Old Laptops as Secondary Monitors | Hacker News Reader

Old Laptops as Secondary Monitors

rgoswami.me

91 pointsHaoZeke44 comments

Windows has a built in "project" functionality where you can use any other windows device as a secondary screen - not only it's super easy to use(press win+p, select the device, done) it's also very very smooth, and the other device appears as a native secondary screen in all settings panels.

The only limitation here is that it's WiFi only, and only on devices with an Intel CPU as it's using Miracast underneath. But I use a £29 Tesco tablet with a crappy Atom CPU for this and it's fantastic as a portable secondary screen that works without any cables and literally takes 2 seconds to set up.

Can you link the tablet?

It's this one, but I don't think they are available anymore:

https://www.amazon.co.uk/Tesco-Connect-Intel%C2%AE-Flash-Dri...

Only limitation? ...

It is amazing to me that stuff like that is included in an operating system.

Very cool, but at the same time pretty much unusable then. I'm not gonna choose CPU vendor because of that. And wifi? Yeesh.

If you want to project from desktop PC to laptop one problem is that not all WIFI adapters support this. Seems to be the feature that is needed is WiFi-Direct [1].

At least some RealTek chips support this, for example RTL8192CU. I got it working by ordering cheap (€4.79, delivered) USB-WIFI stick from eBay [2].

[1] https://en.wikipedia.org/wiki/Wi-Fi_Direct [2] https://www.ebay.com/itm/300M-USB-RTL8192CU-Wifi-Adapter-pas...

Using older laptops as secondary monitors instead of a tablet like iPad might have additional advantage of protection against potential battery problems as laptops are generally protected against constant charging issues and many older ones also function without a battery.

My iPad got its battery bulged within a year after using it as secondary display[1]. I'm not going to trust devices with battery for applications involving constant charging anymore, at least not the ones without removable batteries or provide greater control over hardware (Pine Tab?).

[1] https://twitter.com/heavyinfo/status/1302310594423345152

No conclusion can be made from your sample size of one. Such battery issues may arise with any device, plugged in or not.

As the sibling says, I'm not sure you can conclude that battery management is faulty in the ipad (and in tablets / phones in general) while laptops are (generally) well protected.

My own testing shows something different:

* 4 yo MBP: got a battery bulge

* 4 yo iPhone: No bulge

* 5 yo Samsung tablet: No bulge

* 3 yo Samsung GS5 phone: bulge

All devices are plugged in practically all day long.

I think that the actual factor is heat management. The MBP is my main computer. The bulge developed around the release of mac os high sierra when for some reason the external GPU was running full tilt and the computer would get pretty hot pretty often. Changed the battery after the heating situation subsided, no bulge since. That was 2.5 years ago.

Ditto for the GS5 which I would often use for wifi connection sharing and would also heat up quite often.

The tablet and phone both sit around doing nothing all they long so they basically never heat up.

If we're talking about laptops with heat issues, discussing macbooks seems pretty pointless. Most business-class laptops are clearly designed to survive being plugged in for a few years without getting a beer belly.

The point wasn't to discuss the macbook's heat issue, I think those are rather well known around these parts.

My point was that the beer belly wasn't caused because the laptop was plugged-in but because it got hot.

So barring issues with botched software as was the case of my macbook, I don't think some devices are better suited than others to be plugged in all the time. Especially for doing something as lightweight as being used as en external monitor. I've been using that mbp for 2.5 years all day every day, plugged in, for actual work (among which compiling stuff) and the "new" battery is still fine.

The point is they aren't. Mac batteries fail too. Batteries are consumables.

The iPad Air 2 complaint was a 6 year old device. It needs a battery replacement. This is normal lithium battery longevity.

Point taken, but now tell me which of those was easy to repair?

I'm not sure what the point of the question is. If it's that tablets and phones are harder to service, it's a fairly well known fact. Although some non-apple laptops are fairly hard to service, too. I'm thinking of some HP Elitebook models we have at work (not sure about the model number).

However, my point was that the issue wasn't related to the devices being plugged in all day long but to the overheating. I don't think a device used as a display would be particularly taxing on the CPU to have it heat up. For example, I've used both the tablet and phone to watch videos for extended periods (>2h) and they got barely warm.

In my case I don't think it was related to overheating at all as apart from being charged all the the time it was used utmost 1 hour a day for YT although battery did loose its ability to retain charge within couple of months(from being perfect) once I started to use it as secondary monitor.

This happened with my iPhone 5c too, which I used for displaying terminal(But removed before bulging).

Newer Apple devices/iOS supposedly prevents overcharging, that might also explains Sidecar integration with macOS.

I can't comment on the behavior you noticed other than saying that the devices seem defective to me, but I may be wrong.

> Newer Apple devices/iOS supposedly prevents overcharging, that might also explains Sidecar integration with macOS.

I'm not an expert on Li-Ion batteries, but my understanding is that this is a separate issue.

What this does ins't preventing overcharging, it just charges the battery less than what it's fully rated for, the idea being that you'll probably not need the full charge, hence the description of that iOS feature saying it tries to learn when you use the device to know when it needs to be fully charged.

My understanding is that LI-Ion batteries may see less degradation if they aren't always charged to 100% of their rated capacity, especially if this capacity is "pushed too far", for example by manufacturers looking to extract the longest possible advertised battery life for a device with the smallest possible size. This is something that I expect most phones and tablets to attempt to maximize.

Overcharging would mean, to me, attempting to keep on charging the battery once its rated charge has been reached. The point of my original comment is that I don't believe that leaving a device plugged in after it says the battery is at 100% would keep on trying to charge the battery, as was the case for example with "dumb" NiCd and NiMH chargers. The battery control circuitry would stop charging once it deems the battery full, so leaving the device plugged in would simply have it use the power from the mains instead of from the battery. Which should actually help with battery aging, since it eliminates "useless" cycles (useless because the device doesn't need to work on battery since mains power is available).

A problem is that almost all smartphones/tables don't support charge limiting feature. Business laptop like ThinkPad and competitors support to set max % of battery charging rather than 100%. It significantly increases battery life.

Any idea why that is? Somebody on Quora suggested it was mostly about people not being able to figure it out, which I'd believe. Plus some guesses about the way people just change their phones frequently enough for modern batteries anyway.

I did find somebody who had a very clever hack:

https://chargie.org/

which basically puts a physical kill switch on the charger, along with an app to measure current battery level, without having to root the phone.

I have also no idea. Possibly we can say it's just lazy or aiming planned obsolescence.

Chargie looks cool project! I'll buy it.

If any mainstream unix-like OS kept the promise that "everything is a file" (like Plan9), adding a secondary monitor from another pc could be easy like:

    mount /dev/screen2 user@remotehost:/dev/screen1

That is so easy it makes me want to cry

There are absolutely no security considerations there, though.

Honest question: what stops any unix to achieve the same thing through a similar interface?

it's conceivable one could build a Direct Rendering Manager kernel device that is a virtual software display, that stores buffers & makes them accessible over the network. It might expose a vnc connection that the other laptop can log in to.

Mount in Linux is only for filesystems though, so it'd never look & join with the same kind of pervasive, ubiquitous any-interface slickness that plan9 had.

You could also use tools like Synergy or input director, they make it so that you can use 2 pcs with one set of keyboard and mouse. It works great and you can even game with it, very low latency. The benefit is that you have a separate pc, so you could use Windows and Linux etc.

I would recommend the fork, Barrier, over Synergy. Synergy had bad practices with their 2.0 release a few years ago, so much so that they were forced to go back to working on the 1.x versions.

Details please?

For the release of the 2.x versions: instability, removal of functionality for the same license, lack of downgrade rights[5], required connection to Symless servers[1][2] (including storing machine profile data). Compounded by the upgrade fee.

This all happened a few years ago, and given their downgrade partnership with LinusTechTips[6] plus community backlash, they are probably okay as long as you only get the 1.x versions.

Still, with those issues, and for a program that is basically a very useful cross-computer keylogger, I would think twice before trusting Symless.

Barrier has it's bugs, but does it's simple job of keyboard/mouse/clipboard sharing and without the shady practices.

To be clear on where they stand in relation to one another: Barrier is a strictly FOSS fork of an older 1.x version of Synergy. Synergy's 1.x source code is FOSS (I don't know if 2.x is/was), but they require a paid license for their binaries; Barrier has free binary releases.

More sources: [1]https://members.symless.com/forums/topic/3829-is-synergy-20-...

[2]https://members.symless.com/forums/topic/6190-synergy-stoppe...

[3]https://members.symless.com/forums/topic/4863-couldnt-connec...

[4]https://linustechtips.com/main/topic/878226-psa-synergy-20-i...

[5]https://superuser.com/questions/1367713/are-programs-like-sy...

[6]https://www.youtube.com/watch?v=D9u1vX-pvLs&t=8m50s (part of a project video, I skipped to the relevant part)

Yeah I bought a license some years ago, 1.x still works well. Just heard of Barrier though. Might try it out.

I paid for 1 and 2, but switched to Barrier a few months back. It’s been great. Like the older version, it just works.

Definitely give Barrier a swing.

Ah, it didn't make it into the post but I tried them and felt like the plain peripheral share described in the post was smoother and needed less setup.

When my employer used to sell a raspberry pi kit, we'd occasionally get people asking if they could just plug the hdmi cable from the pi into a laptop hdmi port. Because, the cable is bidirectional, why wouldn't the signal be bidirectional?

Well, depends on the people. This used to work with iMacs, although with display port instead of hdmi.

https://www.lifewire.com/use-imac-as-monitor-with-target-dis...

The big laptop manufacturers each have one or two mobile displays these days, e.g. stuff like the Thinkvision M14, which is basically just the display portion of a 14" thinkpad. These are USB-C only though, so compatibility is rather limited and getting these to work on something without USB-C requires about 100 € in adapters (Wacom Link - 75 €, USB-C PSU - 25-30 €).

Asus Zenscreen and others have build in displaylink, so it works over USB3 with $3 adapter.

I was using a ThinkVision M14, but my USB C port died on me.

If USB-C isn't an option, there are portable gaming monitors with HDMI inputs as well that are slightly cheaper, like the Gaems m155.

Or you can strip out the LCD and attach it to a LCD driver board for $20.

I also prefer this. Removes the extra bulk, and adds a simple HDMI input. I think smaller LCDs can even run entirely off 5V (USB) power.

and then spend 15 minutes putting my fingers on ice and 5 days with a painful blister because I've just soldered my finger accidentally.

Some of us are not as skilled.

Wear gloves.

have you ever successfully soldered BGAs or other tiny connectors with heat resistant gloves?

I'm not as skilled, as I've mentioned. For me the software screen cast solutions are way more practical.

You’ll find for most of them it involves just plugging in a ribbon cable, no soldering needed =)

Or... if your old laptop doesn't boot up, you can (apparently) pull out the laptops display panel, attach it to a control board and use just the display independently.

This DIY perks video was eye opening for me: https://www.youtube.com/watch?v=CfirQC99xPc .

What I'm personally looking for is the ability to create/grab virtual displays from MacOS. I'm guessing that Luna Display dongles are EDID dummy plugs that are used also to trigger GPUs to render for VFIO setups. I think those dummy plugs can also work for a Mac. Haven't tried that though.

https://shop.astropad.com/products/luna-display

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