Previous to using the MBED, I spent several years using the PIC and using sleep mode, started designing battery operated projects. e.g. an egg timer whose battery's (2 x AAA) have so far lasted 4 years.!

Today I experimented with the mbed connected to the QVGA LCD display from Mikroelectronica. Used PWM o/p for led backlight via 5R resistor and digital I/O to supply Vcc to the display.

Used a 3v6 lithium battery with the +ve lead connected directly to the 3V3 regulator on the mbed. Also removed the blue power indicator LED ( 2ma ).

After displaying a test screen on the display I ended the software with:

()clear screen on LCD ()PWM o/p zero (LED backlight off) ()digital I/O cleared to zero (power to LCD off) ()deepPowerDown (Sleep)

Hooking up my Keithley rs232 multimeter I measured a current consumption of 3 mA and once the mbeD was in sleep a consumption of 5.78 microamps.

the lithium battery voltage is now connected to the Keithley data logger and over the last hour the voltage has dropped from 3.750 to 3.749 volts.

Is there anything else I can do,either in software or hardware to reduce the 'sleep' discharge current to less than 1 microamp?

First thing is to check where the current is going. I would connect the ammeter in line with both the display electronics and the backlight then put it to sleep and see what the individual current drain from those two items is.

Also note that your battery voltage drop of 1 mV is meaning less as that is resolution limit of the meter.

Also note that 5.78 uA is pretty good and works out to 39 years for a 2000mAH battery. How long are you planning on running it in sleep?

My £800 2000 Keithley 6.5 digit multimeter has pretty good resolution.

Mistake.I was measuring the current on the VOUT line.Now current consumption of MBED is 134 mA in normal operation and 84 mA in 'sleep mode'.I expected sleep mode to produce a current consumption of a few nA just like the PIC.

Is the MBED designed for 3v6 battery operation and if so,how is it possible to adapt the mbed?

http://mbed.org/cookbook/Power-Management has some info on this issue.

After further investigation,the only feasible way to operate the EMBED on battery power is to use an 8-pin PIC with a solid state relay to switch the power to the MBED.

The PIC can then be put to sleep,disconnecting the power to the MBED and woke up from sleep with a simple push to make swit5ch connected to RB0 or RB4-7.

Might be an idea to design a battery powered MBED II Simon?

Regards RG

Hi Jim,thanks for reply, don't worry I've checked out the entire MBED website and have noted the power-Management page.Please see my latest post. Thank you and good mbed'ing

cheers.

I think, if you take of the power of the ethernet, and USB, you could reduce amount of current drawn. Not sure if it's possible, but I think so.

Lerche

Hmmm, tinkering with USB etc won't really help even if MBED current consumption is reduced to 1 mA.The battery will still discharge in a matter of days.

I have a LCD connected to a PIC in 'sleep' for the past 2 years and the battery has not discharged at all!

I think Christian refers to switching off the mbed interface chip.

Have you checked out this page:

http://mbed.org/users/no2chem/notebook/mbed-power-controlconsumption

Note that it also helps to disable the blue power-on LED (requires soldering it out).

You could also go for the 'mbed-mini' board that has no interface chip at all and still is largely compatible with mbed.

'mbed-mini' Are you referring to the LPCXpresso?

If so, the Code Red demo compiler does not compile C programs and costs £120 for compiler. I also doubt if I can use the LCD libraries as in the MBED compiler and I really don't want to start programming the LCD from scratch.

I have finally realized that the MBED was not designed for battery operation and never will be,especially since it contains an ethernet and usb and 'interface' chip which most mobile phones do not possess and thereby draw plenty of current.

Hi Richard, All,

A couple of things that might be of interest.

There is a new beta version of the interface firmware (will be official live soon) that properly supports power down, leaving just the LPC1768 chip running. See

• http://mbed.org/handbook/Beta

That in combination with some of the other links in this thread should give you some tricks. But as you correctly suggest, the LPC1768 mbed is not really designed for battery powered applications.

We'll, if you can hold your breath a few weeks, we might finally be able to reveal something we've had in the labs for a while; just waiting for the chip we're using on it to be officially announced before we can say anything :D Would love for you to be a beta tester when we can tell you more!

Simon

Information about the 'mini' board is given here

http://mbed.org/users/franzachatz/notebook/reference-design/

It should be compatible with mbed, but has no interface chip, flash or ethernet. Maybe that will do the trick for you.

However, Simon's feedback regarding some new hardware sounds very interesting too.

'MINI' look interesting.How do I get my mits on one as failed to find any supplier.

Simon's new hardware looks very promising.Can't wait!

Hi Richard, I havent tested any of these mini boards myself, but if you're interested then get in touch with the developer Franz Achatz. His notebook page shows this emailaddress: franz[at]achatz[dot]nl.

BTW you can find other 'minimal' LPC1768 boards through google or on ebay at a cost of about $30. See picture below as an example:

This one gives you easy access to all the pins and provides some basic stuff like powersupply. You may want to add a serialport driver to get the bootloader going. The board has JTAG and also supports USB bootloader.

Regards, Wim