Hi all,
may be that my question is stupid and a typical beginner struggle.
but yet i did not figure out how to connect via a simple serial cross over cable to a jeenode?
So any tip will be welcome.
A simple serial connection
(13 posts) (3 voices)-
Posted 02/12/2009 14:26:52
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Standard RS232 uses anything from +/- 5V all the way up to +/- 25V as signal levels, while the JeeNode uses 3.3V logic signals. You will need an "RS232 to TTL level converter" to connect the two together. Most of the units I see are for 5V circuits, though - I don't know of a solution for 3.3V, but I'm sure they must exist since all the ARM etc chips also run at 3.3V (or even lower).
I've only been using USB via the USB-BUB board at http://moderndevice.com/connect to connect JeeNodes to a PC/Mac - there are several similar interfaces.
Posted 02/12/2009 19:30:25 -
Hello,
I've successfully connected my JeeNode to a serial port RS232 using a JeePlug board, 4 resistors, 2 transistors and a diode.
Details and background about a conversion circuit can be found here http://chaokhun.kmitl.ac.th/~kswichit/ap275/ap275.htm it makes an excellent description.
I use 2nd version of the described level convertor (as I had 2 NPN transistors somewhere) and soldered everything on a JeePlug together with a DB9.
It easily transports bits at 57600 bits/sec and I successfully used it to upload new sketches. I have to remark however that the Arduino "upload" button won't work out of the box if you just implement TX and RX. The 328 needs to be reset to start the bootloader which is done through the JeeNode.RST pin. I do it manually after I pressed the upload button (there seems to be a timewindow of roughly 1 second to reset the thing after you pressed the button).
Eventually the reset can also be automated if you hook up RS232.pin4 as I found in http://arduino.cc/en/uploads/Main/ArduinoSeverinoSchematic.png
Which is an alternative serial hookup from Arduino.About 5.0V or 3.3V, I do not need to care actually. I just power the JeeNode using any compatible source and connect the ground to the ground of the level-shift circuit.
An alternative is to use the MAX232 chip to make the conversion (iso discrete transistors), but this is a little more expensive and requires the chip to be powered.
Regards,
Charlie
Posted 03/12/2009 20:42:05 -
Yes, pin 4 is DTR - and since it's hooked up through a capacitor, you can probably just wire it straight through - no need for level converters.
As for the 5V/3.3V issue - the circuit you refer to mentions a 5V supply, which I assume you're hooking up to whatever goes into the JeeNode before the voltage regulator. On the TX side (towards RS232), that's fine, but I suspect that the incoming RX level will be higher than 3.3V. This is probably ok because there is a 1 k? current limiting resistor in the circuit, and the ESD diodes will take care of it.
I'd like to try this out some day, and summarize in a weblog post (am always looking for fun stuff to write about...). If we could power a JeeNode off a standard RS232 port, that would be cool too. Probably much harder to do. One thing I'd be interested in, is to hook up a JeeNode to an old printer via its serial port - then send stuff to print over the air. But hey ... that's just one of the crazy ideas floating around :)
Anyway - great solution!
Posted 04/12/2009 00:06:17 -
Hello,
thank u good ideas! I'll have a try on it.
@charlie: the link you provided does not work.
Regards
Roger
Posted 04/12/2009 13:13:32 -
Just to follow up - the MAX3232E chip can run from either 3.3V or 5V.
Here's info on how to steal a bit of power from an RS232 port - http://www.tkk.fi/Misc/Electronics/circuits/rspower.html
Not enough to run the wireless continuously, but it could charge a supercap or battery for intermittent wireless use.Posted 04/12/2009 21:27:42 -
Indeed, the link seems to be 'Forbidden' now. I can understand why, it unlocks some dark secretes of how simple RS232 level conversion can be!
And then there is our Big Brother Google:
Search om "simple RS232 level converter using transistors"
And use the "In cache" link. There you have it.I've added the pin4.DTR capacitor to my backlog.
The power harvesting from RS232 looks interesting, especially in the context of the printer story. Found any links on storing the 11mA current in a supercap?
Jee-greetings,
Charlie
Posted 05/12/2009 19:19:59 -
Regarding the link - could be automatic bandwidth limiting kicking in (though I doubt it's from our little gang...). I usually take snapshots of stuff instead of just bookmarking interesting links, so here's a PDF of that page, via the wiki - http://wiki.jeelabs.net/p/admin/download.html?attachid=38484 (with a top-o'-the-hat to DevonThink, my archiver).
As for supercap use - should not be hard: some RS232 lines -> diodes -> tied together to supercap -> JeeNode regulator. Probably add resistors (1 k??) in front of the diodes so the supercap doesn't look like a short when starting out empty.
Posted 05/12/2009 23:41:40 -
Hello,
some follow up
I tried to hook up the DTR signal to reset the JeeNode, guess what, it did not work...
First I tried a direct connection (DTR reset pin FDTI) as this is very close to what the arduino serial guys do (DTR - capacitor 100n - RST pin 328 with pullup 10k) - no luck.
My -usb based- serial port issues 0V when in idle and switches to 5V when programming/uploading, falls back to 0V when done/fails upload. My guess is that it does not work because the 3.3V 328 is used iso 5V (arduino serial) and therefore the 'negative push' of the 5V load capacitor is not hard enough for a reset at the right moment.Then I created an invertor (same as in the RxD with diode) and gave it a go, but... no go.
Then I tried hooking up with and without invertor directly to the reset pin in the ISP programmer (you never know...) but again no luck.
If someone ever gets the reset working using simple transistor/resistor networks from a RS232 let me know.
Since I'm getting bored doing a manual reset I think I'll buy a USB-BUB or FDTI cable for X-mas. Any shopping advice? (Destination is Europe/Belgium)
Regards,
Charlie
Posted 14/12/2009 21:07:29 -
I don't know what's going on. Straight into into cap/pull-up and then inverter would have been my bet. Even without level converter, with a resistor and diode's to clamp at GND and +3.3V, perhaps.
Not sure what sort of shopping advice you're after... do you want me to tell you that the Jee Labs shop is a not a bad place to go to? I'm, eh - p r o b a b l y - not the most impartial guy in the world for that ;)
Posted 14/12/2009 22:47:03 -
I already pointed my family to the Jeeshop, so more jee-stuff to play with :-)
Specifically I was looking for a shop that sells the USB-BUB. Moderndevice sells them of course but only with paypal (which I don't have). FDTI cable is a little to expensive imo.
Regards,
Charlie
Posted 15/12/2009 06:30:46 -
The JL shop also has USB-BUBs, since it's such a common item with JeeNodes.
Posted 15/12/2009 11:38:01 -
Great! There are 2 pages full of stuff!
:-)))))Posted 15/12/2009 19:30:02