correction the feedback loop is currently applying |
| Speed Offset Type | Whether a Global or Curve offset is active |
| Current Speed Offset | The offset value applied at the current speed |
Below the read-outs is a Calibration Curve graph: a duty-vs-speed trace of the active calibration with its captured points, plus a marker showing the point currently being achieved — from the hall input, Speed Test Mode or Calibration Mode.
While Speed Test Mode is active, these fields switch to show the chosen test speed and resulting motor duty instead.
The bright dot on the graph is the point currently being achieved — from the hall input, Speed Test Mode or Calibration Mode — plotted against the active calibration's duty/speed curve (green dots = captured/sampled anchor points).
| Setting | Description |
|---|---|
| Enable Needle Sweep | Triggers a full-scale needle sweep on power-up |
| Sweep Speed (ms) | Step delay in milliseconds: lower = faster sweep |
| Test Needle Sweep | Trigger a sweep immediately from the browser |
| Calibration Selection | Choose from 18 built-in cluster calibration profiles |
| Maximum Speed (km/h) | Upper end of the cluster's speed scale |
| Maximum Hall Frequency (Hz) | The input frequency that corresponds to Maximum Speed |
| Speed Offset Value | Fixed offset added to or subtracted from all speed readings |
| Positive Offset | Direction of the fixed offset (add or subtract) |
| Speed-Dependent Offset Curve | Enable a 5-point curve offset in place of the global offset |
| Cluster in MPH | Convert the km/h input signal to mph before looking up the motor duty |
| Average Filter Samples | Median smoothing window (1–10) for the incoming signal; higher = steadier but slower |
| Setting | Description |
|---|---|
| Reverse Direction | Drive the direction pin HIGH to flip the motor direction |
| Feedback Enable | Turn the closed-loop PID duty trim on or off (not available on legacy PCBs) |
| Min Feedback Speed (km/h) | Below this speed the loop runs open-loop (feed-forward only) to stop low-speed hunting; 0 = always closed-loop |
| PID Kp / Ki / Kd | Feedback loop gains (defaults 0.15 / 1.3 / 0) |
| Reset PID Defaults | Restore the tuned default gains |
| Performance Array Value | Index of the active calibration array |
| Incoming Pulses | Raw frequency value from the ISR |
| Raw Count | Number of samples accumulated so far |
| LED Counter | ISR pulse counter (also drives the onboard LED blink) |
Reverse Direction drives GPIO 10 HIGH instead of LOW, flipping the rotation direction for clusters whose motor is mounted the opposite way round. Feedback Enable turns the closed-loop PID trim on; the sliders below it tune the loop and Reset PID Defaults restores the tuned baseline (0.15 / 1.3 / 0). See Closed-Loop Feedback (PID) below for how it works.
Contains the Calibration Builder and Speed Test Mode.
Calibration Builder
- Tick Enable Calibration Mode — the motor now follows the big duty read-out instead of the speed source.
- Change the duty to the maximum value (4096). Adjust the trimmer to achieve maximum cluster value.
- Change the duty with the −50 / −10 / −1 / +1 / +10 / +50 buttons until the needle sits exactly on a speed mark.
- Pick that speed from the Target speed or type it in and press Capture Point. Each capture is listed under Captured Points and can be removed individually.
- Repeat across the scale, name the calibration, then Generate & Apply to preview it live and Save to Device to store it. Export / Import shares it as a text block.
Speed Test Mode
Locks the motor to a user-chosen speed so the cluster can be observed
without a speed signal. The chosen speed passes through the full offset and
calibration process, to give a realistic preview. With feedback enabled the closed
loop drives to that speed; the dashboard updates in real time to show the chosen speed
and the resulting motor duty.
Example above: five points captured (0, 40, 95, 150, 200 km/h) for a custom "VW Bay VDO 90mph" build, with the duty point sitting at 742/4095 (18.1%). Once at-least two points are captured, Generate & Apply interpolates the full curve and Save to Device remembers it — it then appears as the ★ Custom entry in the Configuration tab's calibration list.
Upload a new compiled .bin firmware file directly from the browser — no USB cable required. The device reboots automatically after a successful flash.
With Feedback Enable on (Advanced tab), the firmware measures the BLDC motor's feedback pulses and trims the PWM duty so the needle holds its reading under load or voltage sag — rather than relying on the open-loop calibration alone.
How It Works
- The feedback pulse on GPIO4 is counted and converted to a frequency (Hz), then smoothed with an exponential moving average.
- The requested speed is converted to a target frequency using a fixed full-scale reference (254 Hz at maximum speed, measured on the bench and defined into the firmware) so the loop needs no per-user frequency calibration.
- A PID controller calculates a duty correction that is added to the feed-forward calibration duty. A small dead-band with integral hold prevents needle shudder around the target.
- Below Min Feedback Speed the loop reverts to open-loop feed-forward to avoid low-speed hunting where the motor can't run smoothly.
Tuning — the default gains (Kp 0.15, Ki 1.3, Kd 0) suit the supplied motor and cluster combination; the integral term carries most of the correction. Adjust from the Advanced tab if needed, and use Reset PID Defaults to return to the tuned values. The Status Monitor shows the live measured speed, the PID trim being applied and the raw tacho frequency so you can see the loop working.
Each calibration profile is a 386-element uint16_t array stored in flash (PROGMEM). The array index represents speed in km/h (0–385) and the array value is the 10-bit PWM duty cycle (0–1023) that drives the motor to produce the corresponding reading on that cluster.
index 0 → duty 0 (motor off / dead band)
index 50 → duty ~60 (motor at ~50 km/h cluster reading)
index 120 → duty ~130 (motor at ~120 km/h cluster reading)
...
index 200 → duty ~195 (motor at full scale for a 200 km/h cluster)
Values near index 0 are 0 — the motor's dead band where it will not yet turn. Values plateau near the top because the cluster needle is at full deflection.
Hall sensor pulse
│
▼ incomingHz()
Measures pulse interval → calculates frequency (Hz)
│
▼ speedControlTask
map(frequency, 0, maxFreqHall, 0, maxSpeed) → speed in km/h
│
▼ RunningMedian filter (averageFilter samples, default 6)
Smoothed median speed value
│
▼ applyConfiguredSpeedOffset()
Speed ± global offset OR speed ± curve offset for that band
│
▼ Optional: × 0.621371 if "Cluster in MPH" is enabled
│
▼ findClosestMatch()
Scans motorPerformance[] for the closest matching speed value
Returns the array index = 10-bit duty cycle
│
▼ setMotorDuty() — native LEDC IDF driver, 10 kHz
Motor PWM output on GPIO 2
Default hall-sensor scaling: 1 Hz = 1 km/h. This matches 02J / 02M gearbox sensors used in most VW/Audi applications. Adjust
maxFreqHallandmaxSpeedtogether if your sensor has a different ratio (e.g. set both to 160 for a sensor that outputs 160 Hz at 160 km/h).
To check what duty a profile produces at a given speed, index directly:
// Direct lookup — returns the 10-bit duty for 80 km/h on the active profile
uint16_t duty = motorPerformance[80];findClosestMatch() does the inverse: given a target speed value, it walks the array to find the entry whose value is closest to the target and returns the index as the duty cycle. This gracefully handles calibration arrays that are not perfectly monotone.
Two offset modes are available and are both configured from the Configuration tab.
Global Offset (default)
A single fixed value is added to or subtracted from every speed reading before the calibration lookup. Useful for correcting a systematic bias across the whole scale caused by motor preload or cluster wear.
5-Point Curve
Five independent offsets replace the global offset when enabled. This corrects clusters whose response is non-linear and cannot be fixed by a single constant.
| Point | Speed band |
|---|---|
| 1 | 0 – 50 km/h |
| 2 | 50 – 100 km/h |
| 3 | 100 – 150 km/h |
| 4 | 150 – 200 km/h |
| 5 | 200+ km/h |
Each point accepts ±20 km/h. Enable the Speed-Dependent Offset Curve checkbox on the Configuration tab to activate.
The firmware includes a universal reduced-power codeblock (power_manager - used in SpeedPulser Pro, Can2Cluster and other projects) that activates automatically 1 minute after the last WiFi client disconnects. This cuts current through the on-board linear regulator, directly reducing its heat output — important for long ignition-on times.
What changes when idle:
| Action | Saving |
|---|---|
| WiFi radio off | ~80–120 mA average (single biggest saving) |
| CPU: 160 MHz → 80 MHz | Moderate reduction in active current |
| Bluetooth controller released at boot | ~60 KB RAM freed; small idle current saving |
| WiFi modem-sleep while clients are connected | Minor saving without losing connectivity |
| Reduced WiFi TX power | Adequate for in-car range; further small saving |
Waking back up:
As soon as a device reconnects to the WiFi AP, full power is restored automatically — the radio comes back up, the CPU returns to 160 MHz, and the web server resumes. A power-cycle (ignition off/on) will also restore WiFi.
The LOLIN C3 Mini's maximum CPU frequency is 160 MHz; the power manager auto-detects this at compile time and adjusts accordingly.
New firmware can be flashed without removing the unit from the vehicle:
- Build the project in PlatformIO → locate the
.binfile in.pio/build/lolin_c3_mini/. - Connect to the
SpeedPulserWiFi AP. - Open the OTA tab in the browser.
- Select the
.binfile and click Upload. - The device flashes and reboots automatically.
| GPIO | Function |
|---|---|
| 2 | Motor PWM output (LEDC 12-bit, stepped to 5 V via NPN transistor) |
| 4 | Motor tacho feedback input (falling-edge interrupt counter; used by the PID loop) |
| 5 | Speed pulse input (falling-edge interrupt) |
| 8 | Onboard LED (blinks to confirm incoming pulses) |
| 10 | Motor direction (LOW = normal, HIGH = reversed) |
| Parameter | Value |
|---|---|
| Frequency | 10 kHz |
| Resolution | 12-bit (0–4095) |
| Driver | Native ESP-IDF ledc_set_duty / ledc_update_duty |
Built-in calibration tables were captured at 10-bit and are scaled up to the 12-bit hardware domain automatically; the Calibration Builder captures new points at full 12-bit resolution.
| Task | Core | Period |
|---|---|---|
speedControlTask |
0 | Continuous loop |
eepromTask |
0 | 2 000 ms |
powerManagerTask |
0 | 5 000 ms check interval |
| Library | Purpose |
|---|---|
mathieucarbou/ESPAsyncWebServer |
Async web server (ESP-IDF 5.x compatible fork) |
mathieucarbou/AsyncTCP |
Underlying TCP for AsyncWebServer |
bblanchon/ArduinoJson |
JSON serialisation for REST API |
RobTillaart/RunningMedian |
Median filter for speed smoothing |
Platform: pioarduino/platform-espressif32 (Arduino-ESP32 3.x / ESP-IDF 5.x)
- Open the project folder in VS Code with the PlatformIO extension installed.
- Confirm
env:lolin_c3_miniis selected inplatformio.ini. - Build Filesystem Image (PlatformIO sidebar) — packages the web UI files from
data/into a LittleFS image. - Upload Filesystem Image — flashes the web UI to the SPIFFS/LittleFS partition.
- Build & Upload — flashes the main firmware.
- Open the Serial Monitor at 115 200 baud to confirm startup messages.
Serial debug output is controlled by
-D serialDebug=1inplatformio.ini. Set to0for production builds to avoid stalling if no USB-CDC host is connected.
| Version | Summary |
|---|---|
| V1.01 | Initial release |
| V1.05 | Global speed offset |
| V1.06 | Pulse timeout / reset-to-zero |
| V1.07 | 160 mph MK2 Golf calibration (Charlie) |
| V1.09 | Martin Springell MK1 Golf calibration |
| V1.11 | WiFi settings page |
| V1.12 | Mercedes W123 calibration |
| V1.13 | Calibration selection in WiFi |
| V1.15 | Calibration test mode via WiFi |
| V1.17 | Smiths 70 mph calibration |
| V1.18 | Over-the-Air updates |
| V1.19 | Smiths 90 mph calibration |
| V2.00 | Ported to PlatformIO |
| V2.10 | LEDC hardware PWM; FreeRTOS tasks; new REST API tabbed web UI; power management module |
| V2.20 | "Cluster in MPH" conversion option |
| V2.21 | Fixed LEDC driver for Arduino-ESP32 3.x (ledc_set_duty / ledc_update_duty) |
| V3.00 | PCB revision to include Motor Feedback + Reverse option and two Buck Converters (one for the motor, one for the ESP32) |
| V3.01 | PID Calibration, Calibration Builder + Calibration Curve |
| V3.02 | Smoother needle sweep |
| V3.0x | Various multiple tweaks |
| V3.10 | Tighter PID control, feedback check for legacy PCBs etc |