| 摘要 |
A system is described for asynchronously sequentially sending sensor measurements down a common output signal wire in a time multiplexed manner. The primary embodiment describes an array of capacitive pressure sensors C1a, C1b to C1n and C1(n+1). Each sensor unit in the chain comprises an RC circuit and a schmitt trigger which is used to compare the voltage across the pressure sensing capacitor to a threshold. The value of the capacitance effects the time delay before the input to the Schmitt trigger reaches the voltage threshold required to turn on the output of that Schmitt trigger. This converts the capacitance value to a variable time delayed voltage step. When the output of the Schmitt trigger goes high current flows through the next force sensing capacitor to ground. This current flow is detected using a bipolar transistor connected to the output line. When the output of the preceding Schmitt trigger goes high the next pressure sensing capacitor in the chain begins charging. The result is a series of low voltage pulses on the output line (see fig. 4). The time between each pulse represents the capacitance of each sensor stage. The time delays can be read by a microcontroller. The principle could be applied to other sensor types such as inductive, resistive, switch based, etc. |
