Dedicated tap-tempo clock project using ATtiny861

[hab]

Long story very short, I've now got tap-tempo versions of tremolo, phaser and chorus. Not wanting to keep stepping on each of them individually I set out to build a dedicated tap-tempo unit that could synchronize all of them at once.

Full source code and an example schematic can be found here: http://www.sabrotone.com/?p=4283.

Suggestions, feedback etc. is welcome. If there's any demand for it I'll put up a few pre-programmed chips for sale as well.

Anyway, enjoy

[free electron]

Hey!
Looking at the schematic, i'd have a few suggestions:
- analog VCC filtering: usual approach is to add a small LC filter, 10uH + 100n cap placed close to the pins.
- add 100n caps between the ADC inputs and GND, again, close to the ADC inputs to further reduce the noise and get more precise conversion result.
- i would add some sort of protection for the ADJUST_INPUT, especially if you plan to plug some external sources. At least some resistance in series, which will limit the input current of the internal clamping diodes.
- to separate the outputs from what they will drive you could use a standard optocouplers, like the small PC817 or 4N25. If the tap tempo pedal has a tap footswitch input, usually there is a pull up resistor inside and an open collector output will be enough to drive it. By doing this you will also break the ground loops created by the signal and clock/tempo carrying cables, there will be no need for the ground lift switches. I have built myself a 3 way tap tempo splitter box some time ago, just a momentary footswitch driving a set of 3 4N25s, isolated output jacks, E of the output transistor goes to GND/SLEEVE, C to the TIP. Simple and works great.

Generally, exposing bare inputs and outputs pins without any sign of protection to the external world and whatever people will plug in there is asking for trouble. To get some inspiration on that topic, take a look at the schematics of different digital pedals (boss delays etc) and see how are the tap tempo/expression pedal inputs done.     

[hab]

Excellent advice. This is stuff I have very little experience with, so it's highly appreciated. Thanks!

[hab]

Thanks for the advice, free electron. Have updated the schematic with most of your suggestions.