how to measure the distance using SRM400(Sonar Ranging Module)?

You still have not given enough detail for anyone to help you. What distance are you trying to measure? What microprocessor setup are you using to process the signal? The data sheet says the unit can measure up to 150cm. I'm not very familiar with ultrasonic measurements, but I'm going to guess the 150cm limit is because of the stepped gain setup that is part of the IC that is used on the module. If you are trying to use the module to measure farther than 150cm, maybe you need to look for a different solution, like the system that is used for ultrasonic tape measures.

Tom

well...

i am measuring for the distance of 25-150cm, using the PW-0268 IC.

operating voltage is 6-10Vdc.with the 400EP14D ultrasonic transducer to detect the distance of the object.

you said..

operating voltage is 6-10Vdc.with the 400EP14D ultrasonic transducer to detect the distance of the object.

OK, now for the next question, what are you using to process the analog output from the module. These modules are designed to have their output go to a microprocessor with the proper software running, to determine the actual distance. The microprocessor initiates the process by sending a trigger to the module, then it looks at the output of the module to see how long it takes for the echo to get back. It then uses software to convert that time to a usable distance measurement. As I said, if you have good pulses coming out of the module, but are getting bad numbers, perhaps your microprocessor side is not working as it should.

Tom

the equipment that i used were the waveform generator, the oscilloscope, and the power supply.

you said....

These modules are designed to have their output go to a microprocessor with the proper software running, to determine the actual distance.

however,in the information given,it doesnt mentioned there is a need of a software.i had checked the waveforms at different testpoints and the outcomes were the same as what the information given on the website.when i probed at pin 10,i found out there were returning ECHOes (as what i expect),

thank you

Just so I can use "round numbers," let's say that the speed of sound in air is 25,000 cm/sec, which means that 25 cm distance is covered in 1/1000 sec. Now, let's say the ultrasonic frequency is 50,000 Hz. Velocity = frequency X wavelength. The wavelength of a 50,000 Hz ultrasonic wave is 25,000/50,000 = 1/2 cm. You can measure the propagation delay time from the time you send the ultrasonic pulse until you receive the return pulse and determine the distance (keep in mind that it takes as long to return from the target as it did to get there, so the time is twice that of the time it takes to travel to the target). Measurements more accurate than a wavelength or so means that you have to look also at phase shift.

we generally consider that the sound speed in air is about 340M/S, so you can calculate the time different of return, then youc an get the distance.

most of universal ultra transducer has 40-44khz resonance frequency. according to instrustion, you can adjust VR1 potentiometer to get the frequency. so that you can get more distance and sentivity.

we can get 10M.

for reference

hello, can you post this schematics in better resolution . thx, joe

dear cnpower,

i had adjusted the VR1 potentiometer,however there was no difference in the waveform. do we really have to use calculation to measure the distance?

if you display in digital. of cause.

see these pic.

i got the same waveforms as the below diagrams.i would like to know how to calculate the distance of the echo?please explain in simple way.thanks

e

<do we really have to use calculation to measure the distance?>

If you are not using a calculation, exactly how are you attempting to measure the distance?! The distance is a function of the time from trigger to the time of the echo, you must use a formula to convert this time to distance, usually, this is done by a microprocessor and software. This could also be done with discrete logic and a display, but that gets complicated, and would be unheard of in these days of $1.00 microcontrollers. If all this information does not make sense, you are going to need some assitance to use this module.

Tom

Dum311,

There is no simple way to explain this, because it seems you don't have a basic understanding of how this module is intended to be used. Please download and read the following datasheet:

<http://focus.ti.com/lit/an/slaa136a/slaa136a.pdf>

This is a Texas Instruments application note that explains how to use one of their microcontrollers for ultrasonic distance measurement. After you read this, hopefully you will have a better understanding of what is required. Good luck.

Tom

thank you for the info.i read it already.i understand the theory operation.

according to the SRM400 module info,it stated

" the pin 1 is a bi-direction pin and is designed as an open collector connection with an internal pull high resistor. when the pin 1 is being pulled low by an external transistor,the RC oscillator generates a tone burst signal at pin 11.after transmit pulse,pin 1 will again go low if a valid echo signal is detected"

oscilloscope setting: 5V/div; 0.5ms/div;200Hz,offset=2.5Vdc;

1. i probed at pin 11,there was tone burst(as shown below)duty cycle=50%

2.i probed at pin1,this is the result ↓ with the same setting but with duty cycle 20%

the problem here,from the SRM400 module which states" after transmit pulse,pin 1 will again go low if a valid echo signal is detected".however,there was no change in the signal. it looks exactly as the input only just inverted.

From your picture(pin 1),I find your module that don't work.

Earlier you said you were getting the same waveforms as shown above, diagram "F" shows the return echo pulse. I'm trying to help here, but you are not being consistent with your questions. I'll ask again; WHAT METHOD ARE YOU USING TO CONVERT THE DIGITAL OUTPUT OF THE MODULE TO A DISTANCE MEASUREMENT?

and

WHAT DISTANCE ARE YOU TRYING TO MEASURE, AND HOW LARGE IS THE TARGET?

Tom

sorry i thought by posting another forum,i will be able to make the question clearly.apologize for the trouble.the method that i am using is just by tuning the VR1 and VR2,then i put a hard object of size 20x20x20(LengthxWidthxThick) in front of the ultrasonic transducer and play within the range of 25-150 cm.

Also, if my math is correct, if your target is greater than 16.5 inches (42cm), it would be off the right edge of your oscilloscope screen. You would need to go to a slower time base like 1ms/div or slower. As the distance to your target increases, so does the time to echo.

The formula I was using is;

(1100x12xT)/2

where 1100 is the assumed speed of sound in feet/sec through air, multiply by 12 to get inches/sec. T is time in seconds. You must divide by two because the time is for a round trip, out to target, then back to sensor, and you want the one-way distance. This formula is directly out of the TI datasheet I pointed you to earlier. Good luck!

Tom

sorry...

after i cross referencing with the user manual of SRM400, it seems that the device is working fine as i got the same readings of waveform as in the user manual. The problem now lies with the VR1 and VR2,which are not functioning as what it said on the manual as they(VR1&VR2) supposed to give different reading of waveform which will then help me to get the measurement i want for it to buzz at a specific distance(25-150cm).

how should i do about it?

thank you

sorry i thought by posting another forum,i will be able to make the question clearly.apologize for the trouble.the method that i am using is just by tuning the VR1 and VR2,then i put a hard object of size 20cmx20cmx1cm(LengthxWidthxThick) in front of the ultrasonic transducer and play within the range of 25-150 cm.

Noted:sorry.there is a mistake in the previous forum.this is the correct one

hi, u said that "after transmit pin1 will again go low if a valid echo signal is detected".. then ,if no echo detect then pin 1 will high?? thanks in advance. sorry for bursting on u..i am new here