HALL EFFECT SWITCHES
A Hall effect switch is a solid state switch that is activated by an external magnetic field. They are completely impervious to dust, dirt or corrosion. They come in a large variety of shapes, sizes and prices, and most of them are for use in industrial automation systems and are not suitable for use on organ keyboards or pedalboards.
After extensive research I have now found an economic and highly effective solution. The switch itself looks like a small plastic transistor, and has three leads; plus, minus and output. The output is normally high and switches to low in the presence of a magnetic field of the correct polarity. It can operate from 3.8v to 30v and can sink a maximum current of 10mA.
It can be used directly to switch my midi encoder system, or with additional electronics to switch 15v at up to 500mA. I have produced a double sided PCB (215mm x 20mm) which mounts 16 switches at the correct spacing for most keyboards (prox .55” pitch) and has an output connector for a 16 way ribbon cable. This is designed to connect directly to my midi encoder boards, but can obviously also be used with any other desired circuitry.
The magnets, which are made from Neodynium Iron Boron and are very powerful, are cylindrical of 6mm in diameter and 2mm thick. They can easily be glued to a suitable point on the keys, depending on the space available to mount the PCB.
On plastic keys, or wooden keys which are pivoted at the back, the magnets can be attached underneath the key somewhere near the front, on centrally pivoted wooden keys they can be stuck either to the top or bottom near the back or on the end. It doesn’t matter whether they are used as normally open or normally closed, as the associated electronics can adjust this as required.
By leaving the leads on the switches about 10mm long, it is easy to bend them slightly to control the depth of touch and to compensate for any unevenness of the keyboards.
I am still experimenting with using this system for a pedalboard. The length of travel is much greater and the small magnets mentioned above are not suitable.
The cost is £48.00 per 16 way PCB (including magnets). This is hardly more than the cost of gold clad contact blocks and gives far superior results.