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SRF04 - Ultra-Sonic Ranger

Technical Specification

This project started after I looked at the Polaroid Ultrasonic Ranging module. It has a

number of disadvantages for use in small robots etc.

1. The maximum range of 10.7 metre is far more than is normally required, and as a

result

2. The current consumption, at 2.5 Amps during the sonic burst is truly horrendous.

3. The 150mA quiescent current is also far too high.

4. The minimum range of 26cm is useless. 1-2cm is more like it.

5. The module is quite large to fit into small systems, and

6. It’s EXPENSIVE.

The SRF04 was designed to be just as easy to use as the Polaroid sonar, requiring a short

trigger pulse and providing an echo pulse. Your controller only has to time the length of

this pulse to find the range. The connections to the SRF04 are shown below:

Summary of content (6 pages)

PAGE 1
SRF04 - Ultra-Sonic Ranger Technical Specification This project started after I looked at the Polaroid Ultrasonic Ranging module. It has a number of disadvantages for use in small robots etc. 1. The maximum range of 10.7 metre is far more than is normally required, and as a result 2. The current consumption, at 2.5 Amps during the sonic burst is truly horrendous. 3. The 150mA quiescent current is also far too high. 4. The minimum range of 26cm is useless. 1-2cm is more like it. 5.
PAGE 2
The SRF04 Timing diagram is shown below. 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. By timing the pulse it is possible to calculate the range in inches/centimeters or anything else.
PAGE 3
Here is the schematic, You can download a better quality pdf (161k) version srf1.
PAGE 4
The circuit is designed to be low cost. It uses a PIC12C508 to perform the control functions and standard 40khz piezo transducers. The drive to the transmitting transducer could be simplest driven directly from the PIC. The 5v drive can give a useful range for large objects, but can be problematic detecting smaller objects. The transducer can handle 20v of drive, so I decided to get up close to this level.
PAGE 5
Maximum range is a little over 3m. As and example of the sensitivity of this design, it will detect a 1inch thick plastic broom handle at 2.4m. Average current consumption is reasonable at less than 50mA and typically about 30mA. Download the source code and a ready assembled hex file. Calculating the Distance The SRF04 provides an echo pulse proportional to distance.
PAGE 6
a pull-up resistor. When left unconnected the SRF04 behaves exactly as it always has and is described above. When the "do not connect" pin is connected to ground (0v), the timing is changed slightly to allow the SRF04 to work with the slower controllers such as the Picaxe. The SRF04's "do not connect" pin now acts as a timing control. This pin is pulled high by default and when left unconnected, the timing remains exactly as before.