hello,
i know it's possible to feed arduino directly to 5v pin if the input is properly regulated. what i don't know is whether a step-up converter meets such a requirements. the idea is to power uno + a tft shield off a single aa battery boosted to 5v using https://www.gme.sk/step-up-menic-z-0-9v-5v-na-5v-usb.
is it safe or i should better step it up to at least 7v and feed it to uno's onboard regulator?
thank you, jose
Powering direct from 5v step-up converter should be fine - BUT you must be careful to never have the 5v stepup converter connected when it's plugged into USB.
That's why I recommend - instead of using the 5v pin - powering it through the USB port by butchering a USB cable, and connecting the power source to power and ground on the USB cable. You can also buy cables with a USB connector on one end, and dangling wires on the other on ebay, but these are slightly more expensive than USB cables... Anyway, the point being to physically guarantee that it won't ever be connected to USB while also powered with external 5v.
This isn't an issue if you use the barrel jack (or vin) to feed the regulator.
Hi
the idea is to power uno + a tft shield off a single aa battery boosted to 5v
I think you need to do some power calculations.
The current being drawn from the battery will be at least 3 times the 5V current supplied to your project.
Power In = Power Out + losses.
Can you tell us your electronics, programming, Arduino, hardware experience?
Tom... 
Doomed to fail.
The AA battery has to deliver 4 or 5 times the current used on the 5volt side.
It will likely drop below 1volt quickly under that load.
Two or three AA batteries in series might work.
I think those modules are designed for a ~3.7volt LiPo.
Leo..
DrAzzy:
Powering direct from 5v step-up converter should be fine - BUT you must be careful to never have the 5v stepup converter connected when it's plugged into USB.
Why is that? Will it feed to or from the USB driver through the power selection MOSFET?
i have zero academic electronic engineering background and been playing with arduino and the likes for less than a year. i am aware of some limits and learning on the go. also have some programming experience but the software part of my project is pretty much finished, the only thing missing is "runs outdoor" feature.
using an usb b port of arduino uno sounds like a good idea - i plan to put it uno into a box and keeping the power source external will enable for an easier battery replacement. yesterday i did a quick test with multimeter.
a good thing is that arduino started and the sketch worked okay. as you indicated, the current draw was higher, even when the arduino went into a sleep. uno itself during a sketch run draws around 210-220 ma, with a step-up-converter it goes to around 500-560 ma. not sure how soon the aa battery will be able to supply >0.9v at this discharging rate so i guess i will just need to measure. if i get a little more than an hour of runtime then i am happy. if not then maybe this could help (also keeping a small form factor: https://www.tindie.com/products/fundamentalz/aa-arduino-power-shield/)
thank you all for valuable comments,
jose
"About an hour" is probably all you'll be able to get. If you're OK with that then good. If not, you've got work ahead of you.
If you want better battery life, answer the following questions:
Exactly what TFT shield are you using? How often do you need to write to the screen? Is there a backlight?
What size/weight constraints do you have for the battery?
What battery life would you consider to be ideal?
There's probably some room to improve your sketch with some power management features, and changing from an Uno to a Pro Mini (exact same chip, just a different board) will help with that.
Another option is to just add more batteries. Or use larger batteries. Or build in a LiPo with a recharging circuit.
hello,
just did a test with a fresh single eneloop pro aaa 930 mah. i was only able to cross a 30 minutes mark before the voltage reached 0.9v and arduino shut itself down. in theory i should be able to reach 80 minutes with an 2500 mah aa on the other hand.. i already ordered the power shield (with lipo step-up) from adafruit..
it's an mcufriend family 2.4" spi based tft: https://www.gme.sk/shield-lcd-tft-2-4-displej-dotykovy-pro-arduino-uno
a big downside of this product is that backlight is powered from a 5v pin without a software ability to turn it off. they say that i may want to put a resistor and control 5v pin externally. but that would mean opening shield up and making things ugly. that is why i need to draw power constantly.
a size of two aa's is an absolute acceptable maximum
90 minutes is fine
i will add more tests until the adafruit shield hits me. j
Yeah, it's the backlight that's killing you there. I have an LCD display, and at max brightness the backlight uses nearly 250 mA. Roasted a poor 7805 that I hadn't heatsinked.
2 AAs is pushing it a bit. Since you can't disable to backlight (or don't know how) it's a huge power sink.
A cheap USB power bank might be worth consideration since they already have the recharging and regulation circuitry built in. Look for ones above 2000 mAh and you could probably get a few hours usable life out of a full charge.
The only downside is that most power banks turn off the output while you are charging them.
The 2500mAh rating is for a slower discharge, like 20 hours. In 1 hour the higher current wastes more energy in the battery's internal resistance.
Here are the test results. All but Eneloop batteries were freshly charged, Eneloop ones were just unpacked and tested immediately. I cannot quite understand how a doublepack of Sony AA's lasted less than a single one.
Anyway the performance of Eneloop Pro 2500 is simply great and totally exceeded my expectations.
| Voltage | Brand | Model name | Listed capacity (mAh) | Connection | Endurance (minutes) |
|---|---|---|---|---|---|
| 9 | Energizer | n/a | 175 | barrel jack | 59 |
| 9 | Tronic | Energy 200 | 200 | barrel jack | 63 |
| 1.2 | Eneloop | AAA Eneloop Pro | 950 | usb-b via step-up to 5V | 39 |
| 1.2 | Sony | AA CycleEnergy | 2000 | usb-b via step-up to 5V | 68 |
| 1.2 | Eneloop | AA Eneloop Pro | 2500 | usb-b via step-up to 5V | 124 |
| 2x 1.2 | Sony | AA CycleEnergy | 2x 2000 | usb-b via step-up to 5V | 31 |
jose1711:
I cannot quite understand how a doublepack of Sony AA's lasted less than a single one.
Did you put one in backwards or something? Or use an old one accidentally? That's a pretty obvious outlier there.
jose1711:
Here are the test results. All but Eneloop batteries were freshly charged, Eneloop ones were just unpacked and tested immediately. I cannot quite understand how a doublepack of Sony AA's lasted less than a single one.Anyway the performance of Eneloop Pro 2500 is simply great and totally exceeded my expectations.
Voltage Brand Model name Listed capacity (mAh) Connection Endurance (minutes) 9 Energizer n/a 175 barrel jack 59 9 Tronic Energy 200 200 barrel jack 63 1.2 Eneloop AAA Eneloop Pro 950 usb-b via step-up to 5V 39 1.2 Sony AA CycleEnergy 2000 usb-b via step-up to 5V 68 1.2 Eneloop AA Eneloop Pro 2500 usb-b via step-up to 5V 124 2x 1.2 Sony AA CycleEnergy 2x 2000 usb-b via step-up to 5V 31
What is your criteria for how long the batteries last, what has to happen for you to say the battery has given its all?
Tom...
What is your criteria for how long the batteries last, what has to happen for you to say the battery has given its all?
the timer started when a sketch displayed a text on the screen (checking touch events in a loop) and stopped as soon as the display showed white and/or started to flicker.
jose1711:
the timer started when a sketch displayed a text on the screen (checking touch events in a loop) and stopped as soon as the display showed white and/or started to flicker.
So you are not measuring the terminal voltage of your batteries and measuring how far you are discharging them.
BAD METHOD.. >:(
You never discharge a battery like that.
You need to research as to how far you can let the terminal voltage of your batteries get down to, before you start damaging the battery and limiting their recharge cycles and life.
Your test should be to determined on how long you can run your project until the batteries get down to their recommended minimum terminal voltage.
Tom... :o
the step-up converter stops working when voltage on the input is below 0.9v which i read is the absolute minimum for several (most?) nimh aa batteries.
jose1711:
the step-up converter stops working when voltage on the input is below 0.9v which i read is the absolute minimum for several (most?) nimh aa batteries.
Did you measure it?
"Absolute" you don't push to this limit EVERYTIME the time.
Personally I would never discharge a NiMh that low.
Tom..