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 » MAX232 Serial level converter :

MAX232 Serial level converter
170 Votes | Average: 4.08 out of 5170 Votes | Average: 4.08 out of 5170 Votes | Average: 4.08 out of 5170 Votes | Average: 4.08 out of 5170 Votes | Average: 4.08 out of 5
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Max 232 level converterWhen communicating with various micro processors one needs to convert the RS232 levels down 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. On the 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

many max232


Thus the RS-232 signal levels are far too high TTL electronics, and the negative RS-232 voltage for high can’t be handled at all by computer logic. To receive serial data from an RS-232 interface 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 lucky you 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 the RS-232 signal voltage levels to TTL logic. It became popular, because it just needs one voltage (+5V or +3.3V) and generates the necessary RS-232 voltage levels.

The requred parts:

Parts for max232 level converter

  • 1 x female serial port connector
  • 1 x max 232
  • 4 x 1uF capacitor
  • 1 x 10uF capacitor
  • Soldering iron, wires, breadboard etc.




max 232 circuit

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94 comments to “MAX232 Serial level converter”

  1. Comment by » Accessing serial console on the Fon :

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

  2. Comment by Microcontroller Programming » Blog Archive » MAX232 Serial level converter:

    [...] Refernce web:  [...]

  3. Comment by Greg:

    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 in the schematic mean or can tou take a picture of the actual finished product? Thanks

  4. Comment by Dave:


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

  5. Comment by Chris:

    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-cup so 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!

  6. Comment by John:

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

  7. Comment by Pasan:

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

  8. Comment by A.I.HAMAD:

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

  9. Comment by Swapnil:

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

  10. Comment by waa:


  11. Comment by Hemantkumar:

    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


  12. Comment by AdLab:

    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 this image MPLAB is fine. If you use programmer then you’ll need to take the PIC out after each program and insert it back into you circuit (time consuming if you are new to this stuff). If you use an ICD then you connect to it while still in the circuit through a socket you fix into your circuit. I don’t know what country you are writing from but in the UK these things can be bought from RS or Farnell. for more PIC tips.


  13. Comment by baseer:

    good excellent

  14. Comment by Loffe:

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

  15. Comment by Blog » Blog Archive » Alternatives circuits of MAX232:

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

  16. Comment by Ajay Bhargav:

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

  17. Comment by 8051, AVR, PIC microcontroller projects, tutorials, books and much more...:

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

  18. Comment by » XBEE wireless modules:

    [...] The XBEE uses 9600 8N1 by default.  To use the XBEE with the picaxe it first must be programmed to use a slower speed.  Fortunately there is a utility build into the picaxe programming envirnoment that will setup the XBEE for you.  A programming board must be build.  This consists of a a MAX3232 (Or since I didn’t have one a MAX232 with voltage divider between the outputs.)   The RX and TX are wired appropriately. Here is a diagram from [...]

  19. Comment by ibrahim:

    how MAX232 is interfaced with C8051F020 microcontroller??

  20. Comment by sushil:

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

  21. Comment by adityasharma:

    datas required for project.

  22. Comment by Ken:

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

  23. Comment by Trey Meyer:

    This circuit works great to talk to my PC, but I have a piece of equipment (video matrix switch) that it won’t work with. 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 issued a “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 something about this equipment that requires more current than the max232 can deliver? Any suggestions?

  24. Comment by Noz:

    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.

  25. Comment by Trey Meyer:

    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 of current problem. I saw on a website somewhere that the impedence of some devices can cause an issue. I thought about building one of the circuits I saw with transistors (that borrow 12v from the dormant receive line). Any luck with this or other suggestions?

  26. Comment by Noz:

    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.

    USB / RS232 / IO Modules

  27. Comment by Tony:

    What is the function of all the capacitors present here

  28. Comment by Glen:

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

  29. Comment by MGIT:

    Why are capacitors being used in the circuit

  30. Comment by ah fatt:

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

  31. Comment by Thomas Thomassen:

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

  32. Comment by Purgedsoul:

    The 10uF is for the charge pump of the MAX232 minimum value based on the datasheet is 1uF for MAX232a its 100nF. 10uF for longer distance (long cables). my two cents.

  33. Comment by 232:

    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??

  34. Comment by zed:

    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 way that anyone knows to get 3.3v from this max 232 chip I would like to know too!!!

  35. Comment by Trey Meyer:

    Hello -

    I left a message in Feb concerning ttl to rs232 conversion. You were generous with suggestions, but unfortunately the problem 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 interface directly 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. A simple ‘copy com1 com2′ with timeout disabled (19200,8,n,1) allows the microcontroller to control the switch indirectly. There are only three wires used both from the controller to the PC and to the switch - tx,rx,gnd. There is no handshaking software or hardware enabled on any of the devices. The message I need to transmit is only a single character, 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 and gnd 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!

  36. Comment by Trey Meyer:

    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) showing on the scope relative to gnd. This is with a purchased level converter from Solarbotics, Ltd.

  37. Comment by Noz:

    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):

    Hope it helps!

    USB / RS232 / IO Modules

  38. Comment by heli:

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

  39. Comment by mohsin:

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

  40. Comment by L Bolton:

    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?

  41. Comment by Manny:

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

  42. Comment by fery:


  43. Comment by don:

    pls i would lke to make a comment about my max232 i was working on a project recently and i decided to connect a dual 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? can any one help? the voltage on pin 6 was -9v and on Pin 2 was +9 volt

  44. Comment by Nirav Sinha:

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

  45. Comment by kontrola:

    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 be on stock in my electronic shop.

    Thanks again :)

  46. Comment by priyanka:

    can i knw y capacitors are used in max 232?

  47. Comment by vinod:

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

  48. Comment by vinod:

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

  49. Comment by vikash:


  50. Comment by mohd fareed:


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


  51. Comment by Mohd Fareed:


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


  52. Comment by Mohd Fareed:


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


  53. Comment by johnny:

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

  54. Comment by johnny:

    can this be interfaced with a pic16f877a?

  55. Comment by siva:

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

  56. Comment by Rizwan:

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

  57. Comment by rangers:

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

  58. Comment by Debricking Fonera Using a Serial cable Alone « Khalbali:

    [...] [...]

  59. Comment by Jim:

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

  60. Comment by Jim:

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

  61. Comment by hiren:

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

  62. Comment by Sami Levian:

    Hi ,

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


  63. Comment by Wuerzelchens blog » Blog Archive » Asus WL 500 gP debricking mit serieller Schnittstelle -:

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

  64. Comment by Andy Martin:

    Thanks, just what I needed !

  65. Comment by Todd:

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

  66. Comment by JB:

    A word of warning. The picture of the capacitors is misleading. The circuit diagram defines electrolytic capacitors - not ceramic capacitors as pictured.

  67. Comment by Amila:

    I want to know voltages of MAX232 when it properly works

  68. Comment by Ozymandias:

    I’ve done exactly the schematic in the picture with electrolytic capacitors( with 1u instead of the 10u one), and pins 11 and 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.

  69. Comment by Ozymandias:

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

  70. Comment by rizal:

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

  71. Comment by doaa mahmoud:

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

    thank you very much

  72. Comment by mark:

    Does anyone know of a max232 pre-assembled kit that uses SMT 232s and available in US? I only need two and don’t want to bother with the PCB/component ordering/packaging issues, but I want it to fit in a D-sub shell.

  73. Comment by priyanka:

    how max 232 can be connected to microcontroller 8051

  74. Comment by Grunt:

    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.

  75. Comment by jason:

    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 convert both of the signal at the same without error? Or any idea that can suggest if I wanted to convert 2 different signal that received wireless from different place respectively.

  76. Comment by baxter:


  77. Comment by WiFi Robot » iAndroBot.Net:

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

  78. Comment by TheWii552:

    What are the capacitors for? power filtering?

  79. Comment by inti student:

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

  80. Comment by GOPINADH:

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

  81. Comment by nica:

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

  82. Comment by Karthik:

    Can somebody help me out on this issue!!! i am working on MAX 232 board. i have connected that board to PC using RS 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 able to receive any response from the board. settings are COM1,8,none,1. My doubt is does the connectors on the MAX 232 board work in the same way as RS 232 or different manner.. somebody kindly help me.

  83. Comment by Alex:

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

  84. Comment by vishwanath:

    i have rigged the circuit on a general purpose pcb but the result is little wierd
    1.sometimes,the circuit works
    2.sometimes it doesnot work
    3.when the rx and tx are shorted,i sometimes get echo even when they are not connected


  85. Comment by tala amit b.:

    plz gie prize of max 232.

  86. Comment by Venkatesh:

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

  87. Comment by venkatesh:

    here the 10uf capacitor is used to remove unwanted ripple
    its absolutely not needed!!!!!!!!!

  88. Comment by venkatesh:

    if u cant see any thing in hyperterminal window
    then the mistake can be 1) you might have the max232 pins 2,3 to max232 inputs in the opposite manner
    2)check the supply,whether it is +5v to the ic
    not many special reasons for it not to work

  89. Comment by Mehdi:

    Special thanks :D

  90. Comment by lekh:

    hey i have built this rs232 circuit with max232 ic and connected it with 89c51 but the output is notcomming so can somebody help what is the problem and also can v use 10microfarad capacitor instead of 1 microfarad

  91. Comment by nibash sahu:

    i used a max 232 chip in rfid based attendance resister ,but i dont know about function and use of max 232 .so pls send me a report on max 232

  92. Comment by Ismail Saeed Kamal:

    thanks for your great post about max232 but what i want to ask it that i am working on the fingerprint based attendance system with atmega32 microcont and fingerprint module sm630 or similar one. Now i want to put max232 between finger print module and atmega32 now where would be the pin of max232 that should act as the input of max32 which is the output of finger print module please tell me this in short or send me on my email

  93. Comment by Nuwan:

    According to your schematic I made the circuit but now problem of detecting the hardware by the PC as I’m using Win 7 , is there any driver for this or any driver which is compatible with this circuit?

  94. Comment by vamshi:

    really help fulll topic
    iam working on RFID security system nd
    i cant get the o/p so
    i thnk i may get the o/p by converting rs 232 to TTL logic
    nd dis is also called interfacing circuit ryt…