My project is a toy so it needs to be somewhat light and very portable. I need 6V for a servo and a brushed DC motor. So far all of the 5V Arduino boards need 7 volts or more. This suggests I need 5 AA batteries. So far, the only way I can figure out how to get to 4 AA's is to use a 3v Arduino board.
Suggestions?
Thanks - Doug
ddmcf:
My project is a toy so it needs to be somewhat light and very portable. I need 6V for a servo and a brushed DC motor. So far all of the 5V Arduino boards need 7 volts or more. This suggests I need 5 AA batteries. So far, the only way I can figure out how to get to 4 AA's is to use a 3v Arduino board.Suggestions?
a) 4xAA isn't really going to give you 6V. The 1.5V of a new battery only lasts a few minutes. An AA battery puts out 1.2 - 1.3V for most of its lifespan.
b) An Arduino will run off (eg.) 4V connected to the "5V input" pin (ie. bypass the regulator) but you won't get 5V on the I/O pins. Will the stuff you have connected to the I/O pins work with a lower voltage?
I plan to use some LEDs, a speaker, maybe a tilt switch etc. so I do not believe any of the input sensors will require 5V.
The brushed motor controller (considering the DRV8833 Dual Motor Driver Carrier) doesn't appear to be limited by 5V. The only spec I can't find is the one on the servo data input. I could assume it's needs a sink but I'm not sure, all it says is that it is 6V.
Thanks, this is very helpful.
This is always a problem. What I do is use boards with lo-dropout v.regs, so they will operate with about Vin = 5.5v
minimum, and then usually 6 NiMH rechargeable AA cells in series, which gives nominal 7.2V fully-charged. Your 6V
motor will run fine at 7.2V, as motors generally are rated over a considerable voltage range, 3V...9V. You can
throttle back the RPMs using PWM.
Also, you have to be careful in specifying which batteries. Nonrechargeable alkaline are 1.5V nominal, rechargeable
NiCad and NiMH are 1.2V nominal. The latter are considered to be discharged at about 1V.
An Arduino will run off (eg.) 4V connected to the "5V input" pin (ie. bypass the regulator)
I wouldn't recommend this with latest versions of Arduino.
The regulator is sensitive to being reverse driven.
Add a diode from 5V (anode) to Vin (cathode) to prevent damaging the regulator.
Somewhat obscure, but I recently bought some NiZn AA batteries (out of curiosity really).
They are rechargeable like NiMH but have a nominal voltage of 1.6V, so four of them make
about 6.5V (more like 7.5V freshly charged though, but should hold above 6V pretty well across
discharge history).
Hard to find, different charger needed, so not particularly practical, but a possible solution.
NiZn AA batteries
Good point, there are also rechargeable Alkaline now, and lithium of course. The all have somewhat different
voltage ratings.
The project is just a "smart" toy for my grand daughter, so power is not a critical issue, I just wanted to keep it light.
Maybe I'll just go with 6 rechargeable AA's for this project and keep my eye on moving to 3v3 for the next project. Now I need to get a handle on any motor noise on the line that needs to be suppressed so it doesn't interfere with the controller.
Whatever Arduino bd you have, check the specs on the v.reg, as it may be low-dropout. However, if it
has a protection diode in series in the Vin line, then you're also gonna lose another 0.7V or so there. If so,
once I had the battery holder wired up, I'd short across the diode.
CrossRoads:
An Arduino will run off (eg.) 4V connected to the "5V input" pin (ie. bypass the regulator)
I wouldn't recommend this with latest versions of Arduino.
The regulator is sensitive to being reverse driven.
Add a diode from 5V (anode) to Vin (cathode) to prevent damaging the regulator.
Can you elaborate on this a little? What does the diode protect, and how? Especially in a battery driven case.
See page 10
came to light earlier this year several folks repeated bricked Arduinos from supplying 5V direct to boards.
Thanks for the link.
Is this a problem caused by the constant low voltage driving the regulator (4v into a 5v input),or is it due to the fact that the batteries will lose V over time and drop below a minimum threshold?
Sometimes I power mine with a 5v phone charger that way and want to make sure I'm not doing anything foolish.
No, I think its more the 5V pin was being driven directly with nothing on the barrel jack input.
Better solution I think is to use the USB input for the power and let the auto switching take care of the power routing.
CrossRoads:
See page 10
http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF
came to light earlier this year several folks repeated bricked Arduinos from supplying 5V direct to boards.
Bob;
I've been thinking about this issue sense you have been raising it a couple of times lately. I certainly understand the issue and warnings about linear voltage regulators can have if there is voltage on their output terminal but no voltage applied to their input terminal, even some very old datasheets for the classic 7805 chips show adding a diode across inputs and output pins for protection from that issue.
However think about the standard Arduino Uno behaviour when it's being powered by USB only, The auto voltage selector circuit detects that there is no Vin voltage available so it turns on the FET switch to route USB +5vdc voltage to the board's Vcc bus which is the same as the 5V pin. So in that case there is +5vdc being felt on the output pin of the on board +5vdc voltage regulator but the regulator of course has no voltage on it's input as there is no Vin present in this case. So how is a different case then if someone is powering the board directly via the 5V and ground pins from an external regulated +5vdc voltage source?
If the newer type voltage regulator has a problem with applying external +5vdc to the 5V pin, I don't see that having any electrical difference then if the board is being USB only powered?
I have never been a fan of powering a standard arduino board via the 5V pin, but that's because of the issue of if you then plug the USB cable to the PC you are effectively 'hardwiring' (through the FET switch) the USB +5 to the external power supplies +5, never a good engineering practice to connect too different voltage sources together without some form of isolation. But in this case we are talking about the vulnerability of the on-board voltage regulator, and again I don't see a different condition for the regulator between being 5V pin powered or USB only powered?
So random users reporting 'bricked' boards is not a new report, but if it can really be caused because the arduino folks changed the brand/model of the on-board voltage regulator we really should try and put that to rest one way or another? We should try and minimize possible myth from facts as best we can by whatever means we have available.
Thoughts?
PS: And yes, like you my favourite way to power a standard arduino board with an external regulated +5vdc source is to take a spare USB cable, lop off the PC end and extract the power and ground wires and wire that to the external 5 vdc power supply. That way you get the advantage on the USB thermofuse and plus the auto-voltage circuit isolation will still function as designed if you care to take advantage of another external voltage source connected to the Vin circuit at the same time.
Lefty
Can I build a project using 4 AA batteries with a 5V Arduino board?
Yes you can. Just connect them and they will work.
I have not done any testing Lefty. I don't have any of the new boards with the later regulator to try this with.
I do see that some of the arduino pages have this added now "Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it. "
I was thinking perhaps connected but unpowered walwarts while powered from USB could be the culprit, but the reverse polarity protection diode should provide Vin isolation in that case.
CrossRoads:
I have not done any testing Lefty. I don't have any of the new boards with the later regulator to try this with.Me neither.
I do see that some of the arduino pages have this added now "Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it. "
Yes, I've seen that. I guess my question would be did they add that because of the recent change of voltage regulator or just because it's not a good engineering practice in general as I talked about below? Does anyone have a contact with a Arduino designer we could ask to find out their reason for posting that 'new' caution/recommendation?
I was thinking perhaps connected but unpowered walwarts while powered from USB could be the culprit, but the reverse polarity protection diode should provide Vin isolation in that case.
Yes, the Vin isolation diode would prevent any current flow from the board to anything connected to the external power connector, powered or off.
Lefty
PS: And yes, like you my favourite way to power a standard arduino board with an external regulated +5vdc source is to take a spare USB cable, lop off the PC end and extract the power and ground wires and wire that to the external 5 vdc power supply.
I'd certainluy go along with that as a recommendation. The few times I use an actual arduino (as I usually have my own design going) I am powered via PC/USB cable for software download/test.
In my designs, I bring in 5V from a walwart to power the card. Or 12V if LED strings are being powered, and use a 7805 regulator.
Or I bring in power via FTDI Basic for bootloading via MKii.
Does anyone have a contact with a Arduino designer we could ask to find out their reason for posting that 'new' caution/recommendation?
I believe they did respond here a while ago, when the issue of bricked Mega's started coming up.
CrossRoads:
Does anyone have a contact with a Arduino designer we could ask to find out their reason for posting that 'new' caution/recommendation?
I believe they did respond here a while ago, when the issue of bricked Mega's started coming up.
Did they state a reason?
Lefty