diff --git a/ChangeLog b/ChangeLog
index ec5366f..4318a88 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,6 @@
+*0.5.1 ()
+    added possibility to connect potentiometer instead of CH3 button
+
 *0.5.0 (23 Apr 2012)
     global menu was restructuralized
     added ability to select number of channels (2-MAX_CHANNELS) for each
diff --git a/MANUAL.txt b/MANUAL.txt
index e97fb2f..3cd6dd0 100644
--- a/MANUAL.txt
+++ b/MANUAL.txt
@@ -197,6 +197,14 @@ Standard menu:
 			 identified by "V" symbol
 	- reverse_long: same as "reverse" + "V" symbol
 	- prev_val_long: same as "prev_val" + "V" symbol
+    -----
+    steps of settings of ch3 potentiometer (if enabled at global config):
+	- sequence:
+	  function -> reverse
+	- function: selected function listed at the end of manual
+	- RE reverse:
+	    0 - no change
+	    1 - swap left/right sides
 		   
 
 
@@ -255,14 +263,22 @@ Operating timers:
 Calibrate menu:
 ===============
 - enter it by wheel right-turn and ENTER-long
-- 6 menu items starts to blink
+- 6 menu items starts to blink (+ 2 arrows if CH3 is potentiometer)
 - use END or ROTATE to change channels
 - there is also channel 3 representing CH3 button (for those who will do
     some 3-position switch/potentiometer modification)
+    > There is 1K resistor connected between CH3 button and +5V, so
+      simply connecting linear potentiometer instead of CH3 button
+      will not work. Usefull results can be done with logarithmic
+      potentiometer 10K which has 1K at half of turn. Or eliminate
+      internal resistor to +5V, connect potentiometer between +5V
+      and GND and potentiometer output instead of CH3 button.
 - there is also channal 4 representing battery voltage
 - calibrate as usual (for channel 1/2 left+mid+right and ENTER)
     > calibrated value will disappear from menu
     > it is not needed to calibrate all values
+- calibrate CH3 potentiometer (if selected at global config)
+    > only left + right positions
 - calibrate battery (it will not be probably needed to use this)
     > select channel 4
     > press ENTER
@@ -313,6 +329,7 @@ Global setup menu:
     d		long press key delay		100...1000 miliseconds
     H		setting of hardware features
 		    reverse rotate encoder	E_N/E_R (Normal/Reverse) - for GT3C
+		    ch3 is potentiometer	P3N/P3Y (No/Yes)
 		    select ppm sync/frame	PTS/PTF (constant SYNC/frame length)
 		    select ppm length		Lxx - 3-18ms for constant SYNC length
 						      9-24ms for constant frame length
diff --git a/TODO b/TODO
index 6b25c62..33938a6 100644
--- a/TODO
+++ b/TODO
@@ -1,10 +1,4 @@
 
-linear CH3 with potentiometer
-    - global option to choose CH3 is a pot
-    - don't read CH3 key in read_keys()
-    - key mapping assign trim function and reverse
-    - at begin of CALC, convert CH3 val to assigned function
-    - calibrate low and high values at calib menu
 ? use also flash memory to store model configs
     - some models in EEPROM
     - other models in FLASH, one empty place
diff --git a/calc.c b/calc.c
index 5e038f2..10316ad 100644
--- a/calc.c
+++ b/calc.c
@@ -269,6 +269,29 @@ static void calc_loop(void) {
     u16 adc_steering, adc_throttle;  // last 4 or 1 ADC values
 
     while (1) {
+
+	// handle channel3 potentiometer, cannot use channel_calib,
+	//   because we don't have calib middle and dead zone
+	if (cg.ch3_pot && !menu_ch3_pot_disabled) {
+	    // do it only if some function is assigned to CH3 pot
+	    if (*ck_ch3_pot_func) {
+		if (cg.adc_ovs_last)  val = adc_ch3_last << ADC_OVS_SHIFT;
+		else		  val = adc_ch3_ovs;
+		// map ch3 pot -5000..5000 range
+		val -= cg.calib_ch3_left << ADC_OVS_SHIFT;
+		val2 = (s16)((s32)(val) * PPM(1000) /
+		       ((cg.calib_ch3_right - cg.calib_ch3_left) << ADC_OVS_SHIFT))
+		       - PPM(500);
+		// safety checks to -5000..5000 limits
+		if (val2 < PPM(-500))	   val2 = PPM(-500);
+		else if (val2 > PPM(500))  val2 = PPM(500);
+		// do reverse
+		if (*ck_ch3_pot_rev)  val2 = -val2;
+		// set value to function
+		menu_et_function_set_from_linear(*ck_ch3_pot_func, val2);
+	    }
+	}
+
 	DIG_mix = menu_DIG_mix * PPM(5);  // to -5000..5000 range
 
 	// set used ADC values
diff --git a/config.c b/config.c
index 38d3b3a..e2fa26b 100644
--- a/config.c
+++ b/config.c
@@ -59,7 +59,6 @@ u8 config_global_set_default(void) {
     cg.reset_beep	= 1;
     cg.poweron_beep	= 1;
     cg.poweron_warn	= 0;
-    cg.rotate_reverse	= 0;		// not-reversed
 
     cg.timer1_type	= 0;		// OFF
     cg.timer2_type	= 0;
@@ -68,12 +67,12 @@ u8 config_global_set_default(void) {
 
     cg.ppm_sync_frame	= 0;		// to constant SYNC length
     cg.ppm_length	= 1;		// 4ms constant SYNC length
+    cg.rotate_reverse	= 0;		// not-reversed
+    cg.ch3_pot		= 0;		// CH3 is button
 
     cg.unused1		= 0;
     cg.unused2		= 0;
     cg.unused3		= 0;
-    cg.unused4		= 0;
-    cg.unused5		= 0;
 
     // set calibrate values only when they are out of limits
     cc |= check_val(&cg.calib_steering_left, 0, CALIB_ST_LOW_MID, 0);
@@ -82,6 +81,8 @@ u8 config_global_set_default(void) {
     cc |= check_val(&cg.calib_throttle_fwd, 0, CALIB_TH_LOW_MID, 0);
     cc |= check_val(&cg.calib_throttle_mid, CALIB_TH_LOW_MID, CALIB_TH_MID_HIGH, 600);
     cc |= check_val(&cg.calib_throttle_bck, CALIB_TH_MID_HIGH, 1023, 1023);
+    check_val(&cg.calib_ch3_left, 0, 512, 0);
+    check_val(&cg.calib_ch3_right, 512, 1023, 1023);
     return cc;
 }
 
@@ -141,6 +142,10 @@ void config_model_set_default(void) {
     cm.channels		= MAX_CHANNELS - 1;	// it is one lower to fit also 8
     cm.unused		= 0;
     memcpy(&cm.key_mapping, &default_key_mapping, sizeof(config_key_mapping_s));
+    if (cg.ch3_pot) {
+	*ck_ch3_pot_func = 0;
+	*ck_ch3_pot_rev  = 0;
+    }
 }
 
 
diff --git a/config.h b/config.h
index 937b7b2..da21d3a 100644
--- a/config.h
+++ b/config.h
@@ -63,11 +63,12 @@ typedef struct {
     u8	ppm_length:4;		// length of PPM sync signal (3..) or frame length (9..)
     u8	ppm_sync_frame:1;	// 0 = constant SYNC length, 1 = constant frame length
 
-    u8  unused1:3;		// reserve
+    u8  ch3_pot:1;		// potentiometer connected instead of CH3 button
+    u8  unused1:2;		// reserve
     u8  unused2;
+    u16 calib_ch3_left;
+    u16 calib_ch3_right;
     u16 unused3;
-    u16 unused4;
-    u16 unused5;
 } config_global_s;
 
 extern config_global_s config_global;
@@ -164,8 +165,10 @@ typedef struct {
 } config_model_s;
 
 extern config_model_s config_model;
-#define cm	config_model
-#define ck	cm.key_mapping
+#define cm		config_model
+#define ck		cm.key_mapping
+#define ck_ch3_pot_func	((u8 *)&ck.key_map[0])
+#define ck_ch3_pot_rev	((u8 *)&ck.key_map[0] + 1)
 
 
 
diff --git a/input.c b/input.c
index a16e209..c9c5615 100644
--- a/input.c
+++ b/input.c
@@ -196,8 +196,11 @@ static void read_keys(void) {
 
     // add CH3 button, middle state will be only in buttons_state,
     //   not in buttons
-    if (adc_ch3_last <= BTN_CH3_LOW)	   buttons1 |= BTN_CH3;
-    else if (adc_ch3_last < BTN_CH3_HIGH)  buttons1 |= BTN_CH3_MID;
+    // do only when CH3 is button, not potentiometer
+    if (!cg.ch3_pot) {
+	if (adc_ch3_last <= BTN_CH3_LOW)	   buttons1 |= BTN_CH3;
+	else if (adc_ch3_last < BTN_CH3_HIGH)  buttons1 |= BTN_CH3_MID;
+    }
 
     // combine last 3 readed buttons
     buttons_state |= buttons1 & buttons2 & buttons3;
diff --git a/menu.h b/menu.h
index 5789a1e..6c13244 100644
--- a/menu.h
+++ b/menu.h
@@ -90,6 +90,8 @@ extern u16 battery_low_raw;
 extern u8 menu_check_keys;
 // temporary flag used when doing reset (global/all models/model)
 extern _Bool menu_tmp_flag;
+// temporary disable ch3 potentiometer when in key mapping menu
+extern _Bool menu_ch3_pot_disabled;
 
 
 
@@ -114,6 +116,7 @@ extern u8 *menu_key_function_name(u8 n);
 extern s8 menu_key_function_idx(u8 n);
 extern u8 menu_key_function_2state(u8 n);
 extern u8 menu_key_function_is_allowed(u8 n);
+extern void menu_et_function_set_from_linear(u8 n, s16 val);
 extern const u8 steps_map[];
 #define STEPS_MAP_SIZE  11
 extern const u16 et_buttons[][2];
diff --git a/menu_global.c b/menu_global.c
index e8d2556..0478c14 100644
--- a/menu_global.c
+++ b/menu_global.c
@@ -279,6 +279,9 @@ static void gs_hardware(u8 action) {
 		cg.rotate_reverse ^= 1;
 		break;
 	    case 1:
+		cg.ch3_pot ^= 1;
+		break;
+	    case 2:
 		if (cg.ppm_sync_frame) {
 		    cg.ppm_sync_frame = 0;
 		    cg.ppm_length = 1;   // 4ms SYNC
@@ -288,7 +291,7 @@ static void gs_hardware(u8 action) {
 		    cg.ppm_length = 11;  // 20ms frame
 		}
 		break;
-	    case 2:
+	    case 3:
 		if (cg.ppm_sync_frame)
 		    // constant frame length
 		    cg.ppm_length =
@@ -303,7 +306,7 @@ static void gs_hardware(u8 action) {
 
     // select next value
     else if (action == MLA_NEXT) {
-	if (++menu_set > 2)  menu_set = 0;
+	if (++menu_set > 3)  menu_set = 0;
     }
 
     // show values
@@ -315,10 +318,14 @@ static void gs_hardware(u8 action) {
 	    lcd_char(LCHR3, (u8)(cg.rotate_reverse ? 'R' : 'N'));
 	    break;
 	case 1:
+	    lcd_chars("P3");
+	    lcd_char(LCHR3, (u8)(cg.ch3_pot ? 'Y' : 'N'));
+	    break;
+	case 2:
 	    lcd_chars("PT");
 	    lcd_char(LCHR3, (u8)(cg.ppm_sync_frame ? 'F' : 'S'));
 	    break;
-	case 2:
+	case 3:
 	    lcd_char_num3(cg.ppm_length + (u8)(cg.ppm_sync_frame ? 9 : 3));
 	    lcd_char(LCHR1, 'L');
 	    menu_blink |= MCB_CHR2;	// blink char2 too
diff --git a/menu_key.c b/menu_key.c
index 46ea4f8..d11b060 100644
--- a/menu_key.c
+++ b/menu_key.c
@@ -191,6 +191,67 @@ static void km_trim(u8 action) {
 }
 
 
+// special function for ch3 potentiometer, select function and reverse
+static void km_ch3_pot(u8 action) {
+    s8 idx;
+    u8 new_idx = 0;
+    u8 *func = ck_ch3_pot_func;
+    u8 *rev  = ck_ch3_pot_rev;
+
+    if (action == 1) {
+	// change value
+	switch (menu_set) {
+	    case 0:
+		// function
+		// select new function, map through trim_functions
+		idx = menu_et_function_idx(*func);
+		if (idx == -1) {
+		    // there can be some bad value from timer when ch3 was not
+		    // set to potentiometer
+		    *func = 0;
+		    idx = 0;
+		}
+		while (1) {
+		    idx = (s8)menu_change_val(idx, 0, trim_functions_max, 1, 1);
+		    new_idx = trim_functions[idx];
+		    if (!new_idx)  continue;				// empty slot
+		    new_idx--;  // was one more
+		    if (menu_et_function_is_allowed(new_idx))  break;	// we have it
+		}
+		// set values to defaults
+		*func = new_idx;
+		break;
+	    case 1:
+		// reverse
+		if (*rev)  *rev = 0;
+		else	   *rev = 1;
+		break;
+	}
+    }
+
+    else if (action == 2) {
+	// switch to next setting
+	if (menu_set || *func) {
+	    if (++menu_set > 1)  menu_set = 0;
+	}
+    }
+
+    // show value of menu_set
+    switch (menu_set) {
+	case 0:
+	    // function
+	    lcd_chars(menu_et_function_name(*func));
+	    break;
+	case 1:
+	    // reverse
+	    lcd_chars("RE");
+	    lcd_char(LCHR3, (u8)(*rev ? '1' : '0'));
+	    menu_blink &= (u8)~(MCB_CHR1 | MCB_CHR2);
+	    break;
+    }
+}
+
+
 
 
 #define KEY_FUNCTIONS_SIZE  32
@@ -362,8 +423,11 @@ static void km_key(u8 action) {
 
 
 @inline static void km_trim_key(u8 action) {
-    if (menu_id < NUM_TRIMS)  km_trim(action);
-    else		      km_key(action);
+    if (menu_id < NUM_TRIMS)
+	km_trim(action);
+    else if (cg.ch3_pot && menu_id == NUM_TRIMS)
+	km_ch3_pot(action);
+    else km_key(action);
 }
 
 static const u8 key_ids[] = {
@@ -409,11 +473,15 @@ void menu_key_mapping_func(u8 action, void *p) {
 	km_trim_key(0);
 }
 
+// temporary disable ch3 potentiometer when in key mapping menu
+_Bool menu_ch3_pot_disabled;
 void menu_key_mapping(void) {
     lcd_set_blink(LMENU, LB_SPC);
+    menu_ch3_pot_disabled = 1;
 
     menu_common(menu_key_mapping_func, NULL, MCF_NONE);
 
+    menu_ch3_pot_disabled = 0;
     lcd_set_blink(LMENU, LB_OFF);
     config_model_save();
     apply_model_config();
diff --git a/menu_popup.c b/menu_popup.c
index 82568d8..e728ae0 100644
--- a/menu_popup.c
+++ b/menu_popup.c
@@ -269,6 +269,24 @@ u8 menu_et_function_is_allowed(u8 n) {
     return 0;					// channel too big
 }
 
+// set function value from linear channel value
+// lin_val in range -5000..5000
+#define AVAL(x) \
+    if (etf->set_func)  etf->set_func(&x, SF_ROTATE); \
+    *(s8 *)etf->aval = (s8)(x)
+#define SF_ROTATE 0
+void menu_et_function_set_from_linear(u8 n, s16 lin_val) {
+    et_functions_s *etf = &et_functions[n];
+    s16 val;
+    if (n == 0 || n >= ET_FUNCTIONS_SIZE)  return;  // OFF or bad
+    // map lin_val between min and max
+    val = (s16)((s32)(lin_val + PPM(500)) * (etf->max - etf->min + 1)
+		/ PPM(1000)) + etf->min;
+    if (val > etf->max)  val = etf->max;	// lin_val was full right
+    AVAL(val);
+}
+#undef SF_ROTATE
+
 // find function by name
 static et_functions_s *menu_et_function_find_name(u8 *name) {
     u8 i, *n;
@@ -310,9 +328,6 @@ const u8 steps_map[STEPS_MAP_SIZE] = {
 #define RVAL(x) \
     if (etf->min >= 0)  x = *(u8 *)etf->aval; \
     else		x = *(s8 *)etf->aval;
-#define AVAL(x) \
-    if (etf->set_func)  etf->set_func(&x, SF_ROTATE); \
-    *(s8 *)etf->aval = (s8)(x)
 static u8 menu_popup_et(u8 trim_id) {
     u16 delay_time;
     s16 val;
diff --git a/menu_service.c b/menu_service.c
index 50412f0..8fbec93 100644
--- a/menu_service.c
+++ b/menu_service.c
@@ -64,6 +64,13 @@ void menu_calibrate(u8 at_poweron) {
     lcd_7seg(channel);
     lcd_menu(LM_MODEL | LM_NAME | LM_REV | LM_TRIM | LM_DR | LM_EXP);
     lcd_set_blink(LMENU, LB_SPC);
+    // blink arrows for ch3 potentiometer also
+    if (cg.ch3_pot) {
+	lcd_segment(LS_SYM_LEFT, LS_ON);
+	lcd_segment(LS_SYM_RIGHT, LS_ON);
+	lcd_segment_blink(LS_SYM_LEFT, LB_SPC);
+	lcd_segment_blink(LS_SYM_RIGHT, LB_SPC);
+    }
 
     while (1) {
 	// check keys
@@ -79,7 +86,7 @@ void menu_calibrate(u8 at_poweron) {
 	}
 
 	else if (btn(BTN_ENTER)) {
-	    // save calibrate value for channels 1 and 2
+	    // save calibrate value for channels 1 and 2 (and 3 if ch3_pot)
 	    // select actual voltage for channel 4
 	    if (channel == 1) {
 		key_beep();
@@ -117,6 +124,21 @@ void menu_calibrate(u8 at_poweron) {
 		lcd_segment(seg, LS_OFF);  // set corresponding LCD off
 		lcd_update();
 	    }
+	    else if (channel == 3 && cg.ch3_pot) {
+		// only if ch3 is potentiometer
+		key_beep();
+		val = ADC_OVS(ch3);
+		if (val < 512) {
+		    cg.calib_ch3_left = val;
+		    seg = LS_SYM_LEFT;
+		}
+		else {
+		    cg.calib_ch3_right = val;
+		    seg = LS_SYM_RIGHT;
+		}
+		lcd_segment(seg, LS_OFF);  // set corresponding LCD off
+		lcd_update();
+	    }
 	    else if (channel == 4) {
 		key_beep();
 		// allow to set actual battery voltage