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 91 
 on: June 29, 2017, 06:30:13 PM 
Started by DaBotz - Last post by DaBotz
My idea was having a PWM frequency tunable between some 200 and 1000-1200 hz... pretty basic, as far as electronics go.

Fast enough to avoid seeing the light flicker (would it be best some exact multiple of the refresh rate? no idea), slow enough that the on/off times of the LED can be ignored hen setting brightness at minimum , and with a chance of tuning it out of resonances with the tablet, should these manifest themselves.

From what you told me before, the LED kit probably can't handle things going much faster than that, anyway... and my soldering ability is not stellar, so slower is going to be better.

 92 
 on: June 28, 2017, 07:29:13 PM 
Started by DaBotz - Last post by Ertew
Oops. I forgot about frequency. I build similar oscillator and notice significant frequency error at 10khz. At 100khz circuit are unstable and way off from simulation. For 1kHz You may expect less than 10% error at frequency. Sorry for scare You.

More important thing: LM358 aren't rail-to-rail amplifier. I expect non-linear distortions near minimum and maximum settings - may be noticeable but not critical.

 93 
 on: June 27, 2017, 08:47:38 PM 
Started by DaBotz - Last post by DaBotz
Thanks for the tit-bit about the LM358, Ertew (though, I thought that a 1Khz max output frequency was pretty basic...).

I can't find that at the local shop, nor the AD8359 that I used with Spice... I'll have to decide for something else anyway, it seems.

On a side note, I have bought a couple of DF9-41-V(the plugs to the DF9-41-P sockets)  that will arrive in a week or so... when they'll arrive, I'll have to try to whip up a longer connection cable for the lcd.

that is going to be frustrating. or fun.

Or frustrating.

I admit that, as it is a bit on the supernumerary side of things, I am taking a lot more risks than usual, on this build.



 94 
 on: June 27, 2017, 07:06:59 PM 
Started by DaBotz - Last post by Ertew
Fingers crossed Smiley

btw, LM358 have very poor performance. Oscillator with this chip will always run slower than with modern op-amp. You may need to tweak values before get it working.

 95 
 on: June 27, 2017, 06:51:38 PM 
Started by ThinWhiteDuke - Last post by Ertew
As far as I know, eDP digital interface is almost identical to DP port. Major differences are:
- different cables and connectors,
- eDP must provide power for crystals (LCD) and LEDs (backlight) while DP only sources video,
- flat panel need control interface for backlight power (different sources describe this as extra wires or embedded protocol) while tegular monitor may be controlled by buttons or PC (depend on implemented features).

 96 
 on: June 27, 2017, 01:04:07 PM 
Started by DaBotz - Last post by DaBotz
In the end, I think that I will replace that capacitor with one of 100nF and the resistance with one 2.5 fixed and a variable (an ungrounded potenziometer) of 0-10k one.

it should give a PWM with a frequency tunable between some 200 hz and a low khz...

[ Attachment: You are not allowed to view attachments ]

I changed the .asc extension to .txt ( it is a text file, after all) - I used LTSpice, from Linear Techcnologies... hence, the choice of the OP-Ampli (I am going to use an LM358 or something the like, in the end).

 97 
 on: June 26, 2017, 08:51:49 PM 
Started by ThinWhiteDuke - Last post by ThinWhiteDuke
I'm guessing that no one knows of any universal eDP controllers out there like there are ones for LVDS lcds. I know NJYTouch has some for some popular eDP based screens but it unfortunately runs off 12v. I'm curious about the one from the Abusemark website though. I know some people here have dabbled with them. I'm curious if the Display Port on those boards can be converted to HDMI with the use of a normal DP->HDMI active adapter purchased from anywhere. On their website they sell a "customized" DP adapter or an HDMI revision of the board but both cost quite a bit extra. Anyone have any experience with that?

 98 
 on: June 24, 2017, 09:46:32 AM 
Started by DaBotz - Last post by DaBotz
Thanks again, Ertew. I see no converter on the power board, though I still have to un-mount it so it could well be on the other side(for the moment, I have no access to my usual working table, so I will have to shelf this project for a little while)...

More than a bit of a Bummer, for me.

---

Yes, I already supposed that I had to build some Analog to PWM converter.

I found a schema, on-line, that should do the trick and, with a small adaptation, being able to provide a tunable frequency

[ Attachment: You are not allowed to view attachments ]

(just using a variable resistor for R4 should allow a certain degree of tune, but I'll look it better when I have a bit of time to install a SPICE and play... if I remember my electrics well, that RC time constant is way too low, off by a couple of magnitudes).



 99 
 on: June 23, 2017, 09:30:44 PM 
Started by DaBotz - Last post by Ertew
I looked at monitor documentation once again. Schematics are for main PCB. This board have analog RGB input only.
There are also second PCB called power board and contain input connectors. If DVI->VGA converter exist, there must be chip for that job. If You cannot found converter chip (min. 20 pins) on power board, this monitor have only DVI-A input.

I'm 100% sure that dimming are realized by PWM output. No one use DAC for analog output. There are only two options: PWM or analog via PWM + resistor + capacitor.
Look at PDF, page 38, top left corner. There are a lot of signals. Somewhere in the middle You can found DIM-ADJ (7) signal. It's connected to two resistors and capacitor.
IMHO You should use DIY analog->PWM converter. Yes, You can get PWM signal by removing capacitor or by connecting directly to chip (left side od R61 ? ). But there are second problem, PWM frequency. LED driver have limited frequency capacity (often above 100hz, rarely above 1khz). On the other hand monitor chip can easily produce PWM signal with range 4khz - 45khz, depend on selected options.

 100 
 on: June 23, 2017, 07:17:27 PM 
Started by DaBotz - Last post by DaBotz
Checked the line...

Output is

 0.1 V   with brightness at 100%

 5 V with brighness at 0%

I fear that it is not a PWM , but a direct analog output, as the LED board doesn't seem to respond much to the brightness control.

(but it heats up less the LED, so, maybe it's just that my etes do not see the difference)

If it is an analog, I suppose I could wip up an analog-PWM converter with a capacitor, a resistor, a diode and the usual double op-ampli chip... I should really need some kind of signal analyzer.   

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