Thingsee Support

Power management: Display & Sensors

Display                  

When something is visible on the Thingsee display it takes 40 – 200 mA. Amount of power depends on the amount of white pixels on the display. Display is normally inactive when your Purpose is active and the device buttons are not pressed.

 

GPS                        

GPS power consumption is a little more difficult to estimate. GPS power need depends on several things:

  • Are the satellites in a good position and is there direct visibility from Thingsee to the satellite?
  • How good assisted position estimate is available? Position estimate is taken from GSM radio and earlier successful position measurements.
  • How good is the GPS position accuracy?

When all these factors are good, position fix can only take one second. If these factors are negative, position fix can take up to 35 seconds. Also, finding out that position cannot be acquired at all takes 35 seconds. If position estimate is available, position fix normally takes maximum 10 seconds. Measuring GPS position minimum every 4 hours will maintain good enough position estimate to keep the measuring time under 10 seconds. If position accuracy is not optimal, position is measured until the accuracy is good enough or 35 seconds is gone (best measurement will be used). Position accuracy is decreased when the device is indoors, there are trees of buildings between the device and the satellites or there are less satellites visible than normally.

Measuring GPS position once per day will always take 35 seconds. Measuring GPS position every 4 hours or less will take 10 seconds or less.

GPS device uses constant 50 mA of power when active.

Duration (s) 1 35
Power consumption (mA) 50 50

 

Sensors                

All sensors take 20 mA power altogether when measuring is active. Amount of power is the same regardless of how many sensors are active. Only Gyro takes extra 4 mA when used. One set of sensor measurements take maximum one second.

Duration (s) 1 1
Power consumption (mA) 20 24

 

Accelerometer    

It is very easy to make a Purpose which causes Thingsee to run all the time and use the battery in four days.

Accelerometer sensor monitors Thingsee acceleration 10 times per second.  This monitoring does not take practically any power. You can set triggers in every direction. Whenever the Thingsee acceleration goes over the trigger value (or under the other trigger value) the device wakes up and starts using power. Should not take any extra power, right?

Well, there are a few things to be taken into account.

First of all, there are two types of acceleration triggers: impact to any direction and accelerations in all directions.

Gravity has no effect to the impact trigger but gravity causes constant 1 g acceleration to the acceleration sensors. This gravity acceleration is divided between the lateral, longitudinal and vertical axes depending to the device orientation. (That is actually very handy if you want to find out the device orientation). Problem here is that setting triggers right is difficult without knowing the device orientation. Other hardware limitation is that the acceleration sensor can only have one positive and one negative trigger value which is used for all the axes. You might want to program different triggers to different axes in your Purpose but in reality the lowest values for positive and negative triggers are used to all axes. If acceleration in any axis is over the trigger value (or under the other) Thingsee wakes up and checks the measurement against all triggers. This is done 10 times per second causing the device to run all the time in practice if for instance gravity happens to point to wrong direction.

It is better not to have acceleration triggers active all the time. Instead, use timer to activate a state with a short acceleration measurement task and after that go back to state without acceleration triggers. If you want Thingsee really wake up only when it is moved, use impact trigger. Again, you have to be careful to have high enough trigger value to prevent keeping Thingsee awake all the time. This of course depends on your application.

Accelerometer does not take extra power, only challenge is to take care that the device is sleeping as much as possible.

 

Luminance sensor

Same caution is needed with the luminance sensor than with acceleration sensor. Luminance sensor monitors the light amount all the time without using practically any power. Again if the amount of light is over the trigger (or under the other trigger) device is awake all the time.

You can prevent keeping the device awake with timers and states. After the original luminance trigger you can for instance go to another state where luminance is deactivated and a timer is activated. After timer go to a third state where luminance is measured. Power consumption can be quite easily controlled with a few states and timers.

Again, like with accelerometer, luminance sensor does not take extra power, only wake up times need to be controlled.

 

What's next?

Power management: Simulator

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