RS232 line driver

[Michel]

I am after a driver like the MAX232 that has 5V levels on one side;
+/- 5 on the other side and only requires a +5V supply. The MAX232
however is a 16 pin device and I am looking for something smaller (8
pins). I only need one Rx and one Tx channel.

I am also thinking, maybe I don't need one and just use 0V and 5V
levels rather than -5V and +5V, but not sure if that will work.

Anybody knows more about that?

Michel

[David Forbes]

The problem is that an RS-232 driver must make more than 5V to meet the
spec., so it will have four capacitors to make +/-10V from +5V, needing
more than 8 pins.

There is another spec RS-423 which is 5V, but I don't think there are
any drivers for it that run from +5V only. The standard river is the
MC3488A, which requires +/-5V.

--
David Forbes, Tucson AZ

[Dalibor Farný]

Hello, look on rs485. I played with it a lot, ready to answer Your questions :-) it works for long distances and allows more devices on one line (bus).

Try to describe your devices more..

Dalibor Farný
http://dalibor.farny.cz

sent from Samsung Galaxy Pad

Dne 24.8.2012 7:46 "Michel" <mic...@xiac.com> napsal(a):

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[Nigel Walker]

If you don't mind surface mount, a MAX3313e is quite small and will do the
job.

Nigel.

[Michel]

I just want to establish some serial communication between my computer
and a PIC controller. Like David mentioned, RS232 is actually +/- 10V
rather than +/- 5V. The levels directly from controller are obviously
only 0V and 5V. Now I am thinking, for the Rx input this is not a
problem because it will easily handle the +/- 10V input signals if I
add a series resistor. But the Tx output needs to go from 0V/5V to +/-
10V which is normally done with a MAX232 for example. The MAX has 4
line converters (2 input; 2 output) but I only need 1 for my Tx
signal. So I was after something smaller like an 8 pin or even a 5 pin
driver that works on just a +5V supply.

Michel

On Aug 24, 5:43 pm, Dalibor Farný <dali...@farny.cz> wrote:
> Hello, look on rs485. I played with it a lot, ready to answer Your
> questions :-) it works for long distances and allows more devices on one
> line (bus).
>
> Try to describe your devices more..
>

> Dalibor Farnýhttp://dalibor.farny.cz

[JohnK]

I thought that the 'dead' band for 232 was -3V to +3V.
I have used 5V with printers and modems of the 1970s/80s.

Some 'cheap' RS232 drivers only used -5V and Gnd. eg the Microbee
computer.

Over short distances all sorts of liberties can be taken - it works; just
don't call it 232 !

John K
Australia

[Terry Kennedy]

On Aug 24, 3:52 am, Michel <mic...@xiac.com> wrote:
> I just want to establish some serial communication between my computer
> and a PIC controller. Like David mentioned, RS232 is actually +/- 10V
> rather than +/- 5V.

Actually, the standard specifies an allowable voltage range from +/-
3V to 15V, with receivers required to tolerate up to 25V. Voltages
less than +/- 3V to are undefined. In the days of TTL design, it was
common to use the +/- 12V rails to power a LM1488 driver. Those of us
who did interface design back in those days used to complain a lot
about substandard implementations which didn't work with certain other
devices.

[JohnK]

RS232 spec is a range of voltage. There is a spec for the max supply volts
and a clarification for the 'logic' level.
eg -16 to -3 is one 'level' and +3 to +16 is the other. [I'll dig out my
copy if needed.]
Many receivers don't implement the dead area and some don't require the
change of polarity, just a change to Gnd.

John K.

----- Original Message -----
From: "Michel" <mic...@xiac.com>
To: "neonixie-l" <neoni...@googlegroups.com>
Sent: Friday, August 24, 2012 5:22 PM
Subject: [neonixie-l] Re: RS232 line driver


I just want to establish some serial communication between my computer
and a PIC controller. Like David mentioned, RS232 is actually +/- 10V
rather than +/- 5V. The levels directly from controller are obviously
only 0V and 5V. Now I am thinking, for the Rx input this is not a
problem because it will easily handle the +/- 10V input signals if I
add a series resistor. But the Tx output needs to go from 0V/5V to +/-
10V which is normally done with a MAX232 for example. The MAX has 4
line converters (2 input; 2 output) but I only need 1 for my Tx
signal. So I was after something smaller like an 8 pin or even a 5 pin
driver that works on just a +5V supply.

Michel

On Aug 24, 5:43 pm, Dalibor Farn� <dali...@farny.cz> wrote:
> Hello, look on rs485. I played with it a lot, ready to answer Your
> questions :-) it works for long distances and allows more devices on one
> line (bus).
>
> Try to describe your devices more..
>

> Dalibor Farn�http://dalibor.farny.cz

[Michel]

This one will actually do the trick and is small enough!

Thanks Nigel!

Michel

[Mark Moulding]

I am after a driver like the MAX232 that has 5V levels on one side;

+/- 5 on the other side and only requires a +5V supply. The MAX232
however is a 16 pin device and I am looking for something smaller (8
pins). I only need one Rx and one Tx channel.

If half-duplex will work, the DS275 might do.  It's an 8-pin chip that steals power from the TxD of whatever you're plugged into to provide the negative swing for your TxD.
~~
Mark Moulding
 

[fixitsan]

I've seen a lot of projects using pics and PC's, with no interface IC, i think just some resistors. The PIC has a good output current from the serial port and most importantly, the later pics have a configureation bit for the UART to send inverted data.
There's a few suggestions here http://www.electro-tech-online.com/microcontrollers/16668-transmit-data-pic-rs232-without-max232.html

I haven't tried it, but if I had nothing to lose I probably would.

[fixitsan]

A few ideas here too http://www.scienceprog.com/alternatives-of-max232-in-low-budget-projects/

[Adam Jacobs]

That is a neat part, too bad that it is no longer in production. Looks like Components Direct sells them individually.

http://www.componentsdirect.com/maxim-ds275-pdip-8-package-rs-232-transceiver.html

I'm not sure that I would start a new design for manufacture with them, though.

-Adam

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[Dalibor Farný]

The best way is to use rs232 to uart converter ($3 or so on ebay), You just plug it into pc and directly connect to rxd and txd of your MCU. This is cheap and easy solution. The converter itself uses a max232 IC to change signals from rs232 to TTL.

Dalibor Farný
http://dalibor.farny.cz

sent from Samsung Galaxy Pad

Dne 24.8.2012 8:52 "Michel" <mic...@xiac.com> napsal(a):

[Michel]

That is interesting, I have to check if my PIC has this inverter bit,
didn't know about that.

I like that 2 transistor solution from the scienceprog website as
well. I actually thought about doing something like that but I wasn't
sure if you can always assume Tx is negative when idle.

My eye fell onto this DS275 chip as well, but indeed, it is no longer
manufactured so i'd rather not choose it.

Thanks for the help and tips!
Michel

On Aug 25, 12:45 am, fixitsan <fixit...@aol.com> wrote:
> I've seen a lot of projects using pics and PC's, with no interface IC, i
> think just some resistors. The PIC has a good output current from the
> serial port and most importantly, the later pics have a configureation bit
> for the UART to send inverted data.

> There's a few suggestions herehttp://www.electro-tech-online.com/microcontrollers/16668-transmit-da...

[threeneurons]

I'm with John, if it for personal purposes, and the run is short (<10ft/3m), you don't need to strictly adhere to the RS-232 spec. Just a pair of transistor inverters, and label the connectors, "Mickey-Comm", and you may just get away with 0-5V. Scope it, at your max intended baud rate, just to make sure the signals aren't badly distorted. If tolerable, your done, and on to the next project.

[Michel]

Yes, I'll give it a shot. My PIC indeed has invertable USART ports so
I'm going to hook it up just like that without transistors but just a
few series resistors. The cable is only short. If it doesn't work
(which I doubt), I can always use that $3 ebay interface that Dalibor
was talking about. I read that most computers these days will already
work with 2V signals on the RS232 port, so it's not very critical.

Michel