diff --git a/src/html.h b/src/html.h
index d664827..15b6fff 100644
--- a/src/html.h
+++ b/src/html.h
@@ -59,8 +59,8 @@ const char html_begin[] PROGMEM = R"(
                     var context = c.getContext("2d");
                     var maxX = 400, maxY = 200;
                     var biasX = 20, biasY = 20;
-                    var curVoltage = 20;
-                    var freq = 16;
+                    var maxVoltage = 20;
+                    var freq = 4/4;
                     function iY(y) {
                         return maxY + biasY - y;
                     }
@@ -71,7 +71,7 @@ const char html_begin[] PROGMEM = R"(
                         context.lineTo(20, iY(i));
                         context.lineTo(15, iY(i));
                         context.moveTo(20, iY(i));
-                        textY = i/200*curVoltage;
+                        textY = i/200*maxVoltage;
                         context.fillText(textY.toFixed(1), 0, iY(i-2.5));
                     }
                     context.moveTo(20, iY(0));
@@ -100,8 +100,6 @@ const char html_begin[] PROGMEM = R"(
                         for (i = 1; i < 200; i++) {
                             context.lineTo(i*2 + biasX, data.data[i] + biasY);
                         }
-                        voltage = data.data[199]*(-0.1)+20;
-                        context.fillText(voltage + " V", 200,20);
                         context.stroke();
                     };
                     function calibrateDevice() {
diff --git a/src/main.cpp b/src/main.cpp
index db6cfe7..fec68b8 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -131,6 +131,19 @@ void webSocketEvent(uint8_t num, WStype_t type, uint8_t * payload, size_t length
     }
 }
 
+void selfTest(){
+    if (millis() - lastTest > 19) {
+        if (!testState) { 
+            digitalWrite(D0, HIGH);
+            testState = true;
+        } else {
+            digitalWrite(D0, LOW);
+            testState = false;
+        }
+        lastTest = millis();
+    }
+}
+
 
 
 void setup(void)
@@ -157,6 +170,7 @@ void setup(void)
     webSocket.onEvent(webSocketEvent);
 
     pinMode(A0, INPUT);
+    pinMode(D0, OUTPUT); //selftest pin
 }
 
 void loop(void)
@@ -168,6 +182,8 @@ void loop(void)
     updateSensors();
     sendDataToSocket();
     
+    selfTest();
+    
     updateCpuTime(1);
     printCpuLoad();
 }
\ No newline at end of file