RS232 TTL level shifter with DTE Port?

[schmadde]

I am using my RPi to monitor and control my central heating boiler via RS232. I had bad luck with USB to serial converters so I would like to use the builtin UART of the Raspberry Pi (BTW: is there really only one available?).

For this to work I need a TTL level shifter. I once bought one on ebay for less than 5€ - but it is a DCE connection. My boiler also has a DCE, so I need DTE on my RPi. All others I have found also are only DCE (i.e. the raspberry is the device to be controlled by another host). I would like to avoid having to build such a circuit myself if there is one readily available (I know, its only a MAX232 and a few parts but I cannot print PCBs and I don't like dangling cables) and also I would not like to combine Null modem cables with 2 gender changers.

Does anybody know of a ready made level shifter with DTE (male) connector? I would have assumed this is required quite often, since there are still a lot of devices with RS232 around and controlling other devices is a standard use case of the Raspberry Pi.

[joan]

Isn't the term DTE/DCE pretty meaningless if you are breaking the wires out. I thought it was a wiring convention.

The Pi's RXD expects 0-3V3. Anything outside that range will eventually damage the gpio. Similarly TXD pumps out 0 or 3V3.

[klricks]

For the TTL to RS232 adapter you MUST get one that has a MAX3232 (not MAX232) chip and power to the MAX3232 MUST be 3V3 (not 5V).

For DTE/DCE, normally when conversion is needed you use a readily available 'gender changer' and probably a NULL modem adapter.

Edit: Sorry I did not read your post carefully.
You would probably have to make your own cables if you don't want to use adapters. Many years ago I used the Serial (DE9) to CAT5 (RJ45) adapters which could be custom wired for the crossover if needed. Don't know if they are still available?

[schmadde]

Isn't the term DTE/DCE pretty meaningless if you are breaking the wires out. I thought it was a wiring convention.

Sure, but I would like to connect the device directly to the db9 connector on the level shifter. I could swap tx and rx cables, but gnd and vcc would still be at the wrong pins.

So it looks like I need to build a custom cable. No big deal but i am amazed that there are a hundred gazillion of different level shifter boards on ebay and all are dce. I would have assumed that the other way round is needed more frequently.

[klricks]

Here are Serial adapters that can be configured. Just use standard Cat5 cables between

DB9 FM:
http://www.showmecables.com/product/DB9 ... ?link=YMAL

DB9 M:
http://www.showmecables.com/product/DB9 ... ?link=YMAL

Also there are plenty of TTL adapters on ebay with either Male or Female DB9 but don't know if NULL adapter would be needed?

Male:
http://www.ebay.com/sch/i.html?_from=R4 ... e&_sacat=0

Female:
http://www.ebay.com/sch/i.html?_odkw=ma ... e&_sacat=0

[schmadde]

Hey thanks for the links. I wonder why I didn't find those on ebay since I thought I had the same search pattern. The configurable DB9<->RJ45 adapters also look fine.