1
\$\begingroup\$

The PCB is the wireless (outside) sender unit for an inside/outside thermometer. I want to create a temperature probe from this PCB so that I can measure a temperature in a very specific place. I need help identifying the temperature sensor component on the PCB. I have had no luck pinning it down with freeze spray. Maybe it's the pair of transistors?

(you can view the images at high resolution by doing right-click > view image) PCB1 PCB2

Following on from the accepted answer (thanks!), I tried moving the component out into a probe.

modified PCB probe in hot water tank port

Temperature agrees with my current wired solution. probe working

\$\endgroup\$
  • \$\begingroup\$ A schematic would help, even with the IC blank. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 12 '15 at 19:50
  • \$\begingroup\$ And one of the transistors is for the DC/DC converter, the other is for the transmitter. \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 12 '15 at 19:52
  • \$\begingroup\$ It's almost certainly that cylindrical object under the IC. If you can provide the IC markings (they are invisible in the photo) the part number can probably be Googled. \$\endgroup\$ – WhatRoughBeast Dec 12 '15 at 20:57
  • 1
    \$\begingroup\$ @WhatRoughBeast The shiny metallic cylinder looks more like a crystal to me. It even has got a pair of capacitors. \$\endgroup\$ – Nick Alexeev Dec 12 '15 at 21:05
  • \$\begingroup\$ @NickAlexeev - That was my thought originally. But then what is in the can at bottom center of the upper photo? \$\endgroup\$ – WhatRoughBeast Dec 12 '15 at 22:11
4
\$\begingroup\$

The following 4 principles of temperature sensors are most common: thermistor, thermocouple, resistive temperature detector (RTD), silicon bandgap.

  • Thermocouple and RTD. Not visible on the photos.
    In addition, they are rarely found in consumer goods that measure around human temperature range. Thermocouples and RTDs require signal conditioning and excitation circuitry, which increases cost.
    prediction: Unlikely

  • Silicon bandgap temperature sensors are found in consumer goods sometimes. They are packaged like transistors or ICs. They may be embedded inside microcontrollers or ASICs.
    prediction: Plausible

  • Thermistor produce a strong signal and don't require much signal conditioning. It's a cost-effective way of measuring temperature in the human range. These are used in consumer goods.
    prediction: Plausible

enter image description here

Hit with chill spray, see what happens.

\$\endgroup\$
  • \$\begingroup\$ I vote for the thermistor, too, because it looks exactly like an NTC we used. It seems to build a voltage divider with the R to the left, supplied by the IC via the two tracks with test points. The track left of the R is the read out voltage. \$\endgroup\$ – sweber Dec 12 '15 at 21:12
  • 2
    \$\begingroup\$ See the two test points near it? I think they are a dead giveaway that there is something of interest. \$\endgroup\$ – PlasmaHH Dec 12 '15 at 21:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.