Contents
- Introduction
- Ratings
- How it Works
- Breadboard Device
- Description
- Materials
- Tools
- Preparing the sensor
- Assembling the breadboard
- Software
- Running the breadboard and collecting data
- Anatomy of an Airlock Bubble
- Full-Featured Device Concept
- Description
- Features
- Control Board
- Control Software
- Optical Sensor
- Temperature Sensor
- Software
- Testing
- Enclosure
- User Manual
- Examples
How It Works
So what sort of sensor do we need to detect bubbles? Nearly all the published homemade bubble counters use an infra-red photo-interrupter sensor for bubble detection. These photo-interrupter sensors are used in many products mainly to monitor the movements of moving parts. There are two active components in a photo-interrupter sensor as shown in the diagram below.
The LED is powered by a DC electrical current and the resultant beam of infra-red light is directed across a gap in the sensor onto a photo-transistor. When light falls on the photo-transistor, it will conduct electrical current. When the light beam is interrupted by some object entering the gap, the electrical current flowing through the photo-transistor is reduced and this change in current can be detected by external electronics. Some photo-interrupter sensors contain an electronic switch so that the output will be set to either a logic high or low voltage depending on what’s in the gap. For most applications, some sort of opaque flag will pass through the gap to indicate the position of a mechanical part and so a switched output would be very suitable. For our purposes, we want an un-switched, analog output from the photo-transistor. This is because a bubble passing through an airlock is not totally opaque and so subtle changes to the photo-transistor current need to be detected and processed.
The photo-interrupter circuit selected for my projects is the HY810A from the HingYip Electronic Co. as shown below. This device seems to be readily available from a number of sources (including Walmart) and costs about $1 but you may have to buy a pack of 10.
The HY810A sensor has a ~10-mm slot and this just fits nicely around the channel in which the bubbles form in a standard 1-piece (s-shaped) air-lock.
The sensor can be secured in position with some black electrical tape or with a specially 3D-printed black clip. The black color will also help minimize any interference from ambient light.