Electrical Engineering Department
BS in Electrical Engineering
W. C. Pilkington
I have been playing the drums for thirteen years. I started out on an electric drum set and then progressed to an acoustic set. I have always wondered what it would sound like to combine the two types of sounds and this senior project dissected that interest to its raw form. Delving into the problems and solutions of combining digital and analog audio signals intrigued me and thus, became my senior project. The design process included research into the analog and digital realms, computer simulations, and actual implementation successes and failures.
The signal path begins at the bass drum where a piezoelectric drum triggering transducer converts vibration into a specific voltage level. This voltage level flows into a voltage comparator circuit. When the threshold voltage, pre-determined through various test methods, of the voltage comparator is exceeded, the rail voltage flows into a voltage-controlled, open-collector N-MOSFET circuit. This acts as a switch which closes when the threshold voltage has been exceeded, completing the circuit of the external trigger pins that directly trigger pre-selected MP3 tracks on an MP3 Trigger circuit. This signal flows into a voltage follower circuit which acts as buffer, eliminating distortion. Finally, the signal flows into a summing circuit with an adjustable gain.
Meanwhile, a microphone picks up the bass drum’s acoustical energy (sound waves) and converts this energy into electrical energy (the audio signal). This signal flows into a preamplifier which boosts the low-voltage signal to a reasonable level. This signal flows into a voltage follower which acts as a buffer for the microphone signal. Finally, this signal also flows into a summing circuit with an adjustable gain.
The summing circuit combines the MP3 audio signal with the microphone signal. The output of this signal connects to an output jack and a quarter-inch cable connects this output jack to a PA system which has a power amplifier. This is necessary in order to drive the speakers.