From: Jim Thompson
Subject: Re: single discrete RS232 driver
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Date: Tue, 17 Dec 2002 20:43:20 GMT
NNTP-Posting-Date: Tue, 17 Dec 2002 15:43:20 EST
Organization: Cox Communications
On 17 Dec 2002 11:17:05 -0800,
Winfield Hill ,
In Newsgroup: sci.electronics.design,
Entitled: "Re: single discrete RS232 driver",
Wrote the following:
|Miguel AB Silva wrote...
|> In the project I'm working in I use a MAX238 to drive 4 RS232 lines and
|> recieve another 4 RS232 lines. My problem is: I need another line to be
|> drived from TTL to RS232 (from a module to a PC computer). IMHO it would be
|> enough to drive this line directly to the RS232 transceiver in the PC (its
|> a control signal with very low speed) as i tested it with the PC´s in the
|> company. Can I assume that this will work with any PC ? Still my boss wants
|> the signal to be interfaced respecting the RS232 interface, i. e., my
|> circuit should output > 3v for one level and < -3v for the complementary
|> level. Can anyone give an hint on how to solve this ? Maybe based on the
|> positive and negative voltages available on certain pins of the MAX ?
| Your boss is correct, it's dangerous to send 0 / +5V signals and depend
| on all RS-232 receivers seeing your signal correctly.
| OK, step carefully, and with respect, you're entering the Mickey-Mouse
| logic zone! After acclimatizing to the special climate of this zone,
| you can easily make a +5 to -10V output swing using a single p-channel
| MOSFET or PNP transistor. I'll leave the gate drive to you. Connect
| the FET's drain to a resistor pulled down to the part's -10-volt pin.
| If you want +/-5V swings, add a second identical resistor to ground.
| When you're finished, tell your boss you're taking part in a great
| engineering tradition. :>)
| - Win
You can easily make RS232-compliant drivers AND receivers with your
garden variety LM339.
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
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