Can RGB pins on LCD RGB be "jumped"?

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bolsoncerrado
 
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Can RGB pins on LCD RGB be "jumped"?

Post by bolsoncerrado »

Hello all!

Excluse my total and blatant ignorance.

I bought an adafruit RGB LCD which comes with 3 backlight control pins (by default it turns on RED). Then you're supposed to "modulate" G and B pins using software code to get different backlight colors.

My question is simple: can be the backlight color be HARD(ware) controlled without the aid of any code?

Which sort of voltage/signal are the GB pins expecting and which resistors ( or pots??) should I need to modulate the amount of G and B colors to mix with the default R to get different backlight colors?

Anyone care to help? :)

Thanks!

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adafruit_support_bill
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by adafruit_support_bill »

The RGB pins can be hard-wired to achieve a fixed color. The backlight is a common-anode LED. If the anode (pin 15) is connected to +5v, the red green and blue cathodes (pins 16, 17 and 18) can be individually pulled to ground to turn on their respective color channels. That gives you 7 possible colors. For a wider selection of colors, you can add resistors in series with any of the cathodes to reduce the output of that channel.

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bolsoncerrado
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by bolsoncerrado »

Great news! I'll do some tests! Thanks again.

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bolsoncerrado
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by bolsoncerrado »

OK so far I've managed to get:

RED (no connection on pins 16/17)
BLUE (red +5, 16 off, 17 GND)
GREEN (red +5, 16 GND, 17 off)
CYAN (red +5, 16 & 17 GND)

In order to get the 3 extra colors you mention, i'd need to cut the RED +5 line and put it to GND?

I mean, BEFORE messing with any resistors. As I see it, cutting the R pin is a point of no (easy) return so I want to be sure hehe

Also, as I'm already getting contrast control from the printer smartcontroller board, would the pot included with the LCD be of any help to achieve color regulation here? (again I'm null to electronics hehe).

Thanks!

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adafruit_support_bill
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by adafruit_support_bill »

The RGB LCD modules have 18 pins.
The common anode pin is the one connected to +5v. That is pin 15.

The 2 cathode pins (16, 17 & 18) control the 3 color channels:

Pin 16 is Red. It would be connected to GND to turn on the red channel.
Pin 17 is Green. It would be connected to GND to turn on the green channel.
Pin 18 is Blue. It would be connected to GND to turn on the blue channel.

16 + 17 = Yellow
16 + 18 = Magenta
17 + 18 = Cyan
16+17+18 = White

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bolsoncerrado
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by bolsoncerrado »

Ah ok I miss named the pin connection. So I can basically put jumpers between them safely, right?

Would adding the 10k POT you supply in between pin 15 and one of the colors' GND allow me to adjust the color combination further or would I blow something?

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adafruit_support_bill
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by adafruit_support_bill »

So I can basically put jumpers between them safely, right?
You can jumper any of the 3 cathode pins to GND to turn them on.
Would adding the 10k POT you supply in between pin 15 and one of the colors' GND allow me to adjust the color combination further or would I blow something?
No. Pin 15 is the common anode. It needs to be connected to +5v.
You could use a pot instead of a jumper between any of the individual cathode pins and GND to vary the intensity of that color.

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bolsoncerrado
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by bolsoncerrado »

Hi Bill,

Appreciate your patience with me ;)

Can you tell me which kind of pot would I need? ;)

Cheers.

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adafruit_support_bill
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by adafruit_support_bill »

Any pot will work. 10K pots are pretty common and these are inexpensive: https://www.adafruit.com/product/356
But a 10K pot will make the LED pretty dim over most of the range.

A 1K pot would give you a bit more control. These are the only 1K pots we carry. You can probably find smaller ones at Mouser or DigiKey.
https://www.adafruit.com/product/1789

With any pot, you can connect one of the outer legs (either one) to GND and the center "wiper" pin to one of the 3 cathode pins on your display.

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bolsoncerrado
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by bolsoncerrado »

Awesome, thanks. I take you mean no +5V is required for the pot to dim the colors.

Thanks again!

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adafruit_support_bill
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by adafruit_support_bill »

Correct. In this case, the pot is just acting as a variable resistor in series with the LED. The more resistance, the dimmer the LED.

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bolsoncerrado
 
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Re: Can RGB pins on LCD RGB be "jumped"?

Post by bolsoncerrado »

Amazing, thanks.

BTW the stock LCD without the POT added is a bit dim... Is there any way to get more light from it?

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Re: Can RGB pins on LCD RGB be "jumped"?

Post by adafruit_support_bill »

You need to connect the pot as shown in the guide. That will allow you to adjust for maximum contrast.

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