DIY MIDI Concertina construction - what to use for the bellows

[Don Taylor]

In another thread, Richard Mellish said:

Quote

I'm not sure whether it should be called a strain gauge or a load cell. Anyway one of these  https://tinyurl.com/2t6txzpd . Then a quad op-amp and a few transistors to provide polarity output (needed for a Anglo keyboard) and an analogue voltage to control amplitude. I can provide more info if desired, but perhaps on a different thread.

So this is that different thread.

 

I would like to see how the bent coat hanger and load cell are used -  a photo or a sketch would be really nice.

 

And your circuit diagram ... pretty please.

 

 

[Richard Mellish]

Can't do a pic at the moment. I did have the two ends connected by the bit of coat hanger, but it needed a bit more work and the ends are separated at present.

 

I'm attaching a PDF of the circuit but it may not make much sense without the description of the rest of the system, and I've realised that that needs an update. I'll post it ASAP.

 

 

MIDI concertina pressure circuit.pdf

[Richard Mellish]

Here is the description.

RM MIDI concertina.pdf

[Don Taylor]

Thanks for this, Richard.  I must admit it is not what I expected and I have to think about it for a bit.  I am planning to use an HX711 load cell amplifier controlled by a microprocesor instead of the discrete electronic components that you are using.

 

I am still puzzled about your use of a a bit of bent coat hanger wire,  are you using this as a hinge between two pieces of wood with a load cell screwed between the wooden ends?

[Richard Mellish]

6 hours ago, Don Taylor said:

Thanks for this, Richard.  I must admit it is not what I expected and I have to think about it for a bit.  I am planning to use an HX711 load cell amplifier controlled by a microprocesor instead of the discrete electronic components that you are using.

 

I am still puzzled about your use of a a bit of bent coat hanger wire,  are you using this as a hinge between two pieces of wood with a load cell screwed between the wooden ends?

Looks like I need to put it back together so I can (a) confirm that it does actually work, and if so (b) post a picture on here.

 

I have a fair amount of experience with discrete components (going back to valves!) and small-scale integration, and at the software end with BBC BASIC, but very little in between, hence my choice of an off-the-shelf MIDI interface rather than a Raspberry Pi or the like. The rest then followed from that.

Your plan is an illustration of there being more than one way to skin the proverbial.