Powering PICAXE 20X2 with a single AA battery

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Sean87

Member
Hi all,

I am almost finished with a 20X2 project and I want to put it in a box :p I want it to be mobile, very light and small...so I am thinking of powering it up with a single AA battery.

I have calculated the max current I will need for this application is about 200mA (Basicly some LED's should be turned on and off).

Is this possible? If so, can you suggest me a DC-DC converter chip with as low as external components required?

Thanks.
 
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BillyGreen1973

Senior Member
search this forum or google for 'joule thief'
fairly basic circuit with only a few components.
Also used in 'emergency mobile phone chargers' that run off just 1 AA.
 
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Sean87

Member
BillyGreen1973 said:
search this forum or google for 'joule thief'
fairly basic circuit with only a few components.
Also used in 'emergency mobile phone chargers' that run off just 1 AA.
Click to expand...
Sounds a bit strange for powering up a MCU :p are you sure people here used this to power up theire picaxes?
 
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manuka

Senior Member
Did I read that right ? 200 mA ? So just how small is your small? What duty cycle? What battery life? Solar power thoughts? Cell phone 3.6V Li-ion battery? Consider the new M2 PICAXEs (some run as low as 1.8V)? What colour LEDs (whites need ~ 3.6V)? FWIW most simple & compact Joule thief approaches can only supply small currents (& they give out rough DC). Skin flints have long hacked solar garden lamp innards to deliver ~5V at ~5mA.

If your end use & budget merit it consider more professional circuitry using the likes of an AS1337 Buck-Boost converter IC, as these are good for higher currents.
 

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premelec

premelec

Senior Member
If you use a garden light up converter note that you need some sort of regulation and a filter capacitor - could be shunt reg [unloaded units easily hit 9v] like a White LED :)
 
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westaust55

Moderator
While I have nevered used the circuit myself, the Joule Thief” circuit concept has been promoted here many times before. I quickly found around 60 posts on the topic. Some are:
http://www.picaxeforum.co.uk/showthread.php?10392-Interesting-solar-garden-lamp/page6
In particular post 55 giving a link to improved “joule Thief” circuits.

http://www.picaxeforum.co.uk/showthread.php?8938-powering-picaxe
See post 10

and
http://www.picaxeforum.co.uk/showthread.php?6719-Picaxe-08M-running-on-3-volts
 
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Dippy

Moderator
Step 1. Go to a large supplier like Farnell.
Step 2. Type "boost" into the search box (for boost regulator).
Step 3. Trawl through the results until you find a few suitable boost regulators. You do the trawling, not me.
Step 4. Download the Data Sheets.
Step 5. Report back here with your findings and let the Old Hacks pick one for you.


Here is an example od something that nearly suits.
http://uk.farnell.com/microchip/mcp1623t-i-chy/ic-boost-reg-pwm-pfm-sot-23-6/dp/1863917?in_merch=New Products&in_merch=Featured New Products&MER=i-9b10-00001144
Data Sheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/41420B.pdf


Now let's look at a potential problem: the 200mA. Nasty.
"Basicly some LED's should be turned on and off.."

Have you actually done ANY calculations to see how long your poor old AA battery (+boost inefficiency+quiescent) will last ?

If we are talking about a pile of typical standard 5mm/3mm LEDs switched on then .... move to high-brightness types and use larger resistors.
With something like Kingbright (cos they're 'king bright :) ) you could treble the in-line Res value and have the same brightness compared to standard cheapo LEDs.

There are many examples of component choice and design where you can lose (or, for this Forum "loose") a lot of power wastage.

Post your circuit - including component values - and some of the more experienced chaps here can whittle it down.
Also the code. It may be that with tinkering with techniques, sleeps/naps etc we can reduce the power even further. You will learn something too so that's good.
Let me just say that for a tiddly battery that any prolonged usage at 200mA is not good at all.
:(
 
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Janne

Senior Member
I second Dippy's advice, go to some big supplier (mouser, farnell, digikey...) and use their tools to find a suitable boost converter for the job.
One big trap with boost converters is, that the current ratings they come with in the catalogs is usually a value that is achieved in optimal conditions. You need to read the datasheets carefully, and then figure out how much it can deliver in your application. I myself fell for this once, i was happy to select a 500mA part for a trinket which needed 200mA, only to discover later that in my conditions it was just barely able to deliver.. I was lucky that time but have learned to read the datasheets more carefully after that.
 
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papaof2

Senior Member
Check the Duracell AA datasheet here http://www1.duracell.com/oem/Pdf/new/MN1500_US_CT.pdf

A 10 ohm load (starting draw = ~150ma) drops the cell voltage to 0.8 volt in about 24 hours. A 3.9 ohm load (starting draw = ~380ma) drops the cell voltage to 0.8 volt in less than 10 hours.

Even with an efficient boost converter, you're looking at maybe one day of operation on a good AA cell. Look into the high brightness LEDs. I have a sample green LED that's annoyingly bright running on a 5 volt supply with a 1K or so resistor (it's on a prototype board I built for someone else so I don't have the board here to verify the value).

John
 
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Dippy

Moderator
I thought I said that in my post?
As well as suggesting posting his circuit so the Old Boys could modify.
Oh, it was on the previous page... so long ago...
Good luck ;)
 
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