I wanted to use a mobile phone battery to run my picaxe connect board. I have a normal xbee module on the board and the battery voltage is 3.7V. When charged this is 4.1V. I was wondering if it is possible to run the xbee module directly from this battery as the specification for an xbee module is 2.8 to 3.4v.
Xbee Module operating from a 3.7V Mobile phone battery
- Thread starter golfdude
- Start date
Pauldesign
Senior Member
Should be fine for short durations but just include a power diode (1N4001/7) in series with the +ve line to drop down 0.7V and the diode will also prevent the battery in case an external PSU is accidentally connected. 
Pauldesign
Senior Member
By short duration, i meant operating when fully charged to 4.1V (without the series diode) might damaged the X-bee module if used extensively.
Dropping to 3.7V is just at the max X-bee voltage rating, so adding another diode will give a typical operation voltage.
An alternative way is to use a series RED LED with or without a 100 Ohm resistor. This add visual display and drop the voltage by almost half. Note different LED colours have different forward conduction voltages and Green LED will drop about 2.5to 3V.
Power diodes and LEDs are active devices, thus will run down the battery easily.
Alternatively just a 100 Ohms series resistor with +ve line will suffice.
Use Ohms Law to choose the appropriate current limiting resistor.
Dropping to 3.7V is just at the max X-bee voltage rating, so adding another diode will give a typical operation voltage.
An alternative way is to use a series RED LED with or without a 100 Ohm resistor. This add visual display and drop the voltage by almost half. Note different LED colours have different forward conduction voltages and Green LED will drop about 2.5to 3V.
Power diodes and LEDs are active devices, thus will run down the battery easily.
Alternatively just a 100 Ohms series resistor with +ve line will suffice.
Use Ohms Law to choose the appropriate current limiting resistor.
hippy
Ex-Staff (retired)
4.1V is 20% over 3.4V so I'd be wary of running it at such a voltage at all. When the XBee is transmitting it draws ~50mA which may be higher than the current rating trough a LED. I've never been sure of 'the magic' in using an R to drop a voltage to an active circuit; doesn't 50mA through 100R make for a voltage drop of 5V and, with uA in standby, not a lot ?
I'd try and find an LDO regulator which has suitable head-room, operate the XBee towards the 2.8V end if required.
I'd try and find an LDO regulator which has suitable head-room, operate the XBee towards the 2.8V end if required.
What has been suggested may be fine fro some things, but some of it worries me.
I'm just going to offer a suggestion assuming that spending an extra 50p to protect your £15 Xbee is desirable.
Did you know you can get regulators with very low dropout voltages?
Some (e.g. made by Torex) have a dropout of 0.06V at 30mA load.
You see, the trouble with diodes is that their forward voltage drop (Vf) varies with load current.
0.7V is the vlaue we are all told at school, but a study of Data Sheets will teach you much more.
At f-all current loads the Vf of your average 1N4xxx will be a lot less than 0.7V.
AND , if you put Xbee to Sleep the current load is f-all.
And I honestly don't know how sensitive XBee is to overvoltage - in my book it's a potentially expensive mistake.
Anyway, as I am a born worrier, then I would consider the regulator as an option.
AND it will give you a stable voltage over the battery life as opposed to diminishing. I'm NOT really a fan of using diodes in apps like this, but then I'm a fussy devil.
To Golfdude and Paul: I really don't think a series 100R resistor for a device that takes f-all when SLEEPING is safe at all. I really think that is asking for trouble.
Yes, it costs more , but XBees are blooming expensive.
There are many types of VLDO regulator (have a look in the Farnell parametric search), Torex was just one that I have used.
Crossed with the hipster. re the resistor. Absolutely. Do NOT do this!!!
I'm just going to offer a suggestion assuming that spending an extra 50p to protect your £15 Xbee is desirable.
Did you know you can get regulators with very low dropout voltages?
Some (e.g. made by Torex) have a dropout of 0.06V at 30mA load.
You see, the trouble with diodes is that their forward voltage drop (Vf) varies with load current.
0.7V is the vlaue we are all told at school, but a study of Data Sheets will teach you much more.
At f-all current loads the Vf of your average 1N4xxx will be a lot less than 0.7V.
AND , if you put Xbee to Sleep the current load is f-all.
And I honestly don't know how sensitive XBee is to overvoltage - in my book it's a potentially expensive mistake.
Anyway, as I am a born worrier, then I would consider the regulator as an option.
AND it will give you a stable voltage over the battery life as opposed to diminishing. I'm NOT really a fan of using diodes in apps like this, but then I'm a fussy devil.
To Golfdude and Paul: I really don't think a series 100R resistor for a device that takes f-all when SLEEPING is safe at all. I really think that is asking for trouble.
Yes, it costs more , but XBees are blooming expensive.
There are many types of VLDO regulator (have a look in the Farnell parametric search), Torex was just one that I have used.
Crossed with the hipster. re the resistor. Absolutely. Do NOT do this!!!
Last edited:
Thanks for your advice. On the board I was using a MCP1702-330 regulator but wanted to get rid of this to save on battery power. I also need to talk to a device that requires 3.3V from the PIC. I have been using two AA batteries to give 3V then taken out the MCP1702-330 and the voltage dividers on the board. I tried 3V button cells (CR2032) but the current drain was to much for these so I decided a mobile phone battery might be the solution but found that when fully charged the voltage was 4.1V. Questions:-
1. Should I be worried about the current drain from the MCP1702-330 regulator?
2. How can I reduce the voltage from the PIC outputs? Maybe I should just power the PIC from the regulator 3.3V supply?
Thoughts anybody?
1. Should I be worried about the current drain from the MCP1702-330 regulator?
2. How can I reduce the voltage from the PIC outputs? Maybe I should just power the PIC from the regulator 3.3V supply?
Thoughts anybody?
Whoa there Big Boy!
You are now starting to drip feed us with more information.
Post your Mk1 circuit schematic and allow others to comment.
I really can't follow your description properly. I'm not going to guess.
Give us a drawing.
And describe the mystrerious "device". Give us a spec or a link or a clue.
if you want people to comment on components then provide us with a link - our time (for most of us) is limited.
The MCP1702 has an excellent quiescent current but a pretty poor dropout (in my opinion).
The device I referred to has a quiescent of 70 microAmps but a far better Dropout.
Life is a compromise - and sometimes will cost you an extra 50 pennies.
If you post your schematic people may be able to hunt around for a good choice of components.
You are now starting to drip feed us with more information.
Post your Mk1 circuit schematic and allow others to comment.
I really can't follow your description properly. I'm not going to guess.
Give us a drawing.
And describe the mystrerious "device". Give us a spec or a link or a clue.
if you want people to comment on components then provide us with a link - our time (for most of us) is limited.
The MCP1702 has an excellent quiescent current but a pretty poor dropout (in my opinion).
The device I referred to has a quiescent of 70 microAmps but a far better Dropout.
Life is a compromise - and sometimes will cost you an extra 50 pennies.
If you post your schematic people may be able to hunt around for a good choice of components.
Attached is the schematic and the datasheet for the pressure/temperature device. I am using the Picaxe connect board but currently designing my own board and I am using a PICAXE 18M2. Battery conservation is a must so I am going to switch off the xbee module when there is no change in the measurement, size is also critical, I want it to be as small as possible. The battery I want to use is a nokia from a mobile phone. Comments or suggestions will be appreciated.
So, the battery you want to use is NOT as shown in the schematic.
Does that mean the only change is this ~4V battery + a regulator?
Running everything at 3V3 makes sense.
The pressure device is only 1mA when converting - I take it you control that via SPI?
You can SLEEP the XBee and PICAXE.
So, all you want is a regulator then?
Go through Farnell's parametric search.
e.g. XC6206. Nice and small and only requies small SMD ceramics - see Data Sheet. http://www.farnell.com/datasheets/578820.pdf
Probably many other options - hunting them down is your mission Jim should you wish to accept it..
For lowest power and longest battery life and assuming you're not doing any ADC you could power the PICAXE directly from the battery and then switch the rest of the circuit including regulator using a MOSFET. The advantages may not be worth the hassle though.
I assume you have hunted through the Forum - there has been A LOT of advice on low power usage recently - have a look.
Does that mean the only change is this ~4V battery + a regulator?
Running everything at 3V3 makes sense.
The pressure device is only 1mA when converting - I take it you control that via SPI?
You can SLEEP the XBee and PICAXE.
So, all you want is a regulator then?
Go through Farnell's parametric search.
e.g. XC6206. Nice and small and only requies small SMD ceramics - see Data Sheet. http://www.farnell.com/datasheets/578820.pdf
Probably many other options - hunting them down is your mission Jim should you wish to accept it..
For lowest power and longest battery life and assuming you're not doing any ADC you could power the PICAXE directly from the battery and then switch the rest of the circuit including regulator using a MOSFET. The advantages may not be worth the hassle though.
I assume you have hunted through the Forum - there has been A LOT of advice on low power usage recently - have a look.
BeanieBots
Moderator
Be aware that short duration could be measured in milliseconds.
Sorry Paul, but that really isn't good advice
Running any semiconductor device over the specified voltage can not only lead to instant destruction but can also do permanent damage to devices that do not get instantly destroyed. This often manifests as increased current draw and significant reduction in longevity.
Semiconductors do not behave in the same way to stress that passives do. It's OK to over-drive a resistor for a short while but NOT a semiconductor.
Strongly suggest the advice already given to use a low-drop-out 3v3 regulator and also run the PICAXE from the same power rail.
Pauldesign
Senior Member
I was just pointing cheap and quick possible options and not considering all the possible conditions/future hazards and sorry Gulf dude, if my suggestion is misleading and Guys (old PICAXE gurus), thanks for the criticisms.
A voltage regulator (esp one with all the fancy features) will always be the best bet but can't a 3V good spec zener diode with a 33 Ohms resistor pair do the trick since the power supply source is just from a battery (not so sure of his intended application/environment).
and not considering all the possible conditions/future hazards and sorry Gulf dude, if my suggestion is misleading and Guys (old PICAXE gurus), thanks for the criticisms. A voltage regulator (esp one with all the fancy features) will always be the best bet but can't a 3V good spec zener diode with a 33 Ohms resistor pair do the trick
since the power supply source is just from a battery (not so sure of his intended application/environment).Paul, maybe you should have a slight re-think.
Are you talking about +4V --- 33R --- 3Vzener--Ground and tap off to get a 3V supply?
Yes, it'll work but very inefficient.
Do the sums.
What's the 'quiescent' power consumption?
You save only pennies and have to visit the site more often becuase of the battery.
And your previous 100R resistor option wouldn't be very "cheap" when the Xbee goes pop! - but, yes, the demise of the Xbee may be "quick".
Do the sums. Think of all the possible conditions.
What would be the voltage drop across that res when XBee is Sleeping?
Therefore, what voltage would Xbee see?
Any 'drop' method will simply follow the battery voltage AND be load dependent.
This method really does have limited applications and requires some thought.
For the extra 50p, a regulator will give safe and consistent operation (of a £15 Xbee) and , diplomatically, is a no-brainer.
Why do you need fancy features? You may have an app where an 'enable' pin is used but not 100% necessary here.
Are you talking about +4V --- 33R --- 3Vzener--Ground and tap off to get a 3V supply?
Yes, it'll work but very inefficient.
Do the sums.
What's the 'quiescent' power consumption?
You save only pennies and have to visit the site more often becuase of the battery.
And your previous 100R resistor option wouldn't be very "cheap" when the Xbee goes pop! - but, yes, the demise of the Xbee may be "quick".
Do the sums. Think of all the possible conditions.
What would be the voltage drop across that res when XBee is Sleeping?
Therefore, what voltage would Xbee see?
Any 'drop' method will simply follow the battery voltage AND be load dependent.
This method really does have limited applications and requires some thought.
For the extra 50p, a regulator will give safe and consistent operation (of a £15 Xbee) and , diplomatically, is a no-brainer.
Why do you need fancy features? You may have an app where an 'enable' pin is used but not 100% necessary here.
BeanieBots
Moderator
@Paul,
In addition to Dippy's sound comments, are you familair with the characteristics of zener diode? If not, dig out the datasheet for 3v zener and have a good look at the graphs then do the calculation suggested by Dippy.
An active Xbee is quite thirsty. Your zener solution must produce enough quiecent current during sleep to also keep it happy when busy. Have a look at it's characteristics over that sort of current range.
The reason this issue exists is because it battery operated, hence wasting all that power would be rediculous. No need for anything other than a plain and simple regulator. It really IS a no-brainer.
In addition to Dippy's sound comments, are you familair with the characteristics of zener diode? If not, dig out the datasheet for 3v zener and have a good look at the graphs then do the calculation suggested by Dippy.
An active Xbee is quite thirsty. Your zener solution must produce enough quiecent current during sleep to also keep it happy when busy. Have a look at it's characteristics over that sort of current range.
The reason this issue exists is because it battery operated, hence wasting all that power would be rediculous. No need for anything other than a plain and simple regulator. It really IS a no-brainer.