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How (not?) to make a Modulation Lever for the REMI

This page is a continuation of an earlier article ... See page 1 here.


Ideally, the Mod Lever should have a rocker or thumb-wheel action with spring return to centre position. Here's the DIY approach I took, not that I recommend it, because it was a lot of work. Alternatively, you could use a linear slider pot, or a mini rotary pot mounted sideways, or a joystick salvaged from a game console or a toy remote controller. The software will (hopefully) compensate for electro-optical and/or mechanical deficiencies such as "zero drift" (spring hysteresis), hyper-sensitivity and other undesirable behaviour.

mod lever pic 1
The spring -- sourced from a clothes peg -- has about the right stiffness for the Mod Lever application.
mod lever pic 2
Mod lever mechanical parts, disassembled. The frame was made from an offcut of 1.2mm Alum. angle, 20 x 16mm. The "armature" was made from 0.8mm Alum., with the spring crimped and glued in place with 2-part epoxy resin (Araldyte). The rocker is made of 12mm thick hardwood.
modlver pic 3
Rocker attached to armature with self-tapper.
modlvr 4
Assembled mechanism, without opto-electronic parts.
pic 5
Assembled mechanism, interior view.
pic 6
Assembled mechanism, exterior view.
pic 8
Assembled mechanism with opto board.
A vane on the armature moves between the LED and the photo-transistor, partially blocking the light. An LDR photo-cell might be better than the transistor to allow greater mechanical displacement, i.e. to reduce the sensitivity.
pic 8
The optics will be covered with matte black paper to block out ambient light. The output voltage swing from the photo-detector is about 2.5V with a 100k emitter resistor. This is just about ideal for input into the ADC on the PIC32. The op-amp (LM358) on the handset circuit board is wired as a non-inverting buffer with very high-Z input.
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handset bottom view
Handset with Modulation Lever fitted.
(Still no side pieces -- I will get around to making the sides one day!)

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handset internal layout
Handset internals modified.
Note that the breath pressure sensor has been relocated to make room for the modulation lever.
Putting the sensor above the T-joiner also helps to prevent moisture from getting inside the sensor.
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Go to REMI page 1
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