This is an old project from 2010 that I decided to share. It was written in Objective-C using Xcode 3.2.2 and is compatible with iOS 4.0 and may be later. It was available on the App Store for several years but has not been updated since. Therefore, I am unsure if it still runs on the latest iPhones and iPads (unfortunately, I don't think so...)
RacingTach is a tachometer designed to measure RPM (revolutions per minute) using sound or any periodic signal generated by engines. It provides precise RPM measurements, up to 100,000, for race cars, motorbikes, trucks, motorboats, R/C models, and even the sounds of airplane propellers or helicopter blades.
The signal is analyzed in real-time using a proprietary FFT algorithm, known for its high-speed performance.
This parameter represents the number of pulses detected by the software during one full revolution of the engine's crankshaft. For combustion engines :
- Four-stroke engines: Two crankshaft rotations per working cycle.
- Two-stroke engines: One crankshaft rotation per working cycle.
So with the microphone or with a cigarette lighter RPM pickup, the formula for determining how many times your engine fires per revolution is :
- 0.5 × number of cylinders for a four-stroke engine.
- 1 × number of cylinders for a two-stroke engine.
Examples :
- Four-stroke, 4-cylinder engine: 0.5 × 4 = 2 sparks per revolution (common for cars).
- Four-stroke, 6-cylinder engine: 0.5 × 6 = 3 sparks per revolution.
- Two-stroke, 2-cylinder engine: 1 × 2 = 2 sparks per revolution.
When using an inductive clamp on a single spark plug wire, the application detects only the pulse from that wire. In this case, the Events per revolution value should be:
- 0.5 for a four-stroke engine.
- 1 for a two-stroke engine.
Adjust these settings based on your engine's specifications to improve RPM measurement reliability.
This parameter fine-tunes the tracking of the RPM frequency peak. Set it as high as possible, but lower it if the harmonic peaks frequently overshadow the fundamental frequency.
This sets the minimum RPM value that triggers the alarm (e.g., the tachometer background blinks). It can help race car drivers know when to shift gears in a manual transmission.
Enable this only if you are using an external microphone away from your iPhone/iPod speaker or if you are using an inductive or cigarette lighter RPM pickup. Otherwise, the alarm sound may interfere with RPM measurements.
If engine noise is drowned out by other sounds or if you need more reliable measurements, consider these options:
- Use an external microphone near the exhaust of your car or motorbike.
- Use an inductive clamp (pickup) on a spark plug wire. This is the best option for gasoline engines.
- Use a cigarette lighter RPM pickup, which extracts RPM data from the ignition noise pulses in the vehicle 12-volt wiring. (Note: This method can be affected by the radiator cooling fan, air conditioning, car radio, or navigation system.)
You can find an electronic circuit diagram for a cigarette lighter RPM pickup here :
You will need a 4 Conductor 3.5mm Plug. It would be useful to build a splitter Adapter Mic/Headphone Converter Cable.
