TX Ultrasound Sensor
Verfasst: 15 Nov 2013, 14:01
Since we have access to the I2C interface now, other interfaces are becoming less interesting,
nevertheless I have taken a look at the TX ultrasound sensor.
It appears that the digital Ultrasound interface is an interrogating system.
When no sensor is connected and the input is in ultrasonic mode, the input is 0V.
When the sensor is connected it rises to about 5V.
At regular intervals the input rises to 10V and subsequently shows a pulse to 0V of approx. 77us.
It is believed that this is the trigger for the sensor to give a reply during the rest of the 10V
period, which may indicate that the sensor is open collector.
It is further believed that the 77us pulse is in fact an asynchronous transmission of 8 bits, no
parity and 1 stop bit containing 00H as data, at 115200 baud.
When the sensor replies, which it not always does, it replies after approx. 100us with two bytes, the first byte always has
its MSB set while the second byte always has its MSB clear. The 7 LSB of the second byte (as LSBs)
together with the 3 LSB of the first byte (as MSBs) form the 10 bit word which is seen as input
value in the TX controller. The purpose of the other 4 bits in the first byte is still unknown.
I do not have a circuit yet to test it out but I already want to share this information.
nevertheless I have taken a look at the TX ultrasound sensor.
It appears that the digital Ultrasound interface is an interrogating system.
When no sensor is connected and the input is in ultrasonic mode, the input is 0V.
When the sensor is connected it rises to about 5V.
At regular intervals the input rises to 10V and subsequently shows a pulse to 0V of approx. 77us.
It is believed that this is the trigger for the sensor to give a reply during the rest of the 10V
period, which may indicate that the sensor is open collector.
It is further believed that the 77us pulse is in fact an asynchronous transmission of 8 bits, no
parity and 1 stop bit containing 00H as data, at 115200 baud.
When the sensor replies, which it not always does, it replies after approx. 100us with two bytes, the first byte always has
its MSB set while the second byte always has its MSB clear. The 7 LSB of the second byte (as LSBs)
together with the 3 LSB of the first byte (as MSBs) form the 10 bit word which is seen as input
value in the TX controller. The purpose of the other 4 bits in the first byte is still unknown.
I do not have a circuit yet to test it out but I already want to share this information.
