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PDF ( 数据手册 , 数据表 ) SRF08

零件编号 SRF08
描述 UltraSonic Ranger
制造商 ETC
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SRF08 数据手册, 描述, 功能
Devantech SRF08 UltraSonic Ranger
This Devantech high performance ultrasonic range finder is compact and measures an amazingly wide
range from 3cm to 6m. The SRF08 interfaces to your microcontroller via the industry standard IIC
bus. This ranger is perfect for your robot, or any other projects requiring accurate ranging information.
There is even a built-in light sensor on the front of the module. You can also get a nifty Lynxmotion
SRF08 Housing for one ranger or for two rangers.
Specifications
Beam Pattern
Voltage
Current
Frequency
Maximum Range
Minimum Range
Max Analogue
Gain
Connection
Light Sensor
Timing
Echo
Units
Weight
Size
see graph
5v
15mA Typ. 3mA Standby
40KHz
6m
3 cm
Variable to 1025 in 32 steps
Standard IIC Bus
Front facing light sensor
Fully timed echo, freeing host computer of
task
Multiple echo - keeps looking after first echo
Range reported n uS, mm or inches
0.4 oz.
43mm w x 20mm d x 17mm h
Specifications subject to change without notice
Mechatronic Systems
MechBot Sensor Overview, Page 1 of 16







SRF08 pdf, 数据表
238 EE
240 F0
242 F2
244 F4
246 F6
248 F8
250 FA
252 FC
254 FE
1
1
1
1
1
1
1
1
1
7
8
9
10
11
12
13
14
15
Take care not to set more than one sonar to the same address, there will be a bus collision and very
unpredictable results.
Current Consumption
Average current consumption measured on our prototype is around 12mA during ranging, and 3mA
standby. The module will automatically go to standby mode after a ranging, whilst waiting for a new
command on the I2C bus. The actual measured current profile is as follows;
Operation
Current Duration
Ranging command received - Power
on
275mA
3uS
+/- 10v generator Stabilization 25mA 600uS
8 cycles of 40kHz "ping"
Ranging
Standby
40mA
11mA
3mA
200uS
65mS
max
indefinite
The above values are for guidance only, they are not tested on production units.
Code
From http://www.robot-electronics.co.uk/htm/srf08bx24.shtml
Connecting Multiple SRF08 Sonar Modules to the BX-24
Mechatronic Systems
MechBot Sensor Overview, Page 8 of 17







SRF08 equivalent, schematic
about 3m range – it is a “typical” value only and not guaranteed, so the real range could be less
depending on ambient temperature and chip tolerances. A further 10mS is specified in order to
recharge the +/- 10v supplies for the op-amp and comparator. The max232 IC is switched off during
echo timing to reduce noise in the op-amps. With the SRF08 the analog circuit has been changed to a
single 5v supply, so the max232 (actually an ST232) does not need to charge up a 22uF capacitor, only
the 100n’s. Recharge time now drops to just 600uS and is taken care of by the processor automatically
when a new reading is requested. A change of processor from the PIC12C508 to the PIC16F872 means
more timers are available and the SRF08 is not stuck with the 36mS watchdog timer. However one of
the problems with terminating the ranging early is that the in-flight “ping” does not know this. It quite
happily bounces off a far wall and returns. Now if it happens to return just after you have started a new
ranging, the sonar will pick up this earlier “ping” and think there is an object much closer than there
really is. The SRF08 allows the maximum gain to be limited to reduce this possibility.
The number of I/O lines required by multiple sonar’s has been an issue with some users. There is also
a problem which has been identified with the basic stamp, which does not treat all I/O lines equally
when timing. When using 16 sonar’s, 32 I/O lines are required. This can be reduced to 17 by gating the
16 echo pulse outputs together with 16 diodes. A further reduction to 6 I/O lines can be achieved by
using a 4 to 16 line decoder such as the CD4514B. This involves the user building additional circuitry.
The SRF08 uses the I2C interface so all 16 sonar’s can be controlled using just 2 I/O lines. The I2C
bus interface is available on popular controllers such as the OOPic, and of course cheap processors
such as many of the PIC family.
On the SRF04, the users host processor is required to time the returning echo. This has been an issue
when using the Stamp, as it does not treat all I/O lines equally. This is an internal problem with the
Stamp and was discovered by Jim Fry of Lynxmotion. The SRF08 does its own internal timing and
sends you the result.
The 50mA max. current required by the SRF04, whilst already far better than the 150mA (2.5A peak)
of the Polaroid units, has been further reduced to 15mA nominal and around 3mA in standby. The
SRF08 automatically goes into standby when it has completed each ranging, and powers up again
when it receives the next command.
Because of the way the SRF04 works, only a single echo can be received. After this the module
powers up its +/- 10v generators again ready for the next trigger pulse. With the SRF08 multiple
echo’s can be received. A buffer stores the first 16 echo’s received. The idea is to be able so see
through open doorways where a standard sonar would just see the door frame.
Finally, to make the SRF08 even more useful, I included a light sensor. This is readable over the I2C
bus just as the sonar data is.
Mechatronic Systems
MechBot Sensor Overview, Page 16 of 16










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