Hi Everyone,
I'm new to the forum and new to the world of Arduino. I have a project I am working on, and I am having battery life issues. I have an Arduino Uno board, with a 10mm white LED wired to it. The (+)wire is in the the 5 volt pin connection on the board and the (-)wire is connected to the GND pin connection. I have a resistor (340 ohms) that the (-)wire runs through. I coded the board to turn the light on for a length of 300ms every 4000ms. I have a small art project that will be up for 3 weeks, I would like to not have to replace the battery. So far I am using a Li 9V battery connected to the board. with it on continuously, the battery lasts around 20 hours. This was a new battery. The forward voltage of the light is 3.5 volts. Again I am new to this. I apologize if I have not provided enough info. Any advice would help.
Thank you
Thanks TanHadron, that was really helpful. I would like to stay with the Arduino platform. I am not quite sure how to work out the necessary power needed. Again I am new to this, and I don't have any background electronics so this is a little foreign to me
According to what I can find on the web, Lithium 9v batteries are supposed to have a capacity of about 1200 milliamp hours. If you're getting 20 hours out of one, that's 1200/20 = 60 milliamp draw. That's pretty close to what Nick Gammon reported with his. If you have a multimeter, you can measure how much yours is drawing, but that's a pretty good ballpark figure.
There are two ways to fix the problem. 1) Draw less current. 2) Supply more battery capacity.
I would like to stay with the Arduino platform
That's a little bit fuzzy, because technically, the bare bones board is still Arduino platform. Are you saying you want to keep the development board and use it to run the art exhibit? If so, that's going to be a major issue. Your little blinky light is not taking up very much power. The development board is. You could use a buck converter to get a little bit more time out of the battery, but other than that if you keep the development board it is going to be very difficult to draw less current.
So let's see how you can supply more battery capacity. Do you have the option of going in and turning off the display at night? That could save you 2/3 of the capacity. However, I'm guessing from the statement that you don't want to change out the batteries, that this isn't how you want to do it. So let's calculate how much battery power you will need to last 3 weeks.
Straight 3 Weeks = 3 * 7 * 24 hours. 504 hours. At 60 milliamp draw, that's 30,240 milliamp hours. That's 25.2 of those Lithium 9v batteries. You could wire up 25 of them in parallel and that would work.
Could you use a standard 6V lantern battery? Alkaline lantern batteries are rated at 26,000 millimap hours. That's 18 days. If you're not open over the weekend, that might work.
"That's 25.2 of those Lithium 9v batteries.You could wire up 25 of them in parallel and that would work." Thats alot of batteries! I am limited on space. Although its a little intimidating, I guess I could build it up from scratch. I am just not familiar with all the components and set up I would need. I am limited on space that is why I was trying to keep the battery small. I have five of these light units to do. I have about an 1 1/4" in. of space where the are being mounted. So maybe we start with Drawing less current? If so can I still use a 10mm white LED? I really appreciate your help. This info is exactly what I i've been looking for. I would say for now, a 6 volt Lantern battery is out. But i will consider it as a last option.
That's a little bit fuzzy, because technically, the bare bones board is still Arduino platform. Are you saying you want to keep the development board and use it to run the art exhibit? If so, that's going to be a major issue. Your little blinky light is not taking up very much power. The development board is. You could use a buck converter to get a little bit more time out of the battery, but other than that if you keep the development board it is going to be very difficult to draw less current.
Initially I meant the Development platform. But it is drawing alot of power. What board would you suggest to go with instead?
Would you be OK with using 3 or 4 AA batteries or AAA batteries? The problem with a 9v battery is that it exceeds the voltage that the microcontroller can use, so a power regulator is necessary. You can get a power regulator that uses very little power if you need, but it would probably be easier to run it on less power.
There are bare bones boards that you can buy. Look at this topic if you are interested in that way to go. If you are low on space, consider the Ardweeny.
http://arduino.cc/forum/index.php/topic,159341.0.html
This particular project could be done with a lot less hardware if you would like. You certainly don't need the power LED. You don't really need the clock crystal or filter caps, or even the reset pin resistor. You could do this entire project with just the microcontroller chip, the current-limiting resistor, the LED, and the batteries.
You could use a smaller microcontroller even. An ATTiny85 would work easily.