I am working on a project that involves powering the Arduino Micro with an external battery. It is this I am having trouble with. From my understanding the required V in should be 7-12V.
Project background:
I am making a portable heart rate monitor and therefore the power source should be able to power an LCD and sensor. As far as the LCD, I am using the Monochrome 0.96” 128x64 OLED Graphic Display, which can be powered with either 3V or 5V. The sensor I am using is the Pulse Sensor, which can also be powered with 3V or 5V, but from experience usinging, 3V provides better functionality. The links to both of these products are provided below:
The components will be in a small casing, which will be 3D printed so I am looking for a small enough battery (rechargeable preferably) or a way to use multiple (1-3) coin cells to power the setup.
This is phase one of the project, so I am aiming for a battery life of at least 30-60 min.
I don't know the exact consumption of your circuit but if size is an issue you can probably use 2xAA if it only has to last an hour. (and you might even be able to use 2xAAA...)
Does it have to be a Micro?
How about a 3.3V, 8MHz ProMini, run from 2xAA or 2xAAA and power everything from 3V.
Use an FTDI Basic for USB interface.
Put a multimeter in series between battery+ and your circuit in mA mode, measure the current flow.
Coin cells won't do it, not enough current flow available, they are designed for very low flow/long life.
It does not have to be a micro, the reason I decided for the micro was to avoid the use of FTDI, but I am still deciding on exactly which board I should use.
I am trying to keep weight to a minimum as well, the objective is that this device can be mounted as a clip so user can see how heart rate changes during an activity
thanks for the explanation of why coin cells will not work
If I were to use a ProMini, does it work the same way, as in simply connect power source to Vin?
Would the 2 X AAA, be enough to power both LCD and Sensor for at least an hour?
Promini - connect 3V to Vcc. (not RAW, that goes thru the regulator).
Some of the Lithium AAA claim 3200mAH capacity.
If your sensor and LCD need 100mA, that'd be enough for 32 hours.
LCD says 20mA, I can't open the sensor page.
Promini with FTDI basic, or USB Light (Arduino's Atmega8U2 like Uno has), laid side by side are smaller than a Micro card I believe.
as far as the current goes and as was explained by CrossRoads, I believe I should be fine because LCD only uses ~20mA, regardless I will measure it once I get a hold of multimeter
@ CrossRoads
I noticed you checked out the LCD link I provided, not sure if you noticed but it mentions that it requires "need a microcontroller with more than 1K of RAM since the display must be buffered" and from my understanding the ProMini provides 1KB, would these two work? The "more than 1K" makes me a bit skeptical
I am trying to keep weight to a minimum as well, the objective is that this device can be mounted as a clip so user can see how heart rate changes during an activity
Could use a small flat LiPo battery then. This one is 1000mAH, 3.7V. Can find smaller. Run thru a silicon diode to drop voltage down to 3 to 3.3V.
With size and weight in mind I am leaning towards the following
The Monochrome 0.96" OLED display and the Pro Mini 3.3V
As a recap, the display requires ~20mA and using a multimeter the sensor I am using requires ~2mA (rounded to whole number), both display and sensor can be powered from 3.3V pin on an UNO therefore as suggested by CrossRoads, the Pro Mini should not be an issue
My only concern/thing I am a bit uneasy is that the display calls for "more than 1K RAM", but I believe the Pro Mini should be able to do the work
As far as battery power, what does diode do?
Also, do you think that what I have in mind will work fine or should I change something else?
Yes, Promini has 2K SRAM, same as the Uno.
I don't think the 3.3V regulator will work correctly with just a 3.7V input, it may need more. That's why I suggested the diode to introduce some voltage drop - and the lower voltage is for the other 2 devices. Promini will run just fine at 8 MHz from 3.7V up to 5.5V.
I think it's this regulator, so 3.7 down to 3.3 might be okay:
