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Driving LCD backlight and contrast ping by Arduino
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BrianHG:

--- Quote from: VEGETA on April 25, 2018, 09:10:25 am ---
--- Quote ---Which 16x2 LCD module?
--- End quote ---

typical one from aliexpress, bought them years ago.

--- End quote ---
You will need to test measure it.  Most older character modules, not counting LED, typically draw 2-5ma.  Yes, it's probably 5x to 10x the power consumption of the Digikey module I listed.  But, you need to measure to see.  They may be low power modules.


--- Quote ---
--- Quote ---DHT11
--- End quote ---

I have a breakout board version of it.

Anyway, here it says 3-5 volts: https://www.adafruit.com/product/386  so 3.3v is enough.


--- Quote ---Using 4 AAA batteries would give you around 1500-3000 hours.
--- End quote ---

1.2v * 4 = 4.8v so you mean connecting dc-dc here to get 3.3v? will work fine. How is it that these give better life?

Plus, how to wire them? will be messy

--- End quote ---
Read duracell data sheets:
9v             https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/MN1604_US_CT1.pdf  At 1ma, expect 700 hours (cell drained down to 5v) (Remember, a 9v battery has 6 really tiny puny 1.5v alkaline batteries in it)
AAA 1.5v https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/MN2400_US_CT1.pdf  At 1ma, expect 1350 hours (cell drained down at 0.9v x 4cell = 3.6v)

https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20180425013022&SearchText=6v+aaa+battery+holder


--- Quote ---
--- Quote ---Now, it will take a little quality programming and clock settings to get that 700-1400 hours.  Tweak everything out really well and you might almost double that.

--- End quote ---

How? you mean the power down line I wrong above?

--- End quote ---
?Typo in your question?
Other than turning on and off the LED backlight, and if you want the character module always on, when programming the Arduino, it is within software that you decide when and how often the CPU is processing and sleeping.  The link you made above to that site specifying the currents drawn by the Arduino at different voltages and either sleeping, or active is available for you to program.  However, if you want the Adrduino to automatically wake up from sleep, the power consumption is a little higher.  Also, the DHT11 also takes some time to sample a reading.  Deciding when to take readings from the DHT11, how often, let the Arduino sleep until the reading is ready, updating the readings once every 5 or 10 seconds, refreshing the LCD display once every 10 seconds.  Have you programmed all unused IO to an output or have pull-up or pull-downs on unused Arduino pins.  How many MHz will you run the Arduino at.  All these little things alter the power consumption when you are counting every 0.05ma or less.  The link you provided to the low power Arduino site has links on how to sleep the processor and wake up options like a timer and/or push button event.  I'm not specialized in Arduino, but with Microchip PIC and the power saving work required for battery powered devices I listed above are prety much universal with all microcontrollers and engineering out every last microamp is part of the game.

Powering down the LCD character module brings you into the 10k hours range as long as the regulator module doesn't eat too much.

Using 3x AAA cells, you dont need any regulator module at all.  In this instance, you can get your current consumption super low.


--- Quote ---
--- Quote ---  It now comes down to the quality of your 9v to 3.5v regulator.
--- End quote ---

Here it is: https://www.banggood.com/Small-Mini-360-Adjustable-DC-Power-Supply-Module-Mini-Step-Down-Module-p-917568.html?rmmds=myorder

--- End quote ---

Either measure that module, or, get the IC datasheet and I suspect the PCB will have the default schematic listed in the datasheet.
VEGETA:

--- Quote ---You will need to test measure it.  Most older character modules, not counting LED, typically draw 2-5ma.  Yes, it's probably 5x to 10x the power consumption of the Digikey module I listed.  But, you need to measure to see.  They may be low power modules.
--- End quote ---

Mine are white characters over blue background. So I guess we need some back light to display them nicely.

Is there such low power LCDs on Aliexpress or so? I wish so but it should work with Arduino libraries.


--- Quote ---Read duracell data sheets:
9v             https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/MN1604_US_CT1.pdf  At 1ma, expect 700 hours (cell drained down to 5v) (Remember, a 9v battery has 6 really tiny puny 1.5v alkaline batteries in it)
AAA 1.5v https://d2ei442zrkqy2u.cloudfront.net/wp-content/uploads/2016/03/MN2400_US_CT1.pdf  At 1ma, expect 1350 hours (cell drained down at 0.9v x 4cell = 3.6v)

https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20180425013022&SearchText=6v+aaa+battery+holder

--- End quote ---

Well, I will try 9v battery first since I have one which is pretty much dead already. This project is not meant to be on all the time since it is portable so I guess 9v battery works fine for now.


--- Quote ---However, if you want the Adrduino to automatically wake up from sleep, the power consumption is a little higher.
--- End quote ---

Yes, something like 2-3 seconds would be nice. I guess the WDT is the one to do this right? I can shut down all other timers and hardware modules except for it.


--- Quote ---Also, the DHT11 also takes some time to sample a reading.  Deciding when to take readings from the DHT11, how often, let the Arduino sleep until the reading is ready, updating the readings once every 5 or 10 seconds, refreshing the LCD display once every 10 seconds.
--- End quote ---

DHT11 is 1 Hz signal sensor, which means 1 signal per 1 second. So I am waiting 3 seconds to get the reading which is more than enough to gather 3 readings not just 1.

My guess was sleep, then wake up after 3 seconds, get DHT11 reading, output it to LCD, back to sleep again. Is there any problem?


--- Quote ---How many MHz will you run the Arduino at
--- End quote ---

It is 16 MHz but if I could get it to be much lower then I would. No need for high speed. Do you know how?


--- Quote ---Powering down the LCD character module brings you into the 10k hours range as long as the regulator module doesn't eat too much.

--- End quote ---

but it is not an option, LCD is the only visible thing in the project xD.


--- Quote ---Using 3x AAA cells, you dont need any regulator module at all.  In this instance, you can get your current consumption super low.

--- End quote ---

It has 1.5*3 = 4.5v so this will power the LCD and Arduino, but we agreed to 3.3v so...? plus wouldn't the drop voltage ruin everything eventually?

If I wack in the DC-DC module, then it is gonna be the same as before.
BrianHG:

--- Quote from: VEGETA on April 25, 2018, 12:40:21 pm ---Mine are white characters over blue background. So I guess we need some back light to display them nicely.
Is there such low power LCDs on Aliexpress or so? I wish so but it should work with Arduino libraries.

--- End quote ---
Verify the modules are 3.3v before buying and choose a light background with dark characters so you can read the module with the backlight off.
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20180425132259&SearchText=lcd+character+16x2+3.3v

--- Quote ---Well, I will try 9v battery first since I have one which is pretty much dead already. This project is not meant to be on all the time since it is portable so I guess 9v battery works fine for now.

--- End quote ---
You will then be using a regulator.

--- Quote ---Yes, something like 2-3 seconds would be nice. I guess the WDT is the one to do this right? I can shut down all other timers and hardware modules except for it.
DHT11 is 1 Hz signal sensor, which means 1 signal per 1 second. So I am waiting 3 seconds to get the reading which is more than enough to gather 3 readings not just 1.

My guess was sleep, then wake up after 3 seconds, get DHT11 reading, output it to LCD, back to sleep again. Is there any problem?
It is 16 MHz but if I could get it to be much lower then I would. No need for high speed. Do you know how?

--- End quote ---
When you get to this point, you will most likely be asking in the microcontroler's section of this forum where the Arduino guys are how to manage Arduino's sleep function and features & how to minimize current consumption.  You will need a DVM and 2 big caps and resistor to power your project and measure how much current it is drawing in real time when programming.

--- Quote ---It has 1.5*3 = 4.5v so this will power the LCD and Arduino, but we agreed to 3.3v so...? plus wouldn't the drop voltage ruin everything eventually?

If I wack in the DC-DC module, then it is gonna be the same as before.

--- End quote ---

The Arduino IC can run directly from 5v to 2.5v (you need to double check the part number with the data sheet, some low power versions work from 3.5v to 1.2v).  The character module also runs from 5v to 3v (The 3.3v versions also run on 5v) and the DHT also runs from 3-5v.  This means with 3x 1.5v batteries, 4.5v is fine for your system.  As the batteries weaken down to 3v, ie 1v each, your system will still work.  No regulator at all.
Though, this means the backlight dims with battery age, which you can software brighten, but, you don't have a regulator eating an extra 0.5ma to 1ma.  Also, if the Arduino has an internal voltage reference & ADC, your Arduino can now also tell you how much battery power you have left and it can automatically compensate the LED brightness as if you had a voltage regulator.  This is getting a little advanced and you might just go for a 9v battery with switching regulator and live with a shorter battery life.
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