Do I need the power supply section on an arduino board, or can I run things straight off a battery?
The 7805 seems like a waste. You need to have at least 7v or more to get past the voltage drop in the 7805, the 7805 itself burns power, and takes up space of its own. I usually use Boarduinos and Boarduinos will fit my latest project, barely. But, I don't have room for a 9v battery.
The Atmega168 datasheet says it will run off of 2.7-5.5v. Can I hook up to a 3.7v lithium cell, straight to my Boarduino where the 7805 + - connections would be? Will my board run slower? Will a 16x2 character LCD display have usable contrast?
The problem with running unregulated power to an ATMega, is that you will sometimes experience strange things such as random shutdowns, false readings, etc. The 7805 helps to streamline the random fluctuations that you get with power supplies.
The 7805 Isn't very big...In fact, it's probably small enough that you could glue it (along with the decoupling capacitors) to the 9V itself.. I don't know what your power/space requirements are, but it seems like the 7805 is small enough to work fine..
The 9v battery will not fit in my project case, though. However, a 1000mah, 3.7v lithium cell phone battery fits perfectly and has 7 times the capacity of a rechargeable 9v.
I don't plan on ever running the device from any sort of mains-powered power supply. Why should a battery require any regulation at all? The voltage will change very slowly as the battery discharges...but what is the effect of this on the chip? I'm not doing any analog processing at all.
but what is the effect of this on the chip? I'm not doing any analog processing at all.
If you are not using any analog to digital processing then the biggest problem is possible random resets. Not sure if the Arduino uses the brown out detection fuse option or not that hold the processor in reset if voltage drops below a certain value. Others may be able to address that.
The only thing I would caution is the potential battery damage to Lithium rechargeable battery cells. If you discharge them to too low a value they can be permanently damaged, I know that and I've done it.
So you really need some kind of low voltage cut off circuitry when using them to protect the battery.
I say go for it. It's a hobby project - I assume you are not using it to run a pacemaker or an airport traffic controller or something else life-critical.
Yes you have the potential to damage your battery. I'd just try to remember to recharge it before it goes completely flat.
This thread is a good example of not providing all the relevent info in the first place, which lead the discussion down the wrong path.
I don't see where I added any info. I explained it all in my first post.
I forgot about the lithium discharge thing. If I leave the device on, it will probably permanently kill my battery eh. Guess I'll have to not do that....and open it up and recharge frequently.
First thing I'll try is see if the LCD has decent contrast at 3.7v.
So you see that the 16MHz crystal will only work when powering the chip from greater than 4.5V. In fact it is not sharply cut of like this see page 306 of the data sheet for a graph.
However, you could run at 8MHz but you have to change the bootloader code and some of the libraries to compensate for the speed. This is what is done on the arduino boards that run on 3V3.
Well, I don't want to change the libraries. If it was just a matter of all my delays lasting twice as long I could deal with it. Looks like I'll have to run running straight off of 4AAAs, or something else besides that awesome 1000mah lithium.
You could wire two of those lipo in series, and go through the regulator. Or wire two of the lipo in parallel, and the voltage would drop half as fast.
Basic lipo facts and warnings:
The full charge on a lipo cell is 4.2V, and the danger point for lipo cells is about 3.50. Most people who use very large lipo batteries are serious about maintaining their recharge ability, so they never drop below 3.7V, reached after burning roughly 80% of the rated mAh capacity. For either series or parallel applications, never try to mix a flat and a full cell, or an old and a new cell. The weaker cell will increase in resistance and heat first, and the circuit will over-stress them both. Excess heat, discharging below 3V, or charging over 4.20V per cell can cause them to catch fire much more easily than other kinds of batteries.
Either Grumpymikes post is wrong or I'm not understanding what he is saying. Or the data is being misread
I am running an ATMega8 with a 3.3V supply (sometimes less) and a 16MHz crystal without problem so I'm wondering if you could explain a little more what you mean
I am running an ATMega8 with a 3.3V supply (sometimes less) and a 16MHz crystal without problem so I'm wondering if you could explain a little more what you mean
It has to do with the way the chips manufacture, ATMEL does their specifications. Max speed Vs supply voltage is rated for worst case condition over full temperature range ratings. As such you could well run trouble free at 16mhz and 3.3vdc, however Atmel will not guarantee that speed at that voltage over all conditions.
The full charge on a lipo cell is 4.2V, and the danger point for lipo cells is about 3.50. Most people who use very large lipo batteries are serious about maintaining their recharge ability, so they never drop below 3.7V, reached after burning roughly 80% of the rated mAh capacity.
To be clear, what I have is not a lipo, to the best of my knowledge. It's a rectangular, 3.7v, 1000mA Lithium battery out of my wife's old LG cell phone. It has a foil covering with plastic end caps and copper contacts. I think it's a lithium ion chemistry, and not actually lithium polymer. Also, I think a battery like this might have built-in undervoltage protection, but I'm not sure.
I will try the 3.7v lithium and see if I get stable running and good LCD contrast. If all else fails, I can buy two very small lipos and run them in series through the 7805, but I would much rather keep my giant 1000ma battery...I think an arduino only draws like a ma so the device should run nearly a month on that thing.
Mine draws 20mA continuous sending a radio burst each 30 seconds giving an LED 3 small flashes at that time . With a 12V 7 A/H battery at 13V start it got it down to under 5 V in 3 weeks. And that's through a $14 voltage regulator that's supposed to be 90% or so efficient. Surprised me .
Running even the small 2 X 16 an LCD would consume more like 20mA wouldn't it?
I'm not sure. In the past, I have used rechargeable 9v (160mAh) batteries in the same configuration, using the 7805 onboard the Boarduino, and it lasts less than 24 hours. I hope to improve that, but maybe a month is a bit much to ask for. I need to look into what kind of power-sleep modes the arduino has and also into powering my LCD with a digital pin so that I can turn it off to save power.
