Since we moved to an apartment with a balcony we wanted to have some plants there. The problem is that we’re a lot better at killing plants than actually taking care of them. And even the few days when we actually did remember to water them, the plants could dry out on hot days.

So, how to solve this? With PowerShell of course! 🙂

You could start of with the Telldus PowerShell Module from this blogpost (though, this one is preferred since it handles credentials a lot better). The module is under development but works for checking temperatures, dimming or turning on/off devices etc.

You also need something to water with, I went with a pump from Gardena which runs for 1 minute when turning it on, or 1 min/24h if turned on constantly. This means that switching it off/on will start a watering session. The waterflow is controlled by using different outlets from the pump.

After adding the devices to Telldus Live! you can just open up your favorite powershell editor, import the module and start coding. (The module requires at least PowerShell v3)

An example of how it can be done follows. (The below module has been updated, make sure you check out the new version that uses a PSCredential among other things!)

First import the module, set the credentials and some variables needed: (passthrough for credentials (using “secure string”) is on the ToDo-list)

Import-Module C:\Scripts\Telldus\Module\TelldusModule.psm1

$Username="[email protected]"
$Password="MySecretPassword"

# At what temperature (and above) should I start the pump?
$WhenToWaterTemp=25

# If the humidity get's below this value, I will also start the pump
$WhenToWaterHumidity=40

# How old could the sensor data be before I'll consider it invalid? (in hours)
$DataAgeLimitInHours=2

# Time zone difference compared to telldus servers.
$TimeZoneDifference=2

You don’t need to check for how old the sensor data is, but these sensors can sometimes stop updating, and if they do when it’s hot outside, you might end up drowning your plants if you schedule the script to run often.

We continue to load the data from the sensors:

You could do it like this:

# Get the balcony sensor ID
$BalconySensor=Get-TDSensor -Username $Username -Password $Password | Where-Object { $_.Name -eq "Balcony" }

# Get the sensor data from that ID
$BalconySensorData=Get-TDSensorData -Username $Username -Password $Password -DeviceID $BalconySensor.DeviceID

Or with a one-liner, like this:

$BalconySensorData=Get-TDSensor -Username $Username -Password $Password | where Name -eq "Balcony" | Get-TDSensorData -Username $Username -Password $Password

We now know the temperature and humidity (depening on your sensor capabilites) on the balcony, or wherever you have your plants. We continue with the logic for watering:

# Calculate when to consider the sensor data too old
$CurrentAgeLimit=(Get-Date).AddHours(-($TimeZoneDifference+$DataAgeLimitInHours))

# Check if the data is too old
if ($BalconySensorData.LastUpdate -gt $CurrentAgeLimit) {
    # Check if it's too hot or too dry
    if ($BalconySensorData.Temperature -ge $WhenToWaterTemp -or $BalconySensorData.Humidity -le $WhenToWaterHumidity) {
        # If it was, let's give them some water by turning the pump off and then back on
        Write-Output "The plants are sweating (dry and/or hot)! I'm going to give them some water..."
        Get-TDDevice -Username $Username -Password $Password | Where-Object { $_.Name -like "Balcony Watering System*" } | Set-TDDevice -Username $Username -Password $Password -Action turnOff
        Get-TDDevice -Username $Username -Password $Password | Where-Object { $_.Name -like "Balcony Watering System*" } | Set-TDDevice -Username $Username -Password $Password -Action turnOn
    }
}
else {
    # The data was too old
    Write-Output "Sensordata is too old!"
}

That’s basically it! I added some functionality for doing push-notifications to my phone (Growl API and Boxcar works great for this). Or you could just send an e-mail (you probably want to know if the sensor data isn’t getting updated, for example).

Hope this gives you an idea on what you can do with PowerShell and home automation.

I will try to add other things that I’ve automated with this module when I get the time!

If you have any suggestions, please leave a comment below!