ME210, Stanford University, Department of Mechanical Engineering, February 28, 2017

IR Receiver Filter Characterizations Ron Guglielmone

INTRODUCTION

In the following sections, three different filters were characterized as part of an IR receiver sub-system. First, a high-pass filter with theoretical cut-off of 900 Hz was tested. Then, a pair of band-pass filters is characterized. These filters are designed to eliminate noise from our sensor system signal chain. Example noise sources would be 60 Hz hum from room lights. DESIGNS

The specific design for a high-pass filter at 900 Hz is displayed below in Figure 1.

Figure 1: high-pass filter design.

A general design for band-pass filters is presented in Figure 2.

Figure 2: band-pass design.

FREQUENCY RESPONSE MEASUREMENTS

High-pass Filter, response to 300 mV PP input sinusoid at various frequencies.

Response at 400 Hz: 42 mV PP

Response at 600 Hz: 124 mV PP

Response at 1 kHz: 488 mV PP

Response at 2 kHz: 556 mV PP

Band-pass Filter (1 kHz), response to 300 mV PP input sinusoid at various frequencies. Note that the band-pass filters incorporate a factor of 10 signal gain at resonance.

Response at 500 Hz: 344 mV PP

Response at 1 kHz: 3.25 V PP

Response at 2 kHz: 438 mV PP

Band-pass Filter (5 kHz), response to 300 mV PP input sinusoid at various frequencies. Again, a factor of 10 gain is seen at resonance.

Response at 3 kHz: 328 mV PP

Response at 5 kHz: 2.5 V PP

Response at 7 kHz: 624 mV PP

OTHER RESULTS

In a separate set of experiments, our sensor signal, measured at a distance of 8 feet from the IR emitter, has been observed at a 50 mV PP maximum. Therefore, an amplifier with gain between 6 to 10 will be employed before the filter section. A comparator will follow these filters, and finally an Arduino will perform frequency detection.