How does laptop lid position sensing work? - Page 1
Forum section: electronics / repair

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 29, 2020, 07:16:18 am
content: I use an external monitor with my laptop without its own screen (lid closed). Every time to turn it on I have to lift the lid, press the power switch and close it. I found it a hassle so wanted to have an external power button (quite often I have other stuff on it, e.g. another laptop. Actually, I wanted it to disappear from the desktop to save space. I can put it below the desktop and leave only the power switch somewhere as its human interface). I did this today - external leads work well but only limited to powering on the machine - it does not complete the boot process (only if I lift the lid again). I changed the power setting in Control Panel (setting it to "do nothing" if closing the lid).Seems like I have to hack the lid sensing mechanism to have it work the way I want. I Googled but found no answer on how the lid position sensing works for this model or similar. It's a Lenovo E560.Some webpages suggest magnetic sensing for some models.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: March 29, 2020, 09:04:32 am
content: Get some magnetic viewing film from ebay and run it round the edge of the screen to find the magnetOr run a magnet around the edge of the computer and see where it is when the laptop goes to sleep. You’ll find some sort of sensor on the board in that position. Never looked at what type is used, maybe a hall sensor, maybe a standard reed switch

author: mikerj
author_rank: Super Contributor
timestamp: March 29, 2020, 09:15:19 am
content: Most always it's a magnet in the lid and a hall sensor in the base on modern stuff (used to be mechanical switches), removing the bezel from the display would confirm this. Sensor likely mounted on the top part of the base that you haven't shown.Note that the fan air intake is on the top, make sure there is sufficient airflow with the screen closed or it will be overheating/throttling.

author: JKKDev
author_rank: Regular Contributor
timestamp: March 29, 2020, 09:56:43 am
content: Here's a thought. Remove the screen assembly altogether. I think the only other thing in the screen assembly apart from screen and camera are the bluetooth antennas. If you don't need BT you're golden.No overheating, no lid problem, lower power consumption

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 30, 2020, 09:17:01 am
content: Quote from: JKKDev on March 29, 2020, 09:56:43 amThis is an option but a bit too radical to me for now.First I may need the screen occasionally. Second, I still want to have BT although its ALMOST useless - I've been struggling to get it connected with my Bose Soundlink (headset) but never with a success (the same with my Toshiba)!Thanks.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 30, 2020, 09:19:34 am
content: Quote from: mikerj on March 29, 2020, 09:15:19 amThanks. Anyway, I have to reopen the whole thing another time. It's a bit hassle but it's now much easier (and I'm more confident) than the first time tearing it apart.Perhaps I can find a reed switch or a hall sensor to detect where the magnet is.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 30, 2020, 09:21:08 am
content: Quote from: PTR_1275 on March 29, 2020, 09:04:32 amYes, using a magnet I may be able to locate the sensor (if it rely on a magnet). Thanks.

author: senso
author_rank: Frequent Contributor
timestamp: March 30, 2020, 02:39:38 pm
content: Never seen anything on laptops besides Hall sensors, most likely the sensor is near the power button, in that auxiliar board and the magnet will be in that zone of the bezel, in fact U1 to the right of the power button seems like the hall sensor, turn the laptop on with the display open and get a magnet near U1 and if the display disables itself thats the sensor.The WiFi antennas are also on the display/lid.Also, your fan is a bit dusty, your heatsink might be in need of a cleanup and a repaste.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: March 31, 2020, 02:05:34 am
content: Quote from: senso on March 30, 2020, 02:39:38 pmThanks. That gives me more certainty. I had a clean of the fan after seeing it dusty (though not thorough).

author: TonyBe
author_rank: Regular Contributor
timestamp: March 31, 2020, 07:50:45 am
content: Hi,without ever opened it: in case of my Lenovo T580, there it a magnet near the touchpad. When i hold a metallic pen close up, it holds on to it. Therefore i really think, that the sensing is made through a hall sensor in the lid itself (most likely near the Webcam). That also makes sense, since the sensor should only react if the lid is closed all the way down. Placing the sensor as far away from the hinge as possible is the easiest way to do this properly (without having to match tight tolerances and complex elektronics with comparators and stuff like that).RegardsTony

author: max.wwwang
author_rank: Frequent Contributor
timestamp: April 01, 2020, 04:29:49 am
content: Quote from: TonyBe on March 31, 2020, 07:50:45 amMakes good sense. Why I'm seeking advice here is because of I want to get as much knowledge/certainty as possible before I even open it again. Thanks.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: April 01, 2020, 07:42:32 am
content: @ Blueskull is right. There is a small strong magnet in the bezel opposite U1 on the daughter board next to the power switch.What's strange is -- having removed the magnet, it still refuses to start unless lifting the lid!

author: JKKDev
author_rank: Regular Contributor
timestamp: April 01, 2020, 02:43:36 pm
content: If the screen still won't turn on after removing the magnet then there has to be another way that the laptop knows of the screen position. Try holding the whole laptop in the orientation that the screen would normally be in (this would point to an IMU in the screen, which could be used to detect the screens orientation - never heard of this approach but the idea came to mind)In regards to the hall sensor:I've just gone over testing some hall sensors on HP laptops. What you are looking for is a SOT-23 package chip that has the single pin on ground and the two other pins should have 3.3V when the lid is open (even when the laptop is off, no battery, just the charger connected - this is in the HP case). If you put a magnet near the package one pin should stay at 3.3V while the other one drops to 0.If you want to you could replace the reed switch with a normal switch between the two pins that aren't on ground and this way you can turn the screen on and off whenever you want.