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1  Screen Tablet malarky / Monitors / Re: Assorted selection of problems with a universal LVDS controller on: November 07, 2016, 03:13:59 PM
The enable output from the MT6820-B is 5V, I believe the LED driver board requires an enable of 3V maximum. It worked well for a short while until it failed causing 10x more current to pass through the resistor and burn it out. I measured a max of 120mA going through the 100Ohm resistor before I realized that the ME15N10 FET had failed. I'm not completely sure what happened to the ME15N10 transistor as it should've been able to handle +/- 20V at the gate, however it did indeed fail.

The reason I suspect I originally used the IRL540N and inverter tester was so that I had a better control of the enable and dim voltages in case of compatibilty issues. It is still true that the IRL540N was a bit redundant, as the enable switch as I could have utilized the variable resistors on the inverter tester board to adjust the enable voltage. This would have meant hacking the inverter tester a little, which at the time seemed a pain in the backside, so I opted to use the HEXFET to control enabling the inveter tester instead.

Obviously now, hacking the inverter tester seems trivial compared to the problems I caused myself. Doh!


IMPORTANT POINT TO NOTE HERE:

Make sure your parts are compatible; The screen I have was originally CCFL and I converted it using a kit from China - I should have checked the board over properly.

Alternatively, make sure you know what voltages are expected at the LED Driver/CCFL inverter end before you go ahead and plug it in to your LVDS controller; you shouldn't need to worry about this if you purchased the LVDS controller and Inverter/Driver as a kit, the seller will have already matched them.



Here's the modification made to get the board running again - Guess who's back!
[attachment=1]

I will need to remove the ME15N10 properly and try and mount the resistor a little better, but it's all working fine now, and the IRL540N requires


-----------------------------------------------------------------------------------
Edit:

This worked OK for a bit until the Vcc pin of the LED driver chip came off. Nevermind, I'll just have to order another and learn from my mistakes.

Also, Ertews method is still sound, it's just that you need to make sure that you do not over-volt the driver/inverter somehow before proceeding.
2  Screen Tablet malarky / Monitors / Re: Assorted selection of problems with a universal LVDS controller on: November 04, 2016, 10:44:12 AM
Hmmmm........ OK, so this could just be coincidence however, today the LED backlight current board burnt out with a huge stink of smoke.  Cry

I suspect that the board - which was from China and very cheap - is at fault rather than the rewiring discussed previously, however I will look into this a bit more and make sure that nothing else got taken out during the event.

Here a pic of the burnt out resistor:

[attachment=1]


Originally this was an SMD resistor of the same value (of which I forget now), however the original resistor cracked in half when I attempted to pull the board from some double-sided tape. Obviously too much current has passed through the resistor but as yet I have no idea why. I'm not even sure if the LEDs are still working.

Disaster!!
3  Screen Tablet malarky / Monitors / Re: Assorted selection of problems with a universal LVDS controller on: November 03, 2016, 02:32:14 PM
Spot the difference. I'll give you a clue:
[attachment=1]

The inverter tested has been stripped virtually bare so just the connector, a resistor, and an LED are present. This was so that I could fully disconnect the backlight if I needed to strip the screen down again. Using the connector on the LVDS controller wouldn't allow this due to being connected to 5V power.

Tested and working, check out the refresh rate and resolution of this bad boy! - ahh, and there's the homeless little HEXFET sitting on the bezel:
[attachment=2]

I left the resistor on the protoboard connected to nothing as I have thousands of them.

2 less components and the OSD now controls brightness.

4  Screen Tablet malarky / Monitors / Re: Assorted selection of problems with a universal LVDS controller on: November 03, 2016, 09:30:12 AM
Haha... Cheesy

Actually that's a very fair point. I did this a few months ago now so I don't remember my reasoning, but I imagine it was just a matter of not seeing the wood for the trees. You're perfectly right that both the resistor and HEXFET aren't really needed. I probably just had the parts laying around and didn't think too much about it, or possibly had intentions to use the BL signal to do something else.

Ertew, thanks. I think I'm going to rewire my setup as per your suggestion since it has the advantage of allowing the backlight to be controlled from the OSD. Nice!

There's an outcome that I hadn't expected when I posted yesterday!

Cheers.  Wink
5  Screen Tablet malarky / Heyaaaalpppp / Re: Known good LVDS cables are shorting when I wire them up on: November 02, 2016, 04:20:15 PM
What controller board and screen are you using? Do you have pictures? You can upload them in the 'Additional Options' when you reply.
6  Screen Tablet malarky / Build Logs / Re: Experimenting with the HP 2710p Tablet PC digitizer (SU-12W18A-01X) on: November 02, 2016, 04:18:32 PM
True it would be a bit fiddly, but it's do-able.

Interesting board by the way, I've not seen that one kicking around before.
7  Screen Tablet malarky / Monitors / Re: Assorted selection of problems with a universal LVDS controller on: November 02, 2016, 04:10:35 PM
This is what my setup looks like:

[attachment=1]
A quick note on the first picture. I've removed the switch and power socket and used jumpers to bridge the gaps as I didn't need these components. This CCFL inverter tester also has a slightly different layout to the one pictured in my previous post but they all work the same.

[attachment=2]

[attachment=3]

Additional components that can be seen are an Atmel ATTiny85 (used to display the status of the LVDS controller via an RGB LED), and an Adafruit AR1100 module (used to get the resistive touch layer to communicate with the pc via USB).

This was a 12.1" point of sale screen which I've hacked to be a small monitor for a small computer that I've built to run a CNC machine that I've almost finished building; was trying to keep the overall footprint of the machine small.
8  Screen Tablet malarky / Monitors / Re: Assorted selection of problems with a universal LVDS controller on: November 02, 2016, 03:55:10 PM
I actually have one of these boards and I know you're frustration.

For clarification this is the board:
[attachment=1]

The red socket is meant to be used with backlights of small screen that can run from a 5V supply, typically this is probably a screen size up to 10". The problem here is that your inverter/LED driver (depending on which you have) is likely to require 12V so what to do?

Well here's what I did. As i mentioned in a post I replied to today, I used an LM2596 step down module, a cheap CCFL tester and a 12V power supply.

The cheap CCFL Inverter tester I used:
[attachment=2]

I ran the 12V straight from the power supply to the tester, and from the tester to - in my case - an LED driver board. I then tapped of the 12V from the power supply to the LM2596 and stepped it down to 5V to driver the MT6820-B, and connected the output of the LM2596 to 5V and GND on the red connector. Problem with this setup is that you have 2 separate circuits, one for driving the LCD and the other for driving the backlight, they are not linked. This means that you manually have to switch the backlight on to see the picture.


03.11.2016 - The following part regarding how I got the backlight to work with the LVDS controller has been shown to me to be, let's say, a little bit pointless. I've kept it in this post for reference, and you can read why it's pointless in the next post by Ertew. All I can say is, we all make mistakes. Smiley


The way I got around this problem was with a simple additional circuit. The additional circuit was comprised of an IRL540N HEXFET and a resistor, and works by utilizing the BL pin of the LVDS controller.

Here's the circuit:
[attachment=3]

When the LVDS controller is power on, the BL pin goes HIGH pulling the 'Gate' pin of the IRL540N high, this effectively turns the IRL540N 'ON' allowing current to flow from the 'Drain' to the 'Source'. This is like physically flipping a switch from 12V to the CCFL inverter tester. When the LVDS controller is turned 'OFF' or put in standby, the BL pin goes low and turns off the CCFL tester.

The resistor value should be fairly high, I think I used a 57Kohm as I had one laying around, but any value above 10Kohm will probably be fine. The resistor is just there to hold the 'Gate' of the IRL540N 'LOW' when the LVDS controller is turned off.
9  Screen Tablet malarky / Build Logs / Re: Experimenting with the HP 2710p Tablet PC digitizer (SU-12W18A-01X) on: November 02, 2016, 02:30:08 PM
I see you're worried about power consumption and heat from the LVDS controller. My suggestion would be to get some cheap switching dc step down modules (such as LM2596) and remove or bypass the linear regulators.

The LM2596 (variable module) is good for stepping down voltages from up to 40V to between 37V and 1.2V and can handle 3A of current. You can also get fixed output versions in values 3.3V, 5V, and 12V.

As a quick note: I would suggest though that some heat would definitely be generated if you stepped down 40V to 1.2V.

[attachment=1]

They don't get hot and they're much more efficient than a linear reg. Only problem here is that you trade of efficiency and thermal benefit with space.
10  Screen Tablet malarky / Build Logs / Re: Here comes UBiQ 2 on: November 02, 2016, 02:19:49 PM
DaBotz I think you have an addiction! Could be worse though.

Another excellent build, nice job!
11  Screen Tablet malarky / Heyaaaalpppp / Re: Has anyone replaced the CCFL in a Cintiq 21UX? on: November 02, 2016, 02:17:46 PM
Wow, nice job.

As for the dust, I certainly haven't found a good way around this yet, once it's in between those layers or behind the glass it's pretty much sticking around.

By the way I'm extremely jealous of your 21UX!


12  Screen Tablet malarky / Tablet Conversion to USB / Re: How to "install" WaxBee converter on Arduino Pro Micro, clones or any ATmega32U4 on: May 10, 2016, 07:04:29 AM
Nice work Bernard! Credit where its due.
13  Screen Tablet malarky / Heyaaaalpppp / Re: Interfacing a TabletPC digitizer on: May 05, 2016, 11:33:12 AM
Ok so the Teensy appears to work fine. You definately have a Teensy/Clonsey version 2.0? I'm just wondering if there might be an issue with the code between versions off Teensy, different setup/pin configs like you suggested. My experience here is limited by the way, I'm familiar with Arduino but have never used a Teensy, or for that matter, done the Waxbee conversion.
14  Screen Tablet malarky / Heyaaaalpppp / Re: Interfacing a TabletPC digitizer on: May 05, 2016, 06:55:15 AM
Did you get your teensy from a reputable source? I read about there being dud Chinese clones that are only good for flashing leds.

Have you checked that the teensy runs other code ok? Maybe see if you can program it with a standard hid template like a mouse or keyboard, at least that was you can confirm the teensy is working correctly. Once you know that you can be sure that something is up with the waxbee programming.

Have you tried a different usb cable? Some only have 2 wires for charging devices only.
15  General Category / Can't stop building / Re: Digital Sketchbook (DSB) on: April 28, 2016, 08:59:56 PM
Haha. The Blender icon is showing on your 1st render!

You could alwasy trim the thickness down a bit by using Cherry ML switches, the lower profile cousin of the MX.

I like your idea for the battery, seems like it could work. Looking forward to seeing how you get on with this.
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