💬 Battery Powered Sensors

[zboblamont]

@nekitoss Not sure where you got your information but my Gas Node is on it's second year running on the same two Varta AA alkalines and been down to -20 on more than a few occasions last winter, typically 4 months below -10... Currently the temperature is -3 and headed to -8 overnight, voltage is 2.98, will probably need to replace them in autumn 2019...

[benhub]

The tap point could be bypassed with a 0.1 uF capacitor

Can someone explain, how exactly I should connect this capacitor? Should it be between A0 and GND? Would be great to see this capacitor in the graphic.

[zboblamont]

@benhub That rather depends what you are quoting from, as could not find the original statement.
If it is to do with stabilising voltage from a point on a resistor divider to read it on the analogue pin, the capacitor is from the analogue pin to ground.
It's purpose to dampen oscillations long enough for the ADC to sample the voltage, but usually only where high value resistances are used.

[tonbor]

The quote is from this sample : Measuring and Reporting Battery Level

Use a 1MΩ (R1) and 470KΩ (R2) resistor in series, connected to the positive terminal on the battery and ground and then connected the tap point to the A0 input on the CPU.

The tap point could be bypassed with a 0.1 uF capacitor to keep the noise level low, at this otherwise high impedance point.

[skywatch]

@tonbor Yes, the capacitor goes from the analog input to ground.

[mfalkvidd]

@skywatch @tonbor @benhub @zboblamont thanks for your input. I have updated the page. I added the text in bold:

The tap point could be bypassed with a 0.1 uF capacitor (connected in parallel with R2) to keep the noise level low

and updated the image. Please let me know if something is still unclear.

[tonbor]

Perfect!

[Macgyver33]

If you remove the regulator and power with 2xAA batteries, do you only need the TX and RX pins for the FTDI programmer and if so can you use the RX and TX pins on the left side instead of the top FTDI pin connector? Trying to think how to connect the FTDI programmer without connecting to it's VCC and ground when there is no regulator on the pro mini.

[mfalkvidd]

@macgyver33 you need rx, tx and gnd.

The pins on the left side and the ones on the top work the same way, you can use the ones on the left if you prefer.

[tiana]

Is exist something "last wish" in MySensors, when battery go below predefined level the device to send last massage to the GW and go sleep forever.
The idea is the controller/application to have information about the device and to be known this device is dead and need battery change.

[mfalkvidd]

@tiana the controller will know the last battery level. Just set the predefined level in your controller?

[tiana]

Yes but in this case the last massage will be the same like the previous, only the battery level will be below some predefined value. i don't like this. I will think how to solve this.

[skywatch]

@tiana - Of course you can do this in your code.

Just read the battery level and when it gets to the lowest level you decide upon (maybe a little testing needed here) then include the line...

if(battery_level_read < battery_low_level){
send.msg(your last message)
sleep(long time period)
}

You need to define all the things above as normal for variables (floats for the battery reading and levels and UL for the long sleep)....

[zboblamont]

@tiana I agree with @mfalkvidd , normally it is the Controller which sends out the warning to change battery, certainly Domoticz has this provision incorporated?
Here the batteries are read at approximate 12 hour intervals, and Domoticz is preset to signal a warning below 1.7v, which is days or even weeks from actually dying. If I'm away or forgetful it will cease updating anyway and flag Red on the display.
Once you have established the consumption curve for your batteries until flat, easy enough to set the warning threshhold before the Node dies...

[kimot]

@tiana
Create dummy contact sensor on your node and if node sends last message, it will trigger this contact before "die".
So controller knows, that it was last message and node is off.
But better is allow controller do its job, like wrote all others.
I personally check battery level and "no incoming messages in supposed interval" to send alert to my e-mail ( and SMS ).
In this example tank level sensors sends every 10min, so after 3 messages lost, I will be informed.

[tiana]

Thanks for the ideas, i will modify the code to use LowPower lib and will cut the power to the radio module to increase battery live, when last massage is send the node will never power the radio module, will be only short interrupt and go again to sleep forever. This will give me power usage 20times more than self battery discharge. Which have to give me node uptime around 260days with coin cell battery.

[kimot]

@tiana
And for what will be that offline node usefull?

[tiana]

Door/Window/Button

[kimot]

@tiana
Forever sleeping door sensor with low battery?

"when last massage is send the node will never power the radio module"

Why door sensor, if it never sends message?

[tiana]

@kimot
At all of the time 328p will be in sleep forever, when button is pressed interrupt is triggered and wake the 328p power ON the radio send info power OFF radio and go sleep forever.
Only when battery level go below critical level. the radio stay OFF and only interrupt and sleep forever.

I am almost ready with the drawings of the hardware, and next week start work on software... you can see the project in the openhardware.io i gonna upload it later tomorrow.