Hi,
I am creating a wearable LED project (8 strips of 6 lights-the LEDs are 5v). I have 3 NiMH batteries putting out 4-4.3 V I am currently powering the Arduino Micro and 1 strip of LED’s just fine off of this. I then saw that the Micro wants between 7 V and 12 V. What kinds of issues arise powering with lower voltage?
Also I was hoping to hook up an accelerometer that needs between 1.8 and 3.6. The 5 V pin puts out around 2 V and the 3 V puts out 0 V (dueto the low input voltage). So I could wire the acceleromter to the 5 V, however, when I plug in a USB to program the Arduino the 5V jumps to the correct level and I would break the acceleromoter.
Any ideas on the best way to provide power to this project would be appreciated!
cytochromec:
Hi,
I am creating a wearable LED project (8 strips of 6 lights-the LEDs are 5v). I have 3 NiMH batteries putting out 4-4.3 V I am currently powering the Arduino Micro and 1 strip of LED’s just fine off of this. I then saw that the Micro wants between 7 V and 12 V. What kinds of issues arise powering with lower voltage?
The timings will be off since the crystal will be running at a slower speed.
Also I was hoping to hook up an accelerometer that needs between 1.8 and 3.6. The 5 V pin puts out around 2 V and the 3 V puts out 0 V (dueto the low input voltage). So I could wire the acceleromter to the 5 V, however, when I plug in a USB to program the Arduino the 5V jumps to the correct level and I would break the acceleromoter.
Any ideas on the best way to provide power to this project would be appreciated!
You’re putting the 4.3V through the regulator which is then dropping it due to the chips voltage drop. You can put the 4.3V into the RAW pin and get 4.3V out of the 5V pin. Since the RAW doesn’t go through the regulator. Since the USB is always 5V internally regulated, there is no need for the Arduino to do anything with it.
You can put a voltage booster on the battery and get 5V if you need it. But you may not depending on your code’s timers. Once you get everything programmed and the timing is satisfactory, then don’t worry about the low voltage.
Thanks for the reply. I will see how the lower voltage affects the timing and hopefully will just adjust the code to compensate.
I don’t see a RAW pin on my board.
http://arduino.cc/en/Main/arduinoBoardMicro
I have a VIN (which is what I am supplying)
Also there is a 5V and a 3.3V which I believe I can use as outputs but can I also use the 5V as an unregulated input instead of the VIN?
Yep, the Micro only has one 5V pin. So the only voltage input is the 5V pin or the USB connector… It looks like the USB doesn’t go through the regulator so if you want you can try to make a USB plug that just has Ground and Positive. This would be connected to the battery at 4.3V.
You might consider hacking the Arduino Pro Mini for very low power, low voltage operation, as described in the following forum thread (see reply #11 et al.). Basically, you remove all the LEDs, regulators, etc. with a touch of the soldering iron tip. Those boards cost about $3.00 each on ebay and in my hands, seem to be well made and reliable. They have a 2x3 programming port for standard ISP programmers. The CPU probably won’t work at 16 MHz with low voltages, so you may need to use the internal 8 MHz oscillator on low voltages. http://forum.arduino.cc/index.php?topic=226261.0
cytochromec:
Hi,
I am creating a wearable LED project (8 strips of 6 lights-the LEDs are 5v). I have 3 NiMH batteries putting out 4-4.3 V I am currently powering the Arduino Micro and 1 strip of LED’s just fine off of this. I then saw that the Micro wants between 7 V and 12 V. What kinds of issues arise powering with lower voltage?
Also I was hoping to hook up an accelerometer that needs between 1.8 and 3.6. The 5 V pin puts out around 2 V and the 3 V puts out 0 V (dueto the low input voltage). So I could wire the acceleromter to the 5 V, however, when I plug in a USB to program the Arduino the 5V jumps to the correct level and I would break the acceleromoter.
Any ideas on the best way to provide power to this project would be appreciated!
How are you getting 4+V from 3 NiMH cells ? They're typically 1.2V / cell w/typical current draw. They might be 1.35V open circuit and just off the charger but that won't last long.
The Micro only “wants” 7-12V if you power it via it’s onboard voltage regulator, which then takes that voltage and regulates it to 5V to power the Micro’s 328p MCU, which runs at 16 MHz. If you want you can supply your own “regulated” 5V and not input power via the Vin pin. To do this you’d connect your battery pack to the 5V pin. But if your battery isn’t “5V” the MCU might not run. The 328 datasheet has a graph of guaranteed relationship between clock speed and supply voltage.
http://www.atmel.com/Images/doc8161.pdf
Maximum frequency is dependent on VCC. As shown in Figure 28-1, the Maximum Frequency vs.
VCC curve is linear between 1.8V < VCC < 2.7V and between 2.7V (=10 MHz) < VCC < 4.5V (= 20 MHz).
So to be guaranteed to run at 16 MHz you need to supply 3.8V. Then again it;s possible you’d get lucky and run at that speed on even less voltage. YMMV. I’d at least try it on your 3 NiMH cells.
I’d have used 4 NiMH cells in a 4-pack to power the Micro and LEDs. Then the 3.3V regulator on the Micro will run just fine and be useful to power your accelerometer.
Mee_n_Mac:
How are you getting 4+V from 3 NiMH cells ? They’re typically 1.2V / cell w/typical current draw. They might be 1.35V open circuit and just off the charger but that won’t last long.
Yeah I was surprised at the high voltage but I will test again after I put a little drain on the batteries.
Mee_n_Mac:
I’d have used 4 NiMH cells in a 4-pack to power the Micro and LEDs. Then the 3.3V regulator on the Micro will run just fine and be useful to power your accelerometer.
That was my original plan until I saw the high voltage using 3. So from what folks have said I can return to that plan.
Mee_n_Mac:
The Micro only “wants” 7-12V if you power it via it’s onboard voltage regulator, which then takes that voltage and regulates it to 5V to power the Micro’s 328p MCU, which runs at 16 MHz. If you want you can supply your own “regulated” 5V and not input power via the Vin pin. To do this you’d connect your battery pack to the 5V pin.
So with 4x1.2 V NiMH I would put 4.8 volts into the 5 V pin instead of putting into the VCC and having the Arduino’s onboard regulator drop the voltage. Then the 3.3 V will output a voltage I can use for the accelerometer.
Thanks to everyone for the help. I will post pictures of the finished project this weekend.
cytochromec:
So with 4x1.2 V NiMH I would put 4.8 volts into the 5 V pin instead of putting into the VCC and having the Arduino’s onboard regulator drop the voltage. Then the 3.3 V will output a voltage I can use for the accelerometer.
That would be my plan. Even at 1.35V each when fresh, that's 5.4V total and just within the spec. You could, just to be extra safe, put a diode btw the batteries and (just) the Micro and thus drop another 0.6-0.7V. Even as the batteries get depleted (they die pretty quickly at about 1.1V) the voltage to the Micro should be about/above 3.7V which should keep the 3.3V regulator in regulation (it's drop out voltage is < 0.3V) and perhaps even keeps the Micro's 328 MCU happy. Run the LEDs directly off the battery.
EDIT : note the discharge curve
http://www.powerstream.com/AA-tests.htm
http://www.powerstream.com/z/AA-NiMH-composite.png
