DESIGNStellaris 2010 Contest Abstract Registration Number TI2822 Handheld Pollen Sensor LM3S9B96 processor Jun 19, 2010

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1 DESIGNStellaris 2010 Contest Abstract Registration Number TI2822 Handheld Pollen Sensor LM3S9B96 processor Jun 19, 2010 Brief Description If you've ever been to a rock show, you probably noticed the black light display, which makes otherwise ordinary looking rocks and minerals give off an eerie greenish glow. The Pollen Sensor built for this project makes use of the same fluorescence property to detect pollen. Fluorescence is where some fraction of the incident light is absorbed, then re-emitted, usually at a longer wavelength, as spontaneous emission. All biological organisms exhibit this phenomenon. Pollen grains contain compounds called flavins, yellow pigments that are strongly fluorescent. I need to say up front that the performance of this sensor is poor because of low signal level. The Complete Document explains this further, and mentions areas for future improvements. The current sensor as built, does detect pollen but only in very high concentrations. The sensor uses an LED to flood a sensing region with light, a large area detector to pick up the fluorescence, and an optical band-pass filter in front of the detector to pass fluorescence wavelength (green) and reject the LED wavelength (violet). The LED beam is modulated to reduce the effect of ambient light. When a particle travels through the beam, an amplitude-modulated pulse envelope is produced. It is amplified then demodulated using a local oscillator that is phase delayed to match the delay in the amplifier chain. A filter following the demodulator removes the carrier frequency. It is further amplified then presented to the A/D converter in the CPU. It also drives an audio amplifier / speaker. Two pulse width modulators in the LM3S9B96 CPU are used. One generates the LED drive and the other generates the phase-delayed local oscillator for demodulation. Once set up and started, the PWMs run independently of the rest of the program. This project uses SafeRTOS to improve the processor s ability to track and report the level of real-time particle pulses. The firmware sets up 3 tasks and 1 queue. When a particle pulse exceeds the threshold of the CPU s analog comparator, and interrupt is generated which wakes up the pulse processing task. This task follows the pulse in real-time, recording the peak and keeping track of the pulse rate. A lower priority task wakes up every 250 msec and updates the bar graph indicator on the LCD display based on the level and rate of the pulses. 1

2 Photo 1 The particle-sensing region is in the upper part of the case. Pollen pulses can be heard from the speaker, with the volume control visible at left. The LM3S9B96 CPU accumulates pollen pulses, and the level is displayed as a bar graph on the second line of the LCD. 2

3 TI EK-LM3S9B92-B Eval Kit with LM3S9B96 CPU Main Breadboard Speaker 5V PA1 PA0 5V POWER RS232 TX RS232 RX J2-1 J2-2 J2-3 J2-4 J9-1 J9-2 SPKR 1 SPKR 2 PE7 PB5 PD2 PA6 PA5 PA3 PA2 SIGNAL LOCAL OSC. LED DRIVE MOSI SELECT SCLK AUX PWR J3-1 J3-2 J3-3 J3-4 J5-1 J5-2 J5-3 J5-4 J8 J6-1 J6-2 J6-3 J6-4 J9-3 J9-4 J9-5 J9-6 J9-7,8 J9-9,10 J4 5V POWER MOSI SELECT SCLK 6V BAT DB9 RS232 DEBUG 4x20 LCD Display AA Cells 5V POWER UNUSED LED DRIVE J1-1 J1-2 J1-3 J1-4 Violet LED LED Driver Breadboard Block Diagram 1 The Pollen Sensor uses the PWMs in the TI LM3S9B96 Cortex-M3 CPU to generate the LED drive and the local oscillator used for demodulation. The A/D converter in the CPU detects the particle pulses and measures their peak level and rate. Pollen levels are displayed on a 4x20 LED display. 3

4 Schematic Page 1 - Demodulator 4

5 Page 2 - Filter 5

6 Page 3 LED Board 6

7 Page 4 Photo-amp 7

8 Page 5 - Power 8

9 Page 6 RS232 & I/O 9

10 Page 7 Top Cover 10

11 Code sample: PULSE Task // // DESIGNStellaris 2010 Contest // Registration Number TI2822 // Handheld Pollen Sensor // LM3S9B96 processor // Jun 18, 2010 // // This module contains the PULSE task. It uses the A/D converter to // determine the peak height of the particle pulse. The A/D // sequence is started when a particle signal goes above a // threshold and causes an interrupt from the Analog Comparator. // #include "inc/hw_memmap.h" #include "inc/hw_types.h" #include "driverlib/gpio.h" #include "driverlib/sysctl.h" #include "driverlib/rom.h" #include "driverlib/adc.h" #include "utils/uartstdio.h" #include "utils/ustdlib.h" #include "SafeRTOS/SafeRTOS_API.h" #include "priorities.h" #include "utilities.h" #include "pulse_task.h" // Global variables extern xqueuehandle global_queuehandle; extern unsigned char global_armed_flg; extern int global_pollen_level; // // The stack for the PULSE task // static unsigned long pulse_task_stack[128]; // // This is the pulse handler task. When a particle enters the LED beam // the signal rises above the threshold of the Analog Comparator. The // comparator in turn generates an interrupt, and the interrupt handler // writes an item into a queue. This task rests in a blocked state, and // this event wakes it up. // // When this task wakes up it repetitively reads the A/D converter to // capture the peak height of the particle pulse. // // The A/D converter is 3.00 volts = full scale = 10 bits so it is about // 2.93 mv per bit // static void pulse_task(void *pvparameters) { 11

12 int i, rr; static portchar queue_rx_buf[10]; volatile int delay, highest; unsigned long adc_buf[1]; unsigned long last_adc_val; while(1) { // This blocks, waiting for an item to appear on its queue. // portmax_delay = 0xFFFFFFFF ticks = 86 seconds at 50MHz rr = xqueuereceive(global_queuehandle, queue_rx_buf, portmax_delay); if (rr == pdpass) { // Output a short pulse on port pin J2 for debug debug_pulse(2); highest = 0; last_adc_val = 9999; // Do a sequence of up to 10K conversions and capture peak height for (i=0; i < 10000; i++) { // Trigger the ADC conversion ADCProcessorTrigger(ADC0_BASE, 3); // Wait for conversion to be completed while (!ADCIntStatus(ADC0_BASE, 3, false)) {;} // Read the ADC Value ADCSequenceDataGet(ADC0_BASE, 3, adc_buf); // Keep track of highest value for this pulse if (highest < (int)adc_buf[0]) highest = (int)adc_buf[0]; // When signal goes below the comparator threshold of mv // and down to 100mV to provide some hysteresis, then declare // that the particle has passed and exit the loop. It must be // below 100mV twice to provide some noise immunity if ((adc_buf[0] < 34) && (last_adc_val < 34)) break; last_adc_val = adc_buf[0]; } // Integrate the peak value just recorded into a variable that // provides a rough indication of pollen level. The value in the // variable will be proportional to particle rate x particle pulse // height. The variable is cleared every 250msec in display_task.c // after it gets displayed global_pollen_level += highest; // Enter a blocked state for a few msec before re-arming comparator xtaskdelay(5); } } } // Re-arm the signal comparator global_armed_flg = true; 12