LCD power requirements

Hello,

I am using a generic 16 x 2 LCD display for my greenhouse automation / monitoring project. I have wired everything up via bread board and I tried to initially use a dedicated power supply just for the bread board as there are a number of sensors all feeding off of the 5v rail, but when I tried to power LCD pin 2 or 3 (not sitting in front of my project) the LCD screen would not work unless I connected it to 5v supply off the Arduino. I am sure that I can power the sensors off of a dedicated supply but I don't know why the LCD doesn't work unless connected to the Arduino? Is that normal or just one of those random things with no logical explanation?

Thanks

You should be able to power your sensors and LCD from the Arduino board or an external supply provided:

  • They are both using the same voltage.
  • There is enough power available
    i.e. the sensors can LED can't want to draw more power than is available.

Have you connected the grounds together? the Uno ground to the power supply ground?

Can you show some photos of how you have things wired up?

--- bill

I am running 5 I2C LCDs off an external power supply. it must share a ground with the rest of the system.

everything grounded to everything else

You should be able to power your sensors and LCD from the Arduino board or an external supply...

LCDs and RF modules and motors are best served with an external power supply. it's a regulator heat issue.

You don't "power" anything from the Arduino - it is in no way a "power supply". You provide power - 5 V regulated - to the Arduino. So whenever such a statement is made, we automatically know there is a connection/ configuration problem.

And if you want help with a project, you show the project, a schematic diagram of the wiring and usable photos of the whole assembly. This is to verify that how you actually connected it matches your proposed schematic. :astonished:

Unless you are a professional photographer, are equipped and know what you are doing, do not attempt to take photos inside.

Take your parts outside in full daylight but not direct sun. Use a real camera able to focus in detail and if it has no "macro" function, keep at least half a metre away and use the (genuine) zoom.

Paul__B:
Unless you are a professional photographer, are equipped and know what you are doing, do not attempt to take photos inside.

My recommendation would simply be if the photo is not in focus, with good lighting and everything clearly visible, don't bother to post it.
From what I've seen, a lot of the bad images are often when people use a cell phone with a crappy camera or use a pocket camera and don't enable macro mode to get the image focused.

--- bill

Easier than taking a picture of my breadboard is to provide a fritzing image.

Relay blocks added for exhaust fan controls. Everything else works, but as I stated, if I power the breadboard independently the LCD no longer works, move back to 5v pin on arduino everything works?

Thanks

lkettlewell:
Easier than taking a picture of my breadboard is to provide a fritzing image.

While it may be easier for you, it doesn't show us what you are really using.
We have seen many cases where people have not wired things up the same way as the diagram or have other wiring or soldering issues.

You also didn't show us the configuration with the external power supply.

We need to see actual photos of your two setups.

The one that works and the one that doesn't.

One issue is that you really shouldn't use pin 1 or pin 0. Those are for the serial port.

--- bill

lkettlewell:
Easier than taking a picture of my breadboard is to provide a fritzing image.

Greenhouse_bb.png

Easy? Yes. Useful - no!

This is the reason we ask for a photograph.

lkettlewell:
Relay blocks added for exhaust fan controls. Everything else works, but as I stated, if I power the breadboard independently the LCD no longer works, move back to 5v pin on Arduino everything works?

Didn't read - or understand - my previous posting? The Arduino is not a power supply. What is powering it?

Useful hint I can deduce from your F****ing diagram (as we call them here :grin: ) - the contrast potentiometer for (pin 3 of) the LCD has one end connected to (some sort of) 5 V. Just remove that connection (or even connect both ends to ground) - works much better when setting the contrast. This will not fix your main problem.

Oh wait! Even stranger! You have a potentiometer connected to the Display backlight. Well, it is rather silly to have that one connected to ground also.

Do not use pin 0 or 1 on the Arduino.

And your suggestion that

lkettlewell:
if I power the breadboard independently the LCD no longer works

Makes me wonder whether you do indeed comprehend that the ground wire on the breadboard must always connect to ground on the Arduino when you connect an alternative 5 V source since that critical ground wire is conspicuously missing from your diagram.

Did I mention? This is the reason we ask for a photograph.

Paul__B:
... since that critical ground wire is conspicuously missing from your diagram.

It isn't just a missing ground connection to the ground rail but there is also no power connection to the power rail in the diagram, nor are their any connections to the LCD.
In the diagram, the LCD module is just laying on top of the breadboard with no connections to anything.
And there is no power being supplied to the Arduino.

--- bill

bperrybap:
nor are their any connections to the LCD. In the diagram, the LCD module is just laying on top of the breadboard with no connections to anything.

Well, fair go, it is after all, a Fritzing, isn't it? :roll_eyes:

I think we may allow that lkettlewell is actually sufficiently intelligent to have a 16 pin header soldered to all 16 pads on the LCD and correctly inserted into the solderless breadboard, in which case the circuit is almost correct save the ground connection and the power connection which he is saying he has made using two alternate methods which have not been properly and adequately described.

When we get those photographs of the two methods of connecting the power, we will know better, won't we? :astonished:

Fair point.

I did realize that the fitzring image was incomplete / incorrect after I hit "GO" but it was the end of a long day.

I apologize for not providing the pictures as requested; I was tempted to follow the condescending tone to take them outside even though it was 2300 and pitch black in the middle of a thunder storm.

I understand that the Arduino is not in, and of itself, a power supply, and to suggest so is ridiculous. I will concede that I didn't know that the GND needs to be connected regardless of what is used for a power supply.

Pins used for the LCD were taken from a published example, I will find another source of information as this community is clearly not the place to ask a question. Because realistically this was the answer to my question. [quote author=Geek Emeritus link=msg=4214843 date=1560889594]
I am running 5 I2C LCDs off an external power supply. it must share a ground with the rest of the system.

everything grounded to everything else

LCDs and RF modules and motors are best served with an external power supply. it's a regulator heat issue.
[/quote]
Everything that has come after has been used to demonstrate superiority in an area, where I had believed this to be an open community.

So, thank you Geek Emeritus, and Paul__B for giving me the benefit of doubt.

lkettlewell:
I will find another source of information as this community is clearly not the place to ask a question.

Alas, the other places are either even worse than this forum (eg stackexchange) of unreliable (eg instructables).

We're pretty much stuck with putting up with the condescending, demeaning tone of this forum, and sifting through the replies for the bits that actually help.

We get what we pay for....

In terms of power and how to power things. The real answer is “It depends”.
It depends on the power needed for your device(s) and how the power is being supplied.
For example, the official Arduino Uno uses a wimpy on board power supply and regulator design, particularly on the older Uno boards.
If you power the Uno using an external supply through the barrel connector, it can generate lots of heat for the regulator.
But the amount of heat and how much power it can supply before it fails depends on the overall current draw and the voltage being supplied to the barrel connector.
i.e. using a 12v power supply will generate more heat and be able to supply less power than than a 6-7 volt supply.

If you use the 5v USB connector for your power, you can supply quite a bit more current to attached devices with no regulator heat issues as it by passes the on board regulator.

For example, I do testing of my lcd library with up to seven LCDs with i2c backpacks and an i2c RTC all being powered by the Arduino board.
The Arduino board is powered by USB and the devices pull power from VCC off the Arduino board.

Some of the 3rd party Arduino clones use a better design and do not have as much as an overheating issue when using a external power supply to power the Arduino clone board.

Things can get a little more tricky if using multiple power supplies.

This is why I was wanting to see photos of what you have and how you have it wired up
since these are important details in solving your issues.

My advice would be to try avoid using an external DC supply going through the barrel connector to power the Arduino.
Ideally, if you can, use the 5v USB for powering everything.
Verify your loads using spec/datasheets and/or a meter. If the loads are too high, try to use the 5v USB for the Arduino board and as else much as you can, then bring in the external power (potentially even a different voltage) for the bigger stuff like motors that can be isolated using transistors, relays, etc…

— bill

spareProfile2:
We're pretty much stuck with putting up with the condescending, demeaning tone of this forum, and sifting through the replies for the bits that actually help.

disclaimer: No reflection on OP.

There'd be a lot fewer replies to sift through if people would spend thirty minutes reading the 'how to use this forum' sticky before posting. I'd guess under five percent do.

A not untypical post:

Thread title: I need help
Thread body: I combined a bunch of codes to blink a light and it doesn't work what could be wrong? It gives an error but I don't know what it means.

It's actually so bad that a first time poster is often rewarded with Karma just for using code tags.

A lot of what is seen as condescension is frustration at having to repeat the same requests for code tags, etc. ad nauseum - to the point that some have templatized (is that a word?) their responses in this area.

The coin has two sides.

dougp:
A lot of what is seen as condescension is frustration at having to repeat the same requests for code tags, etc. ad nauseum - to the point that some have templatized (is that a word?) their responses in this area.

Whatever the word, that is indeed what I have done; parts of my above responses are cut-and-pasted accordingly.

Notably #3.

My other responses are the result of substantially more research and careful composition = time. Which quite frankly, I can ill afford. :roll_eyes:

spareProfile2:
Alas, the other places are either even worse than this forum (eg stackexchange) of unreliable (eg instructables).

We're pretty much stuck with putting up with the condescending, demeaning tone of this forum, and sifting through the replies for the bits that actually help.

You say "demeaning", I say "chiding".

We get what we pay for....

and yet, some still end up in debt.