Author Topic: Reduce data packet interval  (Read 453 times)

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Offline RickHoegberg

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Reduce data packet interval
« on: January 14, 2019, 12:57:22 PM »
Hello Everyone.

I have an Acurite 522 base station, which receives outdoor temperatures from a 606TX sender. The data packet interval is 30 seconds but I would like to reduce that to say 5 seconds. I figure this should not involve much more than altering a resistor or capacitor but Iíve had no luck finding a schematic or block diagram and Iím very rusty at tracing out PC boards.

If anyone has done this, please share. My goal is to put a blob of insulating epoxy on the sender thermocouple and then attach a thin bare wire attached to a copper pipe on my domestic hot water recirculation system. This should allow someone in the bathroom to see on the base station when hot water becomes available (without running water down the drain) after pressing a momentary switch that runs the hot water recirc. pump for a sufficient period.

Clearly, the 606TX sender batteries will be consumed more rapidly but intend to provide a 110VAC - 3VDC power supply.

Any and all help is greatly appreciated.

Offline nincehelser

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Re: Reduce data packet interval
« Reply #1 on: January 14, 2019, 01:24:21 PM »
Schematics are likely unavailable.  Acurite is pretty tight-lipped about such things.

There's also a good chance you'll have to modify the receiver.  The transmission interval is usually built into how the receiver locks on to a particular sensor.

I'd be surprised if it were easy to modify.  The FCC would throw hissy fits if it were trivial to set by the user.

Offline John Z

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Re: Reduce data packet interval
« Reply #2 on: January 15, 2019, 12:12:04 PM »
RickHoegberg,

Ninchelser's observation about having to resynchronize receive window timing is very likely correct.

Changing the send interval is not so easy either. If you open the device, or visit one of the teardown pictures you can find on the web, you will see a component inside that looks like a tiny metal cylinder. That is the quartz crystal that determines all timings for the 606tx. It is a widely available and very inexpensive digital watch crystal. Finding a replacement that runs 6X faster? Slim chance I think. Could the digital logic still work? Probably, but maybe not.

Better to find a different solution.
« Last Edit: January 15, 2019, 12:15:06 PM by John Z »

Offline RickHoegberg

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Re: Reduce data packet interval
« Reply #3 on: January 15, 2019, 12:25:30 PM »
Tight-lipped is true! The fccid listing has everything - except the schematic. So close and yet so far.

I initially shared your concern that the receiver might also need to be modified. However, my searches on the subject have found some incredible sleuthing by various people using data protocol analyzers & even arduinos to reverse-engineer the data packet structure.

Evidently, while an Acurite base-station can see all 433 MHz transmissions it will only display data from a compatibly formatted data packet containing an acceptable sender ID. How often suitable data packets arrive doesn't seem to come into it.

So for now, I'm maintaining some optimism that the sender can be made to transmit data packets more frequently by modifying 1 or 2 components.

I believe you're also correct that modifying things can annoy the FCC. Manufacturers are required to abide by limits on radiated power on an allocated band. An allowed strategy, roughly speaking, is to transmit above 100% in short bursts between longer silences so that the average radiated power is within limits.

However, I'm no manufacturer but a guy in Alaska where I have a square mile to myself and shortening the data packet transmit interval will not cause any interference with anyone else.  :grin:

So I'll throw my original question out again to the good members of this forum - anyone feel they can pinpoint what components determine the intervals between data packet transmissions on the Acurite 606TX?

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Offline John Z

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Re: Reduce data packet interval
« Reply #4 on: January 15, 2019, 12:43:26 PM »
See cylinder labelled X1, bottom right of your pic.

Offline RickHoegberg

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Re: Reduce data packet interval
« Reply #5 on: January 15, 2019, 12:47:55 PM »
Hi John Z.

Going by the photo I posted, there are 2 crystals, X1 & X2. I've not yet determined the frequency for X1, which appears to be in the raw data conditioning section, but X2 is clearly 26 MHz. 

When I opened my 100MTX sender, I found the transmit section has an identical looking crystal marked 13.560 .

100 MTX data interval = 16 sec. Xtal = 13.560 MHz.
606 TX   data interval = 30 sec. Xtal = 26.000 MHz.

I got all excited that the ratio of time intervals and xtal frequencies are the same...except inverted.

All things being equal, how can a faster crystal lead to a longer data interval? Maybe a different pulse divider?

Besides, wouldn't the crystal in the RF transmit section be connected to the 433 MHz carrier used by both senders instead of the delays between data packet sends?

Which takes me to the thermocouple (component RT = resistor thermocouple) data conditioning section in the lower half.

My theory is that the RT is producing data all the time but the RF section is only enabled for perhaps 500 mS (as indicated by the LED blink) every 16 or 30 seconds depending on the unit.

I can confirm that the base station updates the displayed outdoor temperature an instant after the LED blinks on the sender.

So perhaps I'm being stubborn, but I think the sender is solely responsible for how often the base station updates the outdoor temperature.

However, I'm not smart enough to figure out which components on the sender are controlling the 16 or 30 sec delay between enabling the RF transmitter.

Of course I could be massively wrong about everything!


Offline nincehelser

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Re: Reduce data packet interval
« Reply #6 on: January 15, 2019, 12:48:29 PM »
There is a 16 second model that you can find at Walmart for under $10.


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Offline RickHoegberg

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Re: Reduce data packet interval
« Reply #7 on: January 15, 2019, 12:58:21 PM »
Hi again John Z.

Yup, I'm thinking X1 drives what I'm calling the RT data conditioning section below the slit in the PCB....which is probably there to (a) allow ambient air access to the RT and (b) help isolate the lower circuitry from the upper RF section.

However, I also suspect simply changing X1 will put out of spec the data pulse widths that are forwarded to the RF section.

Seems to me that the high side of the LED is directly connected to VCC and therefore the low side gets pulled low for (say) 500 mS every 30 sec. At the same time, the RF section would also be enabled to transmit whatever data it currently is receiving from the RT.

Which means that as few as 1 or 2 components are controlling the time (29.5 sec) the RF section is not enabled.

That's a big time constant. Maybe the large 3.3 microfarad capacitor is the key?

Offline RickHoegberg

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Re: Reduce data packet interval
« Reply #8 on: January 15, 2019, 01:11:07 PM »
Hi John Z.

Wal mart might be an answer. We even got one on Fairbanks a little while ago..although you can double lower 48 prices for anything in Alaska :(

16 sec is better but still a bit slow for my desired purposes; near real-time feedback on my hot water status. I really was hoping for 5 sec. Somehow, 1 sec feels like it might overwhelm the existing design, but if I'm on the right track I can experiment...

I was simply hoping someone had already decoded the circuit and could tell me something like "See C7 and R2 marked 30k? They control the data update interval. Replace R2 with a 5k resistor and you'll only have 5 sec between transmitted data packets."

If no one has ventured down this path though, then I'll try my rusty circuit analysis skills...but if someone has already figured this out I'd be most appreciative.



Offline John Z

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Re: Reduce data packet interval
« Reply #9 on: January 15, 2019, 01:21:05 PM »
My guess is that X1 oscillates at 32,768 Hertz, a standard clock frequency.
The oscillator circuit probably runs continuously and is a micropower clock circuit, so as to not run the battery down quickly. The oscillator circuit and the digital counters it drives would all be integrated on the processor chip protected under the blob. Every 30 seconds the counter would wake up the rest of the processor chip. A reading would be taken, and digitized by an ADC on the processor chip. When the conversion completes, the processor would wake the transmitter and bang out a serial data stream to encode the digitized temperature and humidity into a 433.92 MHz transmission. Then everything goes to sleep again except the X1 oscillator and it's counter circuits.
« Last Edit: January 15, 2019, 01:25:01 PM by John Z »

Offline RickHoegberg

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Re: Reduce data packet interval
« Reply #10 on: January 15, 2019, 01:50:06 PM »
Hi John Z.

I fear you may be correct. There's definitely an integrated circuit (marked U1) hidden under X1.

If as much functionality as you suggest is handled by U1, then there's little to nothing accessible for modifying the quiet period between data packet transmission.

About the only hope I have is that the large 3.3 microfarad capacitor (marked INT - Interval? - Hope spring eternal) determines the quiet period. I plan to swing by Radio Shack and see if I can get a 1 microfarad, 50V electrolytic capacitor and substitute that for the existing 3.3.

This is not a complete wing in the dark. My sender for a different model that transmits every 16 sec has a 2.2 microfarad electrolytic...in line with the non-linear behavior of an RC combination...

Offline John Z

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Re: Reduce data packet interval
« Reply #11 on: January 15, 2019, 01:54:30 PM »
With digital function so cheap these days, and capable of running on vanishingly low levels of power, there is simply no excuse to continue to use the old analog timer techniques, and suffer their tolerances stemming from component variation.
« Last Edit: January 15, 2019, 02:36:21 PM by John Z »

Offline vreihen

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Re: Reduce data packet interval
« Reply #12 on: January 15, 2019, 03:23:21 PM »
With digital function so cheap these days, and capable of running on vanishingly low levels of power, there is simply no excuse to continue to use the old analog timer techniques, and suffer their tolerances stemming from component variation.

This isn't your father's NE555 circuit any more.....  #-o
WU Gold Stars for everyone! :lol:

Offline John Z

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Re: Reduce data packet interval
« Reply #13 on: January 15, 2019, 03:32:49 PM »
Bravo, Vreihen.

Offline RickHoegberg

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Re: Reduce data packet interval
« Reply #14 on: January 16, 2019, 12:03:33 AM »
Ah, the 555 - a classic !

 

anything