SRF04 查看數據表（PDF） - Unspecified

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SRF04

Ultra-Sonic Ranger

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SRF04 Technical Documentation

10/22/12 5:35 AM

10k resistor R6 to restore sensitivity for more distant echo’s.

A convenient negative voltage for the op-amp and comparator is generated by the MAX232. Unfortunately,

this also generates quite a bit of high frequency noise. I therefore shut it down whilst listening for the echo.

The 10uF capacitor C9 holds the negative rail just long enough to do this.

In operation, the processor waits for an active low trigger pulse to come in. It then generates just eight cycles

of 40khz. The echo line is then raised to signal the host processor to start timing. The raising of the echo line

also shuts of the MAX232. After a while – no more than 10-12mS normally, the returning echo will be

detected and the PIC will lower the echo line. The width of this pulse represents the flight time of the sonic

burst. If no echo is detected then it will automatically time out after about 30mS (Its two times the WDT

period of the PIC). Because the MAX232 is shut down during echo detection, you must wait at least 10mS

between measurement cycles for the +/- 10v to recharge.

Performance of this design is, I think, quite good. It will reliably measure down to 3cm and will continue

detecting down to 1cm or less but after 2-3cm the pulse width doesn’t get any smaller.

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. If the width of the pulse is measured in uS, then

dividing by 58 will give you the distance in cm, or dividing by 148 will give the distance in inches.

uS/58=cm or uS/148=inches.

Changing beam pattern and beam width

You can't! This is a question which crops up regularly, however there is no easy way to reduce or change the

beam width that I'm aware of. The beam pattern of the SRF04 is conical with the width of the beam being a

function of the surface area of the transducers and is fixed. The beam pattern of the transducers used on the

SRF04, taken from the manufacturers data sheet, is shown below.

http://www.robot-electronics.co.uk/htm/srf04tech.htm

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