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Support Forum » LCD issue

December 13, 2014
by escartiz
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Hi

I need some help with this new lcd I got of ebay. If you look straight into the lcd I see the squares so I though I most have wire something wrong but then looking at it from the side I do see the "nerdkit is a live" message. Any suggestions what I might be missing? I can't test with the original lcd as it is already installed in another circuit. I double checked the wiring and everything seems fine. I am testing with the "initialload" file. Using a 1k resistor, removing it makes the lcd go blank, not even squares. I hope the lcd is not bad.

Thanks for the help

Pic 1 Pic 2

December 13, 2014
by BobaMosfet
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Yes, you need to adjust your contrast. Pin 3 (Vo) on the display. A 10K-Ohm trimpot will work. Trimpot wiper to Vo.

BM

December 13, 2014
by escartiz
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I had tried with an old 1k pot but nothing happened but I just did it with a multiturn 10k and it worked. awesome Thank you very much :)

December 14, 2014
by JKITSON
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BM

Very good post. This is one I will need to remember..

Thanks

Jim

December 15, 2014
by BobaMosfet
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Jim,

In the kits I sent you, you receive the necessary trimpots and matching schematic so you can see how it connects.

BM

December 20, 2014
by mongo
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I use a trim pot as a divider rather than open-ended. It seems to give better control.

December 21, 2014
by Rick_S
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Same here. It's always worked well for me that way.

December 26, 2014
by Ralphxyz
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Ok, how do you setup a trim pot as a divider rather than open-ended?

BM said "Trimpot wiper to Vo" is that open-ended? It "seems" like it would be a divider.

Ralph

December 26, 2014
by JKITSON
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Ralph..

The trim pot is connected as follows..

one end to ground

one end to vcc (+5v)

wiper or center as output.

Open ended would be with the ground only connected..

Hope this helps

Jim

December 26, 2014
by BobaMosfet
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Ralph-

Any trimpot is a voltage divider. You put the resistor in series between hot and ground,and then you divide the length of that resistor by the position of the wiper. Vo on the Display is attached to the wiper. Thus, by adjusting the trimport, the input to Vo changes.

BM

December 27, 2014
by Ralphxyz
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Thanks I just wanted to make sure and understand the "open ended" phrase.

Ralph

December 27, 2014
by JimFrederickson
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Hello Ralph,

I am still not sure if you have the answer that you were looking for.

There is a "rheostat" which has two connections and is a variable resister. The affect
of this part is mostly to control the current through a particular part of the circuit.

There is also a "Potentiometer" which has three connections and is a variable voltage
divider. (Power and ground usually on the outer pins and then the wiper/voltage
divider output in the middle.) The affect of this part is mostly to control the
voltage through a particular part of the circuit.

If a potentiometer does not have it's ground pin connected, I think that is the more
usual configuration for this, then it acts like a "rheostat". (I believe that is what
is being called "open ended". A potentiometer with one of it's outer pins
disconnected. Usually the ground, but it doesn't make a difference on most Potentiometers.)

Of course if you just use the outer pins and not the center/wiper pin, then you end up
with a fixed resistor of whatever value the Potentiometer is.

So a 10k Linear Pot with the wiper in the middle, is a 5k-5k voltage divider. (So a
divide by 2.)

It would be equivelent to:

         +5v -----5k-----+-----5k----- GND  
                         |  
                         |  
                       +2.5v

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