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MAX232 Serial level converter

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When communicating with various micro processors one needs to convert the RS232 levelsdown to lower levels, typically 3.3 or 5.0 Volts.

Here is a cheap and simple way to do that.

Serial RS-232 (V.24) communication works with voltages -15V to +15V for high and low. Onthe other hand, TTL logic operates between 0V and +5V . Modern low power consumption logic

operates in the range of 0V and +3.3V or even lower.

RS-232 TTL Logic-15V … -3V +2V … +5V High+3V … +15V 0V … +0.8V Low

Thus the RS-232 signal levels are far too high TTL electronics, and the negative RS-232 voltagefor high can’t be handled at all by computer logic. To receive serial data from an RS-232interface the voltage has to be reduced. Also the low and high voltage level has to be inverted.

This level converter uses a Max232 and five capacitors. The max232 is quite cheap (less than 5 dollars) or if youre luckyyou can get a free sample from Maxim.

The MAX232 from Maxim was the first IC which in one package contains the necessary drivers and receivers to adapt theRS-232 signal voltage levels to TTL logic. It became popular, because it just needs one voltage (+5V or +3.3V) and generatesthe necessary RS-232 voltage levels.

The requred parts:

» MAX232 Serial level converter : SoDoItYourself.com http://sodoityourself.com/max232-serial-level-converter/

1 of 13 3/30/2011 9:48 PM

1 x female serial port connector1 x max 2324 x 1uF capacitor1 x 10uF capacitorSoldering iron, wires, breadboard etc.

Schematic

This entry was posted on Monday, February 26th, 2007 at 9:25 pm and is filed under Electronics. You can follow any responses to this entry through theRSS 2.0 feed. You can leave a response, or trackback from your own site.

89 comments to “MAX232 Serial level converter”

Comment by » Accessing serial console on the Fon : SoDoItYourself.com:Monday, February 26th 2007 at 9:48 pm

[...] SoDoItYourself Back to SoDoItYourself.com MAX232 Serial level converter » [...]

1.

Comment by Microcontroller Programming » Blog Archive » MAX232 Serial level converter:Tuesday, February 27th 2007 at 6:54 am

[...] Refernce web: http://sodoityourself.com/max232-serial-level-converter/ [...]

2.

Comment by Greg:Thursday, March 15th 2007 at 1:16 am

what to the symbols represent like the one that looks like + l l any refrence site i can go to to see what these symbols inthe schematic mean or can tou take a picture of the actual finished product? Thanks

3.

Comment by Dave:Thursday, March 15th 2007 at 9:59 pm

@Greg

The || symbols are capacitors. The + marks the plus side of the capacitors if they are polarized.

4.

Comment by Chris:5.


2 of 13 3/30/2011 9:48 PM

Tuesday, March 20th 2007 at 9:57 pm

The schematic shown is exactly what needs to be done and other components (resistors, etc.) are not needed? Also,how can I get a regulated +5v supply for the Vcc? Because I am soldering the circuitry to the DB9 Female solder-cupso I can connect it to my computer and want to make sure it doesn’t harm anything.This was very helpful in my current project, thanks!

Comment by John:Wednesday, April 4th 2007 at 6:11 am

The +5v supply can be generated by an outside source, but is usually supplied by the serial device you are connectingto.

6.

Comment by Pasan:Thursday, April 5th 2007 at 6:28 pm

Im making serial 16X2 LCD for my PC. So now I found what i want. Thank you very much.

7.

Comment by A.I.HAMAD:Thursday, April 19th 2007 at 9:40 pm

It is quit simple circuit and I am already built it , OK. Is it possible to inform me about more details regarding theprocedure of programming a new blank pic 16f84 ? Is Mplab software suitable to work with it ? what kind ofconfiguration that i have to select for this programmer? and the last question what about the voltage 14V which shouldbe provided to pin 4 in many other programmers?Thank you very much

8.

Comment by Swapnil:Thursday, April 26th 2007 at 4:27 pm

This was just what i needed to know. Thanks for the support

9.

Comment by waa:Wednesday, May 9th 2007 at 10:10 am

Waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaah

10.

Comment by Hemantkumar:Tuesday, May 15th 2007 at 11:25 am

In absence of power supply, Can input +15 to -15 volt signal is affected on max232 driver.

and can we receive the data from PC without using capacitor with IC max232 for one side communication

I am not found the internal logical diagram of driver/receiver can you provide me

Thanks

11.

Comment by AdLab:Thursday, May 24th 2007 at 1:18 pm

To A.I.HAMAD,

To program a PIC you’ll either need an In-circuit-debugger (ICD) or a Microchip programmer (like the one in thisimage http://www.mp.ttu.ee/risto/rc/electronics/images/pctorc/07.jpg). MPLAB is fine. If you use programmer thenyou’ll need to take the PIC out after each program and insert it back into you circuit (time consuming if you are new tothis stuff). If you use an ICD then you connect to it while still in the circuit through a socket you fix into your circuit. Idon’t know what country you are writing from but in the UK these things can be bought from RS or Farnell.http://www.sparkfun.com/ for more PIC tips.

Ad

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3 of 13 3/30/2011 9:48 PM

Comment by baseer:Sunday, July 22nd 2007 at 9:53 pm

good excellent

13.

Comment by Loffe:Thursday, August 23rd 2007 at 4:29 pm

Can somebody explain what the 10uF capacitor is for. Is it nessesary? Looking at the charts Maxim supply I can’t seeit.

14.

Comment by Electronics-Lab.com Blog » Blog Archive » Alternatives circuits of MAX232:Friday, August 24th 2007 at 9:39 pm

[...] MAX232 Serial level converter is a wide used chip for converting RS232 logic levels to TTL logic levels that can[...]

15.

Comment by Ajay Bhargav:Tuesday, September 4th 2007 at 6:55 pm

you can make it much more simpler.. by removing the 10uF capacitor from that circuit

16.

Comment by 8051, AVR, PIC microcontroller projects, tutorials, books and much more...:Tuesday, September 4th 2007 at 6:57 pm

@Loffe:that 10uF is a bypass capacitor… usually it should be small like 100nF.. 10uF is a big value

17.

Comment by profmason.com » XBEE wireless modules:Monday, October 22nd 2007 at 5:59 am

[...] The XBEE uses 9600 8N1 by default. To use the XBEE with the picaxe it first must be programmed to use aslower speed. Fortunately there is a utility build into the picaxe programming envirnoment that will setup the XBEEfor you. A programming board must be build. This consists of a a MAX3232 (Or since I didn’t have one a MAX232with voltage divider between the outputs.) The RX and TX are wired appropriately. Here is a diagram fromdoityourself.com: [...]

18.

Comment by ibrahim:Wednesday, November 21st 2007 at 6:12 am

how MAX232 is interfaced with C8051F020 microcontroller??

19.

Comment by sushil:Saturday, December 15th 2007 at 5:34 am

What is the need of capacitors in the circuit..what is their work over there …how can we decide on the value of capacitors??

20.

Comment by adityasharma:Wednesday, January 30th 2008 at 4:14 pm

datas required for project.

21.

Comment by Ken:Tuesday, February 5th 2008 at 11:53 pm

What program did you use to make the schematic, it just looks great…

22.

Comment by Trey Meyer:Wednesday, February 13th 2008 at 7:38 pm

23.


4 of 13 3/30/2011 9:48 PM

This circuit works great to talk to my PC, but I have a piece of equipment (video matrix switch) that it won’t workwith. My pc, however, can talk with the switch just fine.

I wound up using the circuit into serial port b, and then I have serial port a connected to my video switch. I then issueda “copy com2 com1″ command from dos so the output of com2 is routed to com1. Works great, but not very sexy.

I switch pins 2,3 etc. but nothing I have tried will allow the circuit to drive the video switch. Could there be somethingabout this equipment that requires more current than the max232 can deliver? Any suggestions?

Comment by Noz:Saturday, February 16th 2008 at 8:49 pm

Hi Trey,

I think it is more likely that the handshaking lines are not being used. Probably only need the additional RTS/CTS lines.

Look at the MAX232CPE datasheet and you will find that this device can support RTS/CTS too. So use them to see.

BTW - we now do a popular kit version but with the handshaking lines RTS/CTS available.

24.

Comment by Trey Meyer:Sunday, February 17th 2008 at 2:47 am

I appreciate your comments. I am talking to the device using only 2,3 and 5 from the PC, so I discounted handshaking.Also, the documentation for the device says only 2,3 and 5 are used with no flow control. It appears to be some sort ofcurrent problem. I saw on a website somewhere that the impedence of some devices can cause an issue. I thoughtabout building one of the circuits I saw with transistors (that borrow 12v from the dormant receive line). Any luck withthis or other suggestions?

25.

Comment by Noz:Tuesday, February 19th 2008 at 11:17 am

Hi Trey,

Other ICs/vendors do slightly different versions e.g. the ADM232 claims +/-9 output swing at RS232.Usually most claim say 7.8v to 8V into 3K load with 5V supply.If its is just a little low on the voltage for the load then you could try that.

Noz,TronisoftUSB / RS232 / IO Modules

26.

Comment by Tony:Thursday, February 28th 2008 at 9:15 am

What is the function of all the capacitors present here

27.

Comment by Glen:Saturday, March 1st 2008 at 4:13 am

MAX232A versions from Maxim, such as MAX232ACPE, and similar parts available from others require only 0.1uFcapacitors for the charge pump and inverter. They may cost a little more, but the cheaper capacitors usually make upfor it.

28.

Comment by MGIT:Wednesday, March 19th 2008 at 7:21 am

Why are capacitors being used in the circuit

29.

Comment by ah fatt:Tuesday, April 1st 2008 at 5:34 pm

30.


5 of 13 3/30/2011 9:48 PM

i have bit prob with this circuit..when im use this circuit and test it with the hyper terminal program..it doesn’t showanything..im connect this circuit with the RFID reader. when the reader is activate there is nothing appeared in hyperterminal..some one please help me with this situation..

Comment by Thomas Thomassen:Saturday, June 14th 2008 at 10:30 am

I came cross a similar schema, but it was lacking the 10µF capacitor. What’s the purpose of the 10µF cap? Whatversion should I choose?

31.

Comment by Purgedsoul:Friday, July 4th 2008 at 10:19 am

The 10uF is for the charge pump of the MAX232 minimum value based on the datasheet is 1uF for MAX232a its100nF. 10uF for longer distance (long cables). my two cents.

32.

Comment by 232:Friday, July 18th 2008 at 3:07 am

how can I have the output of Tx to produce just 3.3V when it is at logic 1 ??

Is it the Vcc of the max232 just supply 3.3v??

33.

Comment by zed:Wednesday, August 13th 2008 at 2:33 pm

i only have 10uF capacitors available. Will it be OK to use 10uF capacitors for all the circuit or will it cause problems?

@232: i think you may have to use the 3232 chip which operates at LVTTL levels of 3.3v-5.0v. But if there is a waythat anyone knows to get 3.3v from this max 232 chip I would like to know too!!!

34.

Comment by Trey Meyer:Monday, September 1st 2008 at 10:35 pm

Hello -

I left a message in Feb concerning ttl to rs232 conversion. You were generous with suggestions, but unfortunately theproblem still exists. While I have worked around it for several months, I now need a hardware solution.

Here is the setup:A microcontroller circuit needs to control a video switch via rs232. I cannot get the microcontroller to interfacedirectly with the switch either with hand made level converters (using max232 or those I purchased premade).

I can, however, make it work if I interface the microcontroller to a PC com1, and then the PC com2 to the switch. Asimple ‘copy com1 com2′ with timeout disabled (19200,8,n,1) allows the microcontroller to control the switchindirectly. There are only three wires used both from the controller to the PC and to the switch - tx,rx,gnd. There is nohandshaking software or hardware enabled on any of the devices. The message I need to transmit is only a singlecharacter, and I only transmit from the controller to the switch (not bidirectionally).

I assume this must be to voltage levels required by the switch?

1) how can I measure the voltages present from max232? I have a scope, so can I just connect in parallel with TX andgnd and monitor the voltage levels?

2) Do you have a suggestion on another cct that will provide a greater voltage swing?

3) other?

Any help would be appreciated!Trey

35.


6 of 13 3/30/2011 9:48 PM

Comment by Trey Meyer:Monday, September 1st 2008 at 11:13 pm

As a follow up to the above, I did hookup my scope in parallel and I am seeing a 7v swing from 0 (or +/- 7V) showingon the scope relative to gnd. This is with a purchased level converter from Solarbotics, Ltd.

36.

Comment by Noz:Saturday, October 25th 2008 at 1:22 pm

Reply to “Comment by 232:” Friday, July 18th 2008 at 3:07 am

how can I have the output of Tx to produce just 3.3V when it is at logic 1 ??Is it the Vcc of the max232 just supply 3.3v??

_____________________________________________

You should really use something like a MX3232 IC based circuit.This is available here (shamless plug):

http://www.tronisoft.com/4205.php

Hope it helps!

Noz,TronisoftUSB / RS232 / IO Modules

37.

Comment by heli:Saturday, October 25th 2008 at 3:57 pm

plz any one tell me from where i can get the detail internal diagram of max232 ic….i also need to know what is therequirment of capacitor….

38.

Comment by mohsin:Tuesday, November 11th 2008 at 7:55 pm

hi,i m working with serial card but my card seems to give me dummy values.is there any thing wrong with my max232.iused 22mic f capacitor.also i want to know abt voltage value of capacitor.urgent.

39.

Comment by L Bolton:Wednesday, November 19th 2008 at 1:49 am

I am about to build the circuit and note the .1 micofarad cap off pin 6 has the + to the ground line- is this correct?

40.

Comment by Manny:Thursday, November 27th 2008 at 4:44 am

Can someone please e-mail me with a detailed pic of this all set up on a breadboardboard so I can replicate. I’ve beentrying for months to get this to work off and on with no luck. I am Trying to debrick my router. I have a small whiteplastic breadboard. 1 DB9 and 6 1uf cylindrical caps and 6 .1uf ceramic caps but don’t have the 10uf cap but have abunch of other sizes. Also have the max3232cpe can’t figure out how to work this. [email protected] I thank youin advance!

41.

Comment by fery:Wednesday, January 7th 2009 at 7:56 am

good

42.

Comment by don:Wednesday, January 7th 2009 at 5:31 pm

43.


7 of 13 3/30/2011 9:48 PM

pls i would lke to make a comment about my max232 i was working on a project recently and i decided to connect adual power supply to the max232 i.e pin 2 and 6 as required in the data sheet but the chip got fried don’t know? canany one help? the voltage on pin 6 was -9v and on Pin 2 was +9 volt

Comment by Nirav Sinha:Friday, February 6th 2009 at 8:17 pm

Great work.. I got what I was hunting for [:)]

44.

Comment by kontrola:Monday, February 23rd 2009 at 1:32 am

That was what I was looking for. But for my aplication I need 3V, so I guess I have to use MAX3232 . Hope it will beon stock in my electronic shop.

Thanks again

45.

Comment by priyanka:Monday, March 9th 2009 at 9:51 am

can i knw y capacitors are used in max 232?

46.

Comment by vinod:Saturday, March 28th 2009 at 2:45 pm

HIIIIIIIIII,Can we use max 232 as a power supply for Opam.

47.

Comment by vinod:Saturday, March 28th 2009 at 2:46 pm

HIIIIIIIIII,Can we use max 232 as a power supply for Opam . if yes . HOw ?

48.

Comment by vikash:Friday, April 24th 2009 at 8:58 am

good

49.

Comment by mohd fareed:Friday, May 1st 2009 at 6:14 am

hi,

I am usessing (max 232 to usb convertor) hardware.but i needed of driver of this hardware. can you helpo me.

thanks.

50.

Comment by Mohd Fareed:Friday, May 1st 2009 at 6:14 am

hi,

I am usessing (max 232 to usb convertor) hardware.but i needed of driver of this hardware. can you help me.

thanks.

51.

Comment by Mohd Fareed:Friday, May 1st 2009 at 6:15 am

hi,

52.


8 of 13 3/30/2011 9:48 PM

I am usessing (max 232 to usb convertor) hardware.but i needed of driver for this hardware. can you help me.

thanks.

Comment by johnny:Tuesday, May 19th 2009 at 11:20 am

1microfarad caps,how much voltage?is 50v okay?

53.

Comment by johnny:Tuesday, May 19th 2009 at 11:23 am

can this be interfaced with a pic16f877a?

54.

Comment by siva:Tuesday, June 30th 2009 at 10:27 am

i am confused regarding the values of capacitor values ..all the five are 1 micro farad in the datasheet.HEre four are 1micro farad..I have seen soem websites where all the five are 10 micro farad..Willchanging this afftec the prerformance?

55.

Comment by Rizwan:Thursday, September 3rd 2009 at 7:20 am

Hi,Can i interface this adoptor with 8051 uC or the AVR is compulsion………

56.

Comment by rangers:Friday, October 16th 2009 at 5:46 pm

what are the functions of the capacitors of MAX 232.Thanks in advance

57.

Comment by Debricking Fonera Using a Serial cable Alone « Khalbali:Sunday, November 22nd 2009 at 7:09 am

[...] http://sodoityourself.com/max232-serial-level-converter/ [...]

58.

Comment by Jim:Tuesday, December 1st 2009 at 7:27 am

I just built this circuit as shown above and am having some problems. The TTL -> 232 conversion is working perfectlybut the 232 -> TTL is not working. Does anyone have any thoughts on what could be wrong or where to look. I’vedone the obvious double checking of solder joints and double checked my wiring. Thanks in advance.

59.

Comment by Jim:Wednesday, December 2nd 2009 at 3:26 am

Ignore the above post; was able to isolate it to a bad chip. Replaced and it works great.

60.

Comment by hiren:Monday, January 11th 2010 at 5:24 am

i need to convert microcontroller o/p to gsm modem via serial cabel rs232

61.

Comment by Sami Levian:Saturday, January 16th 2010 at 2:59 pm

Hi ,

62.


9 of 13 3/30/2011 9:48 PM

I have MAX232N ,Can i use this Schematic for built RS-233 to TTL ? is different between MAX232 and MAX232Nfor built this circuit ?

Thanks

Comment by Wuerzelchens blog » Blog Archive » Asus WL 500 gP debricking mit serieller Schnittstelle -:Sunday, January 24th 2010 at 11:22 am

[...] der ASUS WL 500g Premium hat 3.3V. Das ist auch eines meiner Probleme gewesen. Ich habe mir nach dieserAnleitung einen TTL converter gebastelt aber nicht wirklich eine Anständige ausgabe auf meiner Konsole [...]

63.

Comment by Andy Martin:Monday, February 8th 2010 at 6:20 pm

Thanks, just what I needed !

64.

Comment by Todd:Thursday, February 25th 2010 at 7:04 pm

Got all the parts to build one, then discovered the MAX233 - all caps built in!

65.

Comment by JB:Thursday, March 4th 2010 at 11:03 am

A word of warning. The picture of the capacitors is misleading. The circuit diagram defines electrolytic capacitors - notceramic capacitors as pictured.

66.

Comment by Amila:Sunday, March 14th 2010 at 11:25 am

Hi,I want to know voltages of MAX232 when it properly works

67.

Comment by Ozymandias:Tuesday, March 30th 2010 at 6:37 pm

I’ve done exactly the schematic in the picture with electrolytic capacitors( with 1u instead of the 10u one), and pins 11and 12( TX,RX) connected for loopback. The problem is that i don’t get anything in hyperterminal (COM1, 9600 baud,8N1, flow none) or tera term. Any ideas to what the problem might be? Thanks.

68.

Comment by Ozymandias:Tuesday, March 30th 2010 at 9:33 pm

I’ve discovered my mistake. The pinout of a female null modem connector is different. 13-2 and 14-3 are the correctmatches. Live and learn.

69.

Comment by rizal:Saturday, April 10th 2010 at 9:34 am

Max232 can works with 2.7 to 5.5 voltage supply. I have an experiment!

70.

Comment by doaa mahmoud:Sunday, June 20th 2010 at 2:41 pm

merci beaucoup , really i need it much more u can imagine

thank you very much

71.

Comment by mark:Friday, July 23rd 2010 at 1:13 pm

72.


10 of 13 3/30/2011 9:48 PM

Does anyone know of a max232 pre-assembled kit that uses SMT 232s and available in US? I only need two and don’twant to bother with the PCB/component ordering/packaging issues, but I want it to fit in a D-sub shell.

Comment by priyanka:Monday, July 26th 2010 at 6:35 am

how max 232 can be connected to microcontroller 8051

73.

Comment by Grunt:Sunday, August 1st 2010 at 3:53 pm

Seems there are two errors:- swap Rx/Tx on µC board,- MAX232 cann’t be feed by 3.3V, you need to use a +5V external power supply.

74.

Comment by jason:Wednesday, September 15th 2010 at 5:09 am

In your circuit, you had used pin 11,12,13,14(T1IN,R1OUT,R1IN,T1OUT).If I want to connect MAX232 to convert 2 different signal, is it possible?For example, pin 11,12,13,14 used to convert SIGNAL 1 and PIN 7,8,9,10 used to convert SIGNAL 2. Can it convertboth of the signal at the same without error? Or any idea that can suggest if I wanted to convert 2 different signal thatreceived wireless from different place respectively.

75.

Comment by baxter:Monday, September 20th 2010 at 6:39 am

Thanks

76.

Comment by WiFi Robot » iAndroBot.Net:Thursday, December 9th 2010 at 4:31 am

[...] Here is a good tutorial on creating your own RS232 converter. [...]

77.

Comment by TheWii552:Saturday, December 11th 2010 at 2:24 am

What are the capacitors for? power filtering?

78.

Comment by inti student:Tuesday, December 14th 2010 at 4:49 pm

i want to use the MAX232 to convert signals at rs232 level to TTL level. but th signal is coming from a single line(Txof a gps). please how can i edit this schematic to suit that.Thanks

79.

Comment by GOPINADH:Thursday, December 23rd 2010 at 3:55 pm

hai can any body send the rating of capacitors in max 232.

80.

Comment by nica:Wednesday, December 29th 2010 at 4:41 pm

for gopinadh -the capacitors is not very importants.can use from 1uF to 10uF/6.3v-16v.

81.

Comment by Karthik:Wednesday, January 5th 2011 at 11:05 am

Can somebody help me out on this issue!!! i am working on MAX 232 board. i have connected that board to PC usingRS 232 connector. i need to write code to write and read from that board in C# .Net. I wrote the code but i am not ableto receive any response from the board. settings are COM1,8,none,1. My doubt is does the connectors on the MAX

82.


11 of 13 3/30/2011 9:48 PM

232 board work in the same way as RS 232 or different manner.. somebody kindly help me.

Comment by Alex:Thursday, January 13th 2011 at 8:22 am

Project on PIC16F877A..using same above burner ckt, no pic detection only messages such as PIC sending unknowndata K”Oh…or handle invalid…what does it mean? Please help me

83.

Comment by vishwanath:Sunday, January 23rd 2011 at 6:39 pm

hi,i have rigged the circuit on a general purpose pcb but the result is little wierd1.sometimes,the circuit works2.sometimes it doesnot work3.when the rx and tx are shorted,i sometimes get echo even when they are not connected

help

84.

Comment by tala amit b.:Friday, February 18th 2011 at 8:26 am

plz gie prize of max 232.

85.

Comment by Venkatesh:Saturday, February 26th 2011 at 4:35 am

@priyanka: here capacitors as dc level shifters,they clamp the voltage level. This is much required,bcoz the dc levelmust be clamped in order to send back the rs232 level back to serial port.

86.

Comment by venkatesh:Saturday, February 26th 2011 at 4:53 am

@loffe:here the 10uf capacitor is used to remove unwanted rippleits absolutely not needed!!!!!!!!!-regardsVENKATESH

87.

Comment by venkatesh:Saturday, February 26th 2011 at 5:06 am

@Ozymandias:if u cant see any thing in hyperterminal windowthen the mistake can be 1) you might have the max232 pins 2,3 to max232 inputs in the opposite manner2)check the supply,whether it is +5v to the icnot many special reasons for it not to work-regardsVENKATESH

88.

Comment by Mehdi:Saturday, February 26th 2011 at 11:31 pm

Special thanks

89.

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