SRF235 - Pencil Beam Ultrasonic Range Finder
Devantech
The SRF235 is a small sonar with an industrial air coupled transducer, giving a very narrow 15° beam width and fast cycling - up to 100Hz update rate.
Technical data
| SRF235 | |
|---|---|
| Range | 10 cm - 1.2m |
| Supply voltage | 5V DC |
| Current (typical) | 25 mA |
| Beam Width | Narrow Beam - Just 15° |
| Dimensions | 34mm x 20mm x 19mm |
| Units | µs/mm/inch |
| Frequency | 235 kHz |
| Interface | I2C |
Richtcharakteristik
The SRF235 is a narrow beam ultrasonic ranger, with a beam width of just 15°. An industrial high frequency air coupled transducer operating at 235KHz is used for both Transmit and Receive. The beam patterns below show compare the 15° SRF235 with the 55° typical pattern of the SRF05.
 |
 |
| SRF235 | SRF05 |
Beschreibung
235KHz ultrasound does not transmit as easily through air as 40KHz does, so the range of the SRF235 is limited to around 1 meter for normal objects out to a maximum of 1.2 meters for a large surface. The use of a single transducer for both transmit and receive means there is a blanking zone out to 10cm, so the effective range is 10cm to 1.2m. The 235KHz narrow 15° beam behaves more like light on a mirror than 40KHz sensors, so looking at a hard flat surface at an angle of more than 8° or 9° will not yield an echo from that surface. It may be that the reflected beam hits an object and bounces back. In this case the echo from the object will detected and the sonar will indicate the total range of sonar to flat surface + flat surface to object. The flat surface its self will be invisible to the sonar. Under the same circumstances, a 40KHz sensor such as the SRF04 would detect the flat surface - not the reflected object.
 |
 |
 |
| At an angle of just 9 degrees, the beam does not reflect back to the sonar | Here there is an object in the path of the reflected beam. The beam will bounce off the object and - | back via the flat surface to the sonar, which will think there is an object off in the distance in front of it. |
Soft furnishings do not reflect well at 235KHz and might not be detected. Please be aware of these characteristics before considering the purchase of an SRF235.
The SRF235 detects hard round objects well, such as table and chair legs etc. This makes the SRF235 ideal for detailed local mapping around the robot, but not for longer range sensing. Using the SRF235 along side a 40KHz sonar, makes an excellent sensor combination.
Connections
The connections to the SRF235 are identical to the SRF08and SRF10 rangers. The "No Connection" pin should be left unconnected. It is actually the CPU MCLR line and is used once only in our workshop to program the PIC18F4220 on-board after assembly, and has an internal pull-up resistor. The SCL and SDA lines should each have a pull-up resistor to +5v somewhere on the I2C bus. You only need one pair of resistors, not a pair for every module. They are normally located with the bus master rather than the slaves. The SRF235 is always a slave - never a bus master. If you need them, I recommend 1.8k resistors. Some modules such as the OOPic already have pull-up resistors and you do not need to add any more.
Registers
The SRF235 appears as a set of 4 registers.
| Location | Read | Write |
|---|---|---|
| 0 | Software revision | Command Register |
| 1 | Unused (reads 0x80) | N/A |
| 2 | Range High Byte | N/A |
| 3 | Range Low Byte | N/A |
Only location 0 can be written to. Location 0 is the command register and is used to start a ranging session. It cannot be read. Reading from location 0 returns the SRF235 software revision. The ranging lasts for 10mS, and the SRF235 will not respond to commands on the I2C bus whilst it is ranging. Locations, 2 and 3, are the 16bit unsigned result from the latest ranging - high byte first. The meaning of this value depends on the command used, and is either the range in inches, or the range in cm or the flight time in uS. A value of 0 indicates that no objects were detected. A new ranging may be initiated as soon as you have the read the range from the last one - no delays are needed.
Manufacturer's data
Technical Specification - link to the manufacturer
FAQ - link to the manufacturer
Accessories
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Product information for: SRF235 - Pencil Beam Ultrasonic Range Finder
Publishing date (date of last technical specification): 2010-11-10
Weight: 7 g
Shipping weight: 100 g
Manufacturer: Devantech
Brand: ROBOT ELECTRONICS
Article number: DEV-SRF235
Manufacturer's part number: SRF235
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updated: 17.11.2023
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ROBOT ELECTRONICS is a brand by English manufacturer Devantech Ltd., based in Norfolk. Product range comprises sensors, in particular ultrasonic or compass, servocontrollers as well as small robot drive systems or relay modules with various interfaces. Sensors are produced in England and are of consistently high quality.
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