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31  Forum 2005-2010 (read only) / Interfacing / Re: XBee 2.5 firmware upload failed... Now a toaster on: September 30, 2009, 12:46:26 pm
I would take this topic up at the Digi support forum at  I think you can wire up a button to the reset line and use a combination of that button and the upload from X-CTU to forcibly reload the firmware.  Take a look at the XBee's datasheet to confirm, however.
32  Forum 2005-2010 (read only) / Interfacing / Re: Blinded by the light on: September 28, 2009, 11:50:21 am
Good ideas.  I'll start with the shielding, and maybe try throwing another photodiode into the mix.  Fortunately, I never buy just one of anything. smiley  I like the idea of finding another photodiode with a smaller FOV, too.
33  Forum 2005-2010 (read only) / Interfacing / Re: Blinded by the light on: September 28, 2009, 10:23:31 am
Here in the US, our electric meters are on the outside of the house.  I could set up a curtain, I suppose, but that would look weird to the neighbors.  ;D

Ok, on to the physical solution, then.  I'm quite impressed with what I'm getting out of my signal filtering, so far; too bad it's not enough!
34  Forum 2005-2010 (read only) / Interfacing / Blinded by the light on: September 28, 2009, 09:10:10 am
Morning, all.  I'm trying to roll my own electric meter reader, a la the Blue Line PowerCost Monitor (or the re-branded Black & Decker one).  My meter flashes an IR LED for every one watt-hour of usage.  I've succeeded in reading, logging and graphing the power consumption rate using an op-amp and a SFH205F photodiode.  My problem seems to occur at around ten to 9 in the morning, when the sun peeks around the house and blinds the photodiode.  I'm trying to find a solution to this problem.

This photodiode purports to have a daylight filter (and is indeed very dark plastic), but that filter doesn't seem to work very well.  It also has a 60 degree viewing angle which I'm thinking may be a problem.  What I believe to be happening is that the photodiode is getting saturated by the sunlight.  This seems strange to me because although I can reproduce the effect on my workbench using a 60 watt lightbulb in *very* close proximity to the sensor, just pointing it at the sky actually seems to blind it even more!  My first pass at the circuit was just the photodiode connected between ground and the inverting input of the op-amp in a current-to-voltage configuration.  I've since added a 1uF capacitor in series with the photodiode to remove the DC component of the signal, so that I'm just amplifying the pulses.  I'm able to confirm with an oscilloscope that I get a nice, clean, 5v, 10ms-wide pulse going to the Arduino, and 0v the rest of the time.  I can see the width of the pulse decrease as I bring my 60W bulb close to the photodiode, until it eventually disappears as the bulb overwhelms the signal from my test IR LED.

Out at the meter, I've got a very ghetto arrangement with the photodiode duct-taped to the meter housing with about 3-4 inches of tape on either side of the sensor.  I probably could just wrap the circumference of the entire glass dome of the meter with tape to try to get rid of any more light coming in (the side of the dome faces more-or-less due South), but this seems like I'm solving the wrong problem.  The Blue Line device does shade the dome a bit, but much less than I'm doing.  

So, I'm running out of ideas.  From a signal-conditioning standpoint, I feel like I've reached the limit of the sensor.  I might be able to isolate the pulse from the noise a little bit more using a signal diode, but I feel like the root cause of the problem is that the noise is overwhelming the signal.  Rather than putting the photodiode right on the face of the meter, I'm thinking that I can try to raise it a half-inch and shield it (think hole drilled in wood with the photodiode recessed), which might prevent incident light from coming into play.  Another possibility is replacing the photodiode with one with a narrower field of view.  Have I missed anything obvious from a sensor and circuitry standpoint?

35  Forum 2005-2010 (read only) / Interfacing / Re: Anything meaningful in this "carrier signal"? on: September 01, 2009, 12:55:08 pm
Interesting.  This is sort of a loaded question and going to showcase my ignorance, but what's the best way to use an Arduino to log this signal?  The parameters seem to be the length of the 5kHz section, the frequency at which it occurs, the actual frequency of the signal (assuming it's constant for a given occurrence), and perhaps its amplitude?  It seems like I could probably put a small capacitor in-line with the signal to remove the DC component, use an op-amp to reduce the in-between sections to zero, look for the rising edge of the 5kHz section, and do some analysis there?
36  Forum 2005-2010 (read only) / Interfacing / Anything meaningful in this "carrier signal"? on: September 01, 2009, 10:56:32 am
My new house has an Itron C1SR electric meter, which sports an IR LED that flashes once for every watt-hour of power usage.  I picked up some IR photodiodes from Mouser this week and used my oscilloscope to verify that the meter's doing what I expected.  It is, mostly, but in addition to a 10ms-wide "usage" pulse, there's also an underlying carrier signal containing a high-frequency ~2ms-long burst that repeats.  Here's a screen-shot from my 'scope:

Is it possible that there's some additional data embedded in that signal, or is it just noise?
37  Forum 2005-2010 (read only) / Interfacing / Re: Building high resolution voltmeter on: June 04, 2009, 05:56:33 am
Would the MAX1204 be suitable for this kind of thing?  Looks simpler to implement, and has an SPI output.
38  Forum 2005-2010 (read only) / Interfacing / Re: Building high resolution voltmeter on: June 03, 2009, 02:37:15 pm
This doesn't answer your question, but have you looked into the AD737?
39  Forum 2005-2010 (read only) / Interfacing / Re: 2 RF transmitters / 1 receiver setup on: June 03, 2009, 07:36:19 pm
The short answer is that, yes, the XBee can do that.  The documentation's pretty good, and Ladyada has some good tutorials on her site for using the XBee (I highly recommend her breakout board).  There are three options that come to mind.  One is digital line passing: you'd set up a pin on the XBee to be a digital input, just like on an Arduino.  The receiving XBee would then be configured to pass that digital signal out through one of its own pins, and then to the "receiving" Arduino.  With this configuration, the Arduino doesn't even need to communicate with the XBee over serial at all.  You can do a similar type of line passing with analog signals; the receiving XBee outputs a PWM signal that matches the analog input on the transmitting XBee.  Finally, you can have the transmitting XBee sample a digital or analog signal (say, 10 times/second) and then send those samples in a packet to the receiving XBee.  This would require processing in the Arduino to pull the sample data out of the packet.  The first two options make the XBee pair act like virtual wires.  There are timing considerations that need to be addressed, and I don't understand the XBee firmware settings very well, but I think you'll find the Ladyada XBee forum quite helpful (especially if you buy her breakout boards!). smiley
40  Forum 2005-2010 (read only) / Interfacing / Re: 2 RF transmitters / 1 receiver setup on: June 03, 2009, 02:38:54 pm
A pair of XBee modules would certainly do that.  If you use API mode on the receiving Arduino, the packets will contain the source address.  Depending on how complex the logic is behind sending the 0 or 1, you may be able to skip the remote Arduino entirely and just use the built-in digital inputs on the XBee module.
41  Forum 2005-2010 (read only) / Interfacing / Re: Howto read digital mileage from Mercedez Vito? on: April 16, 2009, 05:55:43 am
I think you might be able to pull the odometer info via OBD2, but I'm not certain.  There may be a less-direct "miles driven" counter of some type.  Check out the ELM323 chip from ELM Electronics.
42  Forum 2005-2010 (read only) / Interfacing / Re: DS1307 troubleshooting on: March 30, 2009, 09:29:03 pm
That makes two of us.  Oh, well.  :smiley
43  Forum 2005-2010 (read only) / Interfacing / Re: DS1307 troubleshooting on: March 30, 2009, 07:26:33 am
I think my DS1307s are just haunted.  >smiley-sad

I started experiencing the problem before I tried using the SQW/OUT; that just proved to be helpful in showing that the chip is alive (I've been running without serial output, at times).  

The crystal is *not* grounded.  I'm working on perfboard/stripboard and there's no ground plane.  Can I just solder a lead to the crystal and tie that to ground?

Sequence-wise, I've tried everything. smiley The proper sequence, as I see it, is to connect the battery (or ground Vbat) before applying +5V to Vcc.  This will work initially; then if I de-power everything and hook up the battery, the IC is kaput.
44  Forum 2005-2010 (read only) / Interfacing / Re: DS1307 troubleshooting on: March 30, 2009, 07:17:02 am
With the (power-hungry) LED connected directly to SQW/OUT (with an appropriate resistor, and pulled up to +5V), the LED comes on once the chip receives power; this is the default configuration.  The power-on state of the chip is to hold SQW/OUT low, so the LED lights up.  For troubleshooting purposes, once I can talk to the chip, I enable the 1Hz square wave, which makes the LED flash.
45  Forum 2005-2010 (read only) / Interfacing / Re: DS1307 troubleshooting on: March 30, 2009, 07:12:15 am
Vbat is like 3.1V.  It seems like connecting the battery causes the problem, but even after removing it and grounding the Vbat pin, it still won't tick.  It's not even that it won't tick, it won't even *respond*.
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