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TerryC65
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I'm looking for a reasonable miniature HDMI monitor

Wed Feb 27, 2019 4:35 pm

I have been quite a lot of work recently using Pi Zeros to record sensor readings and control pumps and valves in a model river system at our local Model Town. By and large, I'm able to do quite a lot on site by using SSH to log into the individual Pis and SCP or FTP to copy files to and from them. However, the thing that I miss is being able to see the console messages when the Pi boots up and starts running the control / monitoring program.

Previously, I've lugged my old 21" VGA monitor along and using the appropriate adaptors; with that I can watch the Pi booting and view the screen messages as they occur. However, this is a bit of a faff; the mains lead and the video lead are stiff and heavy and I need a table to put the monitor on - this isn't always easy in an inaccessible corner of the site.

To date, we have three Pis running in this system, but we are now ready to implement the full system and will eventually have around 15 Pis all told. Therefore, to make life easier, I'm in the market for a miniature HDMI monitor; something between 7 and 10".

Does anyone have any experience with using a cheap miniature HDMI monitor with a Pi and can make suggestions of what to look out for? BTW, I don't necessarily need the monitor resolution to be good enough to run the desktop, but it would be nice. I also like cheap, but appreciate that the cheaper ones may have problems, so advice on any pitfalls would be appreciated.

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scruss
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Re: I'm looking for a reasonable miniature HDMI monitor

Wed Feb 27, 2019 5:52 pm

good, cheap and small is kind of a "pick any two". Small and HDMI tends to mean Lilliput video monitors and clones, which are not cheap. Cheap small displays tend to be composite and grotty even for command line work.

There are millions of 15 and 17" monitors at computer surplus places right now for less than their disposal cost. Many of them are DVI and VGA only, but HDMI to DVI is a cheap adapter. Bigger than you wanted, I know, but I'd be shocked if you paid £10 for one.
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LTolledo
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Re: I'm looking for a reasonable miniature HDMI monitor

Wed Feb 27, 2019 10:14 pm

I have a 7" HDMI monitor that came in with my very first RPi set.
there is no brand/maker written anywhere

still using it for test setup and now connected to another SBC being used as a media player.
I do have to change the resolution to display fonts bigger as I have trouble seeing small fonts.

Then I also got myself a 10" HDMI screen with built-in speaker. Definitely much better than 7".

both were bought from Amazon.
similar looking one like this
https://www.amazon.com/Loncevon-10-1-Po ... 378&sr=8-5
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Imperf3kt
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 6:07 am

Waveshare makes reasonable quality HDMI screens from 4 inches, to over 10 inches.
May be worth checking out?
There are dozens of clones across the internet too.
55:55:44:44:4C
52:4C:52:42:41

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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 7:24 am

scruss wrote:
Wed Feb 27, 2019 5:52 pm
good, cheap and small is kind of a "pick any two". Small and HDMI tends to mean Lilliput video monitors and clones, which are not cheap. Cheap small displays tend to be composite and grotty even for command line work.

There are millions of 15 and 17" monitors at computer surplus places right now for less than their disposal cost. Many of them are DVI and VGA only, but HDMI to DVI is a cheap adapter. Bigger than you wanted, I know, but I'd be shocked if you paid £10 for one.
I appreciate the thoughts, but using an old 15" monitor with a HDMI / VGA Adaptor is not much better than what I'm using at the moment. The real problem is the weight and the unwieldiness caused by the bulk of the thing and the stiffness of the cabling.

When I said I like cheap, that was slightly tongue in cheek. If I end up discovering that I need to pay £100 + to get a monitor that actually works properly with an RPi, then I may abandon the idea. However, if I get a reasonable number of responses that say that a 10" HDMI Monitor with low voltage adaptor for around £50 provides a reasonably acceptable display in the shell, I would probably get one. If such a beast provided a usable desktop display, then I'd be happy.

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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 7:29 am

LTolledo wrote:
Wed Feb 27, 2019 10:14 pm
Then I also got myself a 10" HDMI screen with built-in speaker. Definitely much better than 7".

both were bought from Amazon.
similar looking one like this
https://www.amazon.com/Loncevon-10-1-Po ... 378&sr=8-5
Thanks. I note that the UK price is is almost the same number in GPP as the US price in dollars :x

It looks interesting though.

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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 7:36 am

Imperf3kt wrote:
Thu Feb 28, 2019 6:07 am
Waveshare makes reasonable quality HDMI screens from 4 inches, to over 10 inches.
May be worth checking out?
There are dozens of clones across the internet too.
Thanks. The 10.1 inch version is probably outside my budget and the 7" one is at the bottom end of my size range, although at 1024x600 resolution it might still do the desktop OK. I would need a case for my requirement, which adds a bit to the price.

I'd be interested to hear from someone who has a small monitor that is still available to purchase new from the usual suspects.

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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 8:27 am

TerryC65 wrote:
Wed Feb 27, 2019 4:35 pm
However, the thing that I miss is being able to see the console messages when the Pi boots up and starts running the control / monitoring program.
You could do that with a serial console cable. From a serial terminal on another computer you can see the console output, including boot messages, and even login without a network connection. I use cheap CP2102 USB-TTL (3.3V) adapters I get from eBay for less than $2.
Image

TerryC65 wrote:
Thu Feb 28, 2019 7:36 am
Thanks. The 10.1 inch version is probably outside my budget and the 7" one is at the bottom end of my size range
If you can live with 5 inch, this one is pretty affordable.
Image
Picture is link...
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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 8:39 am

HawaiianPi wrote:
Thu Feb 28, 2019 8:27 am
You could do that with a serial console cable. From a serial terminal on another computer you can see the console output, including boot messages, and even login without a network connection. I use cheap CP2102 USB-TTL (3.3V) adapters I get from eBay for less than $2.
I couldn't do that since many of my GPIO pins and in particular the ones shown in your image, are used to power / read sensors. However, if I can get a console through a USB adaptor on the Pi to another USB adaptor on my laptop, then I could have the answer.

HawaiianPi wrote:
Thu Feb 28, 2019 8:27 am
I'd have to get it shipped, since it doesn't appear to be available in the UK. I'd also rather have something a little bigger. Thanks for the suggestion though.

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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 9:20 am

How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
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Gavinmc42
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 11:03 am

15 Pi's, sounds like you are becoming a network administrator.
My Linux knowledge has mostly been single Pi based but I seem to remember something about logging to an admin Linux box.
Google found this first, jogged the memory about logs file redirection.
ttps://www.eurovps.com/blog/important-linux-lo ... onitoring/
Grab some books on Linux Administration?

Get bigger box with 4K output, 4K TV and see all the log files at once?
With my fading eyesight I am tending to smaller screens much closer, Mobile phones have become my screens.
Re-purpose some tablets and old phones?
Is there an app for this?
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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 11:27 am

Gavinmc42 wrote:
Thu Feb 28, 2019 11:03 am
15 Pi's, sounds like you are becoming a network administrator.
Not really, but I have been a Linux user at home and (to a lesser extent at work) for around 20 years. My home router hosts a heterogeneous network of Windows, Linux, Android and entertainment devices, so I'm used to keeping an eye on a network. However, the Model Town's system is a bit different (see below).
Gavinmc42 wrote:
Thu Feb 28, 2019 11:03 am
My Linux knowledge has mostly been single Pi based but I seem to remember something about logging to an admin Linux box.
Google found this first, jogged the memory about logs file redirection.
ttps://www.eurovps.com/blog/important-linux-lo ... onitoring/
Grab some books on Linux Administration?
Not all of the logs mentioned in that link are relevant to us. The system is using a private wired network and the various Pis are all connected as clients to our 'Master Pi'. We create our own log file to record the activity in the system, including levels and the state of the various valves etc. I only wrote a small part of this software and the networking part in particular was written by another team member. There is (currently) a wireless router connected to the system to make development a bit easier, but there is no connection to the Internet.

Eventually, we intend to connect the whole system to an IP65 Monitor so that staff and Visitors can see what's going on, but there will still be no direct connection to the Internet.
Gavinmc42 wrote:
Thu Feb 28, 2019 11:03 am
Get bigger box with 4K output, 4K TV and see all the log files at once?
With my fading eyesight I am tending to smaller screens much closer, Mobile phones have become my screens.
Re-purpose some tablets and old phones?
Is there an app for this?
All good ideas, but I'm not sure what is feasible. If anyone knows an easy way to view the main terminal of a Pi through a phone, tablet or laptop, I'd love to hear of it. (I am still thinking about how I could connect via a serial link as mentioned by HawaiianPi above.)

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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 11:31 am

TerryC65 wrote:
Thu Feb 28, 2019 8:39 am
I couldn't do that since many of my GPIO pins and in particular the ones shown in your image, are used to power / read sensors.
The specific pins you need are:
  • Pin #8 (GPIO 14 TXD)
  • Pin #10 (GPIO 15 RXD)
  • Any ground pin.
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 11:40 am

HawaiianPi wrote:
Thu Feb 28, 2019 11:31 am
The specific pins you need are:
  • Pin #8 (GPIO 14 TXD)
  • Pin #10 (GPIO 15 RXD)
  • Any ground pin.
Hmmm. Your picture also shows a connection to 5 V?

Also, I've stumbled across this https://www.raspberrypi.org/forums/view ... 76#p526976, which suggests that I need (and should use) 3.3 V, (which is used to power elements of the interfacing to every Pi in the system).

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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 11:41 am

Use a wireless Pi as a webpage server.
Put the address up and vistors can log on with their phones?

I've recently been playing with Bluetooth LE, I think this is called Eddystone beacons.
I think even microbits can transmit the URL's via BLE.
You might be able to use the same method but with secure access to check logs?

BLE has a serial mode that works like wireless UART.
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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 11:52 am

Gavinmc42 wrote:
Thu Feb 28, 2019 11:41 am
Use a wireless Pi as a webpage server.
Put the address up and visitors can log on with their phones?
We actually have a TP-Link WiFi Outdoor AP which is serving up a Kiddies Quiz and Audio Guides through a Pi 3 at the moment. One plan is to link into this to provide the interface for the River System Visitor Display, so we can have it somewhere convenient for the Visitors, (but not needing to be near to the Cat 5 Ethernet). The intention is that the Visitors only get access to the info, the staff get access to the controls and the developers go in via the wired network.
Gavinmc42 wrote:
Thu Feb 28, 2019 11:41 am
I've recently been playing with Bluetooth LE, I think this is called Eddystone beacons.
I think even microbits can transmit the URL's via BLE.
You might be able to use the same method but with secure access to check logs?

BLE has a serial mode that works like wireless UART.
Very interesting. I'll look into that, although I have no problem checking logs over SSH from my phone or laptop using the temporary Wireless AP connected to the wired network as mentioned above. Thanks for your suggestions.

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scruss
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 3:55 pm

TerryC65 wrote:
Thu Feb 28, 2019 11:27 am
If anyone knows an easy way to view the main terminal of a Pi through a phone, tablet or laptop, I'd love to hear of it.
I doubt you'd see the console boot messages — certainly not the very first ones — but VNC Connect (free with Raspbian) has direct capture mode that can redirect the framebuffer to a VNC client.
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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 4:07 pm

scruss wrote:
Thu Feb 28, 2019 3:55 pm
I doubt you'd see the console boot messages — certainly not the very first ones — but VNC Connect (free with Raspbian) has direct capture mode that can redirect the framebuffer to a VNC client.
Unless I've completely misunderstood, that redirects the desktop, not the console. We have to run our software in the shell because the Pi Zero hasn't got enough grunt to handle all of the workload and run an X session as well.

It would probably work if we were using Pi 3s, but that would cost us approx $25 dollars more per device or nearly $400 for the finished system (not to mention the inflated power budget).

The Pi Zero does a grand job of monitoring and recording sensor values and twiddling the odd control line, but it's pretty slow in the desktop.

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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 5:33 pm

from my link:
VNC Server can remote the screen of Raspberry Pi apps that use a directly rendered overlay, such as Minecraft, the text console, the Pi camera module, and more
(emphasis mine)
So yes, the console.

I run the desktop from a Zero via VNC too. Fast it isn't but it works reliably.
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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 5:39 pm

scruss wrote:
Thu Feb 28, 2019 5:33 pm
from my link:
VNC Server can remote the screen of Raspberry Pi apps that use a directly rendered overlay, such as Minecraft, the text console, the Pi camera module, and more
(emphasis mine)
So yes, the console.
I missed that. I'll have to give it a go.

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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 5:52 pm

Yes, it works. It isn't tremendously fast. Make sure to set the screen resolution in raspi-config otherwise it may not be usable.

This from a headless Raspberry Pi Zero W on a breadboard:
Screenshot from 2019-02-28 12-47-13.jpg
vnc console mode from a raspberry pi zero
Screenshot from 2019-02-28 12-47-13.jpg (58.91 KiB) Viewed 2108 times
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Re: I'm looking for a reasonable miniature HDMI monitor

Thu Feb 28, 2019 10:19 pm

TerryC65 wrote:
Thu Feb 28, 2019 11:40 am
Hmmm. Your picture also shows a connection to 5 V?
Yes, in that example shot I was using the USB-TTL adapter to power the Pi Zero. Note that there is nothing connected to the Pi0 power port. You don't need the 5V pin for serial I/O.

which suggests that I need (and should use) 3.3 V
The CP2102 outputs 3.3V TTL.
My mind is like a browser. 27 tabs are open, 9 aren't responding,
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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Fri Mar 01, 2019 9:59 am

HawaiianPi wrote:
Thu Feb 28, 2019 10:19 pm
Yes, in that example shot I was using the USB-TTL adapter to power the Pi Zero. Note that there is nothing connected to the Pi0 power port. You don't need the 5V pin for serial I/O.

The CP2102 outputs 3.3V TTL.
Thanks. I completely misunderstood how the device works. Now, AIUI, the USB adaptor gets it's power from the laptop / PC and the Pi powers the data on the UART pins from its end.

I've just ordered one from eBay and will give it a try. If need be I can move functions from those GPIO pins, since I've only built three of the 15 installations to date.

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Re: I'm looking for a reasonable miniature HDMI monitor

Sat Mar 02, 2019 11:32 am

Make a RS485 network instead of 232?
Not full duplex but that might not matter if you have the right protocol.
You will get faster data speeds and it only needs a 8pin dip chip as an interface.
What is the fastest UART speed anyway?

Zero's don't have Ethernet and the Zero W are twice the price.
Zero's + RS485 network. You can even use Cat 5 and put power over it.
On my list of things to try with Pi's.
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TerryC65
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Re: I'm looking for a reasonable miniature HDMI monitor

Sat Mar 02, 2019 11:55 am

Gavinmc42 wrote:
Sat Mar 02, 2019 11:32 am
Make a RS485 network instead of 232?
Not full duplex but that might not matter if you have the right protocol.
You will get faster data speeds and it only needs a 8pin dip chip as an interface.
What is the fastest UART speed anyway?
I don't need fast, the Unix terminal was never fast and I just want to view the console boot messages and the output from our software.
Gavinmc42 wrote:
Sat Mar 02, 2019 11:32 am
Zero's don't have Ethernet and the Zero W are twice the price.
Zero's + RS485 network. You can even use Cat 5 and put power over it.
On my list of things to try with Pi's.
No Zeros don't have Ethernet, but it is still cheaper to buy a Zero + a cheap USB / Ethernet Adaptor, than it is to buy a Pi 3. The Pi 3 is an excellent piece of kit, but we don't need the performance boost and the physical size would have made packaging a bit more difficult.

When we did the system design for this project, we looked at many options for communication. We decided against RS485 because it added complexity to the Interface design and we would have had to deal with addressing in our software. We chose Cat 5, because it is very reliable, (eg not subject to drop-outs because a Visitor is standing in the wrong place) and can be used to carry a lot of data with simple well established protocols, right down to the addressing. BTW. I'm not talking about my desire to view console messages now, I'm talking about how the 15 Pis communicate with each other.

We originally powered out first remote and it's associated sensors using PoE. In the end it was decided to drop that because the Gate Valves in the system need more power than can be safely put down a length of Cat 5 (the PoE spec is very specific about this). Also, although you can buy cheap PoE Injectors and Splitters on eBay, they don't really meet the PoE spec. To do that you need to put 48 V on the cable at a maximum of 400 mA. At the receiving end you then have to convert the 48 V to useful voltages, such as 5 V for the Pi and 12 V for the Sensors and Gate Valves for our case. In the end it was easier and cheaper to just put a high current 12 V PSU adjacent to each Pi and / or Gate Valve and derive all the power from that.

By all means try these things, but bear in mind that they have their limitations. However, you may not have such onerous requirements as we have :)

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