This page lists the sensors that we have for the grovepi, along with code samples to read from each one.
List of sensors
| Sensor | Grove connection | Description |
|---|---|---|
| Button | digital | Switches on when pushed |
| Tilt switch | digital | Switches on when tilted one way |
| Passive infrared | digital | Fires in response to human motion. |
| Ultrasonic Ranger | digital | Measures distance to the nearest object. |
| Digital humidity and temperature | digital | Measures temperature in C and humidity percentage |
| Rotary Angle | analog | Detects which way the knob is turned. |
| Light | analog | Measures amount of light |
| Sound and Loudness | analog | Measures sound waves |
| Analog temperature sensor | analog | Responds to ambient temperature |
| Accelerometer and Gyro | i2c | Measures acceleration and rotation |
| Accelerometer and Magnetometer | i2c | Measures acceleration and magnetic field |
Button
A simple push button, outputs 1 if it is pressed or 0 otherwise.
sensor_pins={ "button":4 }
# button on digital pin 4
sensors.set_pins(sensor_pins)
while True:
b=sensors.button.get_level()
print(b)
# 1 if button pressed, 0 otherwise
Tilt switch
A tilt switch is a small tube with a ball bearing in. When it is tipped one way, the ball bearing contacts with the switch and the sensor outputs 1, otherwise it outputs 0.
sensor_pins={ "tilt":4 }
# button on digital pin 4
sensors.set_pins(sensor_pins)
while True:
t=sensors.tilt.get_level()
print(t)
# 1 if switch is tilted one way 0 otherwise
Passive infrared
A passive infrared sensor (PIR) is designed to detect human motion in the area in front of the sensor. They are commonly used to switch security lights or burglar alarms. When someone moves in front of the sensor it outputs 1 for several seconds. When no motion is detected it outputs zero.
One detail of this sensor is that there is a little ‘jumper’ on the board which is made of three pins with a little cap across two of them. If you move the cap so it is covering the central pin and the pin marked H, the PIR is set to retriggerable mode, which means the PIR will come on continually when motion is detected. In non-retriggerable mode (central pin and L) the PIR will turn on when motion is first detected, then turn off for a bit, rather than continually triggering. For many projects retriggerable mode makes most sense and is easiest to understand.
sensor_pins={ "pir":7 }
# button on digital pin 7
sensors.set_pins(sensor_pins)
while True:
m=sensors.pir.get_level()
print(m)
# 1 if motion sensed, 0 otherwise
Ultrasonic Ranger
The ultrasonic ranger detects the distance of objects in front of the sensor and returns the distance in centimetres. It is commonly used in car parking sensors. If no object is detected within the range (about 4-5 metres ish), it returns a very high value. It works by sending out pulses of ultrasound and measuring what time the pulse is reflected back. Because of this, reading the sensor takes some time (about 1/20th of a second), so using a lot of ultrasonic reads can slow down your sensor processing. The ultrasonic ranger is connected to a digital pin on the grovepi.
sensor_pins={ "ultrasonic":6 }
# button on digital pin 6
sensors.set_pins(sensor_pins)
while True:
d=sensors.ultrasonic.get_level()
print(d)
# Distance in cm
Digital humidity and temperature
The DHT sensor is a small chip which reads temperature in degrees C and humidity as a percentage. Due to the design of the sensor chip, you can only get a new value from this once every 2 seconds, so it is not necessary to read any faster from this sensor.
sensor_pins={ "dht":6 }
# button on digital pin 6
sensors.set_pins(sensor_pins)
while True:
t,h=sensors.dht.get_level()
print(t,h)
# temperature in degrees C, humidity as a percentage
Rotary Angle
A potentiometer / rotary angle sensor - turn the knob clockwise and it goes higher, turn it anticlockwise it goes lower. At the extreme anti-clockwise and clockwise ends of the rotation the value reaches 0 and 1023 respectively
sensor_pins={ "rotary_angle":2 }
# button on analog pin 2
sensors.set_pins(sensor_pins)
while True:
r=sensors.rotary_angle.get_level()
print(r)
# 0 = anticlockwise fully, 1023= clockwise fully
Light
A light sensor - this outputs 0 in complete darkness, and higher values when light shines on the sensor. The absolute value of the sensor for any given light level can vary quite a lot between different sensor boards, and also depends on ambient temperature, so it is best to use this to detect changes, or broad levels of light, rather than to consider any particular number as meaning exactly the same light level
sensor_pins={ "light":1 }
# button on analog pin 1
sensors.set_pins(sensor_pins)
while True:
l=sensors.light.get_level()
print(l)
# 0 = dark, 1023= very bright
Sound and Loudness
The sound and loudness sensors both contain a microphone and convert the sound level at the microphone into a value between 0 and 1023, where 0 = silence and 1023 is extremely loud. Because of the nature of sound as a vibration, this often requires quite a lot of filtering to get a usable signal, because the sampling of the sound signal could hit anywhere on the sound wave. The loudness sensor has a little screwdriver potentiometer to adjust the microphone level, and also some very minor filtering which aims to make it better respond to sound loudness.
sensor_pins={ "sound":0 }
# button on analog pin 0
sensors.set_pins(sensor_pins)
while True:
s=sensors.sound.get_level()
print(s)
# 0 = quiet, 1023= very loud
Analog temperature sensor
The analog temperature sensor is a thermistor, a resistor which changes resistance depending on temperature. It outputs an arbitrary value between 0 and 1023, where higher values are hotter. The response of individual sensors varies enough that it is not easy to convert this value into an absolute value in C; if you want degrees C, you would probably be better off using the DHT sensor].
sensor_pins={ "temperature":1 }
# button on analog pin 1
sensors.set_pins(sensor_pins)
while True:
t=sensors.temperature.get_level()
print(t)
# 0 = very cold, 1023= very hot
Accelerometer and Gyro
There are two different accelerometer boards in our kits. If you only want to read from the accelerometer, then either board will work fine for you. The accelerometer tells you how much acceleration the board is undergoing, measured in m/s^2; because the accelerometer senses all acceleration, including constant acceleration due to gravity of 9.8m/s^2 downwards, you can use this sensor to tell which way up the board is by looking at which way the gravity vector is pointing. You can also detect freefall by looking at the magnitude of the sensor; when a sensor is being dropped, it will have an accelerometer magnitude of roughly zero.
The accelerometer/gyro board also has a gyroscope sensor, which tells you how fast it is rotating around each axis. If you want to know which axis (x,y,z) is which on the board, there’s a little diagram marked on each sensor board.
# accelerometer and gyro on any i2c pin
sensor_pins={ "accel":0,
"gyro":0}
sensors.set_pins(sensor_pins)
while True:
# acceleration in x,y,z axes
ax,ay,az=sensors.accel.get_xyz()
# magnitude of acceleration
am = sensors.accel.get_magnitude()
# rotation around x,y,z axes
rx,ry,rz=sensors.gyro.get_xyz()
# magnitude of rotation
rm = sensors.gyro.get_magnitude()
print(x,y,z,am,rx,ry,rz,rm)
Accelerometer and Magnetometer
The accelerometer/magnetometer board has an accelerometer as described above. It also has a magnetometer, which detects the orientation and strength of the earth’s magnetic field. This can be used as a compass, to tell which way the board is pointing in the world.
# accelerometer and magnetometer on any i2c pin
sensor_pins={ "accel":0,
"magnetometer":0}
sensors.set_pins(sensor_pins)
while True:
# acceleration in x,y,z axes
ax,ay,az=sensors.accel.get_xyz()
# magnitude of acceleration
am = sensors.accel.get_magnitude()
# magnetic field strength in x,y,z axes
mx,my,mz=sensors.magnetometer.get_xyz()
# magnitude of magnetic field
mm = sensors.magnetometer.get_magnitude()
print(x,y,z,am,mx,my,mz,mm)