Displaying potentiometer value on LCD display - Current limitations?

I have a 25K OHM potentiometer wired to (3x) 1.05a drivers. I'd like to display the amount these drivers are dimmed on an LCD display. From what I've read, it may not be possible to achieve my goals with Arduino.

When you are using an external power supply, through the barrel power connector, you are limited by the local 5V regulator, which is rated for a maximum of 1 Amp. However, this it also thermally limited, meaning that as you draw power, the regulator will heat up. When it overheats, it will shut down temporarily.

I decided to post to the forums in hopes that someone maybe knows a way to do this.

Thanks in advance.

Do you even have a clue how much you can do with 1A of power? What are you doing that requires allot of power? I don't really understand what your goals are here?

Mikeb1970: Do you even have a clue how much you can do with 1A of power? What are you doing that requires allot of power? I don't really understand what your goals are here?

Yes...I'm designing a lighting array using Chip On Board (COB) LEDs for horticulture. The fixture will be (14x) COBs driven @ 1.05a giving them a fV of 51.5 for roughly 54w/COB and 757w for the fixture as a whole. I'm aiming to achieve 1,500 PPFD (Photosynthetic Photon Flux Density) over a 4'x4' footprint. You need a lot of light to do that.

I looked into Darlington Arrays and even they are rated @ 1.5a. Ideally the fixture would be dimmed using one potentiometer, and the dimming value be shown on an LCD display.

Do you have any ideas?

I will have a look at the datasheets and try to think of a solution.

Yours,

Mike

Mikeb1970: I will have a look at the datasheets and try to think of a solution.

Yours,

Mike

Thanks Mike, I appreciate it!

What datasheets? There is no mention of a driver part number, no links, nothing to do here with the exception of wondering what the heck Mikeb1970 is researching...

OP: please post the part number or a link to of the specific led driver you plan to use.

avr_fred: What datasheets? There is no mention of a driver part number, no links, nothing to do here with the exception of wondering what the heck Mikeb1970 is researching...

OP: please post the part number or a link to of the specific led driver you plan to use.

I'll be using 3 of these http://datasheet.octopart.com/HLG-320H-C1050B-Mean-Well-datasheet-99346265.pdf

HLG-320H-C1050B

Olympian:
I have a 25K OHM potentiometer wired to (3x) 1.05a drivers.

I’d like to display the amount these drivers are dimmed on an LCD display.

From what I’ve read, it may not be possible to achieve my goals with Arduino.

The datasheet suggests that you can connect the DIM pins (DIM+ and DIM-) in parallel, and control several drivers with one pot.

Pot value must be >= 100k/N drivers to get full brightness.
A 25k pot would be ok for four drivers, but not for three.
Three drivers and a 25k pot would be ~75% max LED brightness power.

If… you can do this, then there will be a voltage (0-10volt) across the DIM pins, that could be measured with a DMM.
It seems this is all secondary (low voltage side), so an Arduino should also be able to measure that voltage.
Because the 1:1 voltage divider to bring that 10volt down to 5volt is connected in parallel with the pot, resistor values have to be high. e.g. 47k:47k is essentially the impedance of another LED driver.

Not sure what current limitation has to do with it (the quote).

You can also turn things around, and let the Arduino be the ‘pot’ that controls the drivers.
All you need is four PWM pins, four opto couplers and four resistors.
That will PWM the LED drivers with a value generated by the Arduino.
The Arduino will know that value, so can also display it on an LCD.
Leo…

Wawa: The datasheet suggests that you can connect the DIM pins (DIM+ and DIM-) in parallel, and control several drivers with one pot.

Pot value must be >= 100k/N drivers to get full brightness. A 25k pot would be ok for four drivers, but not for three. Three drivers and a 25k pot would be ~75% max LED brightness power.

If... you can do this, then there will be a voltage (0-10volt) across the DIM pins, that could be measured with a DMM. It seems this is all secondary (low voltage side), so an Arduino should also be able to measure that voltage. Because the 1:1 voltage divider to bring that 10volt down to 5volt is connected in parallel with the pot, resistor values have to be high. e.g. 47k:47k is essentially the impedance of another LED driver.

Not sure what current limitation has to do with it (the quote).

You can also turn things around, and let the Arduino be the 'pot' that controls the drivers. All you need is four PWM pins, four opto couplers and four resistors. That will PWM the LED drivers with a value generated by the Arduino. The Arduino will know that value, so can also display it on an LCD. Leo..

You can dim 3 drivers with a 25K pot if you wire a 10K resistor in series with the drivers/pot.

I'm happy to hear you believe this is possible. By current limitation, I was concerned Arduinos weren't capable of measuring this much current. Now that I know that is not the case, I think I'll delve into Arduino a bit deeper.

Is there any advice you can give that would aid an Arduino noob in tackling this project? 4 PWM pins, 4 Opto couplers, 4 Resistors. That gives me a good start, but I've got a ways to go. Thanks for the input.

Olympian: You can dim 3 drivers with a 25K pot if you wire a 10K resistor in series with the drivers/pot.

I'm happy to hear you believe this is possible. By current limitation, I was concerned Arduinos weren't capable of measuring this much current. Now that I know that is not the case, I think I'll delve into Arduino a bit deeper.

Is there any advice you can give that would aid an Arduino noob in tackling this project?

4 3 PWM pins, 4 3 Opto couplers, 4 3 Resistors. That gives me a good start, but I've got a ways to go.

Yes, you only loose some of the lower dimming range.

No current is being measured. Just voltage across the pot.

Start with an Uno, and play with the examples that come with the IDE. If you understand the basics, then come back to your LED drivers.

Make sure you understand the two options. 1) leave the pot, and measure voltage across the one pot. 2) replace the pot for three optos, and let the Arduino do PWM dimming (plants probably won't mind). Leo..

Wawa: Yes, you only loose some of the lower dimming range.

No current is being measured. Just voltage across the pot.

Start with an Uno, and play with the examples that come with the IDE. If you understand the basics, then come back to your LED drivers.

Make sure you understand the two options. 1) leave the pot, and measure voltage across the one pot. 2) replace the pot for three optos, and let the Arduino do PWM dimming (plants probably won't mind). Leo..

So with option (1) could I solder my driver's dimming lead wires to the potentiometer AND wires for connecting to my Arduino system? I'd assume you can but doesn't hurt to ask.

Olympian: So with option (1) could I solder my driver's dimming lead wires to the potentiometer AND wires for connecting to my Arduino system? I'd assume you can but doesn't hurt to ask.

Never used this driver, but it seems you can connect Dim(-) to Arduino ground, and DIM(+) with a voltage divider to an analogue pin. Measure DIM(+/-) voltage with a DMM. It might not be 0-10volt. Post a hand-drawn diagram, so we can check. Leo..

Wawa:
Never used this driver, but it seems you can connect Dim(-) to Arduino ground, and DIM(+) with a voltage divider to an analogue pin.
Measure DIM(+/-) voltage with a DMM. It might not be 0-10volt.
Post a hand-drawn diagram, so we can check.
Leo…

I measured the dimming leads and it peaked @ 70mV and stabilized between 58-60mV.

I took a crack at merging some code snippets together from tutorials I found.

#include <LiquidCrystal.h>	// include the library code:

LiquidCrystal lcd(7,8,9,10,11,12);	// Initialize the library with the numbers of the interface pins

const int analogInPin = A0;

int sensorValue = 0;	// Value read from the pot
int outputValue = 0;	// Value displayed on LCD

void setup()
{
	Serial.begin(9600);	// Rate of data transmission
	// set up the LCD's number of columns and rows:
	lcd.begin(16, 2);
	lcd.clear();
}

void loop()
{
	sensorValue = analogRead(analogInPin);	// Reading Potentiometer
	outputValue = map(sensorValue, 0, 1023, 0, 100); // Formatting reading

	lcd.setCursor(0,0); // Sets the cursor to col 0 and row 0
	lcd.print("Dimming %: "); // Prints Dimming % to LCD
	lcd.print(outputValue); // Prints formatted dimming value to LCD
	delay(1000);
}/**
https://create.arduino.cc/projecthub/Guitarman1/displaying-sensor-values-on-lcd-c0c44f?f=1
https://hobbybotics.com/tutorials/tutorial-measure-voltage-across-a-potentiometer/
**/

Olympian: I measured the dimming leads and it peaked @ 70mV and stabilized between 58-60mV.

That does not make sense. It should be 5-10volt DC between the two DIM pins with the pot on max brightness. Leo..

Wawa: That does not make sense. It should be 5-10volt DC between the two DIM pins with the pot on max brightness. Leo..

Apologies for the late response. Do I need to wire the pot to all 3 drivers with the 10k resistor to get the correct reading?

Yes, must measure that voltage with pot/resistor connected, and set to max brightness. Result would be useless otherwise. Leo..

Wawa: Yes, must measure that voltage with pot/resistor connected, and set to max brightness. Result would be useless otherwise. Leo..

I wired the 3 drivers up with the 10k resistor and 25k pot. I measured the D/C while turning the pot and it dims all the way down to 30%. I must be measuring the pot wrong because I can't get any measurements that make sense, but everything is definitely wired up correctly. I did find this though.

Before going into further details some basics electric characteristics of "3 in 1 DF " , regarding Dim- & Dim+ wires :

Vd: 10VDC +/- 0.5 V Id_max : 500uA (per driver ) Vdext _max : 11 VDC

Where Vd is the voltage between Dim+ & Dim - , Id_max is the max output current (signal current ) and Vdext_max is the max External voltage that can be applied .

Total Power dissipation of Dim circuit : 0.005 W = 5mW .

So it looks like I should be good.