initial commit

Makefile

@@ -0,0 +1,13 @@
+CFLAGS= -D__LINUX__ -c -Wall -O2
+LIBS = -lm -lbb_scd41 -lpthread
+
+all: sensor2json
+
+sensor2json: main.o
+	g++ main.o $(LIBS) -o sensor2json
+
+main.o: main.cpp
+	g++ $(CFLAGS) main.cpp
+
+clean:
+	rm *.o sensor2json

main.cpp

@@ -0,0 +1,113 @@
+//
+// Write SCD4x sensor values into a JSON file
+// written by Larry Bank Feb 13, 2026
+//
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdint.h>
+#include <dirent.h>
+#include <bb_scd41.h>
+#include <time.h>
+
+SCD41 co2;
+
+void CreateJSON(const char *filename, int iCO2, int iTemp, int iHumidity)
+{
+FILE *f;
+char szTemp[256], szOut[1024];
+time_t tt;
+
+	f = fopen(filename, "w");
+	if (f) {
+		tt = time(NULL);  // get the current system time
+		strcpy(szOut, "{\n  \"data\": [\n    {\n");
+// CO2 value
+		strcat(szOut, "      \"make\": \"Sensirion\",\n      \"model\": \"SCD41\",\n");
+		strcat(szOut, "      \"kind\": \"co2\",\n");
+		sprintf(szTemp, "      \"value\": %d,\n", iCO2);
+		strcat(szOut, szTemp);
+		strcat(szOut, "      \"unit\": \"ppm\",\n");
+		sprintf(szTemp, "      \"updated_at\": %lu\n    },\n    {\n", (unsigned long)tt);
+		strcat(szOut, szTemp);
+// Temperature value
+                strcat(szOut, "      \"make\": \"Sensirion\",\n      \"model\": \"SCD41\",\n");
+                strcat(szOut, "      \"kind\": \"temperature\",\n");
+                sprintf(szTemp, "      \"value\": %.2f,\n", ((float)iTemp)/10.0f);
+                strcat(szOut, szTemp);
+                strcat(szOut, "      \"unit\": \"celcius\",\n");
+                sprintf(szTemp, "      \"updated_at\": %lu\n    },\n    {\n", (unsigned long)tt);
+                strcat(szOut, szTemp);
+// Humidity value
+                strcat(szOut, "      \"make\": \"Sensirion\",\n      \"model\": \"SCD41\",\n");
+                strcat(szOut, "      \"kind\": \"humidity\",\n");
+                sprintf(szTemp, "      \"value\": %d,\n", iHumidity);
+                strcat(szOut, szTemp);
+                strcat(szOut, "      \"unit\": \"percent\",\n");
+                sprintf(szTemp, "      \"updated_at\": %lu\n    }\n  ]\n}\n", (unsigned long)tt);
+                strcat(szOut, szTemp);
+		fwrite(szOut, 1, strlen(szOut), f);
+		fflush(f);
+		fclose(f);
+	}
+} /* CreateJSON() */
+
+int main(int argc, char *argv[])
+{
+int i, iBus;
+DIR *pDir;
+struct dirent *pDE;
+uint32_t u32Buses = 0; // available I2C bus numbers (0-31)
+
+        
+        printf("sensor2json example\n");
+        printf("Finds which I2C bus has the supported sensor, then\ninitializes, configures, and loops updating the json with the latest sensor values.\n");
+        if (argc != 2) {
+            printf("usage: sensor2json <json file>\n");
+            return -1;
+        }
+	// I2C buses in Linux are defined as a file in the /dev directory
+        pDir = opendir("/dev");
+	if (!pDir) {
+		printf("Error searching /dev directory; aborting.\n");
+		return -1;
+	}
+	// Search all names in the /dev directory for those starting with i2c-
+        while ((pDE = readdir(pDir)) != NULL) {
+		if (memcmp(pDE->d_name, "i2c-", 4) == 0) { // found one!
+                    iBus = atoi(&pDE->d_name[4]);
+		    u32Buses |= (1 << iBus); // collect the bus numbers
+		}
+	}
+	closedir(pDir);
+	if (u32Buses == 0) { // Something went wrong; no I2C buses
+	    printf("No I2C buses found!\n");
+	    printf("Check your system configuration (e.g. raspi-config)\n");
+	    printf("to ensure that I2C is enabled.\n");
+	    return -1;
+	}
+	// Search each I2C bus for a supported proximited sensor
+        for (iBus=0; iBus<32; iBus++) {
+	    if (u32Buses & (1<<iBus)) { // a bus that we found in /dev
+                i = co2.init(iBus); // scan for supported sensors
+                if (i == SCD41_SUCCESS) {
+                    printf("Found a device on i2c-%d!\n", iBus);
+		    break;
+		}
+	    }
+        } // for each possible bus
+	if (iBus == 32) { // scanned all buses and didn't find anything
+            printf("No supported device found\n");
+	    printf("Your system may require sudo to access I2C.\n");
+            return -1; // problem - quit
+	}
+        printf("SCD41 detected and initialized\n");
+	co2.start(); // start the sensor with the default options
+	while (1) {
+		co2.getSample();
+                CreateJSON(argv[1], co2.co2(), co2.temperature(), co2.humidity());
+		usleep(5000000); // one sample every 5 seconds
+	}
+return 0;
+} /* main() */