Digital FD-8 pedal

In Roland FD-8 Issues: Hall Sensor Modification we described how a ratiometric hall sensor could replace the resistor film to solve reliability issues with the Roland FD-8 high hat pedals. Even though that Hall Sensor hack works, an MCU based approach might have some additional advantages:

• complete variable resistance to be compatible with other drum modules
• adjustable sensitivity curve
• detection of foot-down velocity (which is currently limited to one static velocity)
• auto-calibration, i.e. no need for pots to set the right trigger points.

We're currently working on a "more digital" version, based on a MCU and a digital potentiometer. We're using the following hardware:

• attiny13 MCU: 8-pin (6 io), 10-bit ADC.
• Two MCP41010 digital potentiometers in series (10K each, because when we sourced it, a single 50K version was a lot more expensive on ebay).
• Honeywell SS490 ratiometric hall effect sensor.

Additionally (and optionally) we're adding:

• a switch (button) to start calibration
• an LED, because every MCU project should have an LED

The circuit essentialy does the following: using the adc, the output voltage of the hall sensor is measured. This is then used to determine a corresponding resistance and that resistance value is programmed into the digital pots. Easy.