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Topic: Powering atmega328p with batteries (constant voltage requirement) (Read 5401 times) previous topic - next topic

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I am working on a project which has atmega328p and HM-11 bluetooth module. Bluetooth module requires 3.3 volts and likewise atmega328p also requires constant voltage for proper functioning, am I right ?

So, my power supply will be either 3.7 volts one cell Li-po battery or 3-4 AA size 1.5 volts batteries connected in series.

I believe I need some electronics to sustain the constant voltage, since the voltage of the batteries won't stay at the same level as it drains.

I think I need a boost converter and a switching one for efficiency. However, I am not very familiar with that concepts and powering an AVR through batteries.

Appreciate if you can inform me further with suggestions.

Peter_n

I have made a remote arduino two weeks ago:
An Pro Mini with ATmega328P at 8MHz, the voltage regulator removed. That should run at 2.5V to 5.5V.
An DHT22 which needs at least 3.3V.
An cheap 433MHz transmitter of 3V to 12V, but at 3V it has almost no power.
Using the VirtualWire, and Narcoleptic libraries.
With three NiMH AAA batteries.
I did a test with 3.0V and it was still working well. My DHT22 failed 1 in 10 times, but then I just don't transmit the data.

Everything depends on your Bluetooth module.
The ATmega328P can do 2.5 to 5.5V at 8MHz.

zoom

I have made a remote arduino two weeks ago:
An Pro Mini with ATmega328P at 8MHz, the voltage regulator removed. That should run at 2.5V to 5.5V.
An DHT22 which needs at least 3.3V.
An cheap 433MHz transmitter of 3V to 12V, but at 3V it has almost no power.
Using the VirtualWire, and Narcoleptic libraries.
With three NiMH AAA batteries.
I did a test with 3.0V and it was still working well. My DHT22 failed 1 in 10 times, but then I just don't transmit the data.

Everything depends on your Bluetooth module.
The ATmega328P can do 2.5 to 5.5V at 8MHz.
According to datasheet bluetooth module works in the range of 2 - 3.6 volts.
I read that 1.5 volts batteries drop down to 1 volts and then considered empty. So, 2 AA batteries would be 3 volts and drop all the way down to 2 volts. Which is not fine for AVR according to your ratings.

3 AA would provide 4.5 volts, which is higher than the max. voltage the Bluetooth module can stand.

PaulRB

Hi, an atmega328 can run right down to 1.8V at 1MHz, if that's quick enough for your needs. I have not done this myself. I understand you need to compile and burn a version of the bootloader that will run at 1MHz, i've seen instructions on doing this somewhere. That is, unless you want to program the atmega using ISP rather than serial.

Paul

Peter_n

When the ATmega328P is used with low voltages, the clock speed must be low. An 8MHz ATmega328P is still compatible with one of the official supported Arduino boards, but with lower clock speeds you have to make your own bootloader and add you own board definition.

The specifications for the HM-11 are not always the same. Some say 2.5 to 3.7V. Some modules have a voltage regulator on board so the module will work at 5V as well.

A Li-ion battery is 3.0 to 4.2V.

I think you need some kind of buck-boost converter. For example this one : https://www.sparkfun.com/products/11231

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When the ATmega328P is used with low voltages, the clock speed must be low. An 8MHz ATmega328P is still compatible with one of the official supported Arduino boards, but with lower clock speeds you have to make your own bootloader and add you own board definition.

The specifications for the HM-11 are not always the same. Some say 2.5 to 3.7V. Some modules have a voltage regulator on board so the module will work at 5V as well.

A Li-ion battery is 3.0 to 4.2V.

I think you need some kind of buck-boost converter. For example this one : https://www.sparkfun.com/products/11231

This boost converter supplies constant voltage, for instance 3.3 volts, regardless of my input voltage is 3.7 volts or 3 volts, right ? Is this how all buck-boost converters work ? Asking cause a cheaper alternative would be great, since this is quite expensive.

Paul__B

#6
Aug 02, 2015, 11:33 pm Last Edit: Aug 02, 2015, 11:35 pm by Paul__B Reason: Sigh! Always more.
I am working on a project which has atmega328p and HM-11 Bluetooth module. Bluetooth module requires 3.3 volts and likewise atmega328p also requires constant voltage for proper functioning, am I right ?
Umm, exactly no!

These are digital devices - they deal in binary values - HIGH or LOW, but as long as these are adequately distinguished, the exact voltage level is not critical.

The Bluetooth module does not want to see too much voltage, but can tolerate a reasonably lesser voltage.  You need the ATmega328 to be clocked at 8 MHz to operate at these low voltages.

Just use a single lithium cell which holds a very steady voltage by itself - much more practical than alkaline dry cells.  This is how mobile phones operate, and the electronics is designed around them.  They do not use buck-boost converters! :smiley-lol:

If the Bluetooth module is absolutely not specified to tolerate 4V in standby, then you may have to remove the Li-po battery to charge it.

john1993

lowest cost solution is to power both m328 and bt from one li or 3 nixx rechargeable with a diode. slightly more efficient is to use one of the 50 cent ebay step-up modules set to boost a single aa cell to 3.3v.

zoom

Umm, exactly no!

These are digital devices - they deal in binary values - HIGH or LOW, but as long as these are adequately distinguished, the exact voltage level is not critical.

The Bluetooth module does not want to see too much voltage, but can tolerate a reasonably lesser voltage.  You need the ATmega328 to be clocked at 8 MHz to operate at these low voltages.

Just use a single lithium cell which holds a very steady voltage by itself - much more practical than alkaline dry cells.  This is how mobile phones operate, and the electronics is designed around them.  They do not use buck-boost converters! :smiley-lol:

If the Bluetooth module is absolutely not specified to tolerate 4V in standby, then you may have to remove the Li-po battery to charge it.

What is the relationship between charging and 4 volts input to Bluetooth module?

Paul__B

What is the relationship between charging and 4 volts input to Bluetooth module?
Charging voltage on a Li-po battery goes up to about 4.0 or 4.1V (someone may correct me on this) so whatever electronics you have connected must be rated to at least tolerate this voltage even if it is not enabled.

If it - such as the Bluetooth module - is not rated for that voltage, then you will have to disconnect the battery and connect it only to the charger in order to charge it.

Peter_n

The charge voltage is 4.2V for consumer products to get the absolute maximum charge. For medical and military applications, the cell is sometimes charged only to 3.95V.

The Li-ion voltage (when not charged) is 3.0 to 4.2V (or perhaps 4.1V). The 3.0 is already dangerous low.

Here is a nice graph : http://www.richtek.com/battery-management/en/designing-liion.html

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