Warning to users of some vendors LCD keypad shields

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

A 1N5711 or a REAL Germanium (1N34 - 1N60) would be somewhat easier to mount. Any small signal germanium or schottky diode would work as well. If one pulls the base of the 'switch' transistor below about.5 volts, the transistor is in cut off, non conducting. There is however an easier method that doesn't require cutting traces and 'hanging parts on the display... and that is to replace Q1 (9013) with a BS170 or a VN2222, VNK10 or any other n channel small signal enhancement type Mosfet. The circuit looks like it was designed for a Mosfet and someone 'goofed' and put a bi-polar device in it's place.

IMO and direct experience.

Doc

Docedison:
A 1N5711 or a REAL Germanium (1N34 - 1N60) would be somewhat easier to mount. Any small signal germanium or schottky diode would work as well. If one pulls the base of the 'switch' transistor below about.5 volts, the transistor is in cut off, non conducting. There is however an easier method that doesn't require cutting traces and 'hanging parts on the display... and that is to replace Q1 (9013) with a BS170 or a VN2222, VNK10 or any other n channel small signal enhancement type Mosfet. The circuit looks like it was designed for a Mosfet and someone 'goofed' and put a bi-polar device in it's place.

IMO and direct experience.

Doc

On my shield it isn't easier to replace the transistor.
This is originally what I wanted to do.
The problem is that the transistor is on the shield but it is under the LCD module
so it requires removing the LCD module to get to it.
Since the lcd module is soldered to the shield it requires de-soldering all 16 pins on the lcd module header.
I decided it would be easier to simply do a quick cut
and solder in the diode which is completely hidden when the shield is installed.
Plus since I didn't have any surface mount FETs and my though hole FETs wouldn't fit
under the LCD module when it was soldered back in place, it was my only option.

But if PWM backlight dimming is not needed, then the software work around is by far easier than
any hardware mode.

--- bill

I DO Apologize for that BLUNDER, I only looked at it from an engineering (electrical not mechanical) standpoint and the Mosfet is far and away the easiest fix, for that matter good engineering where the Bi-Polar device is just CHEAP when surplus parts are chosen (as they frequently are). I do however stand by my choice of parts, there are any number of small signal schottky diodes that would be a better choice The 1N5711-2 or a now discontinued but available as surplus HP "Hot Carrier" diode HP 5082-0023??? is one and certainly a REAL Ge. diode would work as well.

Doc

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

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.

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

MichaelMeissner:
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 :frowning:

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...

CarlosGz:
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

bperrybap:

CarlosGz:
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?

To be clear, something like this?

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

bperrybap:
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 :slight_smile:

Hello,

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

and advise which would be a good choice?

Many thanks,

Amadeus

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:

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.......

SolarPanels:
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_(SKU:_DFR0009)

Bummer...

[quote author=bwims link=topic=96747.msg912548#msg912548 date=134667261
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_(SKU:_DFR0009)

Bummer...
[/quote]
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.

bwims:
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.

FYI, I am working on my phi-3 shield design right now, a revision of my popular LCD keypad shield with lots of add-ons. It will have what these generic shields don't. You may choose which pin drives the LCD back light and only 3 resistors for 6 buttons on one analog input, of course compatible with phi-1 and phi-2 software and phi_prompt user interface library. I will be releasing the 20X4 version shield first. It will also feature a small proto area for and IC up to 16 pins, for example, shift registers etc can be used to sense/control multiple things via the RJ-45 ports. You can also use DAC or other stuff on the proto area.

Here is an idea:

phi-3 shield.png