diff --git a/src/.gitignore b/src/.gitignore
new file mode 100644
index 0000000..2dc174a
--- /dev/null
+++ b/src/.gitignore
@@ -0,0 +1,2 @@
+logtable.c
+exptable.c
diff --git a/src/Makefile b/src/Makefile
index ac5ab0c..50ef56e 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,5 +1,5 @@
 
-PROJ=blink
+PROJ=ntc
 
 default: all
 all: $(PROJ).hex
@@ -7,6 +7,13 @@ all: $(PROJ).hex
 SN_blink = 1
 MCU_blink = attiny13a
 
+SN_ntc = 1
+MCU_ntc = attiny13a
+logtable.c: ./logtable.py
+exptable.c: ./exptable.py
+	./$< >$@
+C_FILES_ntc = exptable.c
+
 SN_kennung = 1
 MCU_kennung = attiny13a
 
@@ -27,8 +34,7 @@ CC=avr-gcc -Wall -Wno-parentheses -MMD -std=c99 -O3 \
   -fpack-struct \
   -fshort-enums \
   -mtiny-stack \
-  -mint8 \
-  -fverbose-asm
+  -mint8
 
 SN = $(SN_$(PROJ))
 CFLAGS = $($*_CFLAGS) $(DEBUG) -I. -DSN="$(SN)"
@@ -70,6 +76,7 @@ OBJCOPY = avr-objcopy
 # [1:0] CKSEL = 10 (9.6MHz internal oscillator)
 
 lfuse_blink = 0x7a
+lfuse_ntc = 0x7a
 
 # [6]: EESAVE = 0  ! (EEPROM not preserved @ chip erase)
 # [5]: WDTON  = 0  ! (watchdog disabled)
diff --git a/src/blink.c b/src/blink.c
index 4e25198..5970d8c 100644
--- a/src/blink.c
+++ b/src/blink.c
@@ -9,126 +9,77 @@
 #include <avr/interrupt.h>
 #include <avr/sleep.h>
 
-#define Bit(x) (1<<(x))
-#define SetPORT(x) PORTB |= Bit(x)
-#define ClrPORT(x) PORTB &=~ Bit(x)
-#define GetPORT(x) (PINB & Bit(x))
-
 #define RES_PORT  0
 #define TRIG_PORT 1
 #define OUT_PORT  2
 #define LED2_PORT 3
 #define LED1_PORT 4
 
-#define START_PORT OUT_PORT
-
-// 9.6MHz/8/240 = 5kHz
-#define MAX_DC 240
-#define DC_EXP 12
-
-static uint32_t led1_dc;
-
-static inline
-uint8_t get_dc(uint32_t dc) {
-	return dc >> 24;
-}
-static inline
-uint32_t set_dc(uint8_t dc) {
-	return ((uint32_t)dc << 24) - 1;
-}
-static inline
-uint32_t fade(uint32_t dc)
-{
-	uint32_t diff = dc >> (8*((DC_EXP+4)>>3));
-	if (DC_EXP & 4)
-		diff <<= 8 - (DC_EXP&7);
-	else
-		diff >>= DC_EXP & 3;
-	return dc - diff;
-}
+uint8_t tick;
 
 ISR(TIM0_COMPB_vect)
 {
-	SetPORT(LED1_PORT);
+	PORTB |= 1 << LED2_PORT;
 }
 
 ISR(TIM0_COMPA_vect)
 {
-	TIFR0 = Bit(OCF0B);
-	ClrPORT(LED1_PORT);
-	OCR0B = MAX_DC + 1 - (uint8_t)(led1_dc >> 24);
+	PORTB &=~ (1 << LED2_PORT);
+	TIFR0 = (1<<OCF0B);
+	tick = 1;
 }
 
-static inline
-void pulse_led1(uint8_t dc)
+void set_dc(uint8_t dc)
 {
-	led1_dc = set_dc(dc);
-	OCR0B = MAX_DC + 1 - dc;
+	OCR0B = 255 - dc;
+}
+
+uint8_t get_dc()
+{
+	return 255 - OCR0B;
 }
 
 static inline
 void init_timer()
 {
-	DDRB = Bit(LED1_PORT) | Bit(LED2_PORT);
-	ClrPORT(LED1_PORT);
+	DDRB = (1<<LED1_PORT) | (1<<LED2_PORT);
 	TCCR0A = 0x02; // CTC TOP=OCRA TOV=MAX
 	TCCR0B = 0x02; // clk_IO/8
-	OCR0A  = MAX_DC;
-	OCR0B  = 255;  // off
-	TIMSK0 = Bit(OCIE0A) | Bit(OCIE0B);
+	OCR0A  = 254;
+	set_dc(10);
+	TIMSK0 = (1<<OCIE0A) | (1<<OCIE0B);
 }
 
-ISR(PCINT0_vect)
-{
-	SetPORT(LED2_PORT);
-	if (!GetPORT(START_PORT))
-		pulse_led1(MAX_DC);
-	ClrPORT(LED2_PORT);
-}
-
-static inline
-void init_trig()
-{
-	PCMSK = Bit(START_PORT);
-	GIMSK = Bit(PCIE);
-}
-
-
-void init_wdt(uint8_t wdt_period)
-{
-#ifdef WDT_TRIGGERED
-        uint8_t cr = Bit(WDE) | (wdt_period&7) << WDP0 | (wdt_period&8) << (WDP3-3);
-        __asm__("STS %[CSR], %[CE]"     "\n\t"
-                "STS %[CSR], %[WE]"     "\n"
-                ::[CSR] "n" (&WDTCR),
-                 [CE] "r" ((Bit(WDCE) | Bit(WDE))),
-                 [WE] "r" (cr)
-                );
-#endif // WDT_TRIGGERED
-}
+static const uint8_t nticks = 50;
 
 int main()
 {
 	init_timer();
-	init_trig();
-	pulse_led1(MAX_DC);
-	init_wdt(7);
 	set_sleep_mode(SLEEP_MODE_IDLE);
-	uint16_t debug = 0;
+	uint8_t n = 0;
 	while (1) {
-		if (!debug) { 
-			// debug = 0xff00L | OCR0B;
-			ClrPORT(LED2_PORT);
-		}
-		else {
-			if (debug&1)
-				SetPORT(LED2_PORT);
-			else
-				ClrPORT(LED2_PORT);
-			debug >>= 1;
-		}
 		sei();
 		sleep_mode();
-		led1_dc = fade(led1_dc);
+
+		if (PINB & (1 << TRIG_PORT))
+			PORTB &=~ (1 << LED1_PORT);
+		else
+			PORTB |= (1 << LED1_PORT);
+
+		uint8_t dc = get_dc();
+
+		if (dc == 0 && !(PINB & (1 << OUT_PORT)))
+			set_dc(255);
+
+		if (tick) {
+			tick = 0;
+			n = n - 1;
+			if (n == 0) {
+				n = nticks;
+				if (dc)
+					set_dc(dc-1);
+			}
+		}
+
 	}
 }
diff --git a/src/exptable.py b/src/exptable.py
new file mode 100755
index 0000000..e65b97e
--- /dev/null
+++ b/src/exptable.py
@@ -0,0 +1,14 @@
+#! /usr/bin/python3
+
+print("""
+/* generated by exptable.py */
+#include <stdint.h>
+const uint8_t exp_table[] __attribute__((section(".text"))) = {
+""")
+
+for a in range(256):
+    aa = 2 ** ((a+36) / (256+35) * 8)
+    dc = int(aa)-1
+    print(f" {dc}, // {a=} {aa=:.1f} {dc=}")
+
+print("};")
diff --git a/src/logtable.py b/src/logtable.py
new file mode 100755
index 0000000..64b8228
--- /dev/null
+++ b/src/logtable.py
@@ -0,0 +1,17 @@
+#! /usr/bin/python3
+
+from math import log
+
+print("""
+/* generated by logtable.py */
+#include <stdint.h>
+const uint8_t log_table[] = {
+""")
+
+for a in range(32):
+    log2 = log(a+1)/log(2)
+    dc = int(255/5 * log2)
+    print(f" {dc}, // {a+1=} {log2=:.3f} {dc=}")
+    
+
+print("};")
diff --git a/src/ntc.c b/src/ntc.c
new file mode 100644
index 0000000..95d0ad6
--- /dev/null
+++ b/src/ntc.c
@@ -0,0 +1,132 @@
+//
+// blink.c
+//
+
+// !!! int = int8_t
+
+#include <stdint.h>
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/sleep.h>
+
+/* y = exp(x) = exp_table[x]
+ * exp_table[] is stored in flash (section .text)
+ * To read from flash we need the opcode LPM "Load Program Memory"
+ * exp8() is a C wrapper for that asm opcode.
+ *
+ * avr-gcc copies .rodata to RAM, to allow direct variable access.
+ * ATtiny13a has only 64 Bytes of RAM.  A table of size 256 Bytes
+ * needs to go into flash.
+ *
+ * The linker script may provide for a data section in flash, but here
+ * we just drop the table into the .text section.
+ */
+
+extern const uint8_t exp_table[256] __attribute__((section(".text")));
+
+static inline
+uint8_t exp8(uint8_t x)
+{
+	uint8_t r;
+	__asm__(" lpm %[R], Z"
+		: [R] "=d" (r)
+		: [Z] "z" (exp_table+x)
+		);
+	return r;
+}
+
+#define RES_PORT  0
+#define TRIG_PORT 1
+#define OUT_PORT  2
+#define LED2_PORT 3
+#define LED1_PORT 4
+
+#define NTC_PORT LED2_PORT
+#define NTC_ADC 3
+
+static inline
+void init_adc()
+{
+       ADMUX = 0x23;
+       DIDR0 |= 1 << NTC_PORT;
+       // ADCSRB = 0x00;
+       ADCSRA = 0xff;
+}
+
+uint16_t ntc;
+
+uint16_t t_min  = 0x8618;
+
+void set_dc(uint8_t dc);
+
+ISR(ADC_vect)
+{
+	uint16_t a = ADCL;
+	a |= (uint16_t)ADCH << 8;
+#if 0
+	ntc = ((uint32_t)ntc * 255 + a) / 256;
+#else
+	uint32_t a1 = (uint32_t)ntc << 8;
+	a1 -= ntc;
+	a1 += a;
+	ntc = a1 >> 8;
+#endif
+	uint16_t dc;
+	if (t_min < ntc)
+		dc = 0;
+	else {
+		dc = (t_min - ntc) >> 6;
+		if (dc > 0xff)
+			dc = 0xff;
+		else
+			dc = exp8(dc);
+	}
+	set_dc(dc);
+	ADCSRA = 0xff;
+}
+
+uint8_t tick;
+
+ISR(TIM0_COMPB_vect)
+{
+	PORTB |= 1 << LED1_PORT;
+}
+
+ISR(TIM0_COMPA_vect)
+{
+	PORTB &=~ (1 << LED1_PORT);
+	TIFR0 = (1<<OCF0B);
+	tick = 1;
+}
+
+void set_dc(uint8_t dc)
+{
+	OCR0B = 255 - dc;
+}
+
+uint8_t get_dc()
+{
+	return 255 - OCR0B;
+}
+
+static inline
+void init_timer()
+{
+	DDRB = 1<<LED1_PORT;
+	TCCR0A = 0x02; // CTC TOP=OCRA TOV=MAX
+	TCCR0B = 0x02; // clk_IO/8
+	OCR0A  = 254;
+	set_dc(10);
+	TIMSK0 = (1<<OCIE0A) | (1<<OCIE0B);
+}
+
+int main()
+{
+	init_timer();
+	init_adc();
+	set_sleep_mode(SLEEP_MODE_IDLE);
+	while (1) {
+		sei();
+		sleep_mode();
+	}
+}