Circuitry and Electronics:
The circuitry involved in transferring the MIDI data signals to the necessary solenoids includes 6 steps. The flow chart below shows how the signal comes from the MIDI sequencing program to the Crazy J and is played. The electronics that make each step happen are discussed in detail following the chart.
The MIDI Sequencer is connected to the HC11 via a 5-pin DIN connector. Pins 4 and 5 are used to transfer the data between the two. The circuitry necessary for this connection can be seen in the figure below. Note that the incoming data stream connects to the HC11 via Port D, pin 0.
HC11 and Control Board:
The connection between the HC11 and the Control Board is made through Ports B and C. Port B handles the signals for the plucking and Port C handles the signals concerned with the fingering. (The exact pin layout and connection can be found in the Fingering and Pluck Conversion Table in the explanation of the code.) The Control Board contains 5 SN74259 Addressable Latches. Each of these latches has 3 input pins, which represent a binary number corresponding to the 8 output pins. Each latch also has a Data, Write Enable, and Reset input. Since there are 23 solenoids concerned with the fingering, 3 latches process the data sent from Port C. These latches have the Data pins connected, however the Write Enable pins are connected to 3 separate Port C pins. In this way when the Write Enable pin for a certain latch is high, it knows to accept the incoming data stream. The 3 input pins of the three latches are also connected, respectively (A0 to A0, A1 to A1, and A2 to A2). This is the 3-bit binary code that determines which output pin is set high. In the plucking signal processing the signal from Port B comes into two latches. Both of these latches only use 6 of the output pins, since 12 solenoids are involved in the plucking of the guitar. The outputs of the first latch connect to the 6 "left" solenoids in each plucking pair. The other latch outputs connect to the 6 "right" solenoids in each pair. These latches have the same Write Enable pins, but different Data pins coming from Port B. In this way the toggling of the left and right solenoids occurs; the Data pins are toggled, and the correct latch receives whatever comes into its Data pin (since both Write Enable pins are high). The control board then sends the signal from the output pins of the latches to the power boards. LEDs are connected in parallel with the data signals for debugging purposes during initial tests. This allows the signal sent from the computer to be verified as going to the correct solenoid, without connecting the solenoids and seeing which one is powered.
There are two boards which contain the components and circuitry for the 23 solenoids used in the fingering part of the guitar playing (pushing down on the frets). Another board contains the circuitry for the 12 solenoids that pluck the strings. Each board has +36V and Analog Ground coming from the power supply, and Digital Ground, as well as the Digital Signal lines for each solenoid coming from the Control Board. The circuitry used to power the solenoids that pluck the strings can be seen in the following figure.
The Digital Signal and Ground come into the Opto-Isolator on the left side and the solenoid is in the upper right-hand side of the figure. The potentiometers allow the voltage to the transistor to be fine-tuned, and therefore the current through the solenoid. This allows for control of the strength of effort used in plucking each string. The switch connects the 4.3k resistor in parallel, dropping the voltage coming into the Op-Amp. This switch is physically under the lever that controls the pluck rod. When the solenoid is almost fully latched, i.e. the lever is pulled down on the side with the active solenoid, the switch is depressed and the connection made. In this way the solenoids, being intermittent duty, are run at maximum amperage for as little time as is necessary.
The fingering circuits are similar to the plucking circuits, but slightly more complicated. The figure below shows the additions of a 555 Timer and an Analog Switch which help to limit the time that the fingering solenoids are run at full power. These additions require the use of the second Opto-isolator, in parallel with the first, which receives the same signal coming in from the Control Board. Various resistors and capacitors make the circuit work. A second potentiometer is also added to allow for control of the timing of the 555 Timer.
These power boards have banks of connectors which send the MIDI-originated signal on down the line to the correct solenoids and create beautiful music.
The +5V and +10V busses that connect to each of the integrated circuits used on the power boards are created by 317 Voltage Regulators. The circuitry used with the Voltage Regulators can be seen in the figure to the right. The 317 Voltage Regulators operate according to the equation given for Vout. Thus the resistor values used decide the voltage value generated. In the 5V circuit, R2 and R1 have a ratio of 3. In the 10V circuit, R2 and R1 have a ratio of 7. The necessary voltage sources are built on each power board. The Vin line is connected to the +36V on the power supply.