# Introduction
The head of Bittle is designed to be a clip to hold extensible modules. We compiled a sensor pack with some popular modules, but its contents may change in the future. You can also wire other add-ons thanks to the rich contents of the Arduino and Raspberry Pi communities.
You can find the demo codes of these modules in our GitHub repository. They should be in the [ModuleTests](https://github.com/PetoiCamp/OpenCat/tree/main/ModuleTests) folder if you download the whole OpenCat repository.
[Light sensor](https://docs.petoi.com/extensive-modules/light-sensor)
[Touch sensor](https://docs.petoi.com/extensive-modules/touch-sensor)
[Gesture sensor](https://docs.petoi.com/extensive-modules/gesture-sensor)
[PIR motion sensor](https://docs.petoi.com/extensive-modules/pir-motion-sensor)
 [MU vision sensor](https://docs.petoi.com/extensive-modules/mu-camera)
[Ultrasonic sensor](https://docs.petoi.com/extensive-modules/ultrasonic-sensor) (Applicable to Nybble)
You can also purchase the following third-party sensors (such as Seeed studio):
The loudness and light level modules can generate [analog readings](https://github.com/PetoiCamp/OpenCat/tree/main/ModuleTests/test_Loudness_Light) for the corresponding signals and should be connected to the analog Grove socket.
[Grove - Sound Sensor/ Noise Detector](https://www.seeedstudio.com/Grove-Loudness-Sensor.html)
[Grove - Light Sensor v1.2 - LS06-S phototransistor](https://www.seeedstudio.com/Grove-Light-Sensor-v1-2-LS06-S-phototransistor.html)
The touch, reflection, PIR sensors can generate digital 1 or 0 as a switch signal. So they should be connected to the digital Grove socket. In the [demo code](https://github.com/PetoiCamp/OpenCat/tree/main/ModuleTests/test_Touch_Reflection_PIR), we use the fourth socket with D6 and D7.
[Grove - Touch Sensor](https://www.seeedstudio.com/Grove-Touch-Sensor.html)
[Grove - Infrared Reflective Sensor v1.2](https://www.seeedstudio.com/Grove-Infrared-Reflective-Sensor-v1-2.html)
[Grove - mini PIR motion sensor](https://www.seeedstudio.com/Grove-mini-PIR-motion-sensor-p-2930.html)
The [intelligent camera](https://github.com/PetoiCamp/BallTracking), [gesture](https://github.com/PetoiCamp/OpenCat/tree/main/ModuleTests/testGesture), and [OLED](https://github.com/PetoiCamp/OpenCat/tree/main/ModuleTests/testOLED) module should be connected to the I2C Grove socket.
[Grove - Gesture Sensor for Arduino (PAJ7620U2)](https://www.seeedstudio.com/Grove-Gesture-PAJ7620U2.html)
[Grove - OLED Display 0.96" (SSD1315)](https://www.seeedstudio.com/Grove-OLED-Display-0-96-SSD1315-p-4294.html)
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