Max232 Safe to use with 3.3v

max232 3.3v

Hello,

Hope you can help with this post...please bear with me as Im a newbie when it comes to electronics

I am currently using a max232 device to communicate with a hardware device that runs on 5v logic. I connect up to Tx Rx Gnd and Vcc 5V all sourced from the board.

Can the max232 device be connected to a different hardware device where the logic voltage is 3.3V without damaging the hardware device or max232?

Heres my thinking:

* I am usnsure whether the max232 draws 12 volts from my rs232 port... in which case the max232 would always spit out TTL Voltages irrespective of the circuit your working with and would maybe fry the 3.3v board??? (but in which case why draw power from Gnd and VCC at all if you are going to source power from the rs232???)

* Or does the max232 draw its power from Gnd and VCC (which would be 3.3v) in which case the output would either:

a) try hard to maintain itself at TTL levels irrespective of the input voltage and possibly fry the 3.3v chips anyway

b) the device would fail to initialise as the 3.3v input is too low to operate the device

* My final scenario: If i were to connect the Rx and Tx up to the 3.3v board but source Gnd and Vcc from an external 5V supply would this possibly work.. It would certainly initialise the max232 but would the outputs still fry the 3.3v board?


Sorry if this is a reaaly silly question... I have the max232 operating following other peoples guides but have little knowlege of how it works myself as I'm new to electronics hence my newbie style questions

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Many Thanks

3.3v max232

Hi Learntofly,

The MAX232 is designed to operate from a 5 volt supply and the logic
levels will be for a logic family that also runs from a 5 volt supply.
You should use a similar device that operates from a 3,3 volt supply
in order to get the logic levels right. Look here:

**broken link removed**

And select the one that is suitable for your application.

on1aag.

max232 3v3

If you connect one board (3.3Vcc) with another board (5Vcc) then there is another option ..
Forget about MAX232, that's first ..
As far as signals are concerned MAX232 inverts them, so all what you need is to use single stage MOSFET (or BJT) inverter .. see picture below ..
If you connect Tx(3.3V) to RX(5V) connect it's drain (collector) resistor to 5V, but if you connect Tx(5V) to Rx(3.3V) connect the drain(collector) resistor to 3.3V ..

Regards,
IanP

Hi Guys, thanks for valuable discussion. This discussion answered my search for 3.3 V MAX232 communication.

Regards,
Kamesh Kumar S

The device you need is the MAX3223 which is the 3.3V equivalent of the MAX232.

Brian.