simplest circuit to simulate an RS232 signal

[eks32]

Hi,

I've got a timing application for a few sensor channels.

The circuit to monitor the event at each channel works fine, and I'm
thinking that if each channel could just send "some" data over the
serial lines, then a central PC could take care of all the
timestamping.

Is there a dirt simple circuit for emulating an RS232 signal? I'd
prefer to avoid programming micros and having the sensor boards
require oscillators or chips with clocks (power and such). Just the
simplest up/down tick of voltage that a polling serial loop would
recognize as data.

Oh, the sensors will likely have a 3~3.3 V supply.

thank you,

 

[itsmoked]

Personally I cannot understand your question.

Is this a one time test deal or are you going to design something onto a bunch of boards as a product?

You are willing to put circuitry onto a bunch of product boards but don't want to use very small cheap uC to handle this stuff?

The simplest up/down ticks.. How are they supposed to be coordinated with a polling scheme without board to board intelligence?

Simple 'up/down ticks' do not form asynchronous serial data. What about the start bits? What about the stop bits? What about the 8 bits in between?

3V does not qualify for RS232.

Perhaps you could fill us in more.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[eks32]

it won't get productized.
Each serial channel was going to have it's own serial channel.
Yes, it's inelegant, but I wanted to avoid having to pick out a uC and get a development board. The choices are completely bewildering in their scope,
but I completely understand why you'd suggest the uC path.
(btw what is the smallest, easy to program (really cheap uC) ?

I didn't know that about 3V not meeting the on condition for Rs232. I've got an order in on a horowitz&hill to read that chapter, but if there's a good web-based primer for serial communication hardware at the newbie level, I'd appreciate that references as well.

thanks for getting back.

 

[MacGyverS2000]

For small, cheap, and easy to program, look at the 12F series from MicroChip... some of those 6-pin buggers may be just what the doctor ordered, and there's sample code on their website (possibly for other processors, though it could be easily converted) for bit-banging a serial connection on chips that don't have a UART port. For voltage level translation, you'll need a 3V compatible MAX232-style chip.

$2 in parts, a $30 programmer, free MPLAB programming software, and a number of weekends learning how to program the chips in assembly. Doable, for sure...


Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

What's wrong with using the PC itself? Just start up Hyperterminal and type away

TTFN

 

[BrianG]

If I understand your application corectly you have several remote sensor channels, i.e. not part of the PC and using data logging i/o/cards? If so then you cannot easily use RS232 from each sensor device to send data to the PC. Most PCs only have one or perhaps two RSR232 ports, and the multiple transmit RS232 lines (from the several sensors) cannot be joined together as the driver circuits will clash.

The sensors need to use a "multi-drop" signalling scheme like RS485, or similar, so that the respective transmit lines go tri-state (i.e high impedance) when not transmitting. To enable the transmitter on the required sensor to obtain its data, you need to address it from the PC on the commoned receive lines. This is becoming altogether more difficult (though not impossible) for simple hardware. A micro is looking to be favourite.

 

[nbucska]

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