Introduction
There are several reasons to move the project code to the RPi:
- The capability to timestamp the log entries
- File I/O
- Internet connectivity
The first step in this phase is to convert the working Arduino code, into code for the Pi, which can be quite straightforward with C|C++ and the WiringPi library. The code can be found here, but the following discusses the changes from the Arduino code.
Discussion
The first thing I discovered is that the GPIO interrupt is not as responsive as the Arduino because the processor is busy sharing other computer tasks. I opened up the timing range checks in the interrupt handler function to accommodate:
// global declarations
#define SYNC 600
...
void handler() {
static unsigned long duration = 0;
static unsigned long lastTime = 0;
static unsigned int syncSig = 0;
// ignore if we haven't processed the previous full buffer
if (bufferFilled == true) return;
// calculating timing since last change
long time = micros();
duration = time - lastTime;
lastTime = time;
if (inSync) {
if (ringIndex < 129) {
// store data in ring buffer
ringIndex = (ringIndex + 1) % RING_BUFFER_SIZE;
timings[ringIndex] = duration;
//printf("ringIndex=%d %d\n", ringIndex, duration);
bufferFilled = false;
} else {
// verify end of message
if (timings[112] < 200 && timings[113] > 1000) {
bufferFilled = true;
} else {
bufferFilled=false;
}
inSync = false;
ringIndex = -1;
}
} else {
if (duration > SYNC - 100 && duration < SYNC + 100) {
syncSig++;
if (syncSig > 7) {
//printf("Received %d consecutive square waves\n", syncSig);
ringIndex = -1;
inSync = true;
syncSig = 0;
}
} else {
syncSig = 0;
}
}
return;
}
During test and debug, it became apparent that disabling the interrupt is ineffective. This seems to be a minor shortfall within the super-helpful WiringPi library, There is a suggested work-around that helps, although not completely; placing printf() statements within the interrupt handler will demonstrate that. Hopefully a future Python rewrite will overcome this annoyance.
Timestamp
Knowing the time a reading was taken is at the heart of tracking the data. The Pi reports this quite well.
// global declarations
time_t now; // current time for timestamp
char timeStamp[40]; // formatted time
…
// get time stamp for report once the buffer is filled
now = time(0);
strftime (timeStamp, 100, "%Y-%m-%d %H:%M", localtime(&now));
File I/O
The code saves the data into a CSV file as follows:
// global declaration
FILE* fileRain = NULL; // rain log
// save this value to the data log file once the rain measurement is properly extracted
fileRain = fopen("rainlog.txt", "a+");
if (!fileRain) {
printf("File open failure!");
} else {
sprintf(outbuff, "%s, %6.2f\n", timeStamp, (d/100));
fwrite(outbuff, strlen(outbuff), 1, fileRain);
fclose(fileRain);
}
Also include a debug file for unexpected exceptions
// global declaration
FILE* fileDbug = NULL; // debug log
// track errors for future analysis
void sayDebug(char when[]) { // ‘when[]’ is the timestamp string
char dbuff[100];
// save this value to the data log file
fileDbug = fopen("debug-rainlog.txt", "a+");
if (!fileDbug) {
printf("Debug File open failure!");
} else {
sprintf(dbuff,"%s\n", when);
fwrite(dbuff, strlen(dbuff), 1, fileDbug);
// report timing information for debugging
for (int i = 0; i < 113; i+=2){
sprintf(dbuff,"%d %d %d\n", i, (int)timings[i],
(int)timings[i+1]);
fwrite(dbuff, strlen(dbuff), 1, fileDbug);
}
// report all data formated as bytes
int j = 0;
char sTmp[100] = "";
outbuff[0] = '\0';
for (int i = 0; i < 111; i+=2) {
if (j % 8 == 0) {
strcat(sTmp," ");
}
sprintf(outbuff,"%d", t2b( timings[i],
timings[i+1] ) );
strcat(sTmp, outbuff);
j++;
}
//rcat(sTmp, "\n");
sprintf(dbuff,"%s\n", sTmp);
fwrite(dbuff, strlen(dbuff), 1, fileDbug);
sprintf(dbuff,"<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>\n");
fwrite(dbuff, strlen(dbuff), 1, fileDbug);
}
fclose(fileDbug);
}
Redundant Log Entries
The rain gauge transmits about every 15-20 seconds, resulting in plentiful data, to say the least. The following code limits logging to one entry every 5 minutes.
// report the results every 5 minutes
strftime(outbuff, 40, "%M",localtime(&now));
mod = atoi(outbuff) % 5;
//printf( "*** Minutes: %s Remainder: %d ***\n", outbuff,
mod );
if (mod % 5 < lastMod) {
//printf("5 minutes elapsed\n");
printf("%s, %6.2f\n", timeStamp, (d/100));
// save this value to the data log file
fileRain = fopen("rainlog.txt", "a+");
if (!fileRain) {
printf("File open failure!");
} else {
sprintf(outbuff, "%s, %6.2f\n", timeStamp, (d/100));
fwrite(outbuff, strlen(outbuff), 1, fileRain);
fclose(fileRain);
}
}
lastMod = mod;
Next Steps
- Make the data accessible via internet
- Rewrite in Python
Why?
- To make use of the GPIO routines offered by the RPi library that may disable interrupts during analysis.
- There are plentiful examples within the Raspberry Pi community teaching internet connectivity, cloud database updates, etc.
