Environmental Engineering Reference
In-Depth Information
CH1 = 2 V
DC
CH3=2V
DC 1:1
CH1: Capacitor Voltage
50 ms/div
(50 ms/div)
NORM: 20 kS/s
100:1
CH3: 12-Bit Data
=Trace1=
Max
6.640 V
CH1 =2 V
CH3 = 2V
5 ms/div
CH2: Regulated DC Voltage
CH3: 12-Bit Data
FIGURE 4.12
Output waveforms of a capacitor discharge, 3.3-V DC regulation, and 12-bit address/data trans-
mission.
regulator and the 12-bit address/data information transmitted need to be
examined closely.
The results obtained from the energy harvesting circuit design are illus-
trated in
Figure 4.12
. Channel 1 in the figure represents the discharging
waveform of the storage capacitor. Channel 2 shows the 3.3-V DC signal out-
put waveform from the linear regulator, and Channel 3 represents the 12-bit
address/data information transmitted by the HT-12E encoder via the radio
transmitter. The energy consumption of the RF unit is calculated based on the
operating and standby modes of the RF unit. The total latency time required
for 1 digital word transmission is 20 ms; the time during which transmission
is active is 10 ms, and the time during which transmission is on standby is
10 ms. During RF unit operating mode and standby mode, the currents drawn
by the transmitter are 8 mA and 0.1
A, respectively. Therefore, the peak
powers required during transmission and standby are 2.64 mW and 0.33
W,
respectively. The total maximum energy required for 1 digital word trans-
mission is then 26.4
J. Knowing that the harvested electrical energy is 67.61
J, it can be
calculated that around 2.5 digital words can be transmitted with one push of
the piezoelectric push-button igniter. This is verified in
Figure 4.12
. As shown
in the figure, the regulated DC voltage from the linear regulator is sufficient
to make at least two complete 12-bit information transmissions at 3.3-V DC.
It can therefore be seen that the piezoelectric push-button energy harvesting
circuit is able to harness enough energy for two complete transmissions at a
constant 3.3-V DC.
J and the energy required to transmit 1 digital word is 26.4
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