Video about switches for DIY key sensing

I have been doing some experiments and research on sensors/switches for adding MIDI to organ keyboards (because I'm in the middle of a project to do just that). I pulled together what I have learned into a video discussion of the switch types. I am not truly an expert on this, but I wanted to share what I've learned in the hope it's helpful for someone. It certainly would have saved me some time (and burned up components) if I had seen a video like this at the beginning of my project.

https://youtu.be/4H9Q47Goa1A

Happy to get comments/corrections.

Interesting video, esp good explanations for beginner folks.

Further info on optical switches and arduino:

http://forum.hauptwerk.com/viewtopic.php?f=15&t=17358&p=130118&hilit=keyboard+switch#p130044

Mounting components can be an issue.

Rgds,
Ed

That's an extremely informative thread. Thanks for linking to it. Actually I wonder if I should post a link to that thread in the comment text of my video.

I would be interested in any thoughts anyone has about the best way to mount these switches. I was thinking some kind of long perfboard, or perhaps I could mount a bunch of smaller perfboards to something that will hold them in place. I also thought about really basic stuff like a thin strip of wood or a long, think strip of acrylic, but I don't look forward to drilling all those tiny holes! Not to mention I'm not sure how well I could solder without affecting the mounting materials.

https://midi-hardware.com/index.php?section=prod_info&product=HALKA&R2=USD

Rgds,
Ed

I wrote the below-linked document in 2017 so it's probably "old-hat" now. I thought I'd made it available to this forum at the time, but I've just done a search and it doesn't show up
In it I describe how I mounted opto-switches on stripboard - it was quite complicated and involved a lot of cutting of tracks!
I subsequently found that it was neater to mount the opto-switches on short pieces of stripboard with the tracks oriented north-south, and the other circuitry (diode matrix etc.) on long pieces of stripboard with the tracks oriented east-west.
For pedal boards I used opto-switches with a wider gap than those used for manual keyboards.

https://www.dropbox.com/s/989knkoy50zj3b8/Opto-switch%20experiments.zip?dl=0

Graham

Very interesting and helpful, Graham. Thanks! That definitely points me in the right direction. Those super long stripboards don't seem real easy to find, though. At least, not in the places I've been looking.

What' I'm currently thinking is buying the little 2x8cm perfboards you can find in quantity and at low prices and then screwing them in a row into at 2"x2" or so wood backer with standoffs (after attaching and wiring the switches,). Those perfboards come with the screw holes already. Seems easier than the large number track cuts that would be required if I used stripboard. It will require more wires, though. This way, individual groups of 8 cm could be replaced or worked on relatively easily. Not sure how well the switches will do at spanning the gaps between them. I'll do some experiments and report back.

Just a few observations/suggestions:

Hall sensors: Ratiometric sensors are tricky to set up, as you have found, but easily available and nearly as cheap are those with built in Schmitt trigger circuitry which are quite easy to set up. Unfortunately, they tend to have longish turn-on times which makes them complicated to use in matrix arrangements.

Reed Switches: As you say, not easy to use for keyboards and additionally I found the 'ticking' as they open and close irritatingly audible. They are a good choice for pedal-boards though.

Optical Interrupters: These are still my first choice for keyboards, and are easy to incorporate in matrix designs. A couple of points to consider: There are considerable energy savings to be had in wiring the LED's in series. Blocks of eight, with one series current limiting resistor per block are especially convenient for matrix designs, in non-matrix arrangements you can chain a few more depending on the power supply voltage. Also, keep the sensor emitter load quite low. About 1k Ohms will enable them to turn on fairly quickly. In my experience, much more than that and latency can become an issue.

Over the years, there has been quite extensive and detailed discussion of these issues on the forum.

The video would be quite useful I think to anyone beginning on DIY work of this kind.

Nick

The trade-off is long stripboards with many track cuts, or short stripboards and many jumper-wire connections. Short pieces of stripboard or perfboard give more scope for lining up the switches with the keys/shutters.
Photography is not my forte, but hopefully you can see from these photos (link below) how I used short pieces of stripboard with N-S oriented tracks (accommodating 8 opto-switches each) screwed to the side face of a 2” x 1” batten, and long stripboards with E-W oriented tracks screwed to the top face of the batten for the diodes etc.
This was to cater for a scenario where the shutters (or “flags”) had to be attached to the underside of the keys. (Old-school metal chassis Fatar keyboard where some of the traces on the pcb had worn and the rubber contacts no longer functioned.)

https://www.dropbox.com/s/3enkusrg0cr691t/Old-school_Fatar.zip?dl=0

Graham

Photography is not my forte, but hopefully you can see from these photos (link below)

The photo's look OK to me.

Nick

Thanks, Nick.
Driving a mouse is evidently not my forte either!
Link now edited.

Graham

One (slight) negative is not easily being able to do touch response or in the case of a theatre organ - second touch.

Rgds,
Ed

One (slight) negative is not easily being able to do touch response or in the case of a theatre organ - second touch.

In theory I guess you could do it by “double-banking” the opto-switches in a similar way to how the rubber contacts are “double-banked” in touch-sensitive MIDI keyboards – with one extended shutter obscuring or exposing each pair of opto-switches. But I wouldn’t like to try and figure out how to mount the components

Graham

But I wouldn’t like to try and figure out how to mount the components

Oh, come on, Graham. I've been told that you have mastered such abilities long ago. There are some other contributors here that have likewise done so.

One useful available board if you want to set up an 8 X 8 matrix can be obtained from

https://www.shop.gino-midi.nl/product/decoder-met-matrix-bouwpakket-2/?lang=en

as a "special". I have negotiated with Gino to sell a small quantity of these boards as unpopulated at a reasonable cost. (I them install small signal diodes as needed) The only issue is you have to wait until he orders the next batch of them from his supplier. Quite a simple mod is possible. I imagine there may be others who have a matrix board or as John Kinkennon does, design your own PCB. But for my small needs took the easy (lazy) way and ordered them from Gino, who BTW has some nice (other) products as well.

I think it's really neat that this Hauptwerk community is so international.

Right now I'm looking for an available (cheap but good) source for the small Optical Interrupters for Fatar keyboard retrofits. With slow shipping, etc due to the pandemic, lead times can be quite long, yes?

Another technique, if it can be called that I use is when needing to make effectively a "feed thru" wiring connection of an IDE connector. I pull out the as shipped pins of two (identical) IDE connectors and place them "back to back", one on the top side, one one the bottom side of a vector board. Then replace the pins I pulled out with dress maker's straight pins (very cheap) cutting off the excess pin length. In that way you can use ribbon cable(s) on each side of the vector board. You need to "transpose" the ribbon cable connections on one side as, for example pin 1 on the top side is pin 2 on the bottom side, pin 2 on the top side is pin 1 on the bottom side, etc. Maybe not for everyone, but it does make for a "neat" layout . I love IDE connectors and ribbon cables.

Rgds,
Ed

Right now I'm looking for an available (cheap but good) source for the small Optical Interrupters for Fatar keyboard retrofits. With slow shipping, etc due to the pandemic, lead times can be quite long, yes?

I just bought 250 of these HY301-21 interrupters on alibaba (seller: Shenzhen Xinzhongtai Electronic Technology Co., Ltd), which is enough to do 4 manuals. They did have a COVID-related delay and took 9 days to ship it out instead of their usual "next day" shipping. It was 4 days to get from Hong Kong to my doorstep DHL. So that was a total of 13 calendar days. The cost was 23 cents per switch plus $23 shipping (total for 250 switches was $82). If I had bought way more, I bet shipping would not have gone up much if at all.

I didn't really shop around, but that seemed like a reasonable price and reasonable(ish) shipping time. Is that the type of interrupter you were looking for?