| Electronics > Beginners |
| Driving LCD backlight and contrast ping by Arduino |
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| VEGETA:
--- Quote from: BrianHG on April 24, 2018, 11:40:26 pm ---9v batteries don't have a lot of power. Take a look at the graph on the right of page 1 of a top end Duracell: http://www.celltech.fi/fileadmin/user_upload/Celltech/Prod.sheets/Duracell_Ultra-Power_9V.pdf At 50ma, Green curve, you will get just over 10 hours. Cheaper brands can have less than half that operating time. Now, if you go to 6x AA cells (9v), take a look at this chart: http://www.jmargolin.com/furnace/Ultra-Power_AA_MX1500.pdf Looking at the right, the 100ma line, you get around 24 hours, so, at 50ma, you can get around 48 hours of use. Around 5x of a 9v battery. Best thing to do is only turn on the back light when you need to. And anything else, shut down when not in use and put the processor into sleep and see how much you can lower your operating current. Another trick if possible, it to run your project at 3.3v. Current will radically drop with some MCU ICs. --- End quote --- My Arduino pro mini is 5v and I guess the LCD too. I don't currently have a 3.3v regulator to begin with, I only have mini dc-dc converters which can do the job. My other solution was to power it from 3.7v li-ion battery. I have small ones but again, I don't have protection and charge modules. I could power the thing from USB to charge it, then I won't worry about consumption. |
| BrianHG:
--- Quote from: VEGETA on April 25, 2018, 05:24:29 am --- My Arduino pro mini is 5v and I guess the LCD too. I don't currently have a 3.3v regulator to begin with, I only have mini dc-dc converters which can do the job. --- End quote --- Remember, if at 5v your project draws 50ma and you use a LDO, when powering from a fresh battery at 9v, you will consume 50ma from your battery all the way to it's death at around 6v. (This only works if your DC-DC converter takes 9v in directly and operates between 6v&9v) If you use a mini DC-DC converted, or 'buck regulator' set to 5v, with you project consuming 50ma at 5v, when the battery is new feeding the regulator 9v, the current at the battery will be around (assuming 85% efficiency, check converter data sheet) 32ma giving which you might think gives you around 56% more battery life, but, at the battery voltage drops, the current will increase to 50ma, so, lets say you will get 25% more battery life. Now, powering your project with 3.3v, if possible, say your project now draws 32ma. If you had a 3.3v LDO, the draw at 9v will also be 32ma giving you a true 56% more battery life. However, if you were now to use the DC-DC buck regulator, at 9v, your project will draw only 14ma. This is now a huge savings, we are talking a 350% increase in battery life, however, due to current going up as battery voltage drops plus alkaline batteries last much longer the lest power you consume, using the battery charts for 10ma, lets say around 30 hours for the 9v batteries, 250 hours for 6 AA batteries, 100 hours for 4AA batteries. Remember, unlike linear regulators where current consumed is equal to current at the voltage input, regardless of the voltage, with a switching buck converter, current consumed at the voltage input keeps getting less as voltage increases * by loss in efficiency. This is why the 6x AA batteries at 9v perform so much better than 4x AA batteries at 6v. Your best bet is to always measure current with a DVM to be sure. If you have a bench supply, you can confirm the efficiency of your switching DC-DC converter with different power supply voltages (simulating battery voltage drop). You may need a hefty cap on the power going into your regulator to smooth out your DVM current reading. Since I don't know what your device needs to do, I cant recommend much more. I have made a 9v battery powered PIC project with a 2x16 character display in the past, and, I actually powered on and off the LCD character display and everything else from the PIC when not in use and got everything down to an average 2ma draw at the battery giving a respectable 300 hours life, or if I wen with 6x AA cells, I could have had 1400 hours life. |
| VEGETA:
You said you powered the LCD from the pic, was it at 3.3v or 5v? My Arduino pro mini is the 5v 16 MHz version so I don't know if it is possible to work it down to 3.3v, if so, then I guess I need to modify the module itself or just solder the 3.3v power wire directly at the 5v pin. I want 9v battery simply because of space. I must put the project in an Altoid tin that I bought from Banggood so 4AA won't do the job. Anyway, how much current will the LCD back light consume at 3.3v? assuming fully powered not PWM controlled or something. If it has good brightness at 3.3v, then I might use a transistor to connect or disconnect the power to it without arduino pwm. |
| BrianHG:
If you are interested, here is a truly old Dave video on battery capacity: |
| BrianHG:
--- Quote from: VEGETA on April 25, 2018, 07:00:24 am ---You said you powered the LCD from the pic, was it at 3.3v or 5v? My Arduino pro mini is the 5v 16 MHz version so I don't know if it is possible to work it down to 3.3v, if so, then I guess I need to modify the module itself or just solder the 3.3v power wire directly at the 5v pin. I want 9v battery simply because of space. I must put the project in an Altoid tin that I bought from Banggood so 4AA won't do the job. Anyway, how much current will the LCD back light consume at 3.3v? assuming fully powered not PWM controlled or something. If it has good brightness at 3.3v, then I might use a transistor to connect or disconnect the power to it without arduino pwm. --- End quote --- Without specs and looking at what LCD module you have, you are in a grey area. The LCD module I was using at the time did support 3.3v operation and I ran the PIC at 3.3v, 1Mhz. In your case, you will need to breadboard/do some experimentation with different back-light brightness's and voltages and narrow down which components are drawing how much current and what voltages the parts support. Using switching PWM method for the backlight, it doesn't matter whether you power the LED with 5v at a lower PWM set brightness, or at 3.3v at a higher set % PWM brightness, that circuit is near 100% efficient. IE, if you set the 5v PWM to 50%, the LEDs will draw 10ma, not 20ma at 100% brightness. It's just how bright you want the backlight. It's all the other circuits which don't shine, but still generate minute amounts of heat where you get your power savings, like the Arduino itself. Maybe 5v is fine, but, set the oscillator to run at 4MHz, or, keep the Aduino in sleep and only wake up 100 times a second to process whatever work you need done, then remain asleep most of the time. You can cut that 20ma down to 2-5ma. With battery power, every drop counts. Many of my battery projects run my PICs at 32Khz or 400Khz where they draw only 0.1ma to 0.5ma. Also remember, an LDO also draws a few ma just sitting there as well unless you use a special low quiescent current LDO. |
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