diff --git a/lib/sensor_pzem.c b/lib/sensor_pzem.c
new file mode 100644
index 0000000..5780cac
--- /dev/null
+++ b/lib/sensor_pzem.c
@@ -0,0 +1,166 @@
+/* This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+/** library to query measurements from peacefair PZEM-004 and PZEM-004T electricity meter (code)
+ *  @file sensor_pzem.c
+ *  @author King Kévin <kingkevin@cuvoodoo.info>
+ *  @date 2016
+ *  @note peripherals used: USART @ref sensor_pzem_usart
+ */
+
+/* standard libraries */
+#include <stdint.h> // standard integer types
+#include <stdlib.h> // general utilities
+
+/* STM32 (including CM3) libraries */
+#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 "sensor_pzem.h" // PZEM electricity meter header and definitions
+#include "global.h" // common methods
+
+/** @defgroup sensor_pzem_usart USART peripheral used for communication with electricity meter
+ *  @{
+ */
+#define SENSOR_PZEM_USART 2 /**< USART peripheral */
+/** @} */
+
+#define USART_BAUDRATE 115200 /**< serial baudrate, in bits per second (with 8N1 8 bits, no parity bit, 1 stop bit settings) */
+
+/* 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 */
+static uint8_t tx_buffer[7] = {0}; /**< buffer for request to transmit */
+static volatile uint8_t tx_i = 0; /**< current position if transmitted data */
+
+volatile bool sensor_pzem_measurement_received = false;
+
+void sensor_pzem_setup(void)
+{
+	/* enable USART I/O peripheral */
+	rcc_periph_clock_enable(USART_PORT_RCC(SENSOR_PZEM_USART)); // enable clock for USART port peripheral
+	rcc_periph_clock_enable(USART_RCC(SENSOR_PZEM_USART)); // enable clock for USART peripheral
+	gpio_set_mode(USART_PORT(SENSOR_PZEM_USART), GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, USART_PIN_TX(SENSOR_PZEM_USART)); // setup GPIO pin USART transmit
+	gpio_set_mode(USART_PORT(SENSOR_PZEM_USART), GPIO_MODE_INPUT, GPIO_CNF_INPUT_PULL_UPDOWN, USART_PIN_RX(SENSOR_PZEM_USART)); // setup GPIO pin USART receive
+	gpio_set(USART_PORT(SENSOR_PZEM_USART), USART_PIN_RX(SENSOR_PZEM_USART)); // pull up to avoid noise when not connected
+
+	/* setup USART parameters for electricity meter: 9600 8N1 */
+	usart_set_baudrate(USART(SENSOR_PZEM_USART), 9600); // the electricity meter uses a fixed baud rate of 9600 bps
+	usart_set_databits(USART(SENSOR_PZEM_USART), 8);
+	usart_set_stopbits(USART(SENSOR_PZEM_USART), USART_STOPBITS_1);
+	usart_set_mode(USART(SENSOR_PZEM_USART), USART_MODE_TX_RX);
+	usart_set_parity(USART(SENSOR_PZEM_USART), USART_PARITY_NONE);
+	usart_set_flow_control(USART(SENSOR_PZEM_USART), USART_FLOWCONTROL_NONE);
+
+	nvic_enable_irq(USART_IRQ(SENSOR_PZEM_USART)); // enable the USART interrupt
+	usart_enable_rx_interrupt(USART(SENSOR_PZEM_USART)); // enable receive interrupt
+	usart_enable(USART(SENSOR_PZEM_USART)); // enable USART
+
+	/* reset buffer states */
+	tx_i = 0;
+	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
+		return;
+	}
+	if (type>=MAX) { // invalid type
+		return;
+	}
+	tx_buffer[0] = 0xB0+type; // set request nibble and type nibble
+	tx_buffer[1] = (address>>24)&0xff; // set address
+	tx_buffer[2] = (address>>16)&0xff; // set address
+	tx_buffer[3] = (address>>8)&0xff; // set address
+	tx_buffer[4] = (address>>0)&0xff; // set address
+	tx_buffer[5] = 0; // only used to set alarm
+	tx_buffer[6] = 0; // to calculate checksum (sum of all previous bytes)
+	for (uint8_t i=0; i<LENGTH(tx_buffer)-1; i++) {
+		tx_buffer[6] += tx_buffer[i]; // calculate buffer
+	}
+
+	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
+}
+
+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
+		return measurement;
+	}
+	if ((rx_buffer[0]&0xf0)!=0xa0) { // not a response received
+		return measurement;
+	}
+	if ((rx_buffer[0]&0x0f)>=MAX) { // not a valid response type received (actually 4 and 5 are valid, but should not happen when using this code
+		return measurement;
+	}
+	uint8_t checksum = 0; // calculate checksum (sum of all other bytes)
+	for (uint8_t i=0; i<LENGTH(rx_buffer)-1; i++) {
+		checksum += rx_buffer[i]; // calculate buffer
+	}
+	if (checksum!=rx_buffer[6]) { // checksum does not match
+		return measurement;
+	}
+	measurement.valid = true; // all checks passed
+	measurement.type = rx_buffer[0]&0x0f; // save type
+	switch (measurement.type) { // decode value depending on type
+		case VOLTAGE:
+			measurement.value.voltage = ((uint16_t)rx_buffer[1]<<8)+rx_buffer[2]+rx_buffer[3]*0.1;
+			break;
+		case CURRENT:
+			measurement.value.current = rx_buffer[2]+rx_buffer[3]/100;
+			break;
+		case POWER:
+			measurement.value.power = ((uint16_t)rx_buffer[1]<<8)+rx_buffer[2];
+			break;
+		case ENERGY:
+			measurement.value.power = ((uint32_t)rx_buffer[1]<<16)+((uint16_t)rx_buffer[2]<<8)+rx_buffer[3];
+			break;
+		default:
+			measurement.valid = false; // unexpected type
+	}
+	sensor_pzem_measurement_received = false; // reset flag
+	rx_i = 0; // prepare buffer to receive next measurement
+	return measurement;
+}
+	
+/** USART interrupt service routine called when data has been transmitted or received */
+void USART_ISR(SENSOR_PZEM_USART)(void)
+{
+	if (usart_get_interrupt_source(USART(SENSOR_PZEM_USART), USART_SR_TXE)) { // data has been transmitted
+		if (tx_i<LENGTH(tx_buffer)) { // not all bytes transmitted
+			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
+		}
+	}
+	if (usart_get_interrupt_source(USART(SENSOR_PZEM_USART), USART_SR_RXNE)) { // data has been received
+		if (rx_i<LENGTH(rx_buffer)) { // receiving response
+			rx_buffer[rx_i++] = usart_recv(USART(SENSOR_PZEM_USART)); // put received byte in buffer
+			if (rx_i>=LENGTH(rx_buffer)) { // buffer full
+				sensor_pzem_measurement_received = true; // notify used response has been received
+			}
+		} else { // previous response not read before receiving the next
+			usart_recv(USART(SENSOR_PZEM_USART)); // drop received buffer
+		}
+	}
+}
diff --git a/lib/sensor_pzem.h b/lib/sensor_pzem.h
new file mode 100644
index 0000000..de41a62
--- /dev/null
+++ b/lib/sensor_pzem.h
@@ -0,0 +1,57 @@
+/* This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+/** library to query measurements from peacefair PZEM-004 and PZEM-004T electricity meter (API)
+ *  @file sensor_pzem.h
+ *  @author King Kévin <kingkevin@cuvoodoo.info>
+ *  @date 2016
+ *  @note peripherals used: USART @ref sensor_pzem_usart
+ */
+#pragma once
+
+/** a measurement response has been received */
+extern volatile bool sensor_pzem_measurement_received;
+
+/** measurements offered by energy meter */
+enum sensor_pzem_measurement_type_t {
+	VOLTAGE = 0,
+	CURRENT = 1,
+	POWER = 2,
+	ENERGY = 3,
+	MAX
+};
+
+/** measurement returned by energy meter */
+struct sensor_pzem_measurement_t {
+	enum sensor_pzem_measurement_type_t type; /**< measurement type */
+	bool valid; /**< is the measurement valid (e.g. format and checksum are correct) */
+	union measurement_t { /**< measurement value */
+		float voltage; /**< measured voltage in volts */
+		float current; /**< measured current in amperes */
+		float power; /**< measured power in watts */
+		uint32_t energy; /**< measured energy in watts/hour (24 bits) */
+	} value;
+};
+
+/** setup peripherals to communicate with electricity meter */
+void sensor_pzem_setup(void);
+/** request measurement from electricity meter
+ *  @param[in] address electricity meter device address
+ *  @param[in] sensor_pzem_measurement_type measurement type to request
+ */
+void sensor_pzem_measurement_request(uint32_t address, enum sensor_pzem_measurement_type_t type);
+/** decode received measurement
+ *  @return decoded measurement (invalid if no new measurement has been received)
+ */
+struct sensor_pzem_measurement_t sensor_pzem_measurement_decode(void);