Weird component in thermal imager - help identifying it please ? - Page 1
Forum section: electronics / general

author: Fraser
author_rank: Super Contributor
timestamp: July 08, 2016, 12:54:38 pm
content: I have been repairing a FLIR MS224 thermal scope and whilst inspecting the PCB for damage I found a component that has me puzzled.The component looks opto- electronic but its position on the pcb makes no dense for that function. It is looking into a dark sealed casing. Thermal cameras have thermal sensors and I wondered if it was something like that but why in a clear case ?I will trace the PCB connections but doubt that will tell me what it is as it looks to connect directly to the microprocessor. Too many connections for a crystal and not a standard encapsulation. It is not faulty but I would love to know if anyone has seen something that looks like this and what it may be.Come on guys, put me out of my miseryFraser

author: Fraser
author_rank: Super Contributor
timestamp: July 08, 2016, 01:01:13 pm
content: update:bktemp has found a die that looks the same.http://media.digikey.com/Photos/AMS-Taos%20USA%20Photos/TSL2561T.JPGIt looks to be a optical sensor with a response similar to a human eye.Why would that live inside the front of a thermal scopes case I wonder. Odder and odder.Fraser

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 08, 2016, 01:03:04 pm
content: Definitely looks optical - Could it be something for a different product variant?Self-destruct if the case is opened ?

author: Fraser
author_rank: Super Contributor
timestamp: July 08, 2016, 01:11:54 pm
content: I have read the datasheet for the device bktemp detailed and I now have a good idea what it is for. Total overkill maybe but it would appear to monitor the rubber button backlight intensity as part of the power management of the unit ! The rubber buttons have a transluscent rear that the sensor monitors. The datasheet indicates that this is an intended use for the sensor to reduce LED backlit keypad power consumption.Over engineered me thinks but I will investigate its operation when the camera is built. Maybe the keypad only backlights in the dark ?That was a really fast component identification. Thank you bttempFraser

author: bktemp
author_rank: Super Contributor
timestamp: July 08, 2016, 01:28:29 pm
content: It may look over engineered, but using such a sensor is the easiest and smallest solution for measuring ambient brightness. If you need to measure the brightness for both indoor and outdoor conditions, you need the large dynamic range otherwise the sensor will either saturate as soon as it sees sunlight or read zero for indoor measurements. If you use a simple photdiode/phototransistor, you probably also need a logarithmic amplifier to squeeze the large dynamic range into a useful voltage for a low resolution ADC.Such a sensor is a nice low power solution for adapting illumination brightness to ambient conditions.I didn't recognize it immediately, but it looked familiar, because I had used this sensor before (in a different package)!

author: Fraser
author_rank: Super Contributor
timestamp: July 08, 2016, 01:32:12 pm
content: bktemp,I see your point.Many thanks for your helpFraser

author: Kilrah
author_rank: Unknown
timestamp: July 08, 2016, 02:20:02 pm
content: Quote from: bktemp on July 08, 2016, 01:28:29 pmStill makes it overengineered if it's for controlling a keypad backlight - saturating in outside conditions is not a problem since backlight is only useful in dark conditions.

author: bktemp
author_rank: Super Contributor
timestamp: July 08, 2016, 02:55:25 pm
content: Quote from: Kilrah on July 08, 2016, 02:20:02 pmMaybe, but it is still the smallest and easiest solution if you need to measure ambient brightness and your microcontroller does not have any ADC input.It is a bit more expensive than a phototransistor, but in those kind of products the margin is high enough to simply use the easiest solution to get the job done.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 08, 2016, 03:36:57 pm
content: Quote from: Kilrah on July 08, 2016, 02:20:02 pmI disagree. It's not trivial to make a sensitive, consistent light sensor that ignores IR. Using an off-the-shelf part that's specifically designed to sense light with eye response is an entirely reasonable decision, minimises design effort, and as this is an expensive product, it really doesn't matter if the sensor costs 30 cents or 3 dollars.

author: Kilrah
author_rank: Unknown
timestamp: July 08, 2016, 03:39:10 pm
content: Quote from: mikeselectricstuff on July 08, 2016, 03:36:57 pmHaven't we had that on every smartphone for a few years now?But yeah I get the point.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 08, 2016, 06:56:59 pm
content: Quote from: Kilrah on July 08, 2016, 03:39:10 pmer, yes, and it probably uses a device just like this, maybe smaller & cheaper