50kHz Beacon and Detector Circuits

Background

The Beacon detector that we had built prior to the design of our robot was built with the intention of detecting an infrared signal at a 2kHz frequency. The filters were modified and specially designed such that the detector could accurately detect the 2kHz frequency and block out lower frequencies (Resonant frequency, 60Hz monitors in lab, etc). The filter had to also block out much higher frequencies as well - sunlight is composed of many different wavelengths of light. 

Summary - we need to  locate the light source (signal) we want to see and ignore (filter) any light sources we don't want to see.

Purpose

The plan for the extra beacon is to have a way for the robot to return home. In a nutshell, we can reverse our robot's operation of getting to a castle to going home from the castle (return back to the home castle which we started). Using a second beacon detector - adjusted so that it can detect the 50kHz frequency IR signal.

It is not necessary, but it is the easiest and most effective way for us to get home to our castle. Preliminary testing of our beacon detector for an IR signal of 50kHz were very promising - we achieved a range of 3 meters total each time.

50kHz IR Beacon 

Limitations

Our IR Beacon was approved by the professor under the conditions that 

• IR Beacon must operate within a frequency (f) of the range 40kHz < f <100kHz

Results

We decided to create the beacon ourselves, as most of the parts were already provided to us in the lab. I found some 555 timers left over, so I decided to work on creating the circuit by using the 555 timer in astable mode to produce a dc waveform with a frequency defined by the resistors and capacitors in series. The 'high' times of the signal waveform are defined by:

Thus, the values chosen to produce the required waveform were : 

• C1 = 22 nF
• R1 = 560 Ohms
• R4 = 100 Ohms

I mainly chose these values because I was supplied a 22 nF capacitor in our parts kit, and the resistors were adjusted accordingly. 

• calculated frequency of the DC waveform is 53.76 kHz, the actual waveform turned out to be around 54.21 kHz. 

ABOVE: Output waveform of the 555 timer circuit in \
Astable Operation with the component values shown above.

Circuit Diagram

Results

We tested each of our components (IR LEDs) in the circuit to ensure that the waveform generated was correctly read by the IR Phototransistor circuit below: