Arduino variometer (power budget)

Projects General Guidance
1

Hi Everybody,
I am building a variometer (modifying the GNUvario project) and flight computer sensor for XCSoar. I am trying to make it as energy efficient as reasonably possible.

The list of components and the expected current consumption is:

  • Arduino pro mini (or other 3.3V) 20mA
  • GPS 45mA
  • 10 DOF sensor (acc + gyro + magnetometer + barometer) 5mA
  • Bluetooth 20mA
  • OLED display 20mA
  • Lipo charge manager 0mA
  • micro SD 30mA
  • buzzer (with L9110H) 10mA

For a total of about 150mA

I am planning to power everything with a 3.7V Lipo for at least 10 hours which calls for a 2000mAh battery or maybe a 18650. Could you help me with the following:

  • Is my current estimate reasonable?
  • Is there a way to reduce energy usage while keeping 5 Hz update rate? (I am not an expert of sleep states and interrupts, point me in the right direction please)

I am thinking of powering buzzer and Arduino straight out of the battery and using a single 3.3V dc-dc regulator for the rest.

  • How do I switch completely off the onboard regulator?
  • It is worth the hassle to modify every single board for... how many mA saved?
  • Do I need to provide an I/O ref voltage to the arduino?

Thanks in advance for any help or comment!

2

How important is the buzzer?

Dig a bit deeper into the gps module before deciding on a sd-thingy. The AdaFruit Ultimate GPS

The other cool feature of the new MTK3339-based module (which we have tested with great success) is the built in
datalogging ability. Since there is a microcontroller inside the module, with some empty FLASH memory, the newest
firmware now allows sending commands to do internal logging to that FLASH. The only thing is that you do need to
have a microcontroller send the "Start Logging" command. However, after that message is sent, the microcontroller
can go to sleep and does not need to wake up to talk to the GPS anymore to reduce power consumption. The time,
date, longitude, latitude, and height is logged every 15 seconds and only when there is a fix. The internal FLASH can
store about 16 hours of data, it will automatically append data so you don't have to worry about accidentally losing data
if power is lost. It is not possible to change what is logged and how often, as its hardcoded into the module but we
found that this arrangement covers many of the most common GPS datalogging requirements.

may not do the data logging that you want but other GPS units could have better data logging capabilities, I've not looked.

3

Most of the power consumption of the Pro Mini is the "power" LED. Smash the LED or de-solder its associated resistor.

GPS, SD and bluetooth will have highly-variable power requirements. Bluetooth only needs max power when actually transmitting. When you build the real device, you will find the long-term power consumption is much lower than these peak values.

4

Thanks for the advice!

Idahowalker:
How important is the buzzer?

Why? I can live without the buzzer. On a modern glider, there is already an instrument that tells you if you are going up or down by sound but not in the old ones or paragliders.

Idahowalker:
Dig a bit deeper into the gps module before deciding on a sd-thingy. The AdaFruit Ultimate GPS may not do the data logging that you want but other GPS units could have better data logging capabilities, I've not looked.

I will have a look. Again I was thinking about the standard format .igc but I can covert it later via software.

MorganS:
Most of the power consumption of the Pro Mini is the "power" LED. Smash the LED or de-solder its associated resistor.

You mean that I can power all the 3.3V out of the pro mini regulator?

MorganS:
GPS, SD and bluetooth will have highly-variable power requirements. Bluetooth only needs max power when actually transmitting. When you build the real device, you will find the long-term power consumption is much lower than these peak values.

GPS has to read at 2~10 Hz and bluetooth has to send data to the phone with the same rate... can I send them to sleep in the meanwhile? Data logging can be buffered and executed once a minute or so.

5

You didn't say which of those devices is 3.3V. I suspect that you would overload the 3.3V regulator on board the Pro Mini. A good switchmode regulator will be much more efficient than the linear one on board the Pro Mini anyway.

The GPS and bluetooth communication channels will be mostly idle, even at those data rates. So the device itself will have overall lower power consumption than the peak required when actually transmitting.