SRF04 module measure distance

Hello!
If you look for SRF04.c on the net you will find many examples.
That said, the best method would be to do it yourself and understand what you are doing. As far as I remember, it delivers a pulse (receive pulse), the length of which is related to the distance. So basically, here is how to measure.
- Set up a timer with some clock. The higher the frequency the better.
- Trigger your timer start with a rising edge interrupt
- Trigger your timer stop with a falling edge interrupt
That's it, you get the value.
Have fun!
Dora

doraemon said:

Hello!
If you look for SRF04.c on the net you will find many examples.
That said, the best method would be to do it yourself and understand what you are doing. As far as I remember, it delivers a pulse (receive pulse), the length of which is related to the distance. So basically, here is how to measure.
- Set up a timer with some clock. The higher the frequency the better.
- Trigger your timer start with a rising edge interrupt
- Trigger your timer stop with a falling edge interrupt
That's it, you get the value.
Have fun!
Dora

Click to expand...

You are wrong my mean . I mean that I want to control direct from STC11 ( above schematic ) . As SRF04 or other ultrasonic module , It is using a microcontoller that programmed. Thus I want to know how to that microcontroller work. As above schemtic , Why does It use 3 pin P5.1 and P5.2 instead of 1 pin P5.1 to generate to transmit ultrasonic ?

Hello!

As I think you use some kind of automatic translation software, it makes your request very difficult
to understand. Example

You are wrong my mean

Click to expand...

???
Is it "You misunderstood my question"?

Beside this:

Why does It use 3 pin P5.1 and P5.2 instead of 1 pin P5.1

Click to expand...

???
For my understanding, P5.1 and P5.2 are 2 pins. But "3 pin" is missing a s, so it may also mean P5.3 which is used to power the MAX3232.

Maybe you want to know why 2 pins instead of 1? You are sending a signal to the piezo device. One way is to put 1 pin to ground and drive the other pin. This is a single end transmission. The voltage at the piezo actuator will go like 0V, 5V, 0V, etc. The amplitude is therefore 5V. If you use both pins and drive them like from 01 to 10, then you will have -1V, 5V, -5V, etc, twice the amplitude.

Dora.

As I understand it, and of course I don't know what code is inside the STC11, P5.1 and P5.2 will be driven in software so they are always at opposite logic levels '01' or '10'. They connect to the two MAX3232 transmit channels so the 3.3V logic levels are increased in voltage to maybe 7 or 8V (whatever the MAX3232 output voltages happen to be). Driving them out of phase gives a greater drive voltage to the T40.

That is not the best way to drive the T40 for best results but it does increase the voltage and therefore range.

Brian.