PU-2: New brain – Arduino Mega

The FCB1010/PU-2 has a new brain. The Arduino Mega (clone) has been connected in place of the main board.

I have removed: the power transformer, the mains/120 volts plug and the on/off switch, because the PU-2 will be bus-powered.

It was a straightforward affair: no new connections were made, no new switches installed. But the connections weren’t done without challenges. As can be seen on the photo above, I had to assemble the cables linking the foot switch boards to the Arduino. This called for a lot of research for the proper connectors: the ones used in the FCB1010 are 2.00 mm pitch. The connectors used on the Arduino, and pretty much everything else around here, are 2.54 mm pitch (0.10″). So I hand built the 14 pin cables using rather expensive connectors (thanks digikey!). I wanted to be able to connect everything else in the FCB1010 using the connectors already in place, so I also had to find matching connectors for the Midi interface, the expression pedals, the switchable jacks, and various LEDs. All 2.0 mm…

The little board on the right of the Arduino is just used as a connecting platform for the various cables. It also shows the single LED resistor used to drive the 12 LEDs of the board. More on that later.

Why an Arduino MEGA?

As this is a prototype, it has to let me quickly modify anything software and hardware. The Mega has 54 digital input/output pins directly accessible on the board. It also has 16 analog input pins. The regular Arduino boards have one set of serial transmit/receive pins. The Mega has 4 sets.

The two cables connecting the switch/LED boards require 25 pins, already more than can be provided by the Arduino Uno/Diecimila/Duemilanove.

Of course, I could have used mutiplexers/shift registers/LED drivers/etc! But this is a prototype. The final version will be much more efficient, pin wise.

LED driving

There are 10 LEDs on the switch boards. Two more are associated with the expression pedals. All have theirs + pins tied together. My idea is to use a single 330 ohms resistor to drive them. This first version on the PU-2 will only turn one LED on at a time.

So, now, let’s start coding!

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