SKXBEE Power Requirements

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SKXBEE Power Requirements

Postby ck88 » Fri Nov 12, 2010 1:06 am

Hello.

I have an SKXBEE and also SKXBEE-PRO for my embedded wireless development. I am curious about SKXBEE's power requirements. From Xbee module's datasheet, it says that Tx current is at 217mA @ 3.3V and Rx current is at 55mA @ 3.3V for Xbee PRO, while Tx current of 45mA @ 3.3V and Rx current of 50mA @ 3.3V for Xbee.

I am wondering, is SKXBEE and SKXBEE-PRO following the same too? SKXBEEs have been interfaced to 5V, so will this affect the power requirements for Tx and Rx?

Currently, I am using 9V batteries, passing through a 5V regulator to provide power for my PIC starter kit, and from the UART 5V and GND, I extended and provide power to the attached SKXBEE/SKXBEE-PRO. I've noticed that, it is consuming quite alot of power, and after quite sometime, there's not much power left to power up my LCD and my LCD fades. My LCD power pin only shows 3.2V and constantly decreasing is SKXBEE is attached. My battery voltage levels has gone down to 7.4 V.

If I detach SKXBEE, I can power up my LCD normally with power back to normal 4.8 - 4.9 V, with 7.4V left on my battery.

Any ideas and suggestions are welcomed. Thank you for your time :)
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Re: SKXBEE Power Requirements

Postby ober » Fri Nov 12, 2010 8:42 pm

ck88 WROTE:Hello.

I have an SKXBEE and also SKXBEE-PRO for my embedded wireless development. I am curious about SKXBEE's power requirements. From Xbee module's datasheet, it says that Tx current is at 217mA @ 3.3V and Rx current is at 55mA @ 3.3V for Xbee PRO, while Tx current of 45mA @ 3.3V and Rx current of 50mA @ 3.3V for Xbee.

I am wondering, is SKXBEE and SKXBEE-PRO following the same too? SKXBEEs have been interfaced to 5V, so will this affect the power requirements for Tx and Rx?

Currently, I am using 9V batteries, passing through a 5V regulator to provide power for my PIC starter kit, and from the UART 5V and GND, I extended and provide power to the attached SKXBEE/SKXBEE-PRO. I've noticed that, it is consuming quite alot of power, and after quite sometime, there's not much power left to power up my LCD and my LCD fades. My LCD power pin only shows 3.2V and constantly decreasing is SKXBEE is attached. My battery voltage levels has gone down to 7.4 V.

If I detach SKXBEE, I can power up my LCD normally with power back to normal 4.8 - 4.9 V, with 7.4V left on my battery.

Any ideas and suggestions are welcomed. Thank you for your time :)


We do not have tools to measure the current usage of SKXBee alone. Anyway it will need to power a power indicator LED, the XBee module and some transistors. I am expecting current around 15 to 20mA on top of current for XBee module.

Of course the power source play a main role in a stable system beside the load. You can try using adapter or higher capacity battery, normal 9V battery is not really in for project development. It might also be the 9V battery is sufficient to power less say 100mA of current, and SKXBee uses 50mA, while LCD + PIC uses 90mA. Taken one of this out of the picture, will make the power stable. Not sure, might be one of the possibilities.

You will need to consider the power wasted on 5V regulator too.
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Re: SKXBEE Power Requirements

Postby yonghui » Sat Nov 13, 2010 3:42 pm

hi,

Skxbee have the onboard regulator for 3.3V to xbee modules. the LCD backlight is also one of the element that consume quite a lot current.

9V cell is having small capacity. mayb shud switch to larger capacity battery or use adaptor.


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Re: SKXBEE Power Requirements

Postby ck88 » Sat Nov 13, 2010 5:12 pm

Hello ;)

Thank you Mr. Ober, for your information and also Mr. YongHui.

I do not power up the back light for the LCD in my project. I am certainly thinking that using an adapter to power up my project will be the ideal way for the debugging and development period. However, for the final stage, as in for presentation, I would need to build a mobile terminal that is battery powered. >.< Yeah, and it's a fact.

For my project, I need to development a mobile terminal, that basically consists of a 4x3 keypad, a 2x16 LCD, an SKXBEE/SKXBEE-PRO, a few LEDs, and optionally a piezo buzzer. Hence, now I would like to know how long does a 9V battery (given if it's a top class 9V battery) would last for my mobile terminal.

Does implementing sleep function for the SKXBEE help a lot in saving power consumption? If it is, I would try to implement that, though I've yet to read on how to do it.

Right now, I am using a PIC starter Kit to develop my project. Its PIC microcontroller is PIC16F877. The PIC starter kit board specs are as follows:

1. 4 LEDs
2. DIP switch
3. 7-seg display
4. LCD connector
5. Keypad
6. RS-232 connector
7. 2 servo connector
8. 2 channel ADC connector
9. RESET switch
10. Power on LED
11. Potentiometer ADC

I am afraid that these board specs are also hogging up power, aren't they?
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Re: SKXBEE Power Requirements

Postby yonghui » Sun Nov 14, 2010 1:11 am

hi,

u are running servo motor?the small 9v battery i think wont last for long. it will be better to take LIPO battery or simple 6x AA size 1.5V battery.


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Re: SKXBEE Power Requirements

Postby ck88 » Sun Nov 14, 2010 1:16 am

Hi,

Oh, no, I am not running any motors. It's just the servo connectors, but I am not connecting any to it.
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Re: SKXBEE Power Requirements

Postby ober » Sun Nov 14, 2010 9:16 pm

ck88 WROTE:Hi,

Oh, no, I am not running any motors. It's just the servo connectors, but I am not connecting any to it.


Sorry to say, but that's really confusing us :D . Yes, the 1st thing I would look for is motor as it will consume greater power than other peripherals. Since you are saying you do not connect it, i do not sure which one is being used in your board.
ck88 WROTE:1. 4 LEDs
2. DIP switch
3. 7-seg display
4. LCD connector
5. Keypad
6. RS-232 connector
7. 2 servo connector
8. 2 channel ADC connector
9. RESET switch
10. Power on LED
11. Potentiometer ADC

-LEDs consume a lot of power too, try to increase the resistor value for LEDs.
-7 seg display another power drinker 8-) , as you have 7 LEDs on it and will you need to on it constantly to show number or value.... worst than 4 LEDs.
-ADC module in PIC also consume power once it is activated.

yes, sleep mode on XBee would say your power, yet you will need to study it, more on software work, another suggestion is to put PIC into sleep mode.

Do let us know the progress.
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Re: SKXBEE Power Requirements

Postby ck88 » Tue Jan 04, 2011 1:38 am

Dear Ober,

I have a question for you regarding SKXBEE. In order to implement sleep function, pin 9 of the Xbee module is needed to be used. Hence, is pin 9 of Xbee module ported out in SKXBEE?

What are the JP2 connections on the right of the SKXBEE? I can't seem to find any explanations on them in the SKXBEE user manual.

Thank you for your kind attention.
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Re: SKXBEE Power Requirements

Postby ABSF » Tue Jan 04, 2011 7:04 am

The 9V battery has really very low capacity as compared to the UM1, UM2 and AA cells. Take a look at the spec for the alkaline Energizer 9V battery here:

http://data.energizer.com/PDFs/522.pdf

The capacity changes depending on the discharge current. If you discharge it at 100mA the capacity is about 500mA/Hr. That means 500/100=5 hours.

I agree with yong hui that it is better to use 6xAA cells to get 9V or used the NiMH 2300mAH cell to get 7.2V. Using NiMH batteries you can get roughly 2300/100=23 hours if you discharge them at 100mA.

There are also RC Model car batteries which are also rechargeable 7.2V high capacity battery.

Is it possible to parallel 2 alkaline 9V batteries using 2 diodes to get longer life? :?: It might be interesting to try it out.

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Re: SKXBEE Power Requirements

Postby ck88 » Thu Jan 06, 2011 11:02 pm

Thank you ABSF and yh for the nice info on batteries.

I am wondering now that LiPo batteries, are they safe for the project I am involved in now which has a PIC starter kit with on board 78L05 voltage regulator, and also LCD, Keypad and SKXBEE starter kit?

I have a LiPo battery rated at 7.4V 850mAh with the discharge of 15C. By what ABSF and yh have mentioned, it should be okay, isn't it?

Thank you!

P/S: Does anyone here know what are the 5-pin JP2 connections on the right of SKXBEE board for? Thanks.
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