You only need to supply a short 10uS pulse to the trigger input to start the ranging. The SRF04 will send out an 8 cycle burst of ultrasound at 40khz and raise its echo line high. It then listens for an echo, and as soon as it detects one it lowers the echo line again. The echo line is therefore a pulse whose width is proportional to the distance to the object. If nothing is detected then the SRF04 will lower its echo line anyway after about 36mS. Here is the schematic, You can download a better quality pdf k version srf1.
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This sensor is a very popular sensor used in many applications where measuring distance or sensing objects are required. The module has two eyes like projects in the front which forms the Ultrasonic transmitter and Receiver. The circuitry inbuilt on the module will calculate the time taken for the US wave to come back and turns on the echo pin high for that same particular amount of time, this way we can also know the time taken.
Now simply calculate the distance using a microcontroller or microprocessor. The following guide is universally since it has to be followed irrespective of the type of computational device used. The current consumed by the sensor is less than 15mA and hence can be directly powered by the on board 5V pins If available.
To start the measurement, the trigger pin has to be made high for 10uS and then turned off. This action will trigger an ultrasonic wave at frequency of 40Hz from the transmitter and the receiver will wait for the wave to return. Once the wave is returned after it getting reflected by any object the Echo pin goes high for a particular amount of time which will be equal to the time taken for the wave to return back to the sensor.
Using this information the distance is measured as explained in the above heading. Applications Used to avoid and detect obstacles with robots like biped robot, obstacle avoider robot, path finding robot etc.
Used to measure the distance within a wide range of 2cm to cm Can be used to map the objects surrounding the sensor by rotating it Depth of certain places like wells, pits etc can be measured since the waves can penetrate through water 2D model of the component Component Datasheet.
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PDF SRF04 Datasheet ( Hoja de datos )