Display negative numbers

PicoTM1637.c

@@ -80,7 +80,7 @@ void TM1637_put_4_bytes(uint start_pos, uint data) {
 /* Convert a number to something readable for the 'put bytes' functions.
  *
  * Warning, input must not be more than 4 digits. */
-unsigned int num_to_hex(int num) {
+  unsigned int num_to_hex(int num) {
   unsigned int hex = 0x0, seg;
   while (num) {
     seg = digitToSegment[num % 10];  // extract last digit as 7 segment byte
@@ -91,21 +91,34 @@ unsigned int num_to_hex(int num) {
 }
 
 void TM1637_display(int number, bool leadingZeros) { 
+  // Is number positive or negative?
+  int isPositive;
+  int isNegative;
+  if (number >= 0) {
+    isPositive = 1;
+  } else {
+    isPositive = 0;
+    number = -1*number;
+  }
   // Determine length of number
   int len = 0;
   int numberCopy = number;
   while (numberCopy) {
     len++;
     numberCopy /= 10;
   }
-  if (len > 4) {
+  if (len > 3 + isPositive) {
     printf("Warning number %d too long\n", number);
-    len = 4;
-    // least signigicant digits will be cut of in num_to_hex
+    len = 3 + isPositive;
+    // least signigicant digits will be lost
   }
 
   // Get hex
   unsigned int hex = num_to_hex(number);
+  if (!isPositive) {
+    hex = (hex << 8) + 0x40;  // add a negative sign
+    len++;  // count negative sign in length
+  } 
   unsigned int startPos = 0;
   if (leadingZeros && (len < MAX_DIGITS)) {
     for (int i=len; i<MAX_DIGITS; i++) {

PicoTM1637.h

@@ -25,26 +25,27 @@ void TM1637_put_2_bytes(uint start_pos, uint data);
  *       to the left */
 void TM1637_put_4_bytes(uint start_pos, uint data);
 
-/* Display a number with 4 digits.
+/* Display a positive number with 4 digits or a negative number with 3 digits.
  *
  * The least significat digit will be put to the right.
  * Arguments:
- *  int number: The number to display (currently only positve)
+ *  int number: The number to display.
  *  bool leadingZeros: If leading Zeros should be displayed or not. */
 void TM1637_display(int number, bool leadingZeros);    
 
-/* Display a number on the 2 leftmost digits on the display. A colon is by
- * default shown, to turn this off use TM1637_set_colon(false)
+/* Display a posetive number on the 2 leftmost digits on the display. A colon is
+ * by default shown, to turn this off use TM1637_set_colon(false)
  *
  * !!! Avoid using this function since it will cause the right side to flicker. 
  * Instead use TM1637_display_both. */
 void TM1637_display_left(int number, bool leadingZeros);
 
-/* Display a number on the 2 rightmost digits on the display. */
+/* Display a positive number on the 2 rightmost digits on the display. */
 void TM1637_display_right(int number, bool leadingZeros);
 
-/* Display two (two digit) numbers on the display. By default there will be a 
- * colon between them. Disable this behaviour with TM1637_set_colon(false); */
+/* Display two (two digit positive) numbers on the display. By default there 
+ * will be a colon between them. Disable this behaviour with 
+ * TM1637_set_colon(false); */
 void TM1637_display_both(int leftNumber, int rightNumber, bool leadingZeros);
 
 /* Turn the colon led on or off. Default is on.

README.md

@@ -3,7 +3,7 @@ TM1637-pico
 #### Control TM1637 based 7-segment display from raspberry pi pico.
 
 ## Features
-* Display a positive 4 digit number
+* Display a positive 4 digit number or a negative 3 digit number.
 * Display two positive 2 digit numbers with (or without) a colon in between.
 * You can choose if you want leading zeros in both of the above cases.
 * Display 4 or 2 digits of raw data.
@@ -12,15 +12,14 @@ TM1637-pico
 The actual communication with the display is handled by the picos pio 
 functionality. When a display function is called, some data is very quickly put 
 into a buffer that the pio has access to. The pio will then, one bit at a time 
-send send the data to the TM1637 display. If to much data is sent to the display 
-in a short period of time, the buffer will become full.
-This will block further execution in the main program if even more data is sent
-to the display. 
+send send the data to the TM1637 display. If you attempt to display too much 
+in a short period of time, the buffer will become full. This will block further
+execution in the main program if even more data is sent to the display. 
 
 This library will only work with the 4 digit version of the display.
 
-To get started have a look at the `examples/demo.c` file. For a full list of functions 
-please refer to `PicoTM1637.h`
+To get started have a look at the `examples/demo.c` file. For a full list of 
+functions please refer to `PicoTM1637.h`
 
 ## Setup
 1. Download the files from this repository and put them in a folder somewhere.

examples/demo.c

@@ -20,16 +20,20 @@ int main()
     TM1637_clear();
     sleep_ms(500);
 
-    // Count up from 0
-    int count = 0;
-    while(count <= 200) {
+    // Count down from 150 to -50
+    int count = 150;
+    TM1637_display(count, false);
+    sleep_ms(500);
+    while(count >= -50) {
       TM1637_display(count, false);
-      count++;
+      count--;
       // The display can not update too often. So even though there is no
       // sleep, this will take a couple of moments.
     }
 
     sleep_ms(1000);
+    TM1637_clear();
+    sleep_ms(500);
 
     // Demo a clock, by default there will be a colon between the numbers.
     int seconds = 0;