You could use "tact switches" embed them in a bottom unit the "float" the top board of the key on top. They have much smaller travel than a micro switch, so something like silicon sealant between the 2 parts of the key, would provide enough squash and travel of the top to press the button.

 

Might mount two pressure sensors, one on each side near front edge of key. With separate switches there should be no interaction between keys. Using comparators, seems that there will be a common for all keys.

 

@pmd34 Seems feasible. I've just ordered one from Farnell to test, should be here monday.

the Key is made of 10mm perspex and will sit on top of a 10mm wooden framework. If the body of the switch is 4mm then I'll rebate a 4mm notch for the switch. then a 4mm notch for 6mm Neoprene tape. This will raise the Key by 2mm above the switch nipple.

When the key is "pressed" it will drop 2mm onto the wooden framework and neither the switch nor neoprene will be fully compressed - that should increase the life of both. Also, depending on the amount of neoprene, it can be adjusted to work for a toddler and an adult.

I know you suggested using a MOSFET to control the lighting circuit, I'm going to test it out over the weekend but I may just pop two micro switches in for the two separate circuits.

 

@DJFantasi: I did see the velostat idea earlier but I'm pretty sure the keys either side would be triggered too.

Not if you cut the Velostat the size of each key. I don’t know how you are making your keyboard, but it shouldn’t be difficult to mount individual Velostat pads that don’t interfere with each other b

 

That would've been perfect! Out of stock.
https://www.adafruit.com/product/3870

I've ordered some Velostat too @djsfantasi !

 

@djsfantasi I wasn't clear I think. The Key is 600mm X 200mm opaque perspex. It will be backlit by LEDs so the Velostat pad cannot be the full footprint of the key. It will just have to be the 10mm strip at the front edge.

The idea of using pressure sensing rather than a microswitch is so that I can have a slab of Perspex (600mm X 1400mm) rather than individual hinged keys. Although I could use individual keys but without a hinge.

I'll give the velostat idea a bash when it arrives.

 

@djsfantasi I wasn't clear I think. The Key is 600mm X 200mm opaque perspex. It will be backlit by LEDs so the Velostat pad cannot be the full footprint of the key. It will just have to be the 10mm strip at the front edge.

The idea of using pressure sensing rather than a microswitch is so that I can have a slab of Perspex (600mm X 1400mm) rather than individual hinged keys. Although I could use individual keys but without a hinge.

I'll give the velostat idea a bash when it arrives.

Can you make cuts in the perspex at the key boundaries leaving them connected by a strip on the back to act as a hinge so it is still just on piece?

 

Can you make cuts in the perspex at the key boundaries leaving them connected by a strip on the back to act as a hinge so it is still just on piece?

@Yaakov, that’s similar to what I thought he was doing. If he cut the keys apart to a point about 50mm from the back, I think the Perspex would be flexible enough to act as its own hinge. Cutting out the black keys is more problematical but not impossible.

 

@Yaakov, that’s similar to what I thought he was doing. If he cut the keys apart to a point about 50mm from the back, I think the Perspex would be flexible enough to act as its own hinge. Cutting out the black keys is more problematical but not impossible.

I'd have it laser cut.

 

How can you backlight opaque Perspex?

 

How can you backlight opaque Perspex?

Depends on the color. Opaque Perspex isn’t totally opaque. EL panels might have enough light to illuminate it. Think light table.

 

@ElectricSpidey I bought a sample and tested it and it works well. The Perspex sits 10mm above the floor panel so a strip of Cool LEDs disperses pretty well.

@Yaakov I got a quote to have it laser cut and it came out at £140 per panel. Given that there are 4 panels and each is already costing around £175 I decided to buy a £140 bandsaw instead!

With regard to you idea of partially cutting the keys and using a sort of "Leaf" effect, I did consider it but check out the key plan attached, given the irregular shapes, I'm not sure. I couldn't cut the white perspex to within 50mm as the white perspex doesn't actually join across the back. The mid-grey is the floor panel - the electrical wiring will be pinned here.

 

@pmd34 Seems feasible. I've just ordered one from Farnell to test, should be here monday.

the Key is made of 10mm perspex and will sit on top of a 10mm wooden framework. If the body of the switch is 4mm then I'll rebate a 4mm notch for the switch. then a 4mm notch for 6mm Neoprene tape. This will raise the Key by 2mm above the switch nipple.

When the key is "pressed" it will drop 2mm onto the wooden framework and neither the switch nor neoprene will be fully compressed - that should increase the life of both. Also, depending on the amount of neoprene, it can be adjusted to work for a toddler and an adult.

I know you suggested using a MOSFET to control the lighting circuit, I'm going to test it out over the weekend but I may just pop two micro switches in for the two separate circuits.

Smart idea, certainly using 2 switches instead of one, it will make your life simpler. Though I cringed at you shopping at farnel, very speedy delivery, but SO expensive!
I buy all my stuff at aliexpress, but the delivery takes a while. If your in the UK: rapid electronics, and CPC are worth looking up.

I would be tempted to use a larger area of neoprene, or whatever spacer, around the whole edge of the key, that way the whole top of the key will move, rather than just a very localized area, which might just result in a bulge in the plastic

For cutting plexy glass, actually a standard wood cutting table saw works very nicely:

Not beautifully beautiful, but very quick and easy. Cutting with something finer like a jig saw tends to melt it and the blade gets stuck.
You can bond it very easily with a bit of acetone, it actually dissolves plexy glass.

For lighting, if you rub up the top surface with sand paper to give it a sand blasted, frosted look you can actually put LEDs around the outside edge and light will come out of the top surface, its not fantastically efficient, but gives a nice effect, and you can even stencil and sand blast it to put logos, letter etc on.
Ooo.. but then you could just buy a strip of LEDs, and they could change colour when you press a key!!

 

Have photo detectors detect interrupted laser beams a few mm off the floor. May take some optical design for a given detector to
cover only one key and to do so completely.

 

I'd never use Perspex/Plexiglas/acrylic for this, especially if your going to use it like a hinge. Acrylic is too brittle, the extra cost of Lexan/polycarbonate is well worth it for something like this.

 

I'd never use Perspex/Plexiglas/acrylic for this, especially if your going to use it like a hinge. Acrylic is too brittle, the extra cost of Lexan/polycarbonate is well worth it for something like this.

There are also a number of other materials, not as durable as polycarbonate, (Lexan), but much less brittle than plexiglass. Of course for this application there is a fair amount of stiffness needed and that does reduce the choices field a bit. The challenge indeed will also be in hiding the wiring. It seems like the TS is wanting the whole assembly to be very thin, which is in conflict with microswitches in general. Foil separated by an elastomer spring still seems like a better choice.

 

Cutting plexiglass/polycarbonate, I've used a carbide blade. You can also "fire polish" the edges if you need too.

Drilling holes which you don't have to do. I had to drill 5/8 holes. The bit I custom ground, so it cut along the edges, more like a pilot point bit. You can use a little water and dishwashing soap as a lubricant,

 

Lots of great ideas chaps.
@pmd34 - I think you need a finer blade, but good idea. I did try the "Fibre optic" effect of putting LEDs on the back edge but no nearly enough light comes through the top surface. As for colour changing LEDs - again, it crossed my mind but for simplicity, and cheapness, I've got for white. Isn't CPC an arm of Farnell?

I'm going to slightly chamfer the edges for some extra demarcation so the slight chipping shouldn't matter.

@DickCappels Nice idea, but I'm really trying to keep it simple!

@shortbus If you have a better idea then I am genuinely listening. I have a 10mm Acrylic sample here and it seems OK. As I mentioned, it will be rebated 10mm around the edge to a depth of 3mm so that the whole key drops into the frame. This should prevent any lateral movement.
https://www.sheetplastics.co.uk/10mm-opal-acrylic-sheet-cut-to-size.html
This is what I have settle on at the moment.

@KeepItSimpleStupid Good tip - cheers. You've made me think that putting a screw hole at the back end might create a stress point. I think I'll just drop the keys into the frame and try to come up with a way to hold them in position when moving the panels.

@MisterBill2 Lexan doesn't appear to come in opal/frosted?

 

The challenge indeed will also be in hiding the wiring.

Most of the wiring will be at the back, covered in a 30mm cowling. The inside of the framework will be painted white and the keys will be frosted/opal so hopefully nothing will show through.

I think the only thing that will show through is the micro switch or velostat at the front edge. I plan to put some white electrical tape all around to give a little bit of a cushion too.

 

This morning I emulated the keyboard with a series of Microswitches and 1N4148 Diodes so I know it will all work. I need to buy a project box now and stuff the electrics into it before starting work on the 1 Octave Panel.

Thanks for your help chaps.