How to communicate serial a controller and PC via UART but without MAX232?

[mexx]

CAN WE DO SERIAL COMMUNICATION FROM COMPUTER TO CONTROLLER THRU UART WITHOUT USING MAX232 CHIP.
THIS IS USED FOR CONVERTING HIGH & LOW OF COMP. TO HIH & LOW OF CONTROLLER?

fixed your broken keyboard!!!!
Or do you really want to "yell" here???
/davorin

 

[checkmate]

avr without max232

Yes. MAX232 is a voltage level convertor. You run the risk of damaging your circuit. RS232 signals run at around +-10V, while most uCs run at 5V or less, and don't tolerate negative voltages too well.

 

[eltonjohn]

max232 negative problem

There are several ways to connect through a RS232 if you don't have a proper VOLATGE driver. But this will limit the speed .. Anyways an inverter is always required .. At the other not just the RS232 voltges are converted to the digital volatges (5V or 3.3V) But also logically they are inverted . So if you have a device and want to receive or transmit from a RS232 device you have to INVERT the logical signal .Now here are the good news .There is an app note from ATMEL avr on how to build a serial programmer .They use a circuit with a couple of transitors and some resistors and some caps that do the job ..very well .SO now your homework is to track down that appnote at the ATMEL site .

Cheers

 

[SphinX]

max232 as negative supply

Salam,

Simple RS232C Level Converter using Transistors

**broken link removed**

Bye

 

[IanP]

max232 negative supply

Comments to link from previous post:
To further improve these circuits configure the RS-232 into "null terminal" and get additional negative supply of RTS-CTS, DTR-DSR,... through diodes. Also, the capacitor value on the negative supply line can be increased from 1uF to 10+uF.
This will ensure that you have positive and negative voltages on the RS-232 Tx line and it should still be above and below the minimum RS-232 levels of +/-3V.

 

[xmli1976]

Re: DO WITHOUT MAX232

Yes,you can.You can use some transister to convert voltage level,such as this:
**broken link removed**

 

[lalu281276]

Re: DO WITHOUT MAX232

MAX232 is very good IC for RS232 communication. this is very cheap and dosn't requires +/- 12V voltage generation. Other methods may require voltage converters and inverter.
you can use comparator for level conversion.

 

[IanP]

Re: DO WITHOUT MAX232

Look lalu281276...
The XXX232 have been on the market for ages...
You will find a lot of new ICs which will give you the same but with or without external caps..
Significant number of COM ports of new computers will accept 0-5V levels...this is not the RS-232 standard but they will still accept it...
Older PCs, most of PLCs an industrial computers will require that you have +/- voltages..something below and above +/-3V..
So, if the aim of this project is not to use a driver designed for this purpose, the answer is yes, you can do it with transistors, diodes, resistors,... but I would not use MAX232 any more...

 

[cesare]

Re: DO WITHOUT MAX232

You can simply use transistors !!!

Usually you do not need a negative voltage as 0V is interpreted as a negative voltage by most RS232 receivers.

Penalty is speed !!

 

[IanP]

Re: DO WITHOUT MAX232

Cesare wrote:

Usually you do not need a negative voltage as 0V is interpreted as a negative voltage by most RS232 receivers.

That maybe true with some new domestic PC, Laptops etc.. but it is not true with older computers, industrial and PLCs. If you build a divice that suppose to performe certain task do it in such a way that it covers all cases..
Always remember about Murphy's laws:

Anything that can go wrong will go wrong.
If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong. Corollary: If there is a worse time for something to go wrong, it will happen then.
If anything simply cannot go wrong, it will anyway.

 

[Kevin Weddle]

Re: DO WITHOUT MAX232

That is an interesting circuit to say the least. The problem is that it is only half duplex. What you really need is a charge pump. This will take care of the voltage levels.

 

[H_u_n_t_e_r]

DO WITHOUT MAX232

yes you can use max233(capasitorless version )
regards.

 

[vinodstanur]

Re: DO WITHOUT MAX232

If u dont have MAX232 and need only to receive data from RS232 then u can use the below circuit.

 

[alexan_e]

Re: DO WITHOUT MAX232

You are answering to a thread opened 7 years ago,
they should be able to find a solution by now...

Alex