Foot switches for PSR S775

I have extended my “Midi Mate” (in previous post) to incorporate four footswitches to control the variation and drum fill selection on the PSR S775. I bought 4 foot switches from Amazon for a total of £10. These are momentary push to make switches that are designed to operate mains voltage for machinery.

I mounted four of these onto a strip of MDF by screwing screws directly into the plastic switch body from underneath. I then connected the outgoing cables to a 5 core cable with four of the switch poles commoned to one wire. (This is the voltage send and the other 4 wires are for the sense)

The five way cable is terminated using a 5 pin DIN plug (as used for MIDI) and this plugs into the Midi Mate unit as shown in the picture:

The four foot switches are connected internally to the electronics that scans the 3×4 keypad using a fourth scan output line. (In the AK47M project this is wired to four push button switches on the front panel.)

When a foot press is detected, the unit sends a series of MIDI messages to select a variation fill and select a new variation. As far as I can see, the MIDI interface does not operate in the same way as the manual push buttons on the keyboard. If the “auto fill” mode is on and you press a new variation button, the keyboard does a drum fill and then starts on the new variation after it completes.

The MIDI interface has ‘ on/off’ messages for drum fills and variations. So if you switch a drum fill on, it keeps repeating until you send a message to switch it off. So what I have done is to send a ‘variation off‘ and a ‘fill on‘ message when the foot switch is pressed down and a ‘fill off‘ and ‘variation on‘ when the foot switch is released. So a fill keeps going as long as the foot switch is held down. The switch springs back by itself when the foot is released and the new variation resumes.

This works fairly well and means that I can operate fills and variation changes whilst using both hands to play the keyboard.

The MIDI messages are  (in HEX):

F0 43 7E 00 ss dd F7

where
dd = Switch On/Off 00H(Off) 7FH(On)

ss = Section

08H MAIN A
09H MAIN B
0AH MAIN C
0BH MAIN D
10H FILL IN AA
11H FILL IN BB
12H FILL IN CC
13H FILL IN DD

 

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