USsubsystem.txt UltraSound sub-system ===================== Overview -------- The UltraSound sub-system uses a Polaroid Ultrasonic system to measure distances from 0.15m up to 2.6m with a resolution of 10mm. The sub- system returns distance-measured information as a 1-byte variable over an RS232 Link @ 9600 Baud. Sweep Servo Connection ---------------------- supplies servo sweep signals, typically moving the servo through a 90 deg. arc. - Signal, +5vDC and Ground connections. Transducer Connections ---------------------- Contact points for the Polaroid Transducer- note that the transducer is polarised and must be connected with the +ve terminal to the +ve pin. Command Mode ------------ The Ultrasound sub-system waits for a 2-byte command string - "T",. Servo position may vary between 0 and 255 corresponding to a servo movement of 180 deg. Note that most servos are only rated for a 90 o sweep. If you intend to drive the servo more than this angle, check it isn’t hitting its internal stops otherwise it may be damaged. Once the command string has been received, the module drives the servo to the required position, takes a distance measurement and returns the result as a one byte number between 15 and 255 representing distances between 0.15m and 2.67m. The module continues to hold the servo in the last specified position until a new command is received. Assembling the Transducer Head ------------------------------ Push contacts onto Transducer (note polarity) and carefully push the transducer into housing. Secure from the inside using hot-melt glue in 2 or 3 places. Remove servo horn fixing screw and then secure the transducer housing to the servo horn with hot-melt glue. Notes ----- After sending its transmission pulses, the transducer is switched off for a period of time corresponding to a distance to target of 150mm. This is to allow the transducer to cease ringing after the pulses have been sent. Best results are obtained with reflections from hard objects perpendicular to the transducer. Soft objects (ie clothes) may absorb the sound pulses and oblique objects reflect the sound away from the transducer (just like a mirror does to light) thereby creating a false impression of open space in front of the transducer. Keep fingers away from the transducer during operation. The pulses are at a voltage of 200V and can give a jolt! The beam width of the sound pulses determines the maximum resolution possible - the software cannot improve on this performance.