Inside a heat detector alarm.
Added 2019-03-25 05:25:48 +0000 UTCThis alarm differs from a traditional smoke alarm by ignoring the smoke and looking for a sudden heat rise instead. That makes it better suited to kitchens and theatre environments where haze is used.
https://www.youtube.com/watch?v=F070CWlaM7o
But there's something weird about the circuitry. A really odd use of a diode in a resistive divider that doesn't seem to make sense.
The detector is also lacking a bit of moisture and dirt protection that you'd expect to be used in its intended environments. Especially on the pads of the heat sensing thermistor itself.
Comments
It's a BiClive combolulation diode
Gordo
2019-03-31 13:46:21 +0000 UTCThat does sound viable. It's quite weird circuitry.
Big Clive
2019-03-26 12:40:18 +0000 UTCThey should rebadge them as cloudchaser-safe fire detectors.
Big Clive
2019-03-26 12:39:52 +0000 UTCI think we have a winner!
Charles
2019-03-25 21:38:09 +0000 UTCOoh, a smoke alarm for cloud chasing vapers....because setting off your smoke alarm every ten minutes gets old, fast.
Steven Raith
2019-03-25 20:35:44 +0000 UTCSince they left out circuitry for functionality mentioned on the packaging I guess there is no guarantee that the circuitry that has been fitted is correct i.e the Zenor diode.
John Russell
2019-03-25 19:34:40 +0000 UTCWe have one in our kitchen and can burn the toast as often as we like.
2019-03-25 18:46:36 +0000 UTCMaybe change in Mosfet / Zener leakage current balances change in thermistor current if temp of both rise together? Hence if only thermistor changes value (heated) then alarm sounds.
L. Brait
2019-03-25 15:33:13 +0000 UTCi have seed 10V Zenors start to conduct @ 9v .. mind you they were very shitty Zeners
God 420
2019-03-25 12:52:27 +0000 UTCI did some googling. The zener in reverse bias but below its breakdown is nearly a constant current device. (Shockley equation exponential part going to zero with increased negative voltage leaving the 1) That would stabilize the current through the thermistor. That could reduce the change in heating in the thermistor from the current and changes in battery voltage. It would make it linear on voltage instead of nonlinear on both voltage and current. Otherwise the thermistor would be heated differently by the sense current based on battery voltage. Just a guess from the sleep deprived and obsessive.
Nani Isobel
2019-03-25 11:38:17 +0000 UTCWas thinking same as Cleveland. Is there any hint that the board is also used in hardwired setups that includes external power supply? That might make sense for voltage protection?
2019-03-25 11:29:08 +0000 UTCIt's a 60V transistor. Much higher than the integrated circuit's rating.
Big Clive
2019-03-25 06:37:51 +0000 UTCThe zenor diode might be if someone made a 9VDC bus to power it or a few of them to pertext the device, just a random guess..lol
Cleveland Prescott
2019-03-25 05:50:05 +0000 UTC
