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Author Topic: Do I need a resistor for this LCD backlight?  (Read 1238 times)
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I just bought an LCD display (http://www.sure-electronics.net/mcu,display/DE-LM005.pdf) and want to power the backlight.  However, I have no idea if I need a resistor!  The datasheet isn't too helpful.  If I don't use a resistor to power the backlight, will I burn out the backlight?
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Probably but a 150 ohm resistor isn't too hard to find GET one and install it B4 you power it up!., I'd stay AWAY from Sure Electronics, I have a 22 letter lone correspondence chain on a "Low Power Pic development board" that I bought from them and couldn't re-program from the ICSP Port... With a Pickit 2 the ICD2 board or a Modified Picstart programmer with a special header... they 'finally' determined that I was attempting to program it improperly (I was supposed to program a regular PIC18F4520 as a low voltage part (PIC18LF4520) even tho the part was marked clearly enough for my old eyes to read unaided. I tossed the board and Sure Electronics... Any body wanna buy an unused 3208 display board (2 Ea) and a "New" style controller, I'd cheerfully trade it for 2 Pro Mini's from Ebay ($10.00 ea 5V 16Mhz). Their (Sure's) policy seems to be to wear you down until you get disgusted enough to quit pestering them, They even demanded it be sent back to Verify my findings... Yeah Right spend $15.00 on postage for a $30.00 board... I'd sooner use a hacksaw and "Fix" it properly first by turning it into 2 really useful paperweights. Cheaper and of much more utility.

Doc
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Probably but a 150 ohm resistor isn't too hard to find GET one and install it B4 you power it up!., I'd stay AWAY from Sure Electronics, I have a 22 letter lone correspondence chain on a "Low Power Pic development board" that I bought from them and couldn't re-program from the ICSP Port... With a Pickit 2 the ICD2 board or a Modified Picstart programmer with a special header... they 'finally' determined that I was attempting to program it improperly (I was supposed to program a regular PIC18F4520 as a low voltage part (PIC18LF4520) even tho the part was marked clearly enough for my old eyes to read unaided. I tossed the board and Sure Electronics... Any body wanna buy an unused 3208 display board (2 Ea) and a "New" style controller, I'd cheerfully trade it for 2 Pro Mini's from Ebay ($10.00 ea 5V 16Mhz). Their (Sure's) policy seems to be to wear you down until you get disgusted enough to quit pestering them, They even demanded it be sent back to Verify my findings... Yeah Right spend $15.00 on postage for a $30.00 board... I'd sooner use a hacksaw and "Fix" it properly first by turning it into 2 really useful paperweights. Cheaper and of much more utility.

Doc
I bought a 20x4 LCD with a backlight for only $10.  It works and it sure is a bargin.
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last month I bought 5 for 8.50 ea... free shipping too... But you did well as they are still at 15 to 20 dollars most places... Still see 16X2 displays for 8 to 12 dollars... maybe I will buy one sometime and get to see 90's technology again. seriously I own two and they are parts of dedicated test equipment or I'd have tossed them both too...


Doc
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You probably need a resistor.  A resistor will never hurt.  Put a 200 ohm or so one on either on +V or 0, it doesn't matter, and if the backlight isn't bright enough for you, adjust it down.
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On all the LCD displays I have used, the backlight LCD A and K wires are soldered on to the board at one end of the display. Use a multimeter to check the resistance between those joints and the backlight connections on the edge of the board. That way, you can tell whether there is already a resistor on the board.
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On all the LCD displays I have used, the backlight LCD A and K wires are soldered on to the board at one end of the display. Use a multimeter to check the resistance between those joints and the backlight connections on the edge of the board. That way, you can tell whether there is already a resistor on the board.
Using a multimeter, I found out that there is no resistance.  However, I traced the connections with my eyes and found a 47 ohm resistor.  I thought this was good enough so I connected the backlight directly to +5v and it worked without burning out!  Thanks for your help.
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last month I bought 5 for 8.50 ea... free shipping too... But you did well as they are still at 15 to 20 dollars most places... Still see 16X2 displays for 8 to 12 dollars... maybe I will buy one sometime and get to see 90's technology again. seriously I own two and they are parts of dedicated test equipment or I'd have tossed them both too...


Doc

May I ask where you bought yours?  The cheapest I have seen is $6 + free shipping on eBay, but it's all the way in Hong Kong!
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Using a multimeter, I found out that there is no resistance.  However, I traced the connections with my eyes and found a 47 ohm resistor.  I thought this was good enough so I connected the backlight directly to +5v and it worked without burning out!  Thanks for your help.

I'm glad you sorted it. To anyone else reading this thread: if you do the same thing and find an SMD resistor in the circuit, always check the resistor value before assuming you don't need an external resistor. 0 ohm SMD resistors are common, and I have seen them used in exactly this situation!
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I recently bought 3 20x4 LCDs from a HK dealer and he had it to me in 8 days, which is fine with me.  Paypal says I paid 23.64 for 3.  I  think these displays are the greatest, a lot easier to use than the serial port if you have limited information to display:



There is a resistor on that backlight.  I forget the value.
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JoeN, that looks exactly like the one I have!  What GPS module is that?
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This one:

http://www.pololu.com/catalog/product/1249

After letting that run for about 10 minutes I put the coordinates into Google Maps and the X was right on my house, about 10-15 feet from where the board actually was.  Very good accuracy, at least if this particular module is representative of the model in general.

The temperature and humidity module is this one:

http://www.sparkfun.com/products/8257
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Code:
... found a 47 ohm resistor.  I thought this was good enough ...

If you think you might use your device outside, or at night, consider using a trim pot so you can adjust the backlighting.
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