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Topic: The right way to drop 6v to 5.5v (Read 448 times) previous topic - next topic

ardandrew

Hi,

I am thinking of using 2 x CR2032 (for space considerations and increased mAh) which would give me 6v to run a 328p chip. I was thinking of using a voltage divider (1MΩ and 100KΩ resistors) that would drop it to 5.45v.

The project would be for a simple countdown timer that would then trigger two 5V active piezo buzzers.

I was wondering if this would be the right approach?

Thanks for any guidance in advance.

vaj4088

It is going to be hard to get enough current through 1 megohm and 100 kohm resistors unless you are planning to put very many in parallel.  Of course I don't know what you are planning because you did not explain. Remember that your Arduino acts similar to an additional resistor except that it is variable.

The voltage divider approach is not practical using batteries as an input.

A series diode (e.g. 1N4001) may be a more practical approach.


Wawa

I am thinking of using 2 x CR2032 (for space considerations and increased mAh) which would give me 6v to run a 328p chip.
Only connecting batteries in parallel will increase mAh.
mAh will stay the same when connecting them in series.
Leo..

raschemmel

Quote
I was wondering if this would be the right approach?
NO.

Voltage dividers are ok for signals or analog input but not for power input voltage reduction.

You would be better to use 3 batteries and use the external dc barreljack as the input.

Also, I would not choose a 2032 coin cell to run a microprocessor , even if it is only an ATMega328.
Find some other battery, like litheum-ion.
Two 18650 batteries in series is 2*3.7=7.4V which is ideal input voltage for a 5V regulator.
So get a 5V regulator, two 18650 batteries , a dual series battery holder, one or two  TP4056 lithium-ion battery chargers and then your set.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

jremington

#4
Aug 25, 2019, 07:03 am Last Edit: Aug 25, 2019, 07:04 am by jremington
An ATmega328 can run for years on a single CR2032 cell, if you do it right. Excellent low power tutorial here.

To get usable volume from the piezo buzzers, you probably need higher voltage, but they could be powered separately.

ardandrew

NO.

Voltage dividers are ok for signals or analog input but not for power input voltage reduction.

You would be better to use 3 batteries and use the external dc barreljack as the input.

Also, I would not choose a 2032 coin cell to run a microprocessor , even if it is only an ATMega328.
Find some other battery, like litheum-ion.
Two 18650 batteries in series is 2*3.7=7.4V which is ideal input voltage for a 5V regulator.
So get a 5V regulator, two 18650 batteries , a dual series battery holder, one or two  TP4056 lithium-ion battery chargers and then your set.
Thanks very much for all the replies and I think will go with raschemmel's suggestion!

ardandrew

It is going to be hard to get enough current through 1 megohm and 100 kohm resistors unless you are planning to put very many in parallel.  Of course I don't know what you are planning because you did not explain. Remember that your Arduino acts similar to an additional resistor except that it is variable.

The voltage divider approach is not practical using batteries as an input.

A series diode (e.g. 1N4001) may be a more practical approach.


I may also give this a go just as an experiment. Thanks for the idea :)

wvmarle

+1 for a single CR2032 if you really want to go low power. Use the internal 8 MHz clock; sleep most of the time; and indeed your project will be able to run for a really long time. Use an RTC with alarm for the countdown part; super low power use, accurate countdown and the MCU can sleep until it's time to sound the buzzer. Well, it doesn't even have to wake up for that, the alarm output of the RTC can activate the buzzer.

2x LiPo makes you lose LOTS of power. About 32% over the regulator - not counting its quiescent current (which can be much higher than what the ATmega328p uses while asleep).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

ardandrew

+1 for a single CR2032 if you really want to go low power. Use the internal 8 MHz clock; sleep most of the time; and indeed your project will be able to run for a really long time. Use an RTC with alarm for the countdown part; super low power use, accurate countdown and the MCU can sleep until it's time to sound the buzzer. Well, it doesn't even have to wake up for that, the alarm output of the RTC can activate the buzzer.

2x LiPo makes you lose LOTS of power. About 32% over the regulator - not counting its quiescent current (which can be much higher than what the ATmega328p uses while asleep).
Thats a brilliant idea!!! Thanks so much for that :0) +1 Karma

Smajdalf

For rough timing use WDT. For precise timing may be used Timer2 clocked by a watch crystal.

I have no idea how loud the buzzers need to be but driving a passive piezzo directly from ATMega pins may do decent sound even at 3V.

This is also interesting low power "tutorial".
How to insert images: https://forum.arduino.cc/index.php?topic=519037.0

TomGeorge

Hi,
What is the application?

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

MarkT

Hi,

I am thinking of using 2 x CR2032 (for space considerations and increased mAh) which would give me 6v to run a 328p chip. I was thinking of using a voltage divider (1MΩ and 100KΩ resistors) that would drop it to 5.45v.

The project would be for a simple countdown timer that would then trigger two 5V active piezo buzzers.
Likely to be beyond the ability of CR2032s to power.  They are spec'd to produce a few milliamps only.
Quote
I was wondering if this would be the right approach?
You need to use a battery capable of producing enough current, perhaps 3x LR44 alkaline coin cells.
CR2032 lithium coin cells are designed to power calculators and other devices that require a few milliamps or less.  They have a 10 year shelf life

Alkaline coin cells can supply many 10's of milliamps happily and 3 of them produce a nice safe 4.5V, no need to reduce voltage.
Quote
Thanks for any guidance in advance.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

ardandrew

For rough timing use WDT. For precise timing may be used Timer2 clocked by a watch crystal.

I have no idea how loud the buzzers need to be but driving a passive piezzo directly from ATMega pins may do decent sound even at 3V.

This is also interesting low power "tutorial".
Thanks for all the replies. I have done a project using a passive 3v buzzer using a transistor to get the full 3v from the battery whereby the base is connected to the ATtiny85 pin and it is plenty loud (not sure the exact SPL) for what I need. This runs from one Cr2032 and has been running for 6 months or so but with light usage.

raschemmel

Well, heck, if you're really going to do that, why mess around with 9400uF when you can use  ONE FARAD !
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

MarkT

Because it will take ages to charge up from the puny coin cell, and use about 1mAh of capacity to do so, and has
a leakage current rating of upto 1.5mA ?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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