and P1 during the read-reset operation for no-event (left)
and event (right). To capture the traces, the read-reset
routine was executed twice. The first execution preset CFE
DOWN. The outcome of its read operation was ignored.
The second execution determined if we had activated
the piezoelectric flapper or not since the first execution.
The bottom trace in Figure 7 shows the sense voltage
on P1. If no event occurs, CFE is still DOWN when the
capacitor state is read. The ferroelectric switching charge
will generate over three volts on the P1 pin from the
charge in CSense. This voltage will be read as Logic 1 by the
If the event occurred during the detection period, no
ferroelectric switching will take place during the read
operation; less charge will flow from CFE to CSense; less
than two volts will be generated on the input P1. This
state will read as Logic 0 by the Arduino.
The ferroelectric event detector adds excitement to a
single bit of non-volatile memory: An outside sensor
performs the write operation so the microprocessor can
detect the occurrence of events in its local environment.
The event detector will remember the event after it occurs
so the controller can be powered off while it waits.
A future article will eliminate the microcontroller
altogether to make a stand-alone memory circuit out of
discrete components. NV
FIGURE 7. Oscilloscope traces for event and no-event
read-reset operations on the event detector.
52 October 2015