Gameboy Mk3 - RPi3 + DPI screen + RTC diy [Completed!]

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razer.93
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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by razer.93 » Tue Dec 12, 2017 2:34 am

salami738 wrote:
Fri Dec 08, 2017 6:27 am
razer.93 wrote:
Wed Dec 06, 2017 1:20 am
...
Anyone knows if there is a 'correft' way to wire a digital pot to a boost converter for the screen backlight?
I assume you use the display "LQ035NC111"?
According to the datasheet the backlight needs 18.6V - 21.0V and 20mA.

In my opinion you need a constant current, not a constant voltage source (boost converter). You can build it yourself or get a ready made lcd backlight driver chip, like: http://www.ti.com/product/tps61160. 1-output-channel, Input: 2,7-18V, Output 2,7-26V 20mA Current. Maybe @kite, or @ZeroBoy can confirm that.

The brightness is then controlled via PWM (f.e. from an analog output from your arduino) or via 1-wire protocol (arduino digital pin). See: http://www.ti.com/product/TPS61160/data ... LVS7915277
I eventually ended up with chaining a current limiter to the boost converter. I used a mosfet transistor couple with a bunch of resistors in order to design a variable current limiter with 0.7v voltage drop-off driven by an arduino (protected with a zener diode). The circuit is pretty simple but the boost converter i made is quite inefficient (5 to 21v reaches ~50% efficiency which is orribile). I ordered an off the shelf on ebay, hoping for improvements.
I also tried using an LM317 used as a constant current regulator but the voltage drop off is about 3v so for now the current limiter seems the best option apart from buying the smd part as you mentioned.

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by salami738 » Wed Dec 13, 2017 12:57 am

Hi, good to hear, that you are making progress. Maybe you could post a schematic, when you are done?

One additional hint: Kite uses the 320x240 dpi display for his boards too and he has his source-code available under: https://github.com/geebles/Super-AIO
Interesting thing about his source code is his lcd initialization: https://github.com/geebles/Super-AIO/bl ... 2a/LCD.ino
At the moment I dont know if it is needed to use the display or if it is only a optimization (better gamma curves etc). I will read the lcd datasheet, if I have the time.

I googled a bit and found the site: http://www.buydisplay.com/default/3-5-i ... lq035nc111. They have the complete datasheets available.

greetings from germany!

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by razer.93 » Wed Dec 13, 2017 8:44 am

salami738 wrote:
Wed Dec 13, 2017 12:57 am
Hi, good to hear, that you are making progress. Maybe you could post a schematic, when you are done?

One additional hint: Kite uses the 320x240 dpi display for his boards too and he has his source-code available under: https://github.com/geebles/Super-AIO
Interesting thing about his source code is his lcd initialization: https://github.com/geebles/Super-AIO/bl ... 2a/LCD.ino
At the moment I dont know if it is needed to use the display or if it is only a optimization (better gamma curves etc). I will read the lcd datasheet, if I have the time.

I googled a bit and found the site: http://www.buydisplay.com/default/3-5-i ... lq035nc111. They have the complete datasheets available.

greetings from germany!
Of course I will post all schematics when I'll test all out.
I saw that particular piece of code and I also had the same doubt! in the first place why is he initializing it with arduino? the screen is wired to the gpios directly, right?

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by salami738 » Wed Dec 13, 2017 12:45 pm

razer.93 wrote:
Wed Dec 13, 2017 8:44 am
salami738 wrote:
Wed Dec 13, 2017 12:57 am
Hi, good to hear, that you are making progress. Maybe you could post a schematic, when you are done?
...
Of course I will post all schematics when I'll test all out.
I saw that particular piece of code and I also had the same doubt! in the first place why is he initializing it with arduino? the screen is wired to the gpios directly, right?
If you look at the display datasheet "3.5 inch 320x240 Dots TFT LCD Display Datasheet", at page 7, you will find the pin layout of the display. I read many posts about using this display, and they often only connect the
Blue/Red/Green Data, HSYNC(36), VSYNC(37) and DLCK(52) to the raspberry.
In addition you have to drive the backlight on the PIN 1-4.
And (atm i think it is optional), you can use the pins marked with SPI to program the display with the arduino, before you use it (See "Driver IC (HX8238) Datasheet" for details). Maybe alternatively you can initialize them with the raspberry, if you have enought free pins (4 are needed).

But please check the pin layout yourself, because my display isn't there yet and I cant test them.

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by fdeluxe » Fri Dec 15, 2017 1:29 am

razer.93 wrote:
Tue Dec 12, 2017 2:34 am
salami738 wrote:
Fri Dec 08, 2017 6:27 am
razer.93 wrote:
Wed Dec 06, 2017 1:20 am
...
Anyone knows if there is a 'correft' way to wire a digital pot to a boost converter for the screen backlight?
I assume you use the display "LQ035NC111"?
According to the datasheet the backlight needs 18.6V - 21.0V and 20mA.

In my opinion you need a constant current, not a constant voltage source (boost converter). You can build it yourself or get a ready made lcd backlight driver chip, like: http://www.ti.com/product/tps61160. 1-output-channel, Input: 2,7-18V, Output 2,7-26V 20mA Current. Maybe @kite, or @ZeroBoy can confirm that.

The brightness is then controlled via PWM (f.e. from an analog output from your arduino) or via 1-wire protocol (arduino digital pin). See: http://www.ti.com/product/TPS61160/data ... LVS7915277
I eventually ended up with chaining a current limiter to the boost converter. I used a mosfet transistor couple with a bunch of resistors in order to design a variable current limiter with 0.7v voltage drop-off driven by an arduino (protected with a zener diode). The circuit is pretty simple but the boost converter i made is quite inefficient (5 to 21v reaches ~50% efficiency which is orribile). I ordered an off the shelf on ebay, hoping for improvements.
I also tried using an LM317 used as a constant current regulator but the voltage drop off is about 3v so for now the current limiter seems the best option apart from buying the smd part as you mentioned.
the manufacturer suggests using this backlight driver: http://www.buydisplay.com/default/led-b ... -5-package It is easily controlled via PWM.

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by salami738 » Fri Dec 15, 2017 1:57 pm

fdeluxe wrote:
Fri Dec 15, 2017 1:29 am
the manufacturer suggests using this backlight driver: http://www.buydisplay.com/default/led-b ... -5-package It is easily controlled via PWM.
Thanks for the tip. This driver is nearly perfect. Can run on batteries directly (2,7 to 5,5V input) and needs only a few external components. Doable with wires only (without pcb).
It would be perfect, if someone designs a PCB with the driver and an FPC Connector.

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by fdeluxe » Sat Dec 16, 2017 8:27 am

salami738 wrote:
Fri Dec 15, 2017 1:57 pm
fdeluxe wrote:
Fri Dec 15, 2017 1:29 am
the manufacturer suggests using this backlight driver: http://www.buydisplay.com/default/led-b ... -5-package It is easily controlled via PWM.
Thanks for the tip. This driver is nearly perfect. Can run on batteries directly (2,7 to 5,5V input) and needs only a few external components. Doable with wires only (without pcb).
It would be perfect, if someone designs a PCB with the driver and an FPC Connector.
I have ordered a lot of them and waiting for them to arrive. What do you mean by "few external components".

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by razer.93 » Sat Dec 16, 2017 11:49 am

fdeluxe wrote:
Sat Dec 16, 2017 8:27 am
salami738 wrote:
Fri Dec 15, 2017 1:57 pm
fdeluxe wrote:
Fri Dec 15, 2017 1:29 am
the manufacturer suggests using this backlight driver: http://www.buydisplay.com/default/led-b ... -5-package It is easily controlled via PWM.
Thanks for the tip. This driver is nearly perfect. Can run on batteries directly (2,7 to 5,5V input) and needs only a few external components. Doable with wires only (without pcb).
It would be perfect, if someone designs a PCB with the driver and an FPC Connector.
I have ordered a lot of them and waiting for them to arrive. What do you mean by "few external components".
You need the inductor of course and a couple of capacitors.
I don't wanna to waste time waiting for them to arrive, solder them and whatsoever... I'm building my personal boost/current constant source with a limiter.
I received the LCD today, I'll keep you up to date

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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by razer.93 » Sun Dec 17, 2017 1:36 pm

It works!
2017-12-17 21.35.25.jpg
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Re: Gameboy Mk3 - RPi3 + DPI screen + RTC diy [WIP]

Post by razer.93 » Tue Dec 19, 2017 3:01 pm

Halfway assembly
IMG_20171219_223715.jpg
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