Analog IO Board PCB

A number of my synth projects require the use of potentiometers.  A while back I made a relatively simple stripboard pot breakout, but it isn’t particularly reliable.

This PCB is a pot breakout that can be used in various ways – either direct, with a 4051 multiplexer, or with an SPI MCP3008 expander.  It also includes an additional section that can be detatched for a seperate 6-way pot breakout.

The build guide can be found here: Analog IO Board PCB – Part 2.

Warning! I strongly recommend using old or second hand equipment for your experiments.  I am not responsible for any damage to expensive instruments!

These are the key Arduino tutorials for the main concepts used in this project:

• Simple Potentiometer Breakout
• Arduino Multi-pot Mozzi FM Synthesis
• Arduino MIDI Mux Step Sequencer
• Arduino Mozzi FM Synthesis with MCP3008

If you are new to Arduino, see the Getting Started pages.

The Circuit

There are two discrete sections to this circuit.  The 6-way pot section is wired directly to its own, independent 8-way header: VCC, GND and the six pot “signals”.

The 8-way pot sections has three modes of operation, all of which are mutually exclusive:

• Direct connections via a 10-way header to VCC, GND and the 8 pot signals.
• Multiplexed connection via a 74HC4051 or CD4051.
• SPI connection to a MCP3008.

On no account should both of the chips be installed at the same time and neither chip should be installed if using a direct connection to the pots.

But the idea is a single PCB with several options to support analog IO.  There is also nothing here about voltage levels, so if your 4051 or 3008 is happy with 3V3 or 5V operation, then either can be used depending on your microcontroller.

PCB Design

The pin header on the left acts as either the SPI interface or the MUX interface.  The pin header on the right is for direct connection only.  The pin header at the bottom is for the bottom six, directly connected pots.

In principle the board could be used for a 14-way pot breakout, using both the right and bottom pin headers, but really it was designed for the bottom section to be detatched and used independently.

Closing Thoughts

I have a number of ideas for relatively simple utility boards like this that I think will be useful in future projects.

I also like the idea of having a single design that can support several modes of operation for differing circumstances.  It makes best use of the manufacturing process as the costs for up to 10 boards is usually the same as the cost for 1 at least for anything within the cheapest 100x100mm size.

These boards have been manufactured using the Seeed Fusion PCB service, which I am happy to continue to recommend. They have been supported with discount vouchers that I’ve been sent by Seeed for my previous projects.

Kevin