Help identify component on wireless therm board

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rickrump
 
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Help identify component on wireless therm board

Post by rickrump »

I am trying, probably fruitlessly, to debug a non-operational wireless thermometer. We have this projection atomic time/temp clock that projects the time and indoor/outdoor temp on our ceiling. We loved it so much we bought 3 of them - as they would fail! (I know, we should have suspected the design.) The indoor clock/temp works fine. But the outdoor temp is very intermittent. When you put in the batteries and press the reset button, the red led will blink and SOMETIMES you will get a few cycles of outdoor temp showing up on the indoor unit. Have tried distance, new batteries, full reset of both units, etc. So bravely I disassembled it and found the attached board. On the back of the board is a small metal can soldered to the board - looks like a crystal case with HR433C on it. (X2 on the board just below the middle coil.) Only 3 (Chinese) hits for the part number on Google but I think this is the 433MHz wireless transmitter.

With my handy-dandy Bus Pirate, I was ready to see what protocol they used to transmit the temperature. So my questions are:

1) where would you begin to troubleshoot this?

2) What the heck is the black round dot in the center of the board. Is that some kind of security cover for an ASIC or something so it can't be reverse engineered?

Thanks for any help. (If I can't get THIS to work, maybe I dump the outdoor unit and switch to an XBee and figure out where to inject the data stream in the indoor unit. But I would still need to figure out the protocol.)
Wireless Therm-em.jpg
Wireless Therm-em.jpg (391.22 KiB) Viewed 8755 times
Thanks,

Rick

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hlantz
 
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Re: Help identify component on wireless therm board

Post by hlantz »

Black blobs of resin are normally officially there for "protection so that ICs don't get damaged"; but yeah, you're right, it's to prevent the competition (and, to a lesser extent, tinkerers like us) from figuring out how things are built.

With the amount of PCB traces going into it, I'm gonna guess it's some form of microcontroller. Especially if you have identifed something that might be the transceiver on the back of the card.

Interesting project to work on, though - I hope you will figure it out!

Philly
 
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Re: Help identify component on wireless therm board

Post by Philly »

I would start by resoldering the collector on the transistor on the bottom left of the pic, the joint looks a little iffy. Got any better pics?

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rickrump
 
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Re: Help identify component on wireless therm board

Post by rickrump »

Here's a photo from the other direction with the light subdued a bit. I looked at that solder connection with a magnifying glass and it is bright and shiny. Looks good.

Rick
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zener
 
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Re: Help identify component on wireless therm board

Post by zener »

The blob is epoxy encapsulant, over a "COB" mounted die. (chip on board). The transistor there is likely actually the temp sensor. It appears some water leaked in? It looks like some rust stains.

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rickrump
 
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Re: Help identify component on wireless therm board

Post by rickrump »

The yellow in the upper left corner is a coating on the PC board. You'll notice it's also in the upper right corner where the black and red power leads come in from the battery.

The RTD is actually on the other side of the batteries at top, with holes in the plastic case to allow the air to circulate (but an o-ring seal to keep water out. The blue leads in the upper left go to the RTD.

Rick

Philly
 
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Re: Help identify component on wireless therm board

Post by Philly »

Have you tried resoldering each connection? Only about 5 mins work there :)

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richms
 
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Re: Help identify component on wireless therm board

Post by richms »

Here is guts of the outdoor sensor for a wireless station I got off ebay to reverse engineer the protocol to get logging

http://picasaweb.google.com/richms/TemperatureLogger#

Same sounding metal can, its part of the RF circuit. At the bottom of the square it is on is 2 connections that was from the micro to the transmitter which is where I tapped into it to sample the RF protocol to reverse engineer. See if you can find the same type of point in your one and use your soundcard or buspirate to see what is happening there.

You might be able too use some pre existing arduino code to decode it, I found that the lacrosse one was virtually identical to the protocol used on those timing wise, these are just shorter and I have no idea how to calculate the CRC so have not bothered for now..

So, if you are wanting to keep using the projector, then a 433MHz transmitter module (the cheap ones of those seem to be fine) and the protocol should be less hard to do than reciveing it. can you put up pics of what the device looks like when working? I was thinking of getting a projector one off ebay but past experience with a projector clock has made me rethink that...

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rickrump
 
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Re: Help identify component on wireless therm board

Post by rickrump »

@richms
Thanks for the info. 2 things:

1) Do you want a picture of the LCD on the front of the receiving clock/temp display OR do you want a picture of what it projects on the ceiling? (That's a little difficult since it has to be dark to see it.)

2) Can you post the make/model of the temperature sender to have the Picassa Google pictures of? I'd like to find one and try it.

Rick

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richms
 
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Re: Help identify component on wireless therm board

Post by richms »

The projected part is of more interest to me.

180534740095 on ebay is the same guy I got it off, he did more sensors for US$6.50 each. The sensors make up a random number 0-FF when powered up and the indoor part will show the first 3 that it sees from when you put batteries in which was a pain to get them showing the ones I wanted on the indoor things since I got 2 indoors and 6 sensors all up.

Im using a 433MHz reciver from a remote control extender because the cheap ebay one I got didnt seem to like the slow data rate of the weather stations - they have some form of AGC in them and the maximum high or low time was too long for it, so it got noise at the ends of bits.

Design has come from here http://www.freetronics.com/products/433 ... ver-shield but I have just wired into the IR repeater's reciever rather than move the 433 reciever to the arduino since the final project will be done with a bare avr to make it small enough to go into an old clock radio with an LCD.

JohnDowdell
 
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Re: Help identify component on wireless therm board

Post by JohnDowdell »

The "metal can" is almost definitely a single port SAW resonator.

wikipedia briefly mentions resonators under this page if anyone is interested in the physics but it wont help you diagnose the unit:
http://en.wikipedia.org/wiki/Surface_ac ... DF_AN1.pdf

I think resistor R12, a 33K (marked 333) is probably going to be your guy. check which side goes to the smd transistor(kind of hidden under a coil in your photo). My bet is that the other side of the R12 goes towards the "blob".

From what i've seen, the bus pirate can diagnose a number of protocols and interfaces. Don't be surprised if the manufacturer has gone for a proprietary protocol. Also, BANNED encoding is a popular encoding method for this type of transmitter. Will bus pirate diagnose BANNED? There are a few types of BANNED encoding though.

There's a number of vendors that sell cheap (<$10) 433.92Mhz receiver modules if you wanted to use that as a diagnosis tool.
Also, I have a cheap 'n nasty radio frequency counter i got off ebay (~$30 - ~50)that i use to check if such an rf circuit is transmitting. You'll probably find that if you apply VCC through a 33k to the same place where the r12 connects to the transistor, you can probably get the transmitter to fire up a carrier on 433.92Mhz. That's if the RF circuit works at all. When i use this method with my frequency counter, it shows 433.92Mhz (or thereabouts) on the display.

Is it possible to manually prompt the device to transmit a report. I guess it would be difficult to diagnose if the data only got sent out once every ten minutes or something.
I take it the blue wires at the designator "RT" on the board go to a thermistor sensor? If the unit only transmits reports on temperature changes, i guess you could heat up then cool down the sensor.

JD

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richms
 
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Re: Help identify component on wireless therm board

Post by richms »

I cant see anything but a black square here on this lousy LCD...

How large are the letters? Can it focus? Im just worried that it will be fixed focus so depending on where its going, it will be too unfocused to see.

The sensors I got with that weather station transmit every few seconds for the first min or so when you put the batteries in, then go back to sending it every 1 min roughtly. You can provoke a transmission by removing and reinstering the batteries which will restart it doing it every few seconds, but with a new random ID.

It doesnt seem to be quite random, I dont know how many codes it will choose from, I have had a couple of double ups of the codes when I was setting up 6 of them.

martin_bg
 
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Re: Help identify component on wireless therm board

Post by martin_bg »

richms wrote:Here is guts of the outdoor sensor for a wireless station I got off ebay to reverse engineer the protocol to get logging

http://picasaweb.google.com/richms/TemperatureLogger#

You might be able too use some pre existing arduino code to decode it, I found that the lacrosse one was virtually identical to the protocol used on those timing wise, these are just shorter and I have no idea how to calculate the CRC so have not bothered for now..
richms, I have the same sensor as yours. I can't read it using the LaCrosse code, do you care to show your code?

Thanks

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