SF30 Accelerated laser rangefinder
Product manual
The USB, serial, and analog output rates are decoupled from the exposure time setting. For example, you can still run with an
exposure time of ~50 microseconds, but only output at 40 results per second on the USB port. Each of these results will be made up
of a single laser shot, but by limiting the output you don't need to process all 20010 shots on your host controller.
7. Communicating with the serial port
The serial port is used to transmit distance readings to an embedded host processor such as the flight controller in a UAV. The
hardware interface uses 3.3 V logic levels and can be connected directly to any similar, compatible interface. The serial port
protocol should be set to 8 data bits, 1 stop bit and no parity or handshaking (8N1).
Figure 6 :: Serial interface connections
Distances are output as a 2 byte binary number. You can identify which byte you are reading by looking at the most significant bit. If
the MSB is not set then you have received the low byte, if the MSB is set then you have received the high byte. The high byte is
always sent first for an individual reading. The remaining 7 bits in each byte combine to make a 14 bit distance reading in
centimetres.
Composition of a reading:
Example of converting the high and low bytes into a reading:
Reading = ((Byte_H & 0x7F) * 128) + (Byte_L & 0x7F)
The “4: Serial port baud rate” selection toggles through all the standard baud rates from 9600 to 1440000.
The “5: Serial port output rate” setting allows the output rate of the serial port to be set to any value within the limits imposed by
the exposure time. Values will also be limited by the serial port baud rate.
Byte
Description
High byte
MSB (Bit 7) set to 1.
Low byte
MSB (Bit 7) set to 0.
Reading bits
13
12
11
10
9
8
7
6
5
4
3
2
1
0
High byte bits
6
5
4
3
2
1
0
Low byte bits
6
5
4
3
2
1
0
Setting
Values
Description
4: Serial port baud rate
9600 … 1440000 bps
Selects the baud rate for the serial port.
5: Serial port output rate
39 … 20010 readings / sec Sets the rate at which new results are output from the serial port when
it is selected using “1: Output type”.
If the chosen serial baud rate is too low then this value will be limited.
The maximum value is limited to the “2: Exposure time” setting.
SF20 Rangefinder - Product manual - Revision 8
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