measure supply voltage

newcode/main.c

@@ -46,14 +46,16 @@ void io_setup(void){
 void modbusGet(void) {
 	if (modbusGetBusState() & (1<<ReceiveCompleted))
     {
+        PORTD.OUTSET = 1 << 5;
         switch(rxbuffer[1]) {
             case fcReadHoldingRegisters: ;
-                modbusExchangeRegisters((uint16_t*)ch_values, 0, 18);
+                modbusExchangeRegisters((uint16_t*)ch_values, 0, 20);
                 break;
             default:
                 modbusSendException(ecIllegalFunction);
                 break;
         }
+        PORTD.OUTCLR = 1 << 5;
     }
 }
 

newcode/pt100.c

@@ -5,7 +5,7 @@
 #include "pt100.h"
 
 uint16_t adc_buffer[AVRG];
-volatile float ch_values[9];
+volatile float ch_values[10];
 
 void adc_init(void){
     ADCA.CTRLB = ADC_FREERUN_bm;
@@ -70,15 +70,21 @@ ISR(DMA_CH0_vect){
     ADCA.CTRLB = 0; // stop ADC
 
     uint8_t old_pin = pin;
-    pin=(pin+1)%9;
+    pin=(pin+1)%10;
-    ADCA.CH0.MUXCTRL = pin << ADC_CH_MUXPOS_gp; // give MUX time to switch during averaging
+    ADCA.CH0.MUXCTRL = pin << ADC_CH_MUXPOS_gp; // give MUX time to switch during calculation
     float temp = avrg(adc_buffer, AVRG);
-
     temp = temp - ADC_0V_COUNT;
     temp = (temp)/ (4096-ADC_0V_COUNT) * ADC_MAX_VOLT;
+
+    if(old_pin <= 8){ /* pt100 temperature channels */
         temp = (temp * REF_OHMS)/(SUPPLY_VOLTS - temp);
         temp = (temp-100)/0.3927; //pt100 formula
         ch_values[old_pin] = temp;
+    }
+    if(old_pin == 9){ /* 24V supply voltage measurement */
+        // resistor devider 33k and 1k
+        ch_values[old_pin] = temp * 34;
+    }
 
     DMA.CH0.TRIGSRC = DMA_CH_TRIGSRC_ADCA_CH0_gc;
     ADCA.CTRLB = ADC_FREERUN_bm; // start ADC again

newcode/pt100.h

@@ -8,7 +8,7 @@
 #define ADC_0V_COUNT 170
 #define ADC_MAX_VOLT 1.95
 
-extern volatile float ch_values[9];
+extern volatile float ch_values[10];
 
 void adc_init(void);
 void dma_init(void);