Figure 5 :: Usb Communications; Figure 6 :: Analog Voltage Connections; Figure 7 :: Serial Interface Connections - Lightware SF11/C Product Manual

Laser altimeter

Table of Contents

Settings can be changed by pressing the <SPACE> key to access the menu and then selecting the menu item that needs changing.

Pressing the <SPACE> key again restarts the measuring process. If no settings are entered then the SF11 automatically restarts after

two minutes. More details of the menu items are discussed in the "Menu options" section below.

If you want to use a different serial emulation program then the USB serial protocol should be set to 921600 baud with 1 stop bit and

no parity or handshaking. All communications are in standard ASCII format.

Analog voltage or alarm interface

The analog or alarm interface on the main connector can be configured to produce either a voltage proportional to the measured

altitude or a high / low alarm signal. The configuration can be changed using menu item <i>.

In analog mode, the maximum distance over which the analog signal is linear can be set using menu item <j>. This allows for higher

resolution if the SF11 is only used for low level flight. In alarm mode, the same setting is used as the switch point for the alarm.

The voltage scale can be set to deliver a maximum of 2.048 V or 3.3 V depending upon menu selection <k>. This scale applies to

both the analog and alarm modes of operation.

In alarm mode, menu item <l> is the hysteresis on the alarm switching distance. This is used to prevent unwanted, rapid switching

when the target is moving around the switching distance. The hysteresis value is symmetrical about the switching point being both

added to and subtracted from the switching point value.

Serial interface

The serial interface on the main connector can be used to output the measured altitude in meters as an ASCII encoded number. This

interface uses 3.3 V logic levels (5 V tolerant) and can be connected directly to any similar, compatible interface. Distances are

transmitted whenever the SF11 receives an ASCII 'd' character from the host controller. The baud rate for the serial interface is

selectable through the USB menu system. The maximum delay between receiving a character and returning the altitude is 25 ms.

The serial interface also supports an ASCII based command set that can be used to read or write values to the SF11. To read a value,

the command starts with a '?' character and to write a new value, the command starts with a '#' character. All command characters

are in upper case and commands end with the <CR> and <LF> characters (ASCII '\r' and '\n').

Commands are echoed back to the host along with the result allowing for totally asynchronous communication with Linux based

controllers. For example, the zero datum offset can be retrieved as follows:

command:

?LO<CR><LF>

reply:

?LO 0.00<CR><LF>

Changing a setting is done in a similar way with the new value appended to the command. The new value is confirmed in the reply.

For example, to change the zero datum offset:

command:

#LO,0.32<CR><LF>

reply:

#LO,0.32 0.32<CR><LF>

Note:

The default baud rate is 115200 bps.

SF11 Laser altimeter - Product manual - Revision 10