![]() This could happen if the excess current draw isn't large enough to causeĪ power issue for the backlight when doing the above test. It is possible that there is still an issue even if the backlight doesn't "blink" during Then set the D10 to OUTPUT for off and INPUT for on. If the backlight, blinks when you touch the D10 wire to VCC, the shieldĭo not set D10 to HIGH or use PWM on this shield unless you modify it.įirst set D10 to LOW. Ground the wire going to D10, the backlight should go off.īriefly (and I mean just a brief touch) connect the wire from D10 to Vcc. When power is turned on, the backlight should light. Hook up ground and 5v to the corresponding shield pins. Refer back to the original post for details.Īttach a wire to the D10 pin on the shield. Use the test sketch, or the hd44780 library and its test sketch to test for the issue. The test below can cause damage to the lcd shield. I attached photos of the emartee board and my diode mod, to allow safe backlight control.įor those wanting to test their shield for this problem, there is an easy test. Once you cut that header pin, there will be no issues and D10 is available for other uses like other shields underneath the LCD/keypad shield. If you don't want/need backlight control and are ok with having the backlight on all the time, cutting the D10 header pin from the lcd/keypad shield might be the easiest solution. On and to output and low to turn the LED off. There is also a software alternative which is to set the pin to input mode to turn the backlight (backlight will also not be 100% off but so dim that you won't see it) Not as power efficient as the diode when d10 is high (wastes about 8ma) but works ok. Under heavy LCD activity with the backlight on.Īs an alternative a 1/8th watt ~510 ohm resistor could be used. I used a germanium diode 1n34a - which worked perfectly and the AVR no longer gets warm The trace can be cut and a diode dead bugged to the board.Īnother issue is that you can't use a typical silicon signal diode like a 1n4148 as the voltageĭrop is too high and the backlight will not go all the way off. ![]() The trace to D10 goes around the header than drops through the board. It turns out that this can actually be done on the emartee board without desoldering Pull the base low but not short out when D10 is HIGH. The answer is to add a diode between D10 and the base so that D10 can The issue I had on my emartee shield is that the pullup and the transistorĪre under the LCD which is soldered to the shield/board, which really limited what could It is also possible to alter the circuit on the shield however, ![]() The real solution is a different backlight circuit design. Overloading the Arduino pin which may eventually cause problems and perhaps Yes the backlight is on and it "appears" to be working but it is massively In those backlight circuit designs, the problem is that the Arduino pin is shorting to ground through the It was supposed to also turn the backlight on when D10 is HIGH. The 4.7k pullup turns on the transistor if D10 is an input and the transistor turns off whenĭ10 is low. ![]() The idea was that the backlight would be on by default and then pin D10 could control it. See the reference schematic (look closely at the transistor that controls the backlight) It is definitely an issue for these LCD keypad shields: While not as good as h/w fix, for many situations it can be "good enough". Has been updated to contain a zip image (SWblCTL.zip) of some additional information Warning to users of some vendors LCD keypad shields - #2 by bperrybap - Displays - Arduino Forum Warning to users of some vendors LCD keypad shields - #99 by system - Displays - Arduino Forum There has been 1 reported case of the test sketch not detecting the issue a Leonardo boardĪnd the Leonardo eventually being damaged after using the backlight. Warning to users of some vendors LCD keypad shields - #4 by bperrybap - Displays - Arduino Forum See response #3 for a safe alternative to using the sketch: The only safe way to verify this issue is to not use the Arduino to try to detect this issue. There is the possibility that running this sketch will damage the AVR on the Arduino board. Since this h/w flaw in the shield is stressing the AVR way beyond its rated limits Warning to users of some vendors LCD keypad shields - Displays - Arduino Forum Warning to users of some vendors LCD keypad shields - #60 by bperrybap - Displays - Arduino Forum See this thread message for the test sketch: I have created a test sketch that will automatically detect if the shield has an issue. See this thread post for more information: You can download a sketch to test the h/w here:įor those that would like to do backlight control, you can use my hd44780 LCD library package (available in the IDE library manager) that supports backlight control and will auto detect this issue and work around the issue in s/w for shields that have the issue.
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