Adding a single zone FSR (Force Sensitive Resistor) sensor is pretty simple thanks to the Snowboard's onboard force touch controller. This force touch controller is able to handle up to 160 single zone FSR sensors simultaneously with total scanning time less than 20 ms (120 us for each single sensor). This onboard controller always scan 160 sensing points when requested. However, in some case, you just want to use one or two FSRs and very fast response from them.
The easiest way to achieve this is to combine the Arduino and reference resistors in the Snowboard.
Let's first start with an example. Wire your FSR and the Snowboard as shown below.
It is convenient to use a small breadboard to implement the wiring above.
Then, upload the following code to the Snowboard.
Run Serial Monitor from Arduino IDE. Squeeze the FSR sensor. You can see that FSR reading is changed according the applied pressure. Speed of reading a single zone FSR sensor is at most 120 us which is quite fast enough for most applications (such as musical instrument).
Now we are in a position to know how it works. On the Snowboard, there are An pins which is part of Snowboard's connectors for force matrix sensors.
These pins are connected to 10 kOhm reference resistor as shown below.
According to the wiring above, an equivalent circuit is constructed as follows. D8 drives the whole circuit by applying 5V. Due to the serial connection of FSR and the 10 kOhm reference resistor, the applied +5V is divided across the two resistors, i.e. FSR and R1. The voltage acroos R1 is measured by A0 (analog input) pin of Snowboard whose value is
A0 (V) = 5 * R1 / (R_FSR + R1)
where R_FSR is the resistane of FSR sensor. It should be noted that this value is decresed according to the applied pressusre. When this voltage is measured by A0 (analog pin), this value is digitized between 0 and 1024. 0 and 1024 correspond to 0V and +5V, respectively.
Since there are six analog pins on the Snowboard, you can attach 6 FSR sensors with this approach. If you need to attach more FSR sensors, then use this method.
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