Rechargeable Coin cell (3.7v) and Xbee

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hugoxp1

Member
Hi,

I'm thinking use one Xbee module with this battery:
http://www.sparkfun.com/commerce/product_info.php?products_id=8818

The problem is that Xbee module only works with 2.8 – 3.4VDC (http://www.digi.com/products/wireless/zigbee-mesh/xbee-digimesh-2-4.jsp#specs)

To drop down from 3.7v to 3.0 I can use a Diode, but I'm wondering: the battery will discharging continuously to 3.6v, 3.5v, 3.4v (...) 3.0v (http://www.sparkfun.com/datasheets/Batteries/Coin_Cell_Battery-PD2450.pdf) so at 3.0v I will have 2.3v (because I'm using the diode) and in this way I will not be able to use all the battery capacity

I'm not be able to use a voltage Regulator (http://www.sparkfun.com/commerce/product_info.php?products_id=595) because to have 3.3v VOut I need to have >4,8 VIn right? (that what is represented in this datasheet: 4.8V<=VIN<=10.3V)

So... what are my options? :eek:
 
J

John West

Senior Member
A possibility - though unfortunately involving more parts - is to have a latching relay bypass the diode when the voltage drops down. Whether that's a reasonable solution depends on the nature of your project and circuitry.
 
D

Dippy

Moderator
Forget diodes.

Look into LDO (Low DropOut) regulators.

There are many suitable devices.
Check out Torex and National Semiconductor.
XC620x series for example should have a dropout of about 0.1V at XBee currents.

You should be able to find several options if you use the search facility in places like Farnell.

TIP: If you select regulators of lower current ratings you will get Lower Dropout specs generally.
 
H

Haku

Senior Member
DC-DC regulator?

This one from DimensionEngineering is pretty good, though take note of the quiescent draw, you could use a transistor or fet to switch the regulator on when you need to use the Xbee.
 
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Dippy

Moderator
I didn't look at the battery link.

200mAh and an Xbee takes about 50mA. Is that really man enough?

But apparently it's a "really cool" battery. So that's alright then. Lordy, they get some real Richard Heads in to write copy don't they.

DC-DC seems a little excessive for this. Cost,complexity, size and power consumption. Up to you. Good luck.
 
D

Dippy

Moderator
Looks like a little chip to me :confused:

Assuming it works then it looks good.
Sorry, I mean 'totally awesome and really cool'. There that's better; why use one word when you can use five. :)

Wasn't a very similar situation involving Xbee discussed just a few days ago and it was agreed that a very LDO 50 pence regulator was a "no brainer"?
Oh I remember now, someone also suggested a resistor to drop the voltage (ooh nasty).
 
B

BeanieBots

Moderator
You should be able to find a 3v LDO regulator that will still give 3.0v for a 3.1v input voltage. I would also suggest that you do not discharge your cell below 3.1v if you want more than a few hundred cycles from it. (despite what THEIR datasheet says).

DC-DC would be nice if you can find one that would give an overall efficiency greater than an LDO linear regulator but I doubt you will.

As for "really cool rechargeable Lithium Ion coin cell ", they actually work better when slightly warm:p
 
D

Dippy

Moderator
Here are some really cool regulators found using Farnell's search box.
There are, no doubt, many more examples.
http://uk.farnell.com/jsp/search/browse.jsp?N=1004527+5058570+401+5054109+5287532+5054076&Ns=PRICE_PLS_006_PRICE1|0&locale=en_UK&appliedparametrics=true&getResults=true&No=0&catalogId=&prevNValues=1004527+5058570+401&filtersHidden=false&appliedHidden=false&originalQueryURL=/jsp/search/browse.jsp?N=1004527&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues=1004527

And remember, even old'uns like the LM2936 aren't bad, though you can do better. Forget about the old fashioned dinosaur regulators. Ok you save pennies but other aspects will be compromised.
 
H

hugoxp1

Member
Serial Data Interface 3.3V CMOS serial UART

Hi,

After take a look in this link: http://uk.farnell.com/jsp/search/browse.jsp?N=1004527+5058570+401+5054109+5287532+5054076&Ns=PRICE_PLS_006_PRICE1|0&locale=en_UK&appliedparametrics=true&getResults=true&No=0&catalogId=&prevNValues=1004527+5058570+401&filtersHidden=false&appliedHidden=false&originalQueryURL=/jsp/search/browse.jsp?N=1004527&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues=1004527 (thank you Dippy) I've choosed this 3.0v VOut LDO: XC6210B302MR (http://uk.farnell.com/torex/xc6210b302mr/v-reg-cmos-ldo-3-0v-smd-6210/dp/1057802?Ntt=XC6210B302MR) but then I saw this comment in Digi webpage (http://www.digi.com/products/wireless/zigbee-mesh/xbee-digimesh-2-4.jsp#specs): "Serial Data Interface 3.3V CMOS serial UART "

My question is: If I will have Xbee and Picaxe 20x2 supplied by 3.0v this will affect "Serial Data Interface"? Do I have to chose a 3.3v Vout LDO?
 
P

Pauldesign

Senior Member
Wasn't a very similar situation involving Xbee discussed just a few days ago and it was agreed that a very LDO 50 pence regulator was a "no brainer"?
Oh I remember now, someone also suggested a resistor to drop the voltage (ooh nasty).
Click to expand...
That works fine for me and has been doing so for the past 3 months. It all depends on the user and the use and just like WWE, please don't try it :)
 
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Pauldesign

Senior Member
My question is: If I will have Xbee and Picaxe 20x2 supplied by 3.0v this will affect "Serial Data Interface"? Do I have to chose a 3.3v Vout LDO?
Click to expand...
So long as the datasheet says X-bee Vcc is within 2.4V to 3.6V, the CMOS-UART logic level will also operate and follows any voltage within that range. Operating voltage/logic level always work over a range.

Note 3V3 is just the typical quiescent voltage. +/-0.3V drifts shouldn't make any different and no cheap voltage regulator esp if use over long periods will provide exactly 3V or the manufacturers rated output voltage.

The output voltage drift is affected by temperature since most commercial regulators uses oven/temperature/voltage control oscillator which drifts with changes in temperature.

Therefore 3V should be be fine and if you're still worry, try Microchip MCP1703 reg.
 
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Dippy

Moderator
Just to clarify this debate about XBees and power supplies and PICAXE I quickly knocked this PDF up. Apologies for typoes or grammar as I haven't got all day sadly.

ALWAYS read the device data sheet.
For a given voltage supply they usually define an acceptable range of logic voltages to the I/O.
 

Attachments

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golfdude

New Member
I tried to run my Picaxe 18m2 and xbee module directly off a CR2032 cell and I found that the cell could not cope with the current drain and therefore the voltage would drop rapidly. I also tried doubling up on the cells in parallel and that didnt work - so just be aware.
 
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Dippy

Moderator
Lordy, why don't you read the cell Data Sheet first?
http://www.farnell.com/datasheets/579569.pdf
http://www.farnell.com/datasheets/80218.pdf

Manufacturers usually give you a figure for the Maximum continuous discharge current.
For those cells this is typically just a few milliamps max.
They give you these data so you can read them :confused:

Anything a lot more will kill it quickly as you found out.
Anything a little more will reduce claimed capacity.
Always read up first.
 
B

BeanieBots

Moderator
Pauldesign said:
no cheap voltage regulator esp if use over long periods will provide exactly 3V or the manufacturers rated output voltage.
Click to expand...
This is where datasheets come into play. Ony an eBeijing one hung low special regulator will fail to meet its output specification. All others WILL.

The output voltage drift is affected by temperature since most commercial regulators uses oven/temperature/voltage control oscillator which drifts with changes in temperature.
Click to expand...
They do WHAT:confused:
There is no VCO in ANY linear regulator and switching regulator employ feedback making switching frequency almost irrelevant to output voltage.
Besides, the whole point of an oven/temperature/VCO (if it where present) is to PREVENT drift:rolleyes:

@hugoxp1,
Please have a read of Dippy's pdf file which covers just about all you need to know.

@golfdude,
Not very surprising. They can't handle of current. Large decoupling caps will help but a CR2032 simply cannot supply that level of current for more than a few seconds. Rechargeable versions will cope better but they will not give many charge/discharge cycles before they are damaged by the excessive current subjected to them.
 
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Dippy

Moderator
Paul, with respect, I appreciate you can't bring yourself to admit that a regulator is better than your resistor-drop scheme, but, honestly, where do you get your info from. It's really up the chute. Sorry.
 
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Pauldesign

Senior Member
Dippy, i do concur the facts and there is no doubts or second thought that a linear regulator is and will always be the best choice over resistors or any such cheap regulation scheme be it for line or load regulation and esp to an active device.

A resistor scheme may come in play where the supply voltage has already been regulated by a regulator and a lower voltage is needed esp by a passive section or passive device in a circuit. (and this is when the temptation sometimes kick-in, as to why not just...)

If i'm not confusing again, wasn't Golfdude initial post based but on cell phone rechargeable battery and not coin battery?

By the way Dippy, that was a good pdf and will be referenced to in future (or why not just add it to the PICAXE and X-bee tutorial) except just the droops which you noted already. ;)
 
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Dippy

Moderator
Well, it was just a 10 minute scribble.

Yes, there are occasions when this method is OK, but I wouldn't want novices to be under any impression that it can replace regulators per se. A resistor scheme is only reliable if the load remains constant-ish.
There are many occasions where a resistor scheme is problematic and, often, a disaster waiting to happen.

Yes, you are confusing again... :)
Hugoxp1's intitial post was referring to a rechargeable battery rated at 3.7V. (too high for XBee).
A drooping battery using a resistor means a drooping 'output'. Yuk! Whereas, a regulator means a constant output . Yummy!

Golfdude waded in at post #16 with a coin cell be used beyond it's ability.


Anyway, I'm puffed out on this subject as it is starting lap 2. I'll leave the choice up to others.

CALLING ALL NEWBIES: You can get regulators (linear and switching) with all sorts of specs and prices.
It is well worth a huntaround on sites like Farnell, RS Components and DigiKey - even if it just to see what is available and to get the DATA SHEET.

Data Sheets are usually lovely. They often tell you all about the product and many even have application circuits to tell you how to use them. Often the Big manufacturers also have things called Application Notes. These give even more details on how to use them and with some devices give code examples too - usually in C , but if you chop off the semi-colons and curly brackets it'll make sense. ;)
 
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