NAME

RPi::Device::DHT11 - Interface to the DHT11 digital temperature/humidity sensor

SYNOPSIS

use RPi::Device::DHT11;

sub MAIN() {
    my $dht = RPi::Device::DHT11.new(pin => 0, supply-interval => 1.5);

    react {
        whenever $dht -> $reading {
            say sprintf "{ DateTime.now.Str }: Humidity is %.2f %%, \t Temperature is %.2f *C", $reading.humidity, $reading.temperature;
        }
    }
}

DESCRIPTION

The DHT11 is a common and inexpensive temperate and humidity sensor with a single pin digital interface. It has a reasonable degree of accuracy ( 1-2% on relative humidity and 0.2°C or so.)

To hook the DHT11 up you only need a pull-up resistor (the datasheets indicate 5KΩ but 10K seems to work fine.) It will not work reliably (or at all,) without the pull-up.

A typical setup would be:

[](examples/hardware/dht11.png)

Please note that because this uses the wiringPi library under the hood the [wiringPi pin numbers](http://wiringpi.com/pins/) are used, so in the above the data line is connected to the sixth pin down from the top on the left (assuming the end with the USB is "down",) which is wiringPi pin 0 (or GPIO 17 in the Broadcom numbering.) You can find the actual numbering for your Raspberry Pi with:

gpio readall

which gives you a convenient table.

The easiest way to use this module is to use the object as a `Supply` as in the example above (it supplies a `Supply` coercion,) this will emit a `Reading` object at a minimum of `supply-interval` seconds frequency (the default is 1.5 seconds which is about the minimum usable value.) The `Reading` object has `temperature` (in degrees Celsius,) and `humidity` (in percentage relative humidity,) attribute.

The `read` method returns a `Reading` object if a valid reading is obtained in `read-retries` attempts, or a type object otherwise, this doesn't place a constraint on how frequently it is called but you are likely to get fewer valid readings if call more frequently than 1.5 seconds.

You could potentially use multiple instances of this on different pins (having more than one on the same pin is guaranteed not to work,) but you should bear in mind that the code has to spin in a tight loop while it is getting a reading so you might experience high processor load and/or unreliable readings if you have too many.