Author Topic: AVR analog I/O to tune expression pedal response  (Read 2346 times)


AVR analog I/O to tune expression pedal response
« on: November 16, 2012, 04:32:50 PM »
Just daydreaming some AVR applications, and thought I'd bounce an idea.

How useful would an AVR chip be that maps the voltage control from an expression pedal to a different voltage curve output? Discrete input could be used to select different mappings, controlled by an onboard toggle or pin jumper. In this way, you could select different settings to find a preferred response to a given pot or LDR expression pedal.

Not sure if this would work or be particularly useful. Also, most AVRs that have analog I/O are of the bigger variety with more pins than needed for this basic function.


Re: AVR analog I/O to tune expression pedal response
« Reply #1 on: November 16, 2012, 08:33:39 PM »
there are 8 pin PICs that can do analog input and PWM output (eg 12F683), i guess AVR has similar devices in a DIP8 footprint

but... you can model a PWM output to your preferred response, then there's the issue of what you are interfacing with: an LDR, an OTA, transistors, etc. Each one has a different response and scaled sensibility. For example, Gain in an OTA is not linear with its control current. An LDR: LED may be somewhat linear only in a narrow range of current (that doesnt start at 0mA), and the photoresistor may have a skewed curve too. Moreso, theres the perceived effectiveness of what you are actually hearing. This is an example for volume control, which usually must be logarithmic to achieve a perceived linear response.

Even if you can think of a purely resistive interface: for example, potentiometer -> microcontroller -> digital pot
there's the problem of resolution. Digital pots has a limited number of steps. If you are mapping to get a logarithmic transfer, most of the useable range will fall into a limited range of those steps, thus drastically reducing output precision.