Anyone know off the top of their head what current the Arduboy draws when based around the 5V Pro Micro?
A lot depends on how many pixels of the OLED display are lit but figure on about 30 to 40 mA.
Arduboy itself is anywhere from 7 to 30 depending on the screen like mentioned, using an arduino and modules usually has some voltage regulators on board so it can probably be a bit more.
The Arduino itself is usually about 3 to 5 on it’s own.
This is all from memory, so probably want to do some research to see how far my swags are.
Voltage regulators themselves don’t draw much current but they dissipate power to bring the voltage down. If the circuitry using the regulated voltage needs 10mA then there’s going to be 10mA going into the regulator and going out, as well. The voltage in is higher than out, though, so with the same current in and out, the voltage drop is where the power goes.
But that’s at the approx. 3.6V that the Arduboy runs at. At the 5V that a Pro Micro is running at, the current will be closer to 7 to 10 mA.
Been my experience that depending on how much you paid for your arduino has a lot to do with the overall quiescent current of the module. So it’s more of a YMMV kind of a statement, and yes ohms law for sure still applies.
Cool thanks for the info everyone. I am just looking at how to make my Arduboy diy project mobile. So I have been looking at using a 9v supply from 6xAAA batteries with a voltage regulator (burning the extra voltage off as heat) to step down to 5v or a 3.7v lipo with a dual booster / battery charger unit or a (think it is called) step down board to take 6v down to 5v.
As this is to be used in a school project for kids I was put off the lipo option due to safety and cost. However I have come across a supplier (trusted) in NZ who is selling a dual boost and charger board for a 3.4v lipo for about $2nz. Still not so sure about the fire hazard for school project.
The voltage regulator is dirt cheap at about $1 but the idea of burning off the voltage as heat seems a bit of a waste.
This is all new to me. Any thoughts?
From the info you have given on current drawn most of the options would work.
Why use a 9V input? A LDO linear regulator should have less than 1V dropout rating, so you only need 6V input. This could be done with 4xAAA alkaline. Note that there’s a 5V LDO regulator on the Pro Micro board, so you don’t need an external one. You just feed 6V or more into the RAW pin and the on board regulator will power the board at 5V. There then will also be 5V available on the VCC pin for the display and other external circuitry.
Another option is to use 4xAAA NiMH rechargable batteries without a regulator. This will give you (close enough to) 5V directly, so you don’t need a regulator. In this case you power the Pro Micro via the VCC pin instead of the RAW pin. However, with this approach, you have to make sure you don’t use alkaline or other 1.5V batteries in place NiMH because the resulting 6V could cause damage without regulation.
4xAAA NiMH cells, unregulated, is what I use for my Arduino Micro based breadboarded system. This is what I measured the current on yesterday to come up with the 30 to 40 mA figure. An Arduino Micro should be similar to a Pro Micro for current draw.
If you use 4xAAA alkaline for 6V then you have to drop the voltage by 1V to get 5V. At (likely worst case) 40mA, a 1V drop will use 40mW. The actual circuitry, running at 5V will also be drawing 40mA, meaning 200mW. So, the regulator is wasting (40/240=) 17% of the total power draw as heat. (And then all the other circuitry eventually turns the rest of the power into heat and light. Then the light is eventually converted into heat as well.)
If you use 4xAAA NiMH, unregulated, then no power (thus heat) is lost due to regulation, meaning batteries of a given mAh rating will last 17% longer.
My suggestion would be to use 3 AA or AAA, you’ll get the most efficiency that way. Adding another battery will make it run longer, but as @MLXXXp noted, you’ll be hitting diminishing returns from the regulator. This will work just fine. A single 9v battery would be just fine too, assuming the display has a voltage regulator on it.
I’ve done some destructive testing on the 32u4 and the SSD1306 oled and around 9v direct is where things start going the way of magic blue smoke.