Hello, I am developing a web server project to monitor my home electrical panel. I use an ESP-12E platform under Arduino IDE 2.0.3. To put it simply, if you start from the code ESP8266WebServer -> AdvancedWebServer example and add a very simple acquisition loop (here burst of 400 values), we see that the time of the analogRead instruction can vary from simple to double randomly. But in the same batch it is constant. Does anyone know why and how to fix it? Thanks. Here is the code which is that of the example in the Arduino IDE only completed with a sampling routine :
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#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <ESP8266WebServer.h>
#include <ESP8266mDNS.h>
const char *ssid = "WiFi network name";
const char *password = "Password";
ESP8266WebServer server(80);
const int led = 13;
//----------------------------------------------
void handleRoot() {
digitalWrite(led, 1);
char temp[400];
int sec = millis() / 1000;
int min = sec / 60;
int hr = min / 60;
snprintf(temp, 400,
"<html>\
<head>\
<meta http-equiv='refresh' content='5'/>\
<title>ESP8266 Demo</title>\
<style>\
body { background-color: #cccccc; font-family: Arial, Helvetica, Sans-Serif; Color: #000088; }\
</style>\
</head>\
<body>\
<h1>Hello from ESP8266!</h1>\
<p>Uptime: %02d:%02d:%02d</p>\
<img src=\"/test.svg\" />\
</body>\
</html>",
hr, min % 60, sec % 60
);
server.send(200, "text/html", temp);
digitalWrite(led, 0);
}
//----------------------------------------------------------------
void handleNotFound() {
digitalWrite(led, 1);
String message = "File Not Found\n\n";
message += "URI: ";
message += server.uri();
message += "\nMethod: ";
message += (server.method() == HTTP_GET) ? "GET" : "POST";
message += "\nArguments: ";
message += server.args();
message += "\n";
for (uint8_t i = 0; i < server.args(); i++) {
message += " " + server.argName(i) + ": " + server.arg(i) + "\n";
}
server.send(404, "text/plain", message);
digitalWrite(led, 0);
}
//--------------------------------------------------------------------
void drawGraph() {
String out;
out.reserve(2600);
char temp[70];
out += "<svg xmlns=\"http://www.w3.org/2000/svg\" version=\"1.1\" width=\"400\" height=\"150\">\n";
out += "<rect width=\"400\" height=\"150\" fill=\"rgb(250, 230, 210)\" stroke-width=\"1\" stroke=\"rgb(0, 0, 0)\" />\n";
out += "<g stroke=\"black\">\n";
int y = rand() % 130;
for (int x = 10; x < 390; x += 10) {
int y2 = rand() % 130;
sprintf(temp, "<line x1=\"%d\" y1=\"%d\" x2=\"%d\" y2=\"%d\" stroke-width=\"1\" />\n", x, 140 - y, x + 10, 140 - y2);
out += temp;
y = y2;
}
out += "</g>\n</svg>\n";
server.send(200, "image/svg+xml", out);
}
//---------------------------------------------------------------
void sampling() {
int lecture[400];
unsigned long times[400];
for (int k=0;k<400;k++){
times[k] = micros();
lecture[k] = analogRead(A0);
times[k] += micros();
delayMicroseconds(10);
}
Serial.print("Total duration for sampling = ");
Serial.println((times[399] - times[0])/2);
delay(2000);
}
//-----------------------------------------------------------
void setup(void) {
pinMode(led, OUTPUT);
digitalWrite(led, 0);
Serial.begin(115200);
WiFi.mode(WIFI_STA);
WiFi.begin(ssid, password);
Serial.println("");
// Wait for connection
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");
Serial.print("Connected to ");
Serial.println(ssid);
Serial.print("IP address: ");
Serial.println(WiFi.localIP());
if (MDNS.begin("esp8266")) {
Serial.println("MDNS responder started");
}
server.on("/", handleRoot);
server.on("/test.svg", drawGraph);
server.on("/inline", []() {
server.send(200, "text/plain", "this works as well");
});
server.onNotFound(handleNotFound);
server.begin();
Serial.println("HTTP server started");
}
//-----------------------------------------------------------------
void loop(void) {
sampling();
server.handleClient();
MDNS.update();
}
Replacing the analogRead() instruction for example with a delayMicroseconds() instruction causes the anomaly to disappear.