feat: differential pressure

Author: Chicken

README.md

@@ -19,6 +19,7 @@ bmp180  | 77      | ??    | pressure
 bh1750  | 5c      | 10    | light
 cajoe   | 08      | 00    | radiation
 ads1115 | 48      | ??    | solar irradiance & rain intensity
+sdp810  | 25      | 362F  | differential pressure
 
 Ads1115 is a 16-bit analog to digital convertor and can have multiple targets.
 

src/db.js

@@ -56,7 +56,8 @@ module.exports = class Database {
                 radiationNow float,
                 radiationAvg float,
                 solarIrradiance int(11),
-                rainIntensity int(11)
+                rainIntensity int(11),
+                differentialPressure float
                 );`
             );
         } catch (e) {
@@ -104,14 +105,15 @@ module.exports = class Database {
             "windDirNow, windGust, windSpeedAvg, windDirAvg, temperature, " +
             "humidity, pressure, lightness, dewPoint, solarIrradiance, "    +
             "absoluteHumidity, feelsLikeTemp, radiationNow, radiationAvg, " +
-            "rainIntensity)" +
-            "VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+            "rainIntensity, differentialPressure)" +
+            "VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
             [
                 Date.now(), data.windSpeedNow, data.windDirNow, data.windGust,
                 data.windSpeedAvg, data.windDirAvg, data.temperature,
                 data.humidity, data.pressure, data.lightness, data.dewPoint, 
                 data.solarIrradiance, data.absoluteHumidity, data.feelsLikeTemp,
-                data.radiationNow, data.radiationAvg, data.rainIntensity
+                data.radiationNow, data.radiationAvg, data.rainIntensity,
+                data.differentialPressure
             ]);
             log("DB", 0, "Saved weather to database.");
         } catch (e) {

src/index.js

@@ -31,6 +31,7 @@ const readPressure = require("./sensors/bmp180");
 const readLight = require("./sensors/bh1750");
 const readRadiation = require("./sensors/cajoe");
 const readAnalog = require("./sensors/ads1115");
+const readDifferentialPressure = require("./sensors/sdp810");
 
 const rain = new (require("./sensors/rs1"))();
 const db = new (require("./db"))();
@@ -149,13 +150,15 @@ parser.on("data", async data => {
         pressure,
         lightness,
         radiation,
-        [ solarIrradiance, rainIntensity ]
+        [ solarIrradiance, rainIntensity ],
+        differentialPressure
     ] = await Promise.all([
         readTemp(),
         readPressure(),
         readLight(),
         readRadiation(),
-        readAnalog()
+        readAnalog(),
+        readDifferentialPressure()
     ]);
 
     // correction math for analog sensors
@@ -197,6 +200,7 @@ parser.on("data", async data => {
         pressure,
         lightness,
         solarIrradiance,
+        differentialPressure: parseFloat(differentialPressure.toFixed(2)),
         radiationNow: radiation,
         radiationAvg: parseFloat(arrAvg(radiationValues).toFixed(2)),
         dewPoint: parseFloat(dewPoint(temp, hum).toFixed(1)),

src/sensors/sdp810.js

@@ -0,0 +1,40 @@
+const { log } = require("../utils");
+const i2c = require("i2c-bus");
+
+const addr = 0x25;
+
+/** 
+ * Read the differential pressure
+ * @returns {Promise<number>} the differential pressure
+ */
+module.exports = async () => {
+    try{
+        let i2c1 = await i2c.openPromisified(1);
+        await i2c1.i2cWrite(addr, 2, Buffer.from([0x36, 0x2F]));
+        await new Promise(res => setTimeout(res, 45));
+        let buf = Buffer.alloc(9);
+        await i2c1.i2cRead(addr, buf.length, buf)
+        if (crc(Uint8Array.prototype.slice.call(buf, 0, 2)) !== buf[2]) throw new Error("Crc 1 failed");
+        if (crc(Uint8Array.prototype.slice.call(buf, 3, 5)) !== buf[5]) throw new Error("Crc 2 failed");
+        if (crc(Uint8Array.prototype.slice.call(buf, 6, 8)) !== buf[8]) throw new Error("Crc 3 failed");
+        let dp = ((buf[0] << 8) | buf[1]) / ((buf[6] << 8) | buf[7]);
+        log("SENSOR", 2, `New differential pressure data, ${dp}`);
+        await i2c1.close();
+        return dp
+    } catch(e) {
+        log("SENSOR", 0, `sdp810, ${e}`, true);
+    }
+};
+
+function crc(data) {
+    const polynomial = 0x31
+    let crc = 0xFF
+    for (const byte of data) {
+        crc ^= byte
+        for (let i = 8; i > 0; --i) {
+            crc = crc & 0x80 ? (crc << 1) ^ polynomial : crc << 1
+            crc &= 0xFF
+        }
+    }
+    return crc;
+}