A write-up of my latest Pi project which is a device to aid those learning (and those teaching others to learn) the art of tower bell ringing.
It requires a lot of practice to do well.
It is true that, fundamentally, you are just pulling on a rope (called a sally in the parlance) but you have to pull just hard enough to allow your bell to be properly controlled and accurately enough so that you are in time with all the other ringers in your band. Many people struggle to learn the art and I am a case in point in that I started to learn to ring but gave up (as too many do) after a few months.
At the start of 2017 a friend (who has rung for years) pointed me in the direction of an article in the Ringing World publication, which was a call-to-arms and a competition to design a pullometer intended to be used as a training aid for bell ringers. The article is here: http://www.jaharrison.me.uk/New/Article ... llenge.pdf.
This was right up my street and I spent much of my free time in the early part of 2017 designing a solution.
The "right" way to measure tension in a rope is to use an offset pulley arrangement whereby the rope runs through a set of three pulleys with the middle one being offset and applying sprung tension to the rope. As the (pulled) tension on the rope changes the position of the middle pulley changes in a way that is proportionate to the pull. This can be measured by a strain gauge. After a bit of thought, I decided not to follow this route as it needed quite a lot of setup if it needed to be mounted and dismounted or moved from tower to tower. I also thought it would be quite noisy because the surface of the rope is not smooth.
I very quickly settled on an IMU-based route and a quick proof of concept using an Arduino, a MPU6050 IMU breakout board and a Bluetooth module showed pretty promising results. The solution involves the device being attached to something called the headstock (a big lump of metal that is attached to both the bell and the axle on which the bell rotates) and so it rotates with the bell. My first test used duct tape to attach the device to the headstock and I have not changed this (its fast, secure and cheap).
Here is a pic of a prototype of the the device:
There is more detail on the technicalities on the project's Github https://github.com/BBUK/Bell-Boy and in particular on the wiki and there will probably be quite a lot here that may be useful to anyone interested in:
(a) battery power to the Pi with on/off switch and low battery detection (using a Pimoroni LiPo shim, 4 diodes, a couple of resistors, a LED and a push button) - I have not looked at the power enable pin on the 3B+ but I suspect something similar could be created using that
(b) wifi access point creation
(c) use of dual MPU6050 IMUs to obtain smoother data and synchronising the FIFOs on the IMUs
(d) Kalman filtering