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| Mac Portable Mods? |
Posted by: hyperneogeo on 2016-09-12 22:18:36
I was wondering if anyone had tried to mod their original portable to include some sort of back light since obviously the upgrade kit is kind of a rare thing.
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Posted by: aplmak on 2016-09-13 08:32:54
Checkout "thetechknight" on you tube... He did a mod once in the past... More recently he's been working on reverse engineering the kit...
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Posted by: tjjq44 on 2016-09-13 10:51:46
Yes he replaced the reflective layer of the lcd by something like "oled" sheet he had to cut to the right size, the kit comes with an inverter you have to place inside the screen case. As far as I remember it was blue backlight but maybe white is also available?
Another drawback is that you can't adjust brightness in software like with the official backlight upgrade kit (which has an expansion card you plug into the rom port to allow communication with the mac).
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Posted by: techknight on 2016-09-13 11:08:55
it was an A4 size EL sheet which is actually kind of pricey, they come in multiple colors including white, but I chose aqua like the timex watches because its cool.
As far as software brightness control, thats why I was reverse engineering the backlit upgrade card, so I can create a new inverter driver card which contains the software interface.
the inverter it comes with works, but its an older iron-core magnetic type that is huge, gets hot, and isnt really a good spot inside the machine to put it. The new inverter that I am working on designing will be high frequency switching so itll be smaller in size.
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Posted by: trag on 2016-09-13 19:48:01
The new inverter that I am working on designing will be high frequency switching so itll be smaller in size. Is there any value in modifying an existing inverter? I just bought four inverters for the Dell Latitude D430 (fluorescent tube for 12" or 13" display) for about $8 each and they're very small, about 135 x 10 x 4 mm.
It seems like those would be great if they would work. I don't know much about inverters though. Is there a bunch of variation in voltage and frequency by model?
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Posted by: hyperneogeo on 2016-09-14 10:33:37
Interesting, thanks for the info. I watched the vid on youtube and it seems techknight really hates the board made by Apple haha.
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Posted by: techknight on 2016-09-14 12:48:54
An existing inverter wont work because Electroluminescent sheets are different from CCFL bulbs.
Most EL sheets need 120 to 400Hz at roughly 100VAC to operate properly, and thats anywhere from 50 to 150mA, whereas CCFL needs a few KV with 10mA or less to operate, and thats at 15Khz+ frequencies. (more like neon, less like EL). Most EL inverters are small transformer switching supplies but they operate at such a low frequency that most use iron core, and they do get quite warm.
But an A4 size sheet uses alot of current. So at say 250 to 400Hz, the transformer is BIG. like wall-wart big.
So what I was going to do was create a 100 to 120VDC switching supply capable to at least 250mA, Trick here is make it 25Khz switching frequency or higher because it will allow for much much smaller magnetics. And a ferrite core transformer.
The output of this of course will be filtered and rectified to DC, then sent into an h-bridge mosfet array. The EL sheet will sit in between the H-Bridge, and itll be up to the MCU to switch the H-Bridge at whatever frequency the EL sheet is most efficient at.
I can control the brightness either via PWM of the 100VDC supply, or even PWM the H-bridge.
Even though this is more convoluted than a regular 2-transistor inverter, it will keep the inverter size down significantly for the type of current I need. I was going to use an AT90PWMXX or even an ATMega microcontroller to accomplish this task, as it has PWM capable timers that I can set. I can use 1 PWM timer to form a feedback loop and run the high frequency switcher, whereas I can use the second PWM to run the H-Bridge, In dual fast-mode so I can get the proper pulse for each side of the bridge. This would effectively create a "modified sine wave" drive to the EL sheet. (like a cheap AC inverter for your car, same design).
Putting all control operations into the micro will also allow me to emulate the backlight control of the portable itself, so I can actually use the screen control panel and adjust the backlight brightness. Reverse-engineering the Apple backlight upgrade will allow me to do that.
The biggest stumbling block for me right now is not the design or build/testing. Thats easy. The problem is the transformer. I need the transformer thats going to provide me the 100VDC at 250mA from the battery bus which is anywhere from 6 to 7.5VDC. Thats a custom thing that has to be custom wound.
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Posted by: trag on 2016-09-14 13:17:01
Thank you, techknight. I appreciate the thoughtful explanation.
Will a switching boost circuit not work? Wouldn't that eliminate the transformer and just need an easier to find inductor? Can one get a factor of 16 out of a switching boost circuit?
How many I/O pins do you need on the microC? I don't know why, but I want to see someone use an 8-pin ATTiny on a project. 🙂
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Posted by: techknight on 2016-09-14 14:23:21
Lol. Closest thing I used an 8 pin ATTiny in was parking break override mods for in-dash DVD players. Newer units require a special sequence and timing to activate.
A boost converter might work, but I dont know how big of a coil I would need and at what frequency to get 120VDC at 250mA. again from 6 to 7.5V. Coil would have to be designed to operate at 6V minimum, and the feedback circuits can dial things down a bit when it gets higher than that.
I tried designing boost converters in the past but the formulas for doing so varied.
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Posted by: rsolberg on 2016-09-14 15:04:54
250mA seems high by a factor of ten or more. Is that a typo, or maybe I'm misunderstanding the context? 250mA at 120V would be 30VA. 30VA/6V would be 5A draw from the Portable's battery.
http://m.electronicdesign.com/boards/transformerless-el-display-driver-uses-lower-voltage-555-ic
This link seems relevant to the discussion of a transformerless driver, but I don't know if it would scale up to an A4 sized panel.
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Posted by: techknight on 2016-09-14 16:31:43
250mA would be the max rated. current draw is way under that, but I wanted to design it that way for safety reasons. If an EL sheet can operate on pulsating DC rather than AC, that would eliminate a large majority of the complexity!
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Posted by: rsolberg on 2016-09-14 17:08:01
gotcha. You wouldn't want your coil to become the fuse if a short were to happen! That driver circuit certainly looks intriguing to this layman. I'm trying to work out the maximum current with the listed components. Any idea what the ballpark is for that EL panel?
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Posted by: techknight on 2016-09-14 17:14:03
I dont know, I have to grab it out of storage and get it up on the bench power supply and test it, figure out what it is. Its an A4 sheet thats cut down to fit inside the LCD panel.
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Posted by: Bunsen on 2016-09-16 03:10:06
What about a LED backlight? A strip of SMT LEDs in plastic tubing could be about the same size as a CCFL tube, and draw way less current.
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Posted by: techknight on 2016-09-16 05:52:58
LED wont between the LCD glass and the PCB, we are talking ~2mm of space in there.
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Posted by: aplmak on 2016-09-16 06:41:19
Techknight I was thinking the same thing... they don't make an "LED" ccfl replacement lcd display tube??? Made for size??
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Posted by: Bunsen on 2016-09-16 07:04:49
LED wont between the LCD glass and the PCB, we are talking ~2mm of space in there. No, of course not. You would have to use them like CCFL tubes - ie, mounted at the sides of a thin layer of light-distributing plastic behind the LCD.
SMT LEDs can be had in way less that 2mm size too.
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Posted by: techknight on 2016-09-16 07:17:45
Here is the problem. the LCD has zebra stripe connectors on all 4 sides. you physically just cannot get it in there. the A4 EL sheet BARELY fits.
I would have to see a drawing to understand the accomplishment.
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Posted by: aplmak on 2016-09-16 07:21:15
Maybe somewhere like here has examples??? Just throwing it out there... http://www.ccflwarehouse.com/
How is the 5126's assembled???
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