Hi,

I have been looking at the consumption tables on page 75 of the waspmote technical guide. Although the current consumptions for transmission and reception are listed, there is no information on the duration of transmissions and receptions. This makes it impossible to calculate the mAh consumption of the XBee modules.

Can anybody please point me in the right direction on where I can find this crucial information? Without this information, committing to use the Libelium solution is like a big gamble in terms of battery and power economy.

Regards...

Hi,

I also looked into this briefly and found this pdf from Digi -> ftp://ftp1.digi.com/support/documentati ... 0991_B.pdf

On page 23 there's a table that gives data throughput under a couple of scenarios as follows:

Configuration Data Throughput
1 hop, Encryption Disabled 27.0 kbps
3 hop, Encryption Disabled 10.9 kbps
6 hop, Encryption Disabled 5.78 kbps
1 hop, Encryption Enabled 20.5 kbps
3 hop, Encryption Enabled 9.81 kbps
6 hop, Encryption Enabled 4.7 kbps

So I guess depending on your situation, work out how much data in total you're trying to send and you can get transmission time roughly.

Maybe libelium-dev has more to add to this but it's a start?

Hi yoshi_jd,

Thanks for this useful information.

I think we can take this a step further with the maximum and minimum message lengths supported at the MAC layer of 802.15.4 to produce some useful analytical results.

Please have a look at Figure 2 in the following pdf:

http://www.google.com.tr/url?sa=t&sourc ... Pw&cad=rja

This indicates that the minimum data payload of ZigBee per MAC frame is 1 byte and the maximum is 102 bytes. Also, the total MAC header overhead for one MAC frame is 31 bytes. We can use these figures and the throughput figures for the encrypted and the clear scenarios you have provided to get some useful timings.

Thanks for the info and the inspiration :)

Regards...

In order to get some real-life quantitative benchmarks, I measured the current consumption of the Waspmotes using my ADC setup on ATMega 2560.

The code I have on the module, puts the waspmote to sleep after starting up. So there is no activity on the module.

I observed two interesting things so far.

1 - The waspmote consumes more current when the switch is in OFF position compared to its ON position. In OFF position the average current is around 116 mA and it drops to about 114.5 mA after the switch is turned ON. In this test, the XBee module was mounted on the Waspmote and was turned ON.

2 - When the XBee module was removed and the Waspmote was turned ON, the current consumption was an average of 113.5 mA. This suggests that the XBee draws about 1 mA while sitting in IDLE.

Based on my measurements, the current consumption of the Waspmotes seem rather high even in sleep mode. Has anybody done similar measurements? If so, how do your results compare to my findings?

Are there any suggestions on how this current consumption can be minimised?

Regards...

Just a quick update on the power measurements issue.

My previous measurements were direcly on the USB power path. It occurred to me that the peripheral USB circuitry may be hiding the actual waspmote power consumption. Therefore, I disconnected the motes from USB and repeated the same measurements with the batteries connected only. Guess what ?

It works exactly as I was expecting and I am now able to get the full dynamic current profile of the waspmotes for various uploaded applications ! I must admit, although the measurements and the compilation of the results are time consuming, they are invaluable and provide a true figure for the current consumptions.

One striking result that I would like to share here is the peak current of a waspmote hits the 450 mA mark at power up for a brief period !!!! In order to capture that make sure you use a sampling freuency of 2 kHz or higher. Otherwise, you may not be able to see this peak figure.

I am still not sure why the same current profile cannot be measured when the waspmote is powered by the USB. Any ideas and feedback on this will be greatly appreciated.

Regards...

Hi Jerrycruise.

I have included the image of my measurement setup in the following link. Please have a look.

http://www.flickr.com/photos/11573533@N00/6777847083/in/photostream

I have built this set up to measure the Waspmote dynamic current consumption under various operation scenarios. however, it can be used to measure any electronic device's dynamic current consumption as well.

You need to plug in the "battery power in" to the battery power source of your device. The "Battery power out" needs to be plugged to the device to power it. This set up is nothing more that a shunt resistor in series to the ground line that connects the battery to the device. The battery GND side of the shunt resistor is called Vin and goes into the (+) input of the Opamp shown. The opamp simply amplifies Vin based on the ratio of two resistors. I have indicated the gain formula on the figure. The opamp I used is LM324 as it is very straightforward with 5V single rail supply.

The Vout of the Opamp is fed to the ADC input of a simple MCU. I have used the Atmega2560 as that's what I had handy but you can use another one that suits your requirements. You need to make sure that the ADC resolution you are using is high enough to capture the minimum variations you are interested in. In my case, I used a 10-bit ADC with 5V max input that gave me 4.8mV of resolution, which was sufficient for my application. I also used 2 KHz of sampling frequency that did the job.

The MCU simply samples the Vout and outputs it to a serial terminal where I copy the Vout variations and simply plot them all in Excel. It's that simple!

A sample dynamic current measurement I captured using the above methodology is given in the following link. The x-axis is in units of milliseconds and the y-axis shows values in millivolts.

http://www.flickr.com/photos/11573533@N00/6777940093/in/photostream

I was able to capture waspmote's peak current consumptions using this same method. I found it to be extremely useful and will be using it again soon in other applications.

I hope you will find this information useful for your application as well. Please let me know how you get on and whether my methodology was helpful.

Good luck!

Regards...

Hi Cryptoman,

the reason why you are not getting the same current profile with the mote connected to the USB is that you have to sum both the current consumed by the Waspmote and the current provided to the battery charger from the USB. If you want an accurate measurement of the total current consumed in the application you will have to monitor both of them.

Regards.

Thanks for this useful info Libelium.

I guess with the USB measurement method there will be a problem of physical access on the Waspmote. Are there test points on the board that I could use to measure both of the current consumptions you have mentioned? If not, then measuring the consumption from a battery seems to be the most straightforward method.

Regards...

Hi Cryptoman,

I'm afraid the test points won't help you to measure the current through the line, only the voltage. As you said, you will have to measure the battery current (without the USB connected).

Regards.

Hi Cryptoman,

can you plz example in detail the measurement process which you have done to get the current consumption of waspmote and xbee .... waiting for your reply thanks