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Author Topic: Warning to users of some vendors LCD keypad shields.  (Read 48045 times)
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Hey! I actually own a "DFRobot I2C / TWI LCD1602 Module"
http://www.robotshop.com/productinfo.aspx?pc=RB-Dfr-69&lang=en-US

wich it comes with the "DFRobot I2C LCD Backpack"
http://www.robotshop.com/productinfo.aspx?pc=RB-Dfr-145&lang=en-US

I would like to know wich is the easiest way to fix the BJT issue in this case. Any one can confirm that the 'A' of diode will be set on BT (P3 of PCA8574)  and the 'K' on the base of BJT  thanx in advance
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Ayer, Massachusetts, USA
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In another post, the user 'dfrobot' (presumably somebody from DFRobot), mentioned that the new version of the DFRobot LCD shield does enable pin 10 to control the brightness.  I tested the board I had ordered from Robotshop.com on May 31st, and setting pin 10 via PWM to 0..255 does control the brightness level.
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Sort of off  topic but I have had business with Robot Shop before and they ARE one of the BEST companies I have found to do business with.
There are a lot of places to buy Cheap parts. Robot Shop is where I go when I need a 'non' cheap part.
If the part cost is over $50.00 That's where I buy it, They have one of the BEST customer Service Dept's I have ever dealt with.....
Robot shop is "on" a complaint immediately and they have yet to disappoint me After 2 4D Systems 32PT SGC displays and issues with the first one...
It didn't look new as the plastic shield cover on the LCD was bubbled and had fingerprints under the film.
Robot Shop sent me a new one and issued me an RMA the next business day.
This is the reason I decided to buy my second from Robot Shop rather than shop around for a better price or faster/cheaper shipping.
To MY Shame I found out from 4D Systems that all their 32PT SGC devices look that way as the film is lifted to inspect the LCD for any cosmetic
damage prior to assembly.

Doc
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In another post, the user 'dfrobot' (presumably somebody from DFRobot), mentioned that the new version of the DFRobot LCD shield does enable pin 10 to control the brightness.  I tested the board I had ordered from Robotshop.com on May 31st, and setting pin 10 via PWM to 0..255 does control the brightness level.

I bought mine a year ago and yes, it have the issue smiley-sad
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I have been done the mod adding a Diode (IN5819)  how you can see in the schematic (I have marked green the new diode in the graphic) . Now I have a new issue with the brightness wich have been decreased...
« Last Edit: August 13, 2012, 06:38:04 pm by CarlosGz » Logged



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I have been done the mod adding a Diode (IN5819)  how you can see in the schematic (I have marked green the new diode in the graphic) . Now I have a new issue with the brightness wich have been decreased...

That is because the diode does not go in series with the pullup resistor to the base of the
transistor but in series with the D10 to connection of the base of the transistor.


--- bill
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I have been done the mod adding a Diode (IN5819)  how you can see in the schematic (I have marked green the new diode in the graphic) . Now I have a new issue with the brightness wich have been decreased...

That is because the diode does not go in series with the pullup resistor to the base of the
transistor but in series with the D10 to connection of the base of the transistor.


--- bill

maybe now i have a bigger problem lol, so, in this case I have to connect the Anode to BT (D10) and the Catode to the the base of the transistor?
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To be clear, something like this?  
« Last Edit: August 13, 2012, 06:37:43 pm by CarlosGz » Logged



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Almost, The diode is flipped/reversed. (I think you would have quickly figured it out)
The diode is used to isolate D10 from the circuit when D10 is high.
The pullup resistor is used to turn on the transistor.
The backlight will be on if D10 is input or HIGH.
Setting D10 to low turns off the backlight.
The diode allows D10 to yank the pullup down to gnd to turn off the transistor when D10 is low.

It works but really isn't a good design, I wouldn't design a circuit like this.

I did it this way because I couldn't easily desolder the LCD on the shield I had to replace
the transistor with an FET. (The transistor was underneath the soldered LCD module)

--- bill
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Almost, The diode is flipped/reversed. (I think you would have quickly figured it out)
The diode is used to isolate D10 from the circuit when D10 is high.
The pullup resistor is used to turn on the transistor.
The backlight will be on if D10 is input or HIGH.
Setting D10 to low turns off the backlight.
The diode allows D10 to yank the pullup down to gnd to turn off the transistor when D10 is low.

It works but really isn't a good design, I wouldn't design a circuit like this.

I did it this way because I couldn't easily desolder the LCD on the shield I had to replace
the transistor with an FET. (The transistor was underneath the soldered LCD module)

--- bill

Hey, thanks for your help, now I understand the question.
I finally won't be able to fix my lcd because of the pcb design and the components placement, so I decided to buy a new one at http://www.electrofunltd.com/ and I have been testing the FMalpartida's library with nice results...
By the way, I would like to reupload the schematic with the diode in a correct placement in case it can help someone smiley


* LCD_Mod3_goodversion.jpg (42.38 KB, 758x651 - viewed 256 times.)
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Hello,

Not quite sure how to pick the most appropriate diode here for the D10 fix, could somebody take a look at the following

http://www.maplin.co.uk/search?criteria=diode&page=1

and advise which would be a good choice?

Many thanks,

Amadeus
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To answer my own question, and to help other users, I found that the "1A Schottky Barrier Rectifiers" on that page, in particular a 1N5817
 worked well. Trick was to cut the track after bugging the diode on.

Worked well until I got over-confident with the "brief" part below:

Quote
Briefly (and I mean just a brief touch) connect the wire from D10 to Vcc.

Cue smell of burning and a slighty dimmer backlight, no on/off control. I imagine the transistor went.

Oh well. You win some you lose some.......
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Thank you dweston and bperrybap

I just noticed that the product page says


"Do not use Pin 10 while this shield is connected"

 http://www.robotshop.com/productinfo.aspx?pc=RB-Dfr-07&lang=en-US


I do not remember that statement when I ordered it

impressive if they have responded to this info so quickly

It looks like robotshop is not dfrobot.
No warning here, and the schematic has not changed...
http://www.dfrobot.com/wiki/index.php?title=Arduino_LCD_KeyPad_Shield_%28SKU:_DFR0009%29

Bummer...
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Ayer, Massachusetts, USA
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Quote from: bwims link=topic=96747.msg912548#msg912548 date=134667261
It looks like robotshop is not dfrobot.
No warning here, and the schematic has not changed...
[url
Yes, robotshop is a distributor for various parts manufactured by others (DFRobot in this case makes the lcd shield).  I've used them in the past rather than ordering straight from DFRobot because Robotshop is USA based and shipping times are much less.  As I mentioned upthread, evidently robotshop hasn't changed the warning, but when I ordered the lcd shield in May, it was the fixed version where button 10 does control the contrast.

IIRC, you can't use servos and the lcd shield together on UNOs because the servo library disables PWM on pins 9 and 10.
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It looks like robotshop is not dfrobot.
No warning here, and the schematic has not changed...

Bummer...
Yes, robotshop is a distributor for various parts manufactured by others (DFRobot in this case makes the lcd shield).  I've used them in the past rather than ordering straight from DFRobot because Robotshop is USA based and shipping times are much less.  As I mentioned upthread, evidently robotshop hasn't changed the warning, but when I ordered the lcd shield in May, it was the fixed version where digital pin 10 does control the contrast.

IIRC, you can't use servos and the lcd shield together on UNOs because the servo library disables PWM on pins 9 and 10.
« Last Edit: September 03, 2012, 09:10:50 pm by MichaelMeissner » Logged

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