PmodMAXSONAR™ Reference Manual
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pin is left at floating or logic level high voltage. The calibration will take 49 ms, and after an additional 100 ms of
waiting time, the module will be able to take measurement readings every 49 milliseconds.
The UART protocol is configured with a baud rate of 9600, 8 bits, no parity, and a single stop bit. When the RX pin
is left floating or held at a logic level high voltage, 5 bytes will be sent out over the Transfer Data (TX) pin beginning
with the capital ASCII character 'R', three ASCII digits representing the detected distance, and a carriage return
character (ASCII character 13).
An analog signal representative of the measured distance of the object in front of the PmodMAXSONAR may also
be read. The output itself has nine bits of resolution, so with a power supply at 3.3V each inch is equivalent to ~6.4
mV. Users that are measuring the incoming analog signal with a popular 10-bit ADC will have to divide their
measured value by 2 before calculating the reported distance.
The PmodMAXSONAR also provides distance data through a pulse-width modulation signal. Every 147 uS that the
pin is measured at a logic level high voltage state is equivalent to 1 inch away. If the signal is measured to be high
for 2.205 milliseconds, then the detected object is 15 inches away from the front of the PmodMAXSONAR. The
maximum measured pulse time of 37.5 milliseconds indicates that there is no object within 255 inches of the
Pmod.
Figure 1. PmodMAXSONAR timing diagram from the MaxBotix datasheet.
