Painted sensors made with Electric Paint and connected to Touch Board can have a variety of shapes, fill patterns and sizes. These parameters will affect the performance and sensitivity of your sensors.
In this tutorial we will give you some guidelines for creating painted sensors. Following these guidelines you should be able to design the best sensors for your specific application.
Size
Small sensors (about the size of a finger print) work best as touch sensitive buttons, while large sensors work better in proximity mode. This is due to the close relationship between the sensors and the objects they are meant to trigger.
Very large sensors, 1m x 1m, that are filled in completely with Electric Paint can have a slow response time. To make a large sensor, one can improve the responsiveness by reducing the fill area with a hatching pattern.
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Shape
Painted sensors can take almost any shape. The difference between a square or circular sensor of the same size and fill is insignificant in comparison to the other factors, like thickness of the paint, length of track leading to the sensor, fill pattern and sensor size.
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Trace Length
Most of the sensors we design have a trace of between 5 – 30cm leading up to the sensor trigger area. We generally make this trace between 3mm and 15mm wide.
If you need a longer trace leading to the sensor, we would not recommend using Electric Paint to make a trace longer than 1m. For traces longer than this we would recommend using a more conductive material such as copper wire or shielded cable as the trace, and then attaching the painted sensor at the end.
This will improve the the reliability of sensors at the end of long traces.
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Fill Pattern
When designing a sensor, the ratio of the conductive surface area (sensor) to the size of the object which is meant to trigger (hand) needs to be considered.
If you aiming to create a sensor that detects the presence of a hand, then the outer limit of the sensor should be larger than a hand. In order to make it more sensitive you can reduce the area of the conductive surface.
For example, a square shaped sensor measuring 20cm x 20cm that is completely filled in with Electric Paint will be less sensitive than the same size 20cm x 20cm sensor with a hatching fill.
Hatching sensors particularly improves the performance and potential range of proximity detection.
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