Main Body's Arduino

Strumming

While we were brainstorming we thought of ideas to create a feeling of a pick being forced over multiple strings. To accomplish this task we used a linear actuator with an attached potentiometer to create the haptic environment. Specifically we used the motorized fader provided by class. We had the idea of creating a virtual spring that would give way once the "string" was passed. The force curve would look similar to a ramp function. To create this kind of feel we needed to know the position and direction of the velocity from the potentiometer. We used an op amp circuit in order to find the velocity direction. The circuit diagram below shows how we found the position and velocity from the potentiometer on the fader motor.

Once we had the position and velocity for the Arduino we used an H-Bridge to control the motor of the fader. We compared the current position to the position of the virtual spring and as the current position came closer to the virtual spring the force would increase. Once the position past the string the force would let up. We used the velocity to determine which direction the fader is moving so that we can get the string feeling regardless of which direction the user was strumming. The code for this can be seen in the Appendix Post under older posts.

Detecting and Sending a Note


To determine when a note was being played we monitored the position of the motorized fader. When it crossed a particular position (designated as a "string")we proceeded to send a note and send a signal to the other Arduino. We used a MIDI to communicate with the computer using the connection diagram found in this tutorial. With that we sent a signal to the computer. The signal consisted of three bytes of data (channel, note, volume). We used channel 1 for all communications. The note was determined by the particular string being strummed and which fret that string was pressed into. So for string 1 we sent a number between 0 and 15 (we had 15 frets and open), for string 2 we sent a number between 16 and 30, and so on up to 6 strings. For the volume we sent a byte between 70 and 110. The particular value was determined by an accelerometer located in the guitar's body. We used an axis aligned with the neck of the guitar and used gravity to determine the tilt of the guitar. We then sent a larger value for the volume when the neck was tilted up and a smaller value when the neck was tilted down. The code for this can be seen below.

Communication to the Other Arduino


Another task that the main body's Arduino had was to send a signal to the other Arduino signaling that a string had been strummed. This is required to allow the other Arduino control the lights and pager motors at the head of the guitar. To do this we were going to send the signal that corresponds to the volume of the guitar when a string is strummed. We went about this by using an analog write to a pin that the other Arduino would read. But since an analog write on the Arduino board produces a PWM and reads a specific value we were only getting 0 or 5 volts reading. To overcome this we put the signal through a low pass filter to smoother the signal out.

To create a low pass filter we had a signal go through a 5.6 kOhm resistor then at this node we had a 1 microFarad capacitor connected to ground and a wire going to the other Arduino. The code that we used to communicate can be seen in the Appendix Post in older posts