diff --git a/lib/sensor_pzem.c b/lib/sensor_pzem.c
index f714dce..0d81d99 100644
--- a/lib/sensor_pzem.c
+++ b/lib/sensor_pzem.c
@@ -16,7 +16,7 @@
  *  @file sensor_pzem.c
  *  @author King Kévin <kingkevin@cuvoodoo.info>
  *  @date 2016
- *  @note peripherals used: USART @ref sensor_pzem_usart
+ *  @note peripherals used: USART @ref sensor_pzem_usart, timer @ref sensor_pzem_timer 
  */
 
 /* standard libraries */
@@ -24,12 +24,14 @@
 #include <stdlib.h> // general utilities
 
 /* STM32 (including CM3) libraries */
+#include <libopencmsis/core_cm3.h> // Cortex M3 utilities
+#include <libopencm3/cm3/nvic.h> // interrupt handler
 #include <libopencm3/stm32/rcc.h> // real-time control clock library
 #include <libopencm3/stm32/gpio.h> // general purpose input output library
 #include <libopencm3/stm32/usart.h> // universal synchronous asynchronous receiver transmitter library
-#include <libopencm3/cm3/nvic.h> // interrupt handler
-#include <libopencmsis/core_cm3.h> // Cortex M3 utilities
+#include <libopencm3/stm32/timer.h> // timer utilities
 
+/* own libraries */
 #include "sensor_pzem.h" // PZEM electricity meter header and definitions
 #include "global.h" // common methods
 
@@ -39,6 +41,12 @@
 #define SENSOR_PZEM_USART 2 /**< USART peripheral */
 /** @} */
 
+/** @defgroup sensor_pzem_timer timer peripheral used for waiting before sending the next request
+ *  @{
+ */
+#define SENSOR_PZEM_TIMER 2 /**< timer peripheral */
+/** @} */
+
 /* input and output ring buffer, indexes, and available memory */
 static uint8_t rx_buffer[7] = {0}; /**< buffer for received response */
 static volatile uint8_t rx_i = 0; /**< current position of read received data */
@@ -69,15 +77,26 @@ void sensor_pzem_setup(void)
 	usart_enable_rx_interrupt(USART(SENSOR_PZEM_USART)); // enable receive interrupt
 	usart_enable(USART(SENSOR_PZEM_USART)); // enable USART
 
+	// setup timer to wait for minimal time before next transmission (after previous transmission or reception)
+	rcc_periph_clock_enable(RCC_TIM(SENSOR_PZEM_TIMER)); // enable clock for timer block
+	timer_reset(TIM(SENSOR_PZEM_TIMER)); // reset timer state
+	timer_set_mode(TIM(SENSOR_PZEM_TIMER), TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP); // set timer mode, use undivided timer clock,edge alignment (simple count), and count up
+	timer_one_shot_mode(TIM(SENSOR_PZEM_TIMER)); // stop counter after update event (we only need to count down once)
+	timer_set_prescaler(TIM(SENSOR_PZEM_TIMER), 550-1); // set the prescaler so this 16 bits timer allows to wait for maximum 500 ms ( 1/(72E6/550/(2**16))=500.62ms )
+	timer_set_period(TIM(SENSOR_PZEM_TIMER), 0xffff/2); // the timing is not defined in the specification. I tested until the communication was reliable (all requests get an response)
+	timer_clear_flag(TIM(SENSOR_PZEM_TIMER), TIM_SR_UIF); // clear flag
+	timer_enable_irq(TIM(SENSOR_PZEM_TIMER), TIM_DIER_UIE); // enable update interrupt for timer
+	nvic_enable_irq(NVIC_TIM_IRQ(SENSOR_PZEM_TIMER)); // catch interrupt in service routine
+
 	/* reset buffer states */
-	tx_i = 0;
+	tx_i = LENGTH(tx_buffer);
 	rx_i = 0;
 	sensor_pzem_measurement_received = false;
 }
 
 void sensor_pzem_measurement_request(uint32_t address, enum sensor_pzem_measurement_type_t type)
 {
-	if (tx_i!=0) { // transmission is ongoing
+	if (tx_i<LENGTH(tx_buffer)) { // transmission is ongoing
 		return;
 	}
 	if (type>=SENSOR_PZEM_MAX) { // invalid type
@@ -93,16 +112,24 @@ void sensor_pzem_measurement_request(uint32_t address, enum sensor_pzem_measurem
 	for (uint8_t i=0; i<LENGTH(tx_buffer)-1; i++) {
 		tx_buffer[6] += tx_buffer[i]; // calculate buffer
 	}
+	tx_i = 0; // remember we have a message to send
 
-	usart_enable_tx_interrupt(USART(SENSOR_PZEM_USART)); // enable interrupt to send other bytes
-	usart_send(USART(SENSOR_PZEM_USART),tx_buffer[tx_i++]); // start transmission
+	if (TIM_CR1(TIM(SENSOR_PZEM_TIMER))&TIM_CR1_CEN) { // timer is already running
+		// at the end of the timer the transmission will start automatically
+	} else { // no timer is running
+		usart_enable_tx_interrupt(USART(SENSOR_PZEM_USART)); // enable interrupt to start sending bytes
+		//usart_send(USART(SENSOR_PZEM_USART),tx_buffer[tx_i++]); // start transmission
+	}
+
+	sensor_pzem_measurement_received = false; // reset flag
+	rx_i = 0; // prepare buffer to receive next measurement	
 }
 
 struct sensor_pzem_measurement_t sensor_pzem_measurement_decode(void)
 {
 	struct sensor_pzem_measurement_t measurement; // decoded measurement to return
 	measurement.valid = false; // wait until the end to ensure validity
-	if (!sensor_pzem_measurement_received) { // no measurement received
+	if (rx_i<LENGTH(rx_buffer)) { // buffer is not full, thus no measurement received
 		return measurement;
 	}
 	if ((rx_buffer[0]&0xf0)!=0xa0) { // not a response received
@@ -125,7 +152,7 @@ struct sensor_pzem_measurement_t sensor_pzem_measurement_decode(void)
 			measurement.value.voltage = ((uint16_t)rx_buffer[1]<<8)+rx_buffer[2]+rx_buffer[3]*0.1;
 			break;
 		case SENSOR_PZEM_CURRENT:
-			measurement.value.current = rx_buffer[2]+rx_buffer[3]/100;
+			measurement.value.current = rx_buffer[2]+rx_buffer[3]*0.01;
 			break;
 		case SENSOR_PZEM_POWER:
 			measurement.value.power = ((uint16_t)rx_buffer[1]<<8)+rx_buffer[2];
@@ -154,7 +181,9 @@ void USART_ISR(SENSOR_PZEM_USART)(void)
 			usart_send(USART(SENSOR_PZEM_USART),tx_buffer[tx_i++]); // transmit next byte
 		} else { // request transmitted
 			usart_disable_tx_interrupt(USART(SENSOR_PZEM_USART)); // disable transmit interrupt
-			tx_i = 0; // ready for next transmission
+			timer_set_counter(TIM(SENSOR_PZEM_TIMER), 0); // reset timer counter to get preset waiting time
+			timer_enable_counter(TIM(SENSOR_PZEM_TIMER)); // start timer between requests
+
 		}
 	}
 	if (usart_get_interrupt_source(USART(SENSOR_PZEM_USART), USART_SR_RXNE)) { // data has been received
@@ -166,5 +195,20 @@ void USART_ISR(SENSOR_PZEM_USART)(void)
 		} else { // previous response not read before receiving the next
 			usart_recv(USART(SENSOR_PZEM_USART)); // drop received buffer
 		}
+		timer_set_counter(TIM(SENSOR_PZEM_TIMER), 0); // reset timer counter to get preset waiting time
+		timer_enable_counter(TIM(SENSOR_PZEM_TIMER)); // start timer between requests
 	}
 }
+
+/** interrupt service routine called on timeout */
+void TIM_ISR(SENSOR_PZEM_TIMER)(void)
+{
+	if (timer_get_flag(TIM(SENSOR_PZEM_TIMER), TIM_SR_UIF)) { // update event happened
+		timer_clear_flag(TIM(SENSOR_PZEM_TIMER), TIM_SR_UIF); // clear flag
+		if (tx_i<LENGTH(tx_buffer)) { // bytes are waiting to be sent
+			usart_enable_tx_interrupt(USART(SENSOR_PZEM_USART)); // enable interrupt to start sending bytes
+		}
+	}
+}
+
+
diff --git a/lib/sensor_pzem.h b/lib/sensor_pzem.h
index c7fa818..19dec12 100644
--- a/lib/sensor_pzem.h
+++ b/lib/sensor_pzem.h
@@ -16,7 +16,7 @@
  *  @file sensor_pzem.h
  *  @author King Kévin <kingkevin@cuvoodoo.info>
  *  @date 2016
- *  @note peripherals used: USART @ref sensor_pzem_usart
+ *  @note peripherals used: USART @ref sensor_pzem_usart, timer @ref sensor_pzem_timer
  */
 #pragma once