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/Develop/Hardware/Projekte/RS232 -> 3.5mm jack with 74HC14/ |
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/Develop/Hardware/Projekte/RS232 -> 3.5mm jack with 74HC14/ |
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”The Final Answer to the RS232 Problem. Part 2/2.“
Last updated: 2016-04-10
Questions & comments to Kio
This RS232 to 5V-SIO adapter is powered from RTS and DTR of the RS232 connector. Hardware handshake is not provided, but RTS/CTS and DTR/DSR are looped back in the connector.
If no plug is inserted at the rear side of the adapter, then TxD is looped back to RxD and the adapter can be used as a loopback device to test the RS232 port or to test itself for functionality.
The adapter does not use a negative voltage, so the lowest voltage level it can send to RxD of the RS232 port is +0V, which is outside the RS232 standard. But nevertheless it works with most RS232 ports. I have tested it to work with the RS232 ports at some 'newer' PCs (year 2000±2) and it should work with all MAX232-powered ports. Due to lack of hardware i have not tested it against an old-fashioned RS232 port powered from ±12V rails, where it is not shure whether the +0V is recognized as negative voltage level as required.
The board is double sided but should be easy to etch and solder at home. Resistor values are choosen for ±8 to ±12V RS232 signal levels. The diodes may also be of Schottky type. The genuine choice for the integrated circuit is a 74HC14 with 6 inverters (thereof 2 actually used) with Schmitt-trigger inputs. But 74HC04 and 74HCT* types should work as well, as other CMOS family types.
RTS and/or DTR must be set to positive polarity (active state) for the adapter to work. Then the LED is lit to indicate operational state. Most terminal programs activate DTR while they are online, so this should be no issue.
The 5V SIO connector with a 3.5mm jack at the rear side is a little bit quirky. This kind of plug creates short-circuits while plugging in and out. I use the following sockets and plugs:
5V SIO Lead
The cable is not compatible with standard audio leads, so i have to solder them myself. The resistors minimize the short-circuit problem (actually they may be superfluous) and the cable is crossed to resolve the brain-dead data direction problem ("TxD!" – "TxD? Which way, in or out?").
| Name | Letzte Änderung | Länge | |||
|---|---|---|---|---|---|
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board rear.pdf | 2010-03-12 15:26 | 18887 | ||
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board top.pdf | 2010-03-12 15:26 | 17718 | ||
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board.png size: 405 × 224 |
2010-03-12 15:28 | 7077 | ||
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component placement.pdf | 2010-03-12 15:26 | 8968 | ||
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RS232 3.0.brd | 2010-03-10 13:27 | 19447 | ||
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RS232 3.0.sch | 2010-03-10 13:29 | 57475 | ||
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RS232 3.1.b#1 | 2010-03-10 14:16 | 19656 | ||
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RS232 3.1.brd | 2010-03-12 15:17 | 19656 | ||
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RS232 3.1.pdf | 2010-03-12 15:19 | 13086 | ||
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RS232 3.1.s#1 | 2010-03-12 15:17 | 59954 | ||
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RS232 3.1.s#2 | 2010-03-11 19:10 | 59762 | ||
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RS232 3.1.sch | 2010-03-12 15:18 | 59930 | ||
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RS232 Adapter v3.1.jpg size: 439 × 741 |
2010-03-12 13:45 | 152412 |
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