dr,A diode would be better than a resistor as that would allow d10 to fully pull the linegoing to the base of the transistor low (which eliminates the current going into it)but would not drive the line high which is where the issue is.An issue with using a resistor will be that while the resistor will protect the pin fromthe transistor drawing too much current when D10 is high,it creates a voltage divider with the existing pullup resistor so the signal goingto the transistor will be some voltage above ground that may not turn off the backlightas it will allow some amount of current to flow into the base of the transistor.The actual current going into the base will depend on the value of the resistoryou select, and value of resistor used on the shield as a pullup and the transistorused on the shield.Since most shields don't provide an accurate schematic with exact parts used,it's not possible to precisely calculate a resistor value or tell if it would completely turnoff the backlight (i.e. it might still be very dim, when you try to turn it off)For sure 125ohm or larger would protect the pin from excess currentbut depending on the other components, it might not fully turn off the backlight.If you wanted to experiment a bit, you could use a pot rather than a fixed resistor.Then when D10 is low, turn down the pot until you see the backlight go off.(there is no overcurrent danger in doing this)You then need to see if that value is large enough to protect d10 from over current.To do that you need to measure the current going through the wire when D10 is raised to high.Since the resistor value of the pot might be low enough to allow excessive current,you should carefully do this test.Just set it all up, but don't fully connect the meter. Then connect the meter. The backlight should light up and you canmeasure the current coming from D10. If it is over 40ma, the resistor valueshould be larger.While there is probably a resistor value that works acceptable, I'd usea diode instead as it won't waste additional power when the backlight is on.--- bill
Is there a specific diode I should use (ie could you link me to a good one)? And I can just connect it between d10 on the shield and the arduino? Does the orientation matter?I truly apologize for the simplistic questions.
Hey guys,I just got this 1602 keypad shield http://imall.iteadstudio.com/im120417018.html and found this thread.I've read through here and did the test - checked out bad, but I'm still very confused as to whether or not this is a shield that has the mentioned problem.If you run the test sketch and it reports the shield has the issue. The shield has the issue.As a noob I see the D10 input mod from post #3 as the best "fix", but I'm unsure as to how to use this.Could someone please upload a sample code with the D10 correction so me and others can test it out and use it in our future sketches?"sample code with the D10 correction" ?I'm not sure what you are asking for.I as well as a few others have posted h/w fixes for the issue.I also posted a text document in a zip file that includes a descriptionof the issue, along with 2 possible s/w only work arounds, along with instructionson how to use them in your sketches.
Hey guys,I just got this 1602 keypad shield http://imall.iteadstudio.com/im120417018.html and found this thread.I've read through here and did the test - checked out bad, but I'm still very confused as to whether or not this is a shield that has the mentioned problem.As a noob I see the D10 input mod from post #3 as the best "fix", but I'm unsure as to how to use this.Could someone please upload a sample code with the D10 correction so me and others can test it out and use it in our future sketches?Cheers!
OP I just tested your sketch and it's fried my brand new Leonardo board
I think you were very clear on the risks of testing this flaw. Just interesting the sketch didn't seem to pick up the issue when I ran it on the Leonardo and ran the BL as if the wiring was good. I have no doubt this is where the damage occurred and not in the microseconds you sketch took to test the fault.
would like to know where is the "test sketch and it reports the shield has the issue. The shield has the issue."the module turns on back lite bright blue with 16 spots on the upper line...