Acceleration
Taking data directly from your built-in accelerometers, this app calculates and displays instantaneous total horizontal acceleration measured in g.
Using The App
Keep the device in one place and direction. Tap 'Calibrate' to let the app find the size and direction of gravity.
Horizontal acceleration is now displayed.
Recording
When 'Record' is tapped, for the next 13 seconds a scatter graph of calculated readings is displayed. Two green arrows let you increase or decrease the vertical scale of the graph.
Smoothing
By default, unsmoothed data from your accelerometers is used. Tapping the 'Smooth' button continuously averages the last last ten readings. This helps to manage results.
Vertical Scale
Use the green arrows to alter the scale on the vertical axis. Points cropped by rescaling are not lost.
Save
Requires upgrade. Tap 'Save' to keep your displayed data. For your convenience it's a one-click process, with files automatically named by date and time. If you've enabled smoothing, that is the data that will be saved. As the app is sandboxed, data cannot be exported except as a picture.
Save Pic
Requires upgrade. The 'Save Pic' button only appears when device is held sideways. A png of your graph is saved into your camera roll. You to view it with any gallery or photo app, or pass it on.
Regeneration and Brake Lights
The brake lights in EVs should turn on during regeneration. The regulations for the UK state that if the deceleration is
- less than or equal to 0.7 m/s/s the signal shall not be generated
- greater than 0.7 m/s/s and less than or equal to 1.3 m/s/s the signal may be generated
- greater than 1.3 m/s/s the signal shall be generated
The 'Lamp' button displays a panel that changes from blue to yellow at 0.7m/s/s, and to red at 1.3m/s/s.
Gravity is taken as 9.81m/s/s in the conversion from g.
Device Check
To make sure that the accelerometers in your device are sensitive enough to give meaningful results, lay it flat with smoothing switched off. Press record, and slowly start to tilt the device towards the vertical.
If there is layering of the scattered dots then your device may not be sensitive enough to give meaningful results.
Upgrade
Save your sets of data to look at later. Also export full-sized pictures of graphs into your camera roll.
Internet
Once installed, no internet connection is required. There are no ads in this app, and no sign-ins required. No data is transmitted from this app.
About
I was following some chat about how deceleration could be measured.
I knew that there were decent accelerometers in many phones and tablets, and assumed there would be suitable apps for measuring this that I could recommend, but couldn't find any that were suitable.
Problems included oversmoothing, the need to precisely line up the device, and accuracy. I dithered a bit, then I wrote this!
This app takes raw data from the accelerometers not the processed data provided by the operating system. When 'Calibrate' is pressed, the magnitude and direction of gravity is measured, relative to the device. The app then continues to collect data from the accelerometers, mathematically projecting it onto the plane perpendicular to the original gravity vector. It reports the magnitude of the projected vector.
This process produces a reliable result for horizontal acceleration, whilst making you aware of jitter and sensitivity.
However, only the magnitude of the acceleration is measured. Forward, sideways and backwards accelerations are not differentiated between. Also, if the device is tilted, it doesn't adjust for the apparent change in the direction of gravity, and shows a false reading.
During calibrating and graphing the frequency of the accelerometers are increased from their resting rate of 10Hz to 100Hz. Immediately afterwards they are returned to 10Hz to minimize battery drain.