Penelope: main sensors

The main sensors of Penelope are arranged on the five boards that are mounted around the robot (on the left, front-left, front, front-right and right sides).

Here is a side view of these boards:

Sonar: is made of two 40 kHz ultrasonic transducers; one sends a "ping" and the other receives the echo reflected by an obstacle ahead.
The distance of this obstacle is estimated by the microcontroller, measuring the time interval between sent and received pulses (sound velocity in dry air is roughly 330 m/sec).
IC3 generates the output pulse that is boosted by IC4 and transmitted by the ultrasonic transducer U2.
The echo is received by U1 and amplified by TR1, IC1a and IC1b. IC2a detects the actual reflections and its sensitivity can be adjusted with R12. IC2b is a low pass filter that finally removes the 40 kHz frequency and outputs a clean digital pulse.
A main problem in this device is the direct wave that runs from the emitter directly to the receiver, because it generates a signal that can mask the real echoes. In order to minimize this effect, the following measures have been adopted:
- mount the ultrasonic transmitter and receiver as close as possible, so that the direct wave affects only the very early part of the echoes
- break down the direct wave by adjusting the nylon screw shown in the picture
- reduce IC2a sensitivity during the arrival of the direct wave, through the network R14, D1, R15, R16, C5.

Light sensor: TR1-TR6 are very efficient photo-transistors because they mount a small lens on top of their cases, therefore they are very sensitive to lights placed direcly in front of them and less disturbed by the environmental light.
IC5 is a comparator that squares the output and its sensitivity can be adjusted with R23.

Sound sensor: the small microphone is mounted inside a plastic funnel that increases the directional sensitivity.
IC6 is a selective 4 kHz filter (the frequency generated by the sound sources during the competition).
IC7a is an amplifier and its sensitivity can be adjusted with R32; its gain varies also according to the signal intensity through the network D7, D8, R33, so that the weaker is the signal, the higher is the amplification.
Finally, D9 and C15 act as a low pass filter and pass to the last amplifier IC7b a tension that is proportional to the sound intensity.

Main Sensors - Electronic layout

Parts list:

Sonar

R1,10,11,13 ... 100 kohm R2 ............ 6.8 kohm R3 ............ 3.3 kohm R4 ............. 27 ohm R5 .............. 1 kohm R6-8,18-20 ..... 10 kohm R9 ............ 3.9 kohm R12 ............ 20 kohm - trimmer R14 ........... 150 ohm R15-17 ......... 33 kohm R21 ........... 2.2 kohm C1,4 ........... 10 nF C2,7 ........... 10 uF - electrolytic C3 .............. 1 nF C5 ............. 47 nF C6 ............ 4.7 nF C7 ............ 100 uF - electrolytic C8 ............ 1.2 nF D1 ............ 1N4149 TR1 ........... BC109 IC1 ........... LM358 IC2 ........... LM393 IC3 ........... NE555 IC4 ........... CD4049 U1 ............ ultrasonic transducer, receiver - 40kHz U2 ............ ultrasonic transducer, transmitter - 40kHz SCREW ......... nylon screw, 3x20mm

Light Sensor

R22 ............ 10 Mohm R23 ........... 100 kohm - trimmer R24 ............. 1 Mohm R25 ............ 10 kohm C9 ............ 4.7 nF D2-6 .......... 1N4148 TR2-6 ......... TIL81 - NPN phototransistor IC5 ........... LM311

Sound Sensor

R26 ............ 15 kohm R27,36 ......... 12 kohm R28 ............ 22 kohm R29,30,34,37 ... 10 kohm R31,33 .......... 1 kohm R32 ........... 200 kohm - trimmer R35 ........... 220 kohm C10,11 ........ 3.3 nF C12,14 ........ 100 nF C13 ............ 10 uF - electrolytic C15 ........... 470 nF D7-8 .......... zener diode - 2.7V - 1/4W D9 ............ 1N4148 IC6 ........... LM741 IC7 ........... LM358 MIC ........... electret sub-miniature microphone (inside the funnel) FUNNEL ........ plastic funnel (mounted through the PCB)

Email: riccardo.rocca@hotmail.com

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