The Shinyei PPD42NS sensor
This sensor emits a low occupancy time signal where the relative time the signal is in low state is measured.
The connections as are follows:
Shinyei pin |
WeMos Pin |
GPIO |
Comments |
1: Common (GND) |
GND |
|
|
2: OUTPUT(P2) |
D6 |
19 |
through voltage divider 5V - 3.3V |
3: INPUT(5V DC 90mA) |
5V |
|
|
4: OUTPUT (P1) |
D7 |
23 |
through voltage divider 5V - 3.3V |
5: INPUT T1 |
D0 |
26 |
DAC |
Reading the signal
To get a feeling about the signals emitted by the Shinyei PPD42NS we first write a very simple program (pulses.py) that reads the P1 data line every 1 ms and saves the result in an array. It does so during 10 s. After data taking, the results are printed on the serial line.
We can run the program with
ampy run pulses.py > data.txt
and thus redirect the results into a file that can be plotted with gnuplot.
The plot shows a measurement where a match has been lighted and the smoke blown into the sensor. The particle concentration can be measured by calculating the relative time the signal is low with respect to the measurement period (low occupancy time).
--
Uli Raich - 2022-06-01
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