why the output of max232 is like this?

Go To Last Post
16 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

hi
i fed 40Khz to max232 and it give me nothing but DC
u can see the circuit and input and output in attachment

Attachment(s): 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm a bit mangler not a sparkie but I thought the capacitors on a MAX232 were supposed to be 1uF? Yours appear to be almost 10 times too small a value. There is a model of 232 that uses smaller caps but it's not a "MAX232". I think it's MAX3232 perhaps?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yes, they should be 1 uF. The MAX3232 uses 100 nF.

Leon Heller G1HSM

Last Edited: Thu. Aug 27, 2015 - 09:54 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Please embed your images, so we can see them - don't attach them, then we can't!

Instructions here: https://www.avrfreaks.net/wiki/em...

 

 

The Tektronix 2465A is a 4-channel scope - so why have 2 separate traces??

 

 

 

I thought the capacitors on a MAX232 were supposed to be 1uF?

 

They are:

 

MAX220, MAX232, MAX232A: Pin Configuration and Typical Operating Circuit

http://www.maximintegrated.com/e...

 

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

awneil wrote:

Please embed your images, so we can see them - don't attach them, then we can't!

Instructions here: https://www.avrfreaks.net/wiki/em...

 

 

The Tektronix 2465A is a 4-channel scope - so why have 2 separate traces??

 

 

 

I thought the capacitors on a MAX232 were supposed to be 1uF?

 

They are:

 

MAX220, MAX232, MAX232A: Pin Configuration and Typical Operating Circuit

http://www.maximintegrated.com/e...

 

thank you a lot

i change it to 1uf but there is not any change.

my 40KHz amplitude is something about 1.4 v . u think its less that what max232 want? 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

my 40KHz amplitude is something about 1.4 v . u think its less that what max232 want? 

You don't have to guess about this stuff- they wrote a datasheet...

 

That clearly shows the chip needs 2V to "see" a high condition. If your signal is just swinging form 0V to 1.4V it will be seen as low all the time.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

RTFM

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

clawson wrote:

my 40KHz amplitude is something about 1.4 v . u think its less that what max232 want? 

You don't have to guess about this stuff- they wrote a datasheet...

 

That clearly shows the chip needs 2V to "see" a high condition. If your signal is just swinging form 0V to 1.4V it will be seen as low all the time.

thanks a lot

my mistake

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

why not first feed it with 5V DC and then 0V DC just as a basic test?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Interesting!

 

I'd not considered driving a piezo with a Max232 chip.

 

Does the Max232 have adequate drive capability to do this well?

 

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

leon_heller wrote:

Yes, they should be 1 uF. The MAX3232 uses 100 nF.

 

Just when you think a '232 number always means  1uF, along comes  SP232ECP, which uses 100nF (min)

 

The SP232ECP was the cheapest simple '232' part we found, that can use 100nF caps.

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

If you disconnect the buzzer and feed a 5 volt square wave to the MAX232's input pin, do you get a +/-9 volt square wave on the output pin that is associated with the input pin?

 

Are TrigP and TrigN complementary? (one is high if the other is low).

 

Can your U9 buzzer handle a 18V square wave without a resistor? 

Why are you putting a 40KHz signal into a buzzer?  There is no creature on earth (to my knowledge) that can hear frequencies that high. 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Cats can hear up to about 64 kHz.

Leon Heller G1HSM

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ross McKenzie ValuSoft Melbourne Australia

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

or perhaps OP want ultrasound

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

There's a popular circuit on the interwebs that uses a max232 to drive an ultrasonic transducer.