diff --git a/CHANGES.txt b/CHANGES.txt
index 3a8b0b0..06e024a 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,3 +1,5 @@
+- ISSUE #21: Problems on clearDisplay and setupDisplay;
+
 Version 2.1.0
 
 - ISSUE #20: Support for negative decimal numbers;
diff --git a/TM1640.cpp b/TM1640.cpp
index 506bf47..9fa4831 100644
--- a/TM1640.cpp
+++ b/TM1640.cpp
@@ -36,3 +36,13 @@ void TM1640::sendChar(byte pos, byte data, boolean dot)
 {
   sendData(pos, data | (dot ? 0b10000000 : 0));
 }
+
+void TM1640::clearDisplay()
+{
+  digitalWrite(strobePin, LOW);
+  send(0xC0);
+  for (int i = 0; i < 16; i++) {
+    send(0x00);
+  }
+  digitalWrite(strobePin, HIGH);
+}
diff --git a/TM1640.h b/TM1640.h
index f26b913..5526647 100644
--- a/TM1640.h
+++ b/TM1640.h
@@ -33,6 +33,8 @@ class TM1640 : public TM16XX
   public:
 	/** Instantiate a tm1640 module specifying the display state, the starting intensity (0-7) data and clock pins. */
   	TM1640(byte dataPin, byte clockPin, boolean activateDisplay = true, byte intensity = 7);
+    /** Clear the display */
+	virtual void clearDisplay();
 
   protected:
     virtual void sendChar(byte pos, byte data, boolean dot);
diff --git a/TM16XX.cpp b/TM16XX.cpp
index 38ad0c8..39f912d 100644
--- a/TM16XX.cpp
+++ b/TM16XX.cpp
@@ -54,6 +54,12 @@ TM16XX::TM16XX(byte dataPin, byte clockPin, byte strobePin, byte displays, boole
 void TM16XX::setupDisplay(boolean active, byte intensity)
 {
   sendCommand(0x80 | (active ? 8 : 0) | min(7, intensity));
+
+  // necessary for the TM1640
+  digitalWrite(strobePin, LOW);
+  digitalWrite(clockPin, LOW);
+  digitalWrite(clockPin, HIGH);
+  digitalWrite(strobePin, HIGH);
 }
 
 void TM16XX::setDisplayDigit(byte digit, byte pos, boolean dot, const byte numberFont[])