Thursday, December 18, 2014

Sensitech TempTale 4 USB Teardown

I was recently at a local recycling centre and saw that they had some second hand temperature data loggers on sale for $2.50.  At that price how could I not buy one to see how they worked.

If you're not familiar with the this kind of data logger, they measure the ambient temperature at regular intervals and log the data to internal memory.  They're typically used to monitor the temperature of stock through a logistics chain, be it refrigerated or not.  For example, if you run a grocery store and you notice that the quality of the fruit on sale isn't of an acceptable standard, you might get your supplier to put one of these in a delivery to monitor the temperature throughout the cold chain.  By doing this you may be able to detect that the refrigeration in the truck isn't at the right temperature.

Temperature Logger
Temperature Logger
The nice thing about this logger is that it has a built in USB cable.  When plugged into a computer the temperature logger appears as a mass storage device containing a pdf report and an encrypted file containing the logged data.

Temperature Logger
USB Cable
From what I can tell, the PDF report isn't actually stored on the logger,  it's generated dynamically from the logged data when the device is plugged in.

PDF Report
Logged Data Report
The specs on the back of the logger are a bit lacking.  It covers a temperature range of 0 to 30 degrees Celsius, and records data every 10 minutes for 111 days.  If you do the math, that comes to 16 thousand samples, that's where the 16K in the device ID comes from.  The SU indicates that this logger is single use, so it's not really any use to me.  There is software to configure the device that may be able to reset it, but it's not free and not worth the effort.  One thing that did surprise me is that there aren't any specifications for accuracy or resolution of the temperature measurements.

Plastic Case
Back Panel and Model Details
As the device was of no value to me I decided to pull it apart.  At first I tried to do it carefully, but when it wouldn't come apart I assumed that it was ultrasonically welded to stop moisture ingress.  So I decide to destructively take it apart.

After removing the sticker that covers the front, you can see the start and stop logging buttons that are an integrated part of the plastic case.  It should also be obvious at this point that they aren't too worried about moisture ingress,  there are holes all over the front panel, and although they're covered by a sticker, it's not ideal.  Having said that, the device isn't designed to have a long life.

Plastic Case
Buttons Moulded into Case
After hacking away at it, I soon found out where the the screws were hidden.

Plastic Case
Hidden Screw
There are little indentations on the back that I thought were part of the case, but it turns out that they are stick on covers that hide the screw head.

Plastic Case
Removing a Screw Cover
My initial guess that the case was ultrasonically welded together was wrong, it's just screws and a rubber seal.

Plastic Case
Rubber Waterproof Seal
When opened you can see the top (it's probably the back, but I'm calling it the top) of the PCB.  Nothing surprising here.  The battery that powers the device can be seen to the right.

Circuit Board
Top Side of PCB
The back side of the device isn't anything special either, the LCD is connected to the board with a standard zebra connector.  The dome contact switches can be seen below the chip on board assembly that contains the LCD driver.

Circuit Board
Back Side of PCB
Let's have a look at the ICs on the PCB.  The first is an Atmel 32 bit micro controller that handles the USB communication, and presumably generates the PDF report when the logger is plugged into a computer.  It's also likely that it coordinates taking temperature measurements and storing them in memory.  To meet the requirement of 111 days of operation it's likely that the micro-controller makes extensive use of sleep modes.

Circuit Board
AT91SAM7S256 32-bit Microcontroller
The 32 KiB Atmel EEPROM is most likely used to store the logged temperatures.  This makes sense at it has enough capacity for 2 bytes per sample.

Circuit Board
AT24C256C 32KiB EEPROM
The Texas Instruments quad FET bus switch is most likely used as a level converter to allow communication between ICs that operate at different voltages.

Circuit Board
SN74CBTLV3126 - Quad FET bus Switch
The purpose of the Winbond 512 kiB flash memory isn't clear to me.  Maybe it extends the program memory of the micro-controller, maybe it holds a template of the PDF report file, could be something else, I'm unsure.

Circuit Board
25X40CLNIG 512 kiB Flash Memory
Finally we come to the actual sensor, it's a bead style thermistor.  I was expecting something different, maybe having it thermally bonded to the case to get a better response.  It could have been mounted a little better, but I guess it does the job.

Circuit Board
Bead Thermistor
You may have a nagging feeling that something is missing.  A temperature logger that runs for 111 days should have some way to keep a stable time base, so there should be a real time clock somewhere, and sure enough, on the back, there's the expected 32 kHz watch crystal.  The traces from the crystal run into the chip on board assembly that contains the the driver for the LCD.

Another thing that I'm not sure about is how the thermistor is read, as the traces run into the chip on board.  I can think of two possibilities here, either there is an A to D converter that reads the thermistor and communicates the data to the micro-controller digitally, or there's a signal conditioning amplifier the feeds the signal to the on board A to D of the micro-controller.

18 comments:

  1. I also picked up one these from RG to see what it did.

    Have you been able to reset/reactivate it at all? Looks like it needs special software.

    ReplyDelete
    Replies
    1. No, unfortunately. I was hoping that it would be easy to reset, but no luck. There is software and it's expensive.
      I've since learned you can get similar one time use ones from China for $20

      http://www.aliexpress.com/item/T011-BSIDE-BTHX60D-Humidity-Waterproof-Single-Use-Mini-USB-Thermometer-Temperature-Data-Logger-Recorder-FREE-SHIPPING/32283662301.html

      Or reusable ones for about $25

      http://www.aliexpress.com/item/RC-5-USB-Temperature-Data-logger-Datalogger-Temp-Recorder-Internal-Sensor/32365239872.html

      So it wasn't worth spending too much time on. If you find out any more about them I'd love to know.

      Delete
    2. The good news for me is that the battery is a 1/2 AA and we use them at work for some of our other temp data loggers. We are now getting TempTale 4 USBs with a refrigerated delivery occasionally, so guess who'll be recycling the batteries?
      If anyone gets their hands on the software to re use these I'd be interested, I hate this throw away world!

      Delete
    3. Seems like such a waste. Good to see someone reusing parts of them.

      Delete
  2. Nice teardown.

    At work we go through about 40 of these a month, we do however send them back to our supplier who (i assume) resets and reuses them.

    I'll ask the folks in trials if they have access to the software to reset/reuse them.

    Interestingly most of ours (Medical cold chain) are 2-8 degrees C, 166 days, 30min delay, 15 min interval. Meaning extensive use of sleep modes.

    ReplyDelete
  3. I have held them. regretly only one use.

    ReplyDelete
  4. Hi, i have this logger too. Its have windbond chip for 500kb. How i can use this chip with usb? I would like to do usb flash drive.

    ReplyDelete
  5. I've been messing around with a couple of these units as well and figured I would share what I have discovered. If you short jumper #1, the unit goes into RESET mode. Unfortunately, I am unable to get past this reset mode currently.

    ReplyDelete
  6. Hi guys - check out www.enviroworld.com.au for a whole range of such loggers. Whilst we have disposable ones so far we never sold any as we hate the waste aspect also. We can do reusable for about the same cost as this Temptale one with software included for free. Happy to give you one to pull apart Grant as I really enjoyed reading how you analysed the other one.

    ReplyDelete
  7. I also have one of these, and should be able to get many more. It would be great to be able to re-use them. Mine is blue, with exposed screws.

    ReplyDelete
  8. I took of the battery and after re installing display stared flashing .But no response upon pressing the buttons

    ReplyDelete
  9. I get these at work also, working in a refrigerated warehouse for imported food. The software provides some info as shown here, in reference to one of the units that was received this morning:
    https://drive.google.com/open?id=0B-kZO6ydBLUwdEV4V0dxY3g4SE0

    ReplyDelete
  10. I have a lot of this useless unit but the battery I loved

    ReplyDelete
  11. There is this ftp server that has the TTMD sw - ftp://remo.agricom.cl/Drivers/Procesos/Sensitech/

    Perhaps you can use it.

    ReplyDelete
    Replies
    1. Thanks for the info. I no longer have one of these units, but I'll keep this in case I find one again.

      Delete