Accelerometer as Tilt Sensor for Expression Pedals

[jkinkennon]

On another forum we are discussing using accelerometers as tilt sensors to read expression pedals. This sounds like an overengineered solution, but it can be less expensive in many cases and may prove more reliable than potentiometers which can become dirty and flood the electronics with redundant messages.

I'm receiving a set of ADXL345 sensors tomorrow morning and have a sample program written to try them out. There's a SparkFun_ADXL345 library available for Arduino and Teensy that appears simple to use. I'll update my findings here. This is not a solution for potentiometers which are already in place, but for expression pedals needing the addition of a mechanical linkage and/or a linear pot, there is a potential for significant cost savings and labor reduction.

[ReinerS]

A friend mailed me an image of his organ (I believe it was build by Mixtuur or Noorlander), and that also just has a tiny little circuitboard under each swell pedal, connected via a ribbon cable. I would bet that they use an accelerometer there, so I suppose this approach is even used comnmercially. Seems like a neat idea to me, maintenance free.
I actually have a tiny little board with that chip plus a pi-pico on it, using it for measuring things, easy to program and spitting out data via serial bus or USB.

[jkinkennon]

Thanks for the info. I can easily believe this has been done. There are European companies who aren't missing a trick.

[IainStinson]

On an organ association visit to Liverpool Anglican Cathedral to see, hear and play the organ, I came across the Willis ‘infinite speed and gradation’ system which is used to control the expression boxes for all the enclosed divisions, including the Echo division installed last year. They offer a different approach to managing the expression boxes. Collin Pykett’s article describes the system well. It takes a while go get used to them! (Think car accelerator pedal…)

“The ISG system is completely different to any other means of controlling the swell shutters invented and it requires the player to develop an entirely new technique for operating them. With all other systems the position of the shutters is always related to that of the swell pedal (shoe) – when the pedal is moved hard over to one extreme or the other the shutters will be either fully open or fully closed, with a correspondence being maintained at all intermediate positions.  In the ISG system, however, this correspondence does not exist.  One cannot infer the position of the swell shutters from that of the pedal, and some form of indicator is therefore required at the console to tell the player where they are.  The pedal itself is also arranged differently to any other in that it is spring loaded, so that it always returns to an intermediate central or neutral position when the player’s foot is removed from it, and in that position the shutters stop moving abruptly (or, at least, they are supposed to).  Away from neutral the position of the pedal determines how fast the shutters move; they close at a speed chosen by the player when the pedal is moved towards the vertical by means of heel pressure, and they open when it is pushed forwards towards the horizontal.”
(See https://www.colinpykett.org.uk/speedandgradation.htm)

Hauptwerk did at one time support this method for controlling enclosed divisions, but I think it was removed some years ago.

The accelerometer could offer a new perspective for the ISG.

Iain

[mdyde]

Hauptwerk did at one time support this method for controlling enclosed divisions, but I think it was removed so years ago.

Hello Iain,

It still has support for that (within the organ definition format, as it was since v2).

[IainStinson]

Thanks Martin.

[jkinkennon]

I have the accelerometer providing a range of 150+ values that appear stable and repeatable. The key was to avoid any complex calculations and just monitor the lower byte of the x-axis value. Things like pitch and roll require complex math that I forgot years ago. Now it's time to set up an expression pedal with the sensor mounted to the underside and see if any extra scaling and ranging will be required beyond what Hauptwerk provides. Currently I'm doing ten samples per second which is more than enough.