Overcome Arduino memory limitations with multiple sensors - c++

Question

I have an Arduino Nano piggybacked on a ENC28j60 ethernet module. I have eight (8) DHT22 sensors (named A, B, C ... H ) and i want to write their temperature and humidity data to Pushingbox.
The program is working great with ONE sensor. So that's good. However when i un-remark (i.e. take out the //'s) for anything more than one sensor, yes even for ONE other sensor, it won't write anything at all.
The arduino IDE complier says:
Sketch uses 23824 bytes (77%) of program storage space. Maximum is 30720 bytes.
Global variables use 1870 bytes (91%) of dynamic memory, leaving 178 bytes for local variables. Maximum is 2048 bytes.
Low memory available, stability problems may occur.
FYI, If i un-remark just one other sensor it goes up +2% to 93% of dynamic memory and stops working. So i'm assuming its a memory problem. i have already removed all floats (and made integers *10 to keep one decimal place of accuracy), i need 8 instances of DHT so considered reducing the library size but the .h seems tiny and pretty lean already (within the .h file it even boasts: Very low memory footprint - Very small code. so i havent modified this or the .cpp.
The overall code i have written is not large, maybe there are some in-efficiencies there, but i can't see that it is going to make anything near the amount of memory saving needed for the next 7 sensors.
The full arduino code (written for all 8 sensors, with 'ghosted' bits for 4 sensors and in use only working for one sensor) is below:
#include "DHTesp.h"
//#include <SPI.h>
#include <UIPEthernet.h>
DHTesp dhtA;
//DHTesp dhtB;
//DHTesp dhtC;
//DHTesp dhtD;
//DHTesp dhtE;
//DHTesp dhtF;
//DHTesp dhtG;
//DHTesp dhtH;
const int ledPin = LED_BUILTIN;
int ledState = LOW;
int interval = 10; // this is the number of seconds between reads (120=2mins)
int numReads = 5; // Number of reads between posting to google docs.
int multFact = 10; // multiplication factor 10 = 1 dec. place 100 = 2 dec places
byte mac[] = {0xBE, 0xEF, 0xDE, 0xAD, 0xDE, 0xAD }; //Ethernet shield MAC. Andy's working {0xBE, 0xEF, 0xDE, 0xAD, 0xDE, 0xAD}
byte ip[] = { 192,168,1,12 }; // Arduino device IP address
char devid [] = "vCE3D036xxxxxxxx"; // Gsheets device ID from Pushingbox ('x's for privacy:)
char server[] = "api.pushingbox.com";
EthernetClient client;
void setup()
{
Serial.begin(9600);
Serial.println ("RESTART");
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}
Serial.println("Trying to connect...");
if (Ethernet.begin(mac) == 0) {
Serial.println("Failed to configure Ethernet using DHCP");
// no point in carrying on, so do nothing forevermore:
while(true);
}
else{
Serial.print("OK, connected. Ethernet ready. ");
// print the Ethernet board/shield's IP address:
Serial.print("IP address: ");
Serial.println(Ethernet.localIP());
}
// give the Ethernet shield a second to initialize:
delay(1000);
Serial.println();
//Serial.println("A-Stat\t\tA-Temp (C)\tA-humdid%\tA-HeatI (C)\tB-Stat\t\tB-Temp (C)\tA-humdid%\tB-HeatI (C)");
Serial.println("\t\t\t\tt-A\th-A\tt-B\th-B\tt-C\th-C\tt-D\th-D\tt-E\th-E\tt-F\th-F\tt-G\th-G\tt-H\th-H");
//hey dB for some reason the Ethernet sheild uses pin D2 :( and pins 10,11,12,13
// https://arduinodiy.wordpress.com/2013/04/07/connect-an-enc28j60-ethernet-module-to-an-arduino/
// assign data pins
dhtA.setup(3);
//dhtB.setup(4);
//dhtC.setup(5);
//dhtD.setup(6);
//dhtE.setup(7);
//dhtF.setup(8);
//dhtG.setup(9);
//dhtH.setup(10); //watchout! i think Ethernet uses this pin too?
pinMode(ledPin, OUTPUT);
//end of void setup
}
void loop()
{
int Ahumid = 0; int Atemp = 0;
int Bhumid = 0; int Btemp = 0;
int Chumid = 0; int Ctemp = 0;
int Dhumid = 0; int Dtemp = 0;
//int Ehumid = 0; int Etemp = 0;
//int Fhumid = 0; int Ftemp = 0;
//int Ghumid = 0; int Gtemp = 0;
//int Hhumid = 0; int Htemp = 0;
int j=0;
for (j = 1; j <= numReads ; j++ ) {
int p = 0;
for (p=1; p <= interval ; p++) {
delay (1000);
// swap the led state
if (ledState == LOW) { ledState = HIGH; } else { ledState = LOW; }
Serial.print (p); //show the seconds passing
Serial.print (",");
digitalWrite(ledPin, ledState);
}
Serial.print (" Reading");
Atemp += dhtA.getTemperature()*multFact; Ahumid += dhtA.getHumidity()*multFact;
//Btemp += dhtB.getTemperature()*multFact; Bhumid += dhtB.getHumidity()*multFact;
//Ctemp += dhtC.getTemperature()*multFact; Chumid += dhtC.getHumidity()*multFact;
//Dtemp += dhtD.getTemperature()*multFact; Dhumid += dhtD.getHumidity()*multFact;
// print the readings
//Serial.print(dhtA.getStatusString());
Serial.print("\t"); Serial.print(Atemp);
Serial.print("\t"); Serial.print(Ahumid);
Serial.print("\t"); Serial.print(Btemp);
Serial.print("\t"); Serial.print(Bhumid);
Serial.print("\t"); Serial.print(Ctemp);
Serial.print("\t"); Serial.print(Chumid);
Serial.print("\t"); Serial.print(Dtemp);
Serial.print("\t"); Serial.print(Dhumid);
Serial.println();
// and so here endeth 'j', the number of reads
}
Serial.print ("Avg...");
Atemp = Atemp/numReads; Ahumid = Ahumid/numReads;
Btemp = Btemp/numReads; Bhumid = Bhumid/numReads;
Ctemp = Ctemp/numReads; Chumid = Chumid/numReads;
Dtemp = Dtemp/numReads; Dhumid = Dhumid/numReads;
// print the averages so we can see what it is going to send
Serial.print("\t\t\t");
Serial.print("\t"); Serial.print(Atemp); Serial.print("\t"); Serial.print(Ahumid);
Serial.print("\t"); Serial.print(Btemp); Serial.print("\t"); Serial.print(Bhumid);
Serial.print("\t"); Serial.print(Ctemp); Serial.print("\t"); Serial.print(Chumid);
Serial.print("\t"); Serial.print(Dtemp); Serial.print("\t"); Serial.print(Dhumid);
Serial.println();
Serial.print ("Prep for upload... ");
if (client.connect(server, 80))
{
Serial.print("Connected OK ... writing...");
client.print("GET /pushingbox?devid=");
client.print(devid);
client.print("&tempA="); client.print(Atemp);
client.print("&tempB="); client.print(Btemp);
client.print("&tempC="); client.print(Ctemp);
client.print("&tempD="); client.print(Dtemp);
client.print("&tempE=29&tempF=39&tempG=49&tempH=59");
//now humidity too
client.print("&humidA="); client.print(Ahumid);
client.print("&humidB="); client.print(Bhumid);
client.print("&humidC="); client.print(Chumid);
client.print("&humidD="); client.print(Dhumid);
client.print("&humidE=26&humidF=27&humidG=28&humidH=29");
client.print("&submit=Submit");
client.println(" HTTP/1.1");
client.println("Host: api.pushingbox.com");
client.println("Connection: close");
client.println();
Serial.println("written OK. & connection closed.");
Serial.println(); //Serial.println();
delay(1000); // maybe take this out to keep time stable?
client.stop();
}
else {
Serial.println("** NO CONNEX **"); Serial.println();
}
//here endeth void loop
}
Extra info (that i dont think is relevant, but maybe): IDE compiler also reports:
WARNING: library DHT_sensor_library_for_ESP32 claims to run on [esp32] architecture(s) and may be incompatible with your current board which runs on [avr] architecture(s).

Answer 1

Use the F macro for double-quoted string literal prints. Instead of this:
Serial.println ("RESTART");
or
client.print("GET /pushingbox?devid=");
... do this:
Serial.println ( F("RESTART") );
or
client.print( F("GET /pushingbox?devid=") );
This will easily save a bunch o' RAM.
I would also suggest using the single quoted literal for single characters, not the double quote:
Serial.print( '\t' );