Microchip’s MPLAB starter kit for dsPIC digital controllers
Welcome to this tutorial on MicroChip’s MPLAB starter kit for dsPIC digital controllers or DSCs. The starter kit is an all in one tool and introduces you to the speech and audio processing capabilities of Microchip’s dsPIC DSCs. This starter kit makes it easy for you to get a jump start on using dsPIC DSCs in your own applications.
Take a look inside the MPLAB’s starter kit for dsPIC DSCs to find important components. Included are:
- a quick and easy single step installation software disk
- the starter kit board
- a USB mini B cable for hardware connection
This cable is the debug interface to MicroChip’s MPLAB IDE and provides power to the starter kit board. To install the starter kit software, insert the CD and follow the instructions. The installer program will install MP LAB IDE, a student version of the C 30 C compiler, demo applications and the starter kit documentation. After the software installation is completed, plug the starter kit board into the USB port of the PC. The entire installation procedure is described in detail in the starter kit of the MP LAB dsPIC DSC’s user’s guide which is available on the CD. You are now ready to experience the included demo or start developing your own speech and audio processing application. Note that the starter kit does not require an external debugger since it already contains the required hardware on the board. A speech, record, and playback demo application is pre programmed on the dsPIC DSC. This demo application uses the ITUT G-DOT 711 algorithm to encode and decode speech data. You can also test other algorithms such as speaks, and G-DOT 726A which are offered by Microchip. You will need a headphone and a microphone for the demo application. These are not included in the starter kit.
Let’s take a closer look at the starter kit hardware. The board has 3 functional sections. The debug and programmer section interfaces with the USB port on the PC and provides debug and programming capability. The dsPIC section hosts the dsPIC DSC. The audio section contains the circuits that are required for record, playback and capture of audio signals. The board comes equipped with a dsPIC 33 FJ 256 GB 506 16 bit digital signal controller with 256 kilobytes of flash memory, 16 kilobytes of RAM and a comprehensive set of peripherals. This device serves as the computational device on the board. A big 18F67J50 8 bit micro controller which serves as a debugger and programmer for the dsPIC device. It also provides the full speed USB interface required to connect the board to the PC. A +3.3 volt regulator that powers the starter kit board via USB. A 4 megabit serial flash memory device to store speech and other data. An audio codec for high fidelity speech and audio applications. This codec is capable of processing up to 32 bit audio data at a sample rate of up to 48 kHz. Analog filters for implementing low cost speech playback using the pulse bit modulation technique. Front end microphone processing circuits consisting of a pre amplifier and an anti aliasing filter. The preamplifier features an adjustable gain for adjusting the microphone sensitivity. The anti aliasing filter provides the required band limiting of the microphone signal before it is processed by the 12 bit ADC on the dsPIC 33 F device. A 100 milliwatt head phone amplifier provides the required amplification of the audio signal for driving a headphone. The volume of the amplifier can be controlled by the dsPIC 33 F device. 3 user defined LEDs and 2 switches which are available for application use. 3 connectors for a USB connection between the board and the PC, a connection to a headphone, and a connection to a microphone or an external audio signal.
The starter kit board features 2 methods for capture and reproduction of audio signals. Both of these methods demonstrate the flexibility of a dsPIC DSC device. The first method uses the dsPIC 33 F DSC 12 bit ADC and the output compare pulse width modulated playback technique to demonstrate a low cost yet effective technique for audio capture and playback. The 12 bit ADC of the dsPIC 33 F DSC provides an effective means for converting analog audio signals to digital signals and applications which are cost sensitive. The output compare PWM playback technique only requires an external fourth order low pass filter to reproduce the audio signal. The order of the filter directly affects the audio quality. Having a higher order filter improves the audio quality. The second or audio codec method uses the external codec for the analog to digital and digital to analog conversion process. The audio codec communicates with the dsPIC 33 F device via its versatile data converter interface or DCI module and the ISQFC module.
The dsPIC 33F device uses the DCI module to communicate audio data with the codec and the ISQFC module to provide control information. The codec is capable of performing a 16, 24 or 32 bit conversion at a maximum sampling rate of 48 KHz. This makes the audio codec ideal for applications that require high quality audio processing. Then either case the board accepts audio input from a microphone or an output of audio equipment such as a CD player. Use jumper J7 to select between the 2 types of input. The input signal is then amplified and anti aliasing filter provides the cut off at 3300 Hrtz for the signal to be fed to the 12 bit ADC. The audio output can be selected between the output of the audio codec or the output of the low pass filter. The low pass filter demodulates the pulse width modulated signal generated by the output compare module. Use Jumper J6 to select between the two. The headphone amplifier amplifies the signal for output to a headphone. An external 4 megabit serial flash memory is available for storing data. This memory can be used in speech, record and playback type of applications. The serial flash memory interfaces to the SPI module on the dsPIC 33F device.
Let’s take a look at the jumpers, connectors and controls on the starter kit board. The board has 3 connectors. Use connector J1 to connect the board to the PC via the USB cable provided in the kit. Use connector J9 labeled Line in slash mike to connect either a microphone or audio equipment such as a CD player. Use connector J8 labeled speaker out to connect to headphones. Potentiometer R 56 labeled mike gain adjusts the microphone preamplifier gain. This potentiometer must be set at the factory default level or turned completely clockwise for a nominal gain setting. The gain can then be increased by turning the potentiometer anticlockwise. Note that increasing the gain too much can cause the input signal to distort and create an audio feedback. The headphone signal is selectable between the output of the output compare, low pass filter or the output of the audio codec. Place jumper J6 at OCPWM position for selecting the output of the output compare low pass filter. Place the jumper in the codec position to use the audio codec. The input signal is selectable between a line level signal and a microphone. With the microphone option the board provides the biasing voltage required by condenser microphones. Set jumper J7 in mike position to select a microphone. Place the jumper in line in position to select a line level input.