The Super Retro Fader Box is designed to interface with a computer via the PIC 18F4550 microcontroller made by Microchip. The block diagram in figure 4 shows how the interface connects with a computer. The unit has two types of interaction, faders and buttons. Faders are continuous controllers that require an analog to digital conversion in order to be understood by the computer. Whereas buttons map well to digital, therefore requiring no conversion. Because of the number of inputs from the mixer two PIC’s are required in order to map all of the controls to the computer.

Each of the PIC 18F4550 microcontrollers has thirteen analog inputs (that have A to D conversion built in) and seventeen digital inputs. But the Super Retro Fader Box has 24 faders and pushbuttons. It would be possible to design a system that used multiplexors to get all of the controls interfaced to one PIC, but a simpler solution is to divide the Super Retro Faderbox into two groups, with each group is assigned to its own PIC.

 

Figure 4. Block diagram the Super Retro Fader Box.

By dividing the Super Retro Faderbox into a top group that consists of the upper bank of faders and buttons and the crossfader on the right of the board, and a bottom group that consists of the bottom bank of faders and buttons and the left crossfader, each group will have the exact same number of controls to map to the PIC. Details for the mappings from one of the group’s controls to the pins on a 18F4550 PIC are found in Table 1.

Figure 5 shows the schematic for one of the groups of the Super Retro Faderbox. The schematic is a simple extension of the “CREATE Hello World” circuit (http://www.create.ucsb.edu/~dano/CUI/) developed by Dan Overholt. The main additions are the inclusion of the slider and pushbutton schematics. The sliders are wired like most potentiometers, in a voltage divider scheme. The pushbuttons control not only the digital input to the microcontroller, but turn on an LED as well. As stated above, the LED is used to tell the user the current state of the button (on or off).

Port Function Application RA0 Analog input 0 Fader 1 RA1 Analog input 1 Fader 2 RA2 Analog input 2 Fader 3 RA3 Analog input 3 Fader 4 RA4 Digital I/O Pushbutton 9 RA5 Analog input 4 Fader 5 RB0 Analog input12 Mixer 13 (crossfade) RB1 Analog input10 Fader 11 RB2 Analog input 8 Fader 9 RB3 Analog input 9 Fader 10 RB4 Analog input11 Fader 12 RB5 Digital I/O USED FOR PROG RB6 Digital I/O USED FOR PROG RB7 Digital I/O USED FOR PROG RC0 Digital I/O Pushbutton 10

Port Function Application RC1 Digital I/O or PWM NOT USED RC2 Digital I/O or PWM NOT USED RC6 Digital I/O Pushbutton 11 RC7 Digital I/O Pushbutton 12 RD0 Digital I/O Pushbutton 1 RD1 Digital I/O Pushbutton 2 RD2 Digital I/O Pushbutton 3 RD3 Digital I/O Pushbutton 4 RD4 Digital I/O Pushbutton 5 RD5 Digital I/O Pushbutton 6 RD6 Digital I/O Pushbutton 7 RD7 Digital I/O Pushbutton 8 RE0 Analog input5 Fader 6 RE1 Analog input6 Fader 7 RE2 Analog input7 Fader 8

Table 1. Mapping of controls to the ports of the PIC 18F4550.

Figure 5. Schematic for one group of the Super Retro Fader Box.
(click to see full size)