How to build your own RS232 to TTL converter


A how-to on making a DIY RS232 to TTL converter by Jestine Yong:

As I read many pages on the internet I saw there is a sort of adapter so called “USB to TTL adapter” who can communicate through with the uC. I had not the time to order one but I give a try to make one for the COM port. Actually it is an RS232 to TTL converter which I found better from my opinion than that USB to TTL adapter.
Here is why I like more this RS232 to TTL adapter than the other one:

  • can be used on a real RS232 port
  • it is a stable voltage level converter
  • can be used on USB port too (through USB to RS232 converter)
  • there is no VCC ( somebody would say it’s a disadvantage but wait…) *
  • it is a real hardware stuff, no emulation etc. (if it is used through a real com port)
  • can be built really cheap and easy

More details at Electronics Repair site.

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  1. ROTFL, if only one can find an RS-232 port these days without opening the casing. Hilarious justifications in the list — “real hardware stuff”. Author should at least read the MAX232 data sheet. A “stable voltage level converter”? Ha ha ha ha ha ha ha ha. MAX232 voltage doublers are unregulated and does not have great drive capability. IIRC it is also not guaranteed beyond the old ~115kbps speed.

  2. The MAX232 is a venerable part. It is easy to obtain in the third-world, especially as Chinese clone/copy parts. The drawback to the MAX232 over more recent (and harder to find parts in the third-world) are the requirement for multiple charge-pump capacitors. But caps are cheap and available. As for the data sheet saying something like “stable voltage level converter”, the MAX232 on the RS-232 side isn’t too bad, especially considering the very wide tolerance range of the RS-232’s accompanying PHY specification. REAL RS-232 serial ports still have use, especially when it comes to interfacing PPS time-keeping signals required by a GPS disciplined NTP server on the RS-232 handshaking pins (plus the NMEA time-stamp on the Rx pin). Plus, you can get a REAL RS-232 PCI card for a PC for a few bucks. A real RS-232 card will not have the timing jitter issues associated with the likes of an RS-232 to USB bridge chip, which wreaks havoc with NTP PPS timing.

  3. Now Drone, your arguments are much better than the writer’s points in support of MAX232. I don’t disagree, and I’m sure it’s still heavily used in industrial control, and the average Stratum-1 NTP server operator. So okay: for the average embedded enthusiast such as Arduino hobbyists, it is easier to pick USB over RS-232 for physical ports when it comes to recent PCs, so that factors into purchase of boards and modules.

    The writer wrote “stable voltage level converter”, not the data sheet. An over-simplification; one can say USB signals has margins and stability too. A knowledgeable person like you says ‘wide tolerance range’, obviously a more accurate characterization of the electrical interface. By contrast, the “stable voltage level converter” is so vague that it is essentially meaningless, akin to a fact-light hand-waving pitch of a salesman.

  4. For the typical hobbyist the RS232 serial port is essentially dead, for all intents an purposes, no exceptions. Sure, specialist applications remain where the RS232 is desirable and survives to this day, but none concern the Arduino (or whatever-Pi) enthusiast. Not to mention the MAX232 is the 5V version, which in modern electronics is just about even more rare than an actual RS232 port (yes, sure, we all know about the MAX 3232…). As for the justifications, to me they sound like “Oooh, shiny! Pretending I do things with this stuff I just found out about more properly than you amateurs feels good so lemme just come up with a few strained reasons why it’s much better…” Yes, when you need one, you need one; but unless you’re trying to plug something into an existing RS232 (or have a special use case that needs it), it’s just not something worth bothering with.

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