Logging pulses from meters

Continuing from the old thread ( http://arduino.cc/forum/index.php/topic,22640.0.html )

Alright, so I'm back :)

A few things:

  • The counters don't appear to share a common ground.
  • I'm pretty comfortable with soldering, just not very comfortable at creating circuit designs :) As long as I have smart people like you to help me through, "rolling my own" opto-isolators sounds like something I can probably handle.
  • These meters appear to have additional outputs that sound pretty promising. They are:

  • "10, Isolated Output (10 Wh/P, Kh = 10)" Definition: Isolated pulse output: 5 watthours on, 5 watthours off, reference to ISOL COM NOT TO BE USED FOR FIELD WIRING

  • "100, Isolated Output (100 Wh/P. Kh = 100)" Definition: Isolated pulse output: 50 watthours on, 50 watthours off, reference to ISOL COM

  • "1000, Isolated Output (1 kWh/P, Kh = 1000)" Definition: Isolated pulse output: 500 watthours on, 500 watthours off, reference to ISOL COM

  • "ISOL COM" Definition: Isolated common for 10/100/1000 isolated outputs

Now, this sounds promising! I've emailed the people who make this meter to ask them what voltage the isolated outputs are giving out. If it's 5V would that mean there is no need for opto-isolators?

Sorry, I've created some confusion by leaving out some important details from the original thread (see link at top).

In summary: At first I was only aware of the 12V counters which are currently hooked up to these meters. The idea was to read the pulses off these lines. These counters do not have a common ground.

Now that I'm gotten my hands on the meters and the manual that goes with them, I've discovered there are 3 additional outputs (the ones I've described above).

I decided to keep the original thread title for consistency. Again, sorry for the confusion.

Regardless of what the voltage is (5V or 12V or whatever), Opto-isolators are VERY STRONGLY recommended, regardless of what response you get (if any) from the vendor. I would absolutely never try this without good isolation!

Thanks! I thought I might be able to cheap out since I'll have to buy ~15 of these, but I'll take your (and AltairLabs's) advice.

Note further that depending on how much power we are talking about, even the 10 Wh/P output may be very slow. You will need to write Arduino code that can handle a slow input wave speed.

Yeah, it sounds like the output will be pretty slow, especially since the loads on these meters aren't going to be a whole lot (camp sites). Thanks for the heads up.

So.. it sounds like I have some opto-isolator shopping to do!

Oh really? The ones I’ve been looking at are $15to$20 $14: http://www.opto22.com/site/pr_details.aspx?cid=4&item=IDC5D

Sorry, I was away for nearly a month. I'm back now.

So, I emailed the manufacturer and asked them exactly how these isolated outputs worked. They replied with the following:

The isolated outputs which are 10, 100, 1000, they are the open collector of the photo-transistor. The isolated com terminal is the emitter of the photo-transistor.

All the isolated outputs are 50% duty cycle.

10 is 10Wh per pulse. 100 is 100Wh per pulse. 1000 is 1000Wh per pulse.

Now, obviously not an expert at this stuff, but to me a photo-transistor sounds like it performs the same job as an opto-isolator. Is this correct? Would using these outputs be easier than adding an opto-isolator to the 12V counter output? And if so, how would I go about feeding this into an Arduino?

Thanks guys! Once again, I really appreciate all your input.

Hey guys, any advice on the last post?


I´m no electronics wizzerd also, but just a few hints

The optocoupler you want to use is a 4N35, the drawing in the old post shows you how to connect If I have read the specs right you don´t want to put more then 6v at the LED (input) side. What I gather form the info on the isolated outputs is, that they will, put in simple terms, shortcut anything you put on them. So If I were you Í´d take a multimeter and a 9v battery and connect one terminal of the battery with one terminal of the isolated output, and connect the other teminal through you multimeter with the battery, and look what´s coming out. I´d bet you´d see pulses of 9v. Now if thats true, why don´t you take 5v (from the arduino board) and put that on the IO and return it to the input of the 4N35 (other side to earth) and put another 5v to the output side of the 4N35, and feed that into a pin on the board. Use the simpelest of schetchs and let LED13 (on the uno thats the buildin LED) get high when the pin gets high. If that works you got yourself a signal.

Now I´m trying to make the same, but I want to database it to the SD card on the Ethernetboard which I want to readout from my computer. Does anybody know of a project where this has been done?

That makes sense! Thanks, I'll give that a try.

As for your project, if you're writing to an SD card, I wonder if you could use one of those Eye-Fi cards that are essentially SD with built in WiFi?

I haven't even began researching the communication aspects of this, but if I do find something that works for me, I'll be sure to let you know.

Thanks for the response! John