EE331 – Microprocessor Hardware and Software

Design Project: Light Organ

Submitted to: Dr. K. Wahid

By: Edward Reed
Geoffrey Matisho

EE 331 Design: Light Organ

Design Goal

The goal of this project is to design, build, and program a light organ. A light organ utilizes LED lights to illuminate upon a changing analog input signal. In this case, the input will be from a microphone, and the illumination of a bank of LED lights willchange with the level of varying sound waves.

Methodology


The light organ will respond to an analog input provided by a small microphone. This analog input will be fed to an analog to digital converter that is built into a PIC16F886 microcontroller. The resulting digital value from the A/D converter will determine which LEDs will be turned on. The LED bank will be controlled by the MCU. Since the analog signal from the microphone will be very minute, it must be steppedup through an amplifier. This amplified signal can be better used in programming since it gives a better resolution from the A/D converter. The value of the binary number produced from the conversion of the input signal will correspond to the number of illuminated LEDs.A block diagram of the methodology is displayed below as Figure 1.

Figure 1: Block Diagram of Light Organ

DesignProcess and Technical Specifications

The first block to be setup is the input sound via the microphone.The microphone is powered by a +5V supply on one terminal and grounded on the other. A 0.001uF capacitor on the powered side of the mic separates the AC from DC and passes the signal to the amplifier.The amplifier consists of a TLC252CP operational amplifier configured as an inverting amplifier with a gain of approximately 3000. The signal is then filtered with a 100uF smoothing capacitor between the output and ground. The output of the amplifier is attached to pin 7 of the PIC16F886, port AN4, which is set up as the input for the analog to digital converter. The code is setup to convert the analog signal to digital, and then depending on the value of the result, activate a number of LED’s connected to PORTC.The pins of PORTC are connected to the gate of logic level MOSFETs. Each MOSFET acts as a switch for a row of four LEDs. As each bit of PORTC goes high, it will activate the corresponding 4 LEDs. The circuit diagram is depicted below as Figure 2.

Figure 2: Circuit Diagram for Light Organ

Microprocessor choice: PIC16F886

The light organ design utilizes the PIC16F886 MCU. This readily available, inexpensive MCU has a frequency range of 32 kHz to 8MHz. It has many input/output channels that can be either digital or analog. The MCU has comparators, a 10 bit, 11 channel Analog to Digital converter, and has two 8 bit as well as one 16 bit timer. This MCU has everything required, with extra pins for trouble shooting and design expansion. The high resolution analog to digital converter is the major reason this MCU is used.

Design Challenges

Through the course of the design, some major challenges should be expected to arise. One major problemis getting a proper signal from the input microphone. The amplification circuit used is not able to produce a large enough signal for talking or ambient noise, but only direct sound from a speaker. To correct for this challenge the range of the signal will be lowered since the difference between low and high sound is only in the range of millivolts instead of volts. Another major challenge is selecting a range for the digital result so that the whole spectrum of lights would be used. Initially only the first and second bank of LEDs would illuminate for sound. This was corrected by coding and lowering the interval required for more LEDs to turn on.

Design Shortcomings and Possible Improvement

The range of the incoming analog signal is a short coming even though it has been corrected for with software. This can possibly be properly fixed using better analog circuitry.Multistage amplification with higher gain-bandwidth-product operational amplifiers can provide a higher voltage signal, and possibly correct this problem. This will not beinvestigated,however,since the focus of the design is on the use and integration of the MCU.One improvement that can possibly be made is to increase the range of the light organ. This can be done by adding more banks of LEDs and adding more cases for sound values.

Member Roles

There were many key tasks involved in creating this project including component research, circuit design and construction, programming, debugging, and testing. First, an overall plan and the circuit design were completed together. Then,In order to efficiently complete the project, the smaller tasks were split up as evenly as possible and completed by the individual group members. Component research and programming was completed by Edward Reed. Circuit construction as well as debugging was completed by Geoffrey Matisho. Once the final circuit and code was constructed, testing and verification was performed by both members together.

Conclusion

Although the operation of a light organ is simple in theory, the design process requires comprehensive knowledge of the microprocessor, as well as the analog circuitry. Through use of the PIC16F886 in the design, a greater level of understanding of the microcontroller was achieved. The light organ required the use of the analog to digital converter, output registers, and a wide range of programming instructions. Successful creation of the light organ provided a solid introduction into the use and operation of the microcontroller, which will be useful in future designs.