generate 40KHz square wave:

hi,
i want to know how can i generate a 40KHz square wave from any kind of microcontroller and by any programming language (assembly/c) it doesn't matter.
i only need to know how it happens??
so plz if anyone read my question i'm asking u to write even a short code that explains about that operation!! even a littel hint maybe it will help me

homework assignment, huh?

Here's a hint:
To get 40khz you need the port to be turned on and off

To give you a further hint, check my tutorials!.

Hint: look for information on crystal/oscillator timings, clock speeds, and timers. And division.


Torben

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Btw....Nice site you have there Nigel

Jim

thanx everyone but i just need more

her project is like mine and i could use ur hints too

Hii, lemme give u a hint!
if u use 89c2051(20pin) uc with 12Mhz crystal, n if u put following loop in yr code,it'll give u 40khz square wave (unipolar,ofcourse!!) at pin 7 of port1.


now, the problem is, OFFtime will be 12usec and ONtime will be 13usec!!
well, this was supposed to be a hint only!

hi ,
and thanx for ur replies but i want to ask u about the following code it's in basic language for microcontroller PIC16F84:
so is it correct???!!!!
plz some one answer me

Hi Remas,
Here is my thoughts..

16F84 is a very outdated PIC. Use something like a 16F88 with a hardware PWM port. That way, you can set up the pwm to run the 38khz IR pulse in the background, while the pic handles the logic.

Get some IR logic modules @ approx £0.50 each. The IR modules are usually held low by the IR beam, and go high when its broken. These are good because they are fairly immune to sunlight/fluorescent light etc..

Plan a flow chart of what the circuit must do, and work out how many inputs/outputs you will need.
Read Nigel's Tutorials..Even if you intend to code in Basic, there is a lot of useful info in there..

Break the circuit into smaller parts....
INPUTS
OUTPUTS
MICROCONTROLLER
POWER SUPPLY
Google each section, as individual problems.Read the datasheet of the parts you choose.
Test each section on a breadboard, then when all your sub-circuits are working, then put it all together.

I would personally reccomend Proton Basic to program your PIC.., but others swear by Swordfish or others.

Good luck!
Jim

thank u jim for ur beautiful way of explaning and advicing, and i understood every thing u said but except this:

you can set up the pwm to run the 38khz IR pulse in the background, while the pic handles the logic.

Click to expand...

what do u mean, plz anyone answer me ??maybe it's impotrant thing that he said??!!!

Read the datasheet of the PIC to learn more about PWM (pulse width modulation).

The short of it is: You can have the PIC output the 40khz signal using the PWM module. This way you can have the signal running while your PIC is busy running other code.

Remas,
as Boomslang said, have a look at a datasheet for a 16f690 or similar PIC. Also Google hardware PWM (Pulse Width Modulation). It's basically a seperate circuit, (portc.5 I think) that can be used to output a pulse, independent of the software. So you don't waste processing time on it.
Its a bit hard to explain here, you need to spend a couple of hours reading up on it.
What Basic compiler are you using?

Jim

hi,
jim u sked me about which compiler am i using? my answer is that i didn't decide yet..
coz i just started to learn microcontroller for my project, i didn't take it in my institute so i'm open for all choises,
i know what i want from the MCU to do, but i just don't know how to get it doing?!
u see my project is about finding distance range using ultrasound sensor.
and as u all know that the ultrasound sensor is devided into two parts: tranasmitter and receiver.
the transmitter needs 40KHz square wave to work, and as i wanted the MCU to control the TX and RX ,
so i said to my self maybe the MCU can generate the 40KHz square wave signal
and i want to tell u that i'm really starting to learn all kind of programming language such as basic, c and assembly ,and up till now i read the datasheet of 3 MCU which are AT89c51 , PIC16F84 ,ATmega32 and finally the one that jim told me about which is PIC16F887
and i don't want u to do it for me! no i really don't.
i tried to write a program above and i asked for ur thoughts? i mean is it right or wrong ..
if it's right i'ld like to complete my project by that MCU and programming lanagage !!
but if it's wrong or u don't know it? so plz i am seeeking for ur advice about which MCU and programming language should i use? that gives me what i want
plz i really like straight commands i mean i prefer using c or basic more than assembly coz i don't like counting cycls for creating delay ..
coz that’s my real problem it’s the delay I mean
want to generate 40 KHz and start a timer that stops when the reciver get the transmitter pulses
thank u for ur time

Hi Remas,
Have a read of this, should tell you all you need to know

Jim

**broken link removed**

hi jim thank u for the great file, but there is somthing in that file i couldn't understand look at this code:
i mean they r saying that this code suppose to generate 40 KHz!! how ?
i know i ask alot, but plz can any one answer me..

remas said:

hi jim thank u for the great file, but there is somthing in that file i couldn't understand look at this code:

Code:

PING:
PING_LOOP = 8 ' Number of cycles in ping

The above command sets a limit variable so that 8 cycles of 40kHz will be generated per "blip".

Code:

PING1:
PORTB = %00010000 ' 1st half of cycle
Delayus 10 ' Create a delay of 10uS
PORTB = %00100000 ' 2nd half of cycle
Delayus 9 ' Create a delay of 9uS

The above code sets all port B pins low except for one pin on one leg of the ultrasonic TX transducer, then waits 10 microseconds, then sets that pin low and sets the other leg of the transducer high. Then it waits for another 9 microseconds. By alternating between low and high on the two legs of the transducer and using the delay values given, a tone very close to 40kHz is produced.

Code:

Djnz PING_LOOP,PING1 ' Special mnemonic to form a fast loop
Return

The above line decrements the variable PING_LOOP and checks whether it has become 0. If PING_LOOP is not yet 0, then the program jumps back to the line which has the label 'PING1:'. The assembler command 'DJNZ' means "Decrement Jump if Not Zero"--i.e. decrement the variable given as the second argument, and if the result of the decrement is not zero, then jump to the label given as the second argument.

i mean they r saying that this code suppose to generate 40 KHz!! how ?
i know i ask alot, but plz can any one answer me..

Click to expand...

I hope that made some sense to you. Do you see how it works now?


Torben

Djnz means 'DECREMENT and JUMP if NOT ZERO' Its like a very fast loop.
The timing is coming from the internal hardware timer. the delays are what set the frequency. (Based on a 4Mhz clock)
As the document says, PortB.4 goes high, and portb.5 goes low for 10 uS, then they switch over. This happens 8 times until it has decremented (counted down) to zero.

Have another look , and see if it makes sense now
Jim

Sorry, Torben beat me to it! (Although he explained it a bit better than me)