Guide

Enter vehicle and gearbox

The app computes power from the rpm, the weight and the gearing. These three values decide the accuracy, so take two minutes here.

1. Create a vehicleOpen Settings, then Vehicles, and add your vehicle. Enter the total weight: scooter ready to ride plus rider plus gear. A Vespa weighs 80 to 120 kg depending on the model, plus the rider.
2. Walk through the gearbox wizardThe wizard asks for frame, primary drive, gearbox and tyre in turn. For Vespa models you can pick the combinations, otherwise enter the tooth counts yourself.
3. Check the tyreThe tyre size decides how far one wheel revolution travels. Use the size that is actually fitted, not the one in the manual.
4. Grant permissionsMicrophone is only needed for measuring without a sensor. Bluetooth is needed for the sensors. Location is optional: it fetches temperature, pressure and humidity for the weather correction and shows GPS speed during sensor runs.

The measurement run

The run is the same for microphone and sensor: one full-throttle pull in one gear, from low rpm to the maximum.

1. Warm up the engineA cold engine makes less power and the measurement is not comparable.
2. Pick a roadStraight, level, dry, no traffic. You need to concentrate on riding, not on the phone.
3. Select third gearLet the revs drop to around 3,000 rpm in third gear. Another gear works too, just enter it in the app.
4. Full throttle to the topOpen the throttle fully and hold it until the rpm stops climbing. Then close it. You don't have to stop exactly at the peak, the app only uses the rising part.
5. Two or three runsRepeat the pull. If the curves lie on top of each other, the measurement is good.

Measuring with the microphone

The app listens to the engine and looks for the firing frequency in the noise. At 6,000 rpm a two-stroke fires 100 times a second, which is a 100 Hz tone with its harmonics. The app follows that line through the recording.

1. Phone in the backpackThe microphone is protected from wind there and still hears the engine well. Not in a jacket pocket: fabric rubs against the microphone.
2. Start recordingTap the plus, choose audio recording, then start. Close the backpack, ride off, do the run, stop, stop the recording.
3. Trim the recordingDrag the handles so only the full-throttle pull remains. Idle, pulling away and gear changes have to go.
4. Check the harmonicsThe app shows the spectrogram and marks the fundamental it found. If it sits on the wrong line, tap the right one. Wipe away any noise, it then shows black.
5. Look at the resultThe power curve appears. How to read it is in chapter 6.

Wiring the MicroDyno-RPM

The MicroDyno-RPM is a small box with a battery. It hangs on the AC output of the ignition with two wires and counts every pulse. Each pulse gets a microsecond timestamp and goes to the app over Bluetooth. There is no recording any more and nothing to clean up: the rpm is live on the phone.

What the sensor does

• Counts pulses: The ignition's AC has a fixed number of waves per crankshaft revolution. An optocoupler turns them into clean digital pulses, galvanically isolated from the vehicle.
• Timestamps them: Every edge is stored with microsecond time, in the sensor itself and live on the phone. If Bluetooth drops for a moment, the app fetches the missing pulses from the sensor after the run.
• Sleeps and wakes: Without an ignition pulse and without a Bluetooth connection the sensor goes into deep sleep after five minutes. The first ignition pulse or a press of the button wakes it again.

Wiring

1. Charge the batteryCharge over USB-C before first use. For a firmware update the battery has to be above 30 percent.
2. Find the AC outputThe sensor's two wires go to the ignition's AC output, the same place the lights get their power from. On electronic ignitions this is usually the terminal labelled AC.
3. ConnectBoth wires to AC. Since it is alternating current the order does not matter. Route the wires so they don't touch the exhaust or moving parts.

Connecting to the app

1. Wake the sensorStart the engine or briefly press the button. The LED blinks slowly while the sensor is awake and waiting for a connection.
2. Start a measurementTap the plus in the app and choose MicroDyno-RPM. The app finds the sensor and connects on its own. The LED then stays on.
3. Check pulses per revolutionLet the engine idle and compare the rpm in the app with what you expect. If it is off by a fixed factor, change the pulses per revolution in the app. The default is 6, which fits most Vespa ignitions.
4. RidePhone in your pocket, do the run as in chapter 2. With the engine running the LED blinks fast. After the run tap stop, the app fetches any missing pulses from the sensor and shows the result.

LED blinks slowly	Sensor awake, not connected. After 5 minutes without a pulse it goes to sleep.
LED on	Connected to the app, engine stopped.
LED blinks fast	Connected, engine running, pulses coming in.
LED off	Deep sleep. An ignition pulse or the button wakes the sensor.

Wiring the MicroDyno-Lambda-RPM

The MicroDyno-Lambda-RPM measures rpm exactly like the RPM sensor and, on top, the air-fuel ratio with a Bosch LSU 4.9 wideband probe in the exhaust. Because the probe has to be heated, this box does not run on a built-in battery but on a 12 V battery. If your scooter has none, a small 12 V battery pack will do.

What the probe does

The wideband probe measures the residual oxygen in the exhaust. That gives lambda: 1.0 means the air matched the fuel exactly. Lower is rich, higher is lean. The app also shows AFR, the air-fuel ratio in kilograms of air per kilogram of petrol. Lambda 1.0 equals AFR 14.7. A two-stroke at full throttle typically runs around AFR 12 to 13.

To measure, the probe's ceramic element has to be heated to around 780 degrees Celsius. The box controls this heater. It only switches the heater on once the engine is really running, because a cold exhaust is wet inside and water droplets on the hot ceramic can crack it.

Wiring

1. Probe into the exhaustThe LSU 4.9 needs an M18×1.5 weld-in boss in the exhaust, as close to the cylinder as possible and angled so the probe points slightly upwards. Then no condensation collects in the probe. Torque per Bosch specification, don't grease the thread.
2. Plug in the probe cableThe probe's six-pin cable goes into the large connector on the box. Keep the cable off the exhaust or it will melt.
3. Red and black to the batteryRed to plus, black to minus of a 12 V battery. The probe heater draws up to 2 amps while heating up, so go straight to the battery and not to the lighting circuit.
4. Two wires to ACThe remaining two wires go to the ignition's AC output after the regulator, exactly as with the RPM sensor. Either way round.

Measuring with the app

1. ConnectTap the plus in the app and choose MicroDyno-RPM. The app recognises the lambda variant automatically and shows the AFR field with the probe state next to the rpm.
2. Start the engine and waitThe state goes from Standby via Heating to Measuring. Only when it says Measuring are the values valid. Before that the app shows the last valid value.
3. Tune at steady throttleFor jetting, ride at fixed throttle positions: quarter, half, three quarters, full. The app smooths the display over one second, the raw data stays in the recording.
4. Do the runDuring the full-throttle pull the app records AFR alongside. In the result the AFR trace is overlaid on the power curve, so you see where the engine goes lean.

Standby	Heater off, waiting for the engine. Normal after switching on and five minutes after shutdown.
Heating	Probe is heating up. Values not valid yet.
Adjusting	Probe is settling. Almost ready.
Measuring	Probe is measuring. AFR and lambda are valid.
NoHeat, Underheat, Overheat	The probe doesn't reach its temperature or exceeds it. Check board voltage, connector and probe seating.
Voltage too low	The battery is too weak for the heater. Charge the battery or check the charging system.

Reading the results

After each run the app shows the curve over rpm: power in red, torque in blue, and the peak values with rpm and speed at the top.

• Change gear and vehicle afterwards: Entered the wrong gear? Change it in the result, the curve is recalculated immediately.
• More views: Rpm over time, speed over time and, for lambda runs, AFR over rpm.
• Compare: Under Results select several runs and choose Compare. The curves are stacked on top of each other.
• Share: Every run can be shared as an image or with raw data.
• Continue on a PC: Switch on cloud sync in the settings. Then open app.microdyno.de in the browser and edit vehicles, runs and results on the big screen. The app works fully without the cloud too.

Firmware update

Both sensors receive new firmware straight from the app over Bluetooth. You never need a cable.

1. Connect the sensorAs for measuring: plus, MicroDyno-RPM, wait for Connected.
2. Check for updatesIn Settings under Rpm sensor firmware you see the installed version. Tap it and the app checks whether there is a newer one.
3. InstallThe app downloads the firmware, verifies the checksum, transfers it to the sensor and waits for the sensor to verify it. Keep the phone close, it takes one to two minutes.
4. Wait for the restartThe sensor reboots and reports the new version. If the transfer fails, the old firmware simply stays in place.

On the MicroDyno-RPM the battery has to be above 30 percent or the sensor refuses the update.

When something doesn't work

Sensor not found	The sensor is probably asleep. Start the engine or press the button, then search again. Bluetooth on the phone switched on? Is the Apple Watch still connected? The sensor accepts one connection only.
Rpm off by a fixed factor	Pulses per revolution don't match the ignition. Change the value in the app until the idle rpm is right.
Rpm jumps or is jagged	Check the wires at the AC output, contacts tight? Sensor firmware up to date? Newer versions filter ignition glitches themselves.
Probe stays in Standby	The box hasn't seen ignition pulses yet or the engine hasn't run for 30 seconds. Check the AC wires, keep the engine running.
Sensor download incomplete	Bluetooth dropped while fetching the pulses. Move the phone closer to the sensor and reload the run under Fetch sensor log.
Power clearly too high or too low	Almost always weight or gearing. Rider included? Real tyre size? Correct gear entered?
Microphone curve unusable	Wind on the microphone or wrong harmonic. Phone deeper in the backpack, tap the correct line in the harmonics editor.

Not listed? Write to support@microdyno.de. A screenshot of the curve and the vehicle data help with the answer.