max232 capacitor value

• Apr 11, 2011

• #1

A

abishekmudalur

Member level 1

Joined

Aug 1, 2008

Messages

36

Helped

2

Reputation

4

Reaction score

2

Trophy points

1,288

Location

coimbatore,india

Activity points

1,519

hi
i m using uart communication wit pic 16f877a...
i hv used 470nF capacitors in the max232 side....is it ok...???
my system gets reset ,when i m using uart....all other progrms working properly....
i checked the same program in some other kit..its working correctly...
wats the prob....??

 

• Apr 11, 2011

• #2

H

hussain_kiet

Full Member level 5

Joined

Mar 15, 2007

Messages

260

Helped

45

Reputation

90

Reaction score

28

Trophy points

1,308

Location

Karachi, Pakistan

Activity points

2,802

you should use 1uF to 10uF capacitors for max232....

 

• Apr 11, 2011

• #3

A

abishekmudalur

Member level 1

Joined

Aug 1, 2008

Messages

36

Helped

2

Reputation

4

Reaction score

2

Trophy points

1,288

Location

coimbatore,india

Activity points

1,519

my processor get resets....do u think its bcz of this capacitor value...

 

• Apr 11, 2011

• #4

ckshivaram

Advanced Member level 6

Joined

Apr 21, 2008

Messages

5,060

Helped

2,150

Reputation

4,306

Reaction score

2,088

Trophy points

1,393

Location

villingen (Germany) / Bangalore

Activity points

30,086

processor reset is not due to capacitor, but you wont get serial output if you use wrong values of cap.... when does the controller reset??? does it happen everytime????? which place of execution of code do you think it gets reset.. which controller are you using????? Does it have an internal watch dog timer??? If so it is getting reset???????????

 

• Apr 11, 2011

• #5

J

Jack// ani

Advanced Member level 3

Joined

Dec 2, 2004

Messages

757

Helped

107

Reputation

222

Reaction score

58

Trophy points

1,308

Activity points

5,006

Value of capacitor depends of version of MAX232 chip used. For MAX232CPE its 0.1uF, for other version it is usually between 1uF to 10uF.

Read the datasheet to know which one you're supposed to use.

 

• Apr 11, 2011

• #6

A

abishekmudalur

Member level 1

Joined

Aug 1, 2008

Messages

36

Helped

2

Reputation

4

Reaction score

2

Trophy points

1,288

Location

coimbatore,india

Activity points

1,519

my controller resets wen serial_out or serial_in occurs.....
i m using 16f877a..
i removed the wdt by "#fuses NOWDT" in the program....
here s my design
one more mistake i made....i wrongly placed 220nF instead of 22pF with crystal osc.....ll it make any difference??

 

• Apr 11, 2011

• #7

H

hussain_kiet

Full Member level 5

Joined

Mar 15, 2007

Messages

260

Helped

45

Reputation

90

Reaction score

28

Trophy points

1,308

Location

Karachi, Pakistan

Activity points

2,802

capacitors will not be the reason for reset...
you should check your config bits for WDT, BOR etc...
also the crystal capacitors should be 22pf not 220nF...

 

• Apr 11, 2011

• #8

A

abishekmudalur

Member level 1

Joined

Aug 1, 2008

Messages

36

Helped

2

Reputation

4

Reaction score

2

Trophy points

1,288

Location

coimbatore,india

Activity points

1,519

but the same prog s executing perfectly in another kit...

 

• Apr 11, 2011

• #9

ckshivaram

Advanced Member level 6

Joined

Apr 21, 2008

Messages

5,060

Helped

2,150

Reputation

4,306

Reaction score

2,088

Trophy points

1,393

Location

villingen (Germany) / Bangalore

Activity points

30,086

your WDT is getting reset at some time or It seems you are encountering Brown out reset....

 

• Apr 11, 2011

• #10

A

abishekmudalur

Member level 1

Joined

Aug 1, 2008

Messages

36

Helped

2

Reputation

4

Reaction score

2

Trophy points

1,288

Location

coimbatore,india

Activity points

1,519

k.....is it needed to change the capacitors from 470nF to 1uF.....
#fuses NOBOR // is it k...

 

• Apr 11, 2011

• #11

H

hussain_kiet

Full Member level 5

Joined

Mar 15, 2007

Messages

260

Helped

45

Reputation

90

Reaction score

28

Trophy points

1,308

Location

Karachi, Pakistan

Activity points

2,802

yes you should change the capacitors value...
NOBOR,NOWDT...

 

• Apr 11, 2011

• #12

A

abishekmudalur

Member level 1

Joined

Aug 1, 2008

Messages

36

Helped

2

Reputation

4

Reaction score

2

Trophy points

1,288

Location

coimbatore,india

Activity points

1,519

thanx....
wat abt crystal capacitors....tat also i need to change???
plz check my diagram.....

 

Last edited: Apr 11, 2011

• Apr 11, 2011

• #13

J

Jack// ani

Advanced Member level 3

Joined

Dec 2, 2004

Messages

757

Helped

107

Reputation

222

Reaction score

58

Trophy points

1,308

Activity points

5,006

Yes, 22pF capacitor is necessary, so better get it replaced.

Also, one more piece of suggestion, place 0.1uF across VDD & GND of the MCU to bypass any possible noise in power supply due to oscillation.

 

• Oct 6, 2013

• #14

A

akhilmolugu

Newbie level 2

Joined

Oct 6, 2013

Messages

2

Helped

0

Reputation

0

Reaction score

0

Trophy points

1

Activity points

11

Jack// ani said:

Yes, 22pF capacitor is necessary, so better get it replaced.

Also, one more piece of suggestion, place 0.1uF across VDD & GND of the MCU to bypass any possible noise in power supply due to oscillation.

Click to expand...

Why only 0.1uF across VDD & GND of the MCU has to be used to bypass any possible noise in power supply due to oscillation? Is there any formulae to calculate the value of capacitor?

 

Last edited: Oct 6, 2013

• Oct 6, 2013

• #15

A

amayilsamy

Advanced Member level 1

Joined

Feb 5, 2013

Messages

420

Helped

38

Reputation

76

Reaction score

34

Trophy points

1,308

Location

Chennai,India

Activity points

3,370

Connect a capacitor between Vcc and ground of max 232. And check proper ground for micro controller and max232.

 

• Oct 7, 2013

• #16

N

nick703

Advanced Member level 1

Joined

Oct 17, 2011

Messages

422

Helped

21

Reputation

44

Reaction score

22

Trophy points

1,298

Location

surat

Activity points

3,987

yes amayilsamy i think u r right so put value on capacitor c3,c4,c5,c6 to 1uF 63v and also put capacitor on max232 vcc means pin no 16 to gnd 100uF 25v .