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PostPosted: Fri Sep 09, 2011 10:14 am 
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Joined: Fri Sep 09, 2011 10:13 am
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Location: Cambridge, England
I have the crimp tools available for making these, but wonder if there's a spec. I already have a USB cable, so it would be handy to be able to interface the unit directly to an RS-232 input. That way I could also hook it directly to my Fez Panda board.


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PostPosted: Tue Sep 13, 2011 2:14 am 
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Joined: Mon Apr 18, 2011 5:26 pm
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Location: Melbourne, Australia
WieserSoftwareLtd wrote:
I have the crimp tools available for making these, but wonder if there's a spec. I already have a USB cable, so it would be handy to be able to interface the unit directly to an RS-232 input. That way I could also hook it directly to my Fez Panda board.

If you google "Current cost cable" there is a wealth of information. http://currentcost.wetpaint.com/page/Current+Cost+Cable#fbid=v_W6kTn7cdn has a fairly good coverage.

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PostPosted: Sun Oct 09, 2011 8:52 am 
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Joined: Sat Apr 16, 2011 5:33 pm
Posts: 6
WieserSoftwareLtd wrote:
I have the crimp tools available for making these, but wonder if there's a spec. I already have a USB cable, so it would be handy to be able to interface the unit directly to an RS-232 input. That way I could also hook it directly to my Fez Panda board.


Details here:

http://www.techtoniq.com/forum/viewtopic.php?f=5&t=385


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PostPosted: Tue Oct 25, 2011 6:01 pm 
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Joined: Thu Sep 22, 2011 6:45 pm
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Did anyone actually get this to work? I've tried connecting my monitor to my Mac using the data cable but the serial port that is created always locks up eventually and requires a reboot. This can take a few hours or a few minutes to occur but it never lasts a day. I've tried a number of different drivers and they all exhibit this problem.

I do have other USB to serial cables that work just fine so I'd like to be able to connect a simple RJ45 to 9-pin D connector into the monitor and into my USB to serial port. I've tried hacking a cable together but no input is seen through the serial port. I simply connected the following:

RJ45 pin 4 (gnd) to DB9 pin 5 (gnd)
RJ45 pin 7 (unit Rx) to DB9 pin 2 (Tx)
RJ45 pin 8 (unit Tx) to DB9 pin 3 (Rx)

Is this all that is required or is a simple cable not sufficient?

Thanks for any input.


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PostPosted: Tue Oct 25, 2011 8:57 pm 
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Joined: Fri Jun 03, 2011 11:12 pm
Posts: 38
Location: UK
rhino7 wrote:
RJ45 pin 4 (gnd) to DB9 pin 5 (gnd)
RJ45 pin 7 (unit Rx) to DB9 pin 2 (Tx)
RJ45 pin 8 (unit Tx) to DB9 pin 3 (Rx)

Is this all that is required or is a simple cable not sufficient?


The serial data connection on the RJ-45 is at (3 volt?) TTL levels and inverted compared to standard RS-232 (often +/- 12 volt)

You should be able to do what you need to do, but you will have to use an RS-232/TTL converter. The link posted above to another forum also explains this.

These can be bought ready made or you could make your own using a MAX3232 chip some capacitors and a bit of veroboard etc.

NOTE!
I deliberately said MAX3232 and not 232. The reason i say this (correct me if i'm wrong someone?) is because most of the energy monitors run off 3 volts and therefore use 3 volt TTL input/outputs instead of the regular 5 volts that a standard MAX232 uses.

I'm trying to remember now what voltage my monitor uses because it's plugged in so i can't check without unplugging it.

I beleive most MAX3232 chips will run happily with both 5V and 3V inputs but that can also depend on the make, as several different chip manufacturers offer the equivalent part but the specs are not always the same, so some may and others may not.

It would also be possible to make a simple data inverter/level shifter out of a transistor and a couple of diodes and resistors etc if you had some electronics knowledge and some parts in your "junk box" so to speak.

I reccomend just buying a level converter, ready assembled from your favourite online auction site or similar which is probably easier and will only cost you a few quid.

Some may be Line powered via the RS-232 it's self or others may require power applied seperately, which could possibly be gained from the RJ-45 as there are some power connections on there as well as the data lines.

Also take note - i hold no responsibility for any damage you may cause to your energy monitor or it's guarantee if you atempt this, so it's down to your knowledge and skill level. This info is only theoretical and i have not tried it myself to say it will work. If done right it should be fine but ultimately it's your responsibility :)


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PostPosted: Thu Oct 27, 2011 3:48 pm 
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Joined: Thu Sep 22, 2011 6:45 pm
Posts: 5
Thanks for posting such a comprehensive response. It was appreciated and helpful. I've ordered a max3232 board from eBay as you suggested as they aren't at all expensive. Hopefully I'll receive it the next few days and will see if it gets around the driver issues.


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