Organ donor – First transplantation : Foot Bass

Two months ago, on my daily hackaday visit, I discovered the amazing idea of Jon Ferwerda who transformed an old 1975 Hammond Organ foot pedalboard into a fantastic bass instrument.

So, I decided that my own broken organ had to be recycled. Indeed, my friend who plays bass with me is not always available and the opportunity to replace him by a foot bass when I’m alone was awesome !

I took my screwdrivers to remove the foot pedal board from the A55  :

I had an old Freescale MC9S08QG8 demo board which was also dying in my garage and decided to use it as the heart of my project.

Then I made an oak case, and placed the A55 pedal board and the MC9S08QG8 demo board inside.

Below, you can see inside the foot bass :

MC9S08QG8 demo board connected to the foot pedal board and back plane:

Foot bass closed :

Foot bass back : I made a custom iron back plane which provide two 6.35 jacks for audio in and out, and a power jack for 12V power supply. Only out jack is connected.

The foot pedal in my gear :

How it works :

– The MC9S08QG8 demo board accepts 12V power supply which is really convenient.

– Each of the 12 foot switches are connected to one GPIO of the MC9S08QG8 microcontroler. The upper C is not used.

– I made a simple C code that generates a square signal on a MC9S08QG8 GPIO pin at a frequency that matches the pushed foot switch. The generated frequencies cover the octave from C2(65.41 Hz) to B2(123.47 Hz) and are 0.2 Hz accurate.

– The output square signal passes through a 2nd order low pass filter to get a pseudo sinus signal with a line amplitude.

– After the low pass filter, the signal goes into the output jack on the back plane, to be amplified externally.

As you can see, in this configuration, the foot pedal case is mostly empty. This is because I thought it would be great having enough space to put a power amp inside. This would allow me using it without external amp. That’s what I’ll do for version 2 !


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