diff --git a/lib/spp_tx.c b/lib/spp_tx.c
new file mode 100644
index 0000000..fdd6edc
--- /dev/null
+++ b/lib/spp_tx.c
@@ -0,0 +1,112 @@
+/* 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 for UART communication to tje Blutooth module
+ *  @file
+ *  @author King Kévin <kingkevin@cuvoodoo.info>
+ *  @date 2016-2020
+ *  @note peripherals used: USART @ref spp_tx_uart
+ */
+
+/* standard libraries */
+#include <stdint.h> // standard integer types
+#include <stdio.h> // standard I/O facilities
+#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 "spp_tx.h" // own definition
+#include "global.h" // common methods
+
+/** @defgroup spp_tx_uart USART peripheral used for UART communication
+ *  @{
+ */
+#define SPP_TX_UART_ID 3 /**< USART peripheral */
+/** @} */
+
+#define UART_BAUDRATE 115200 /**< serial baud rate, in bits per second (with 8N1 8 bits, no parity bit, 1 stop bit settings) */
+
+/* output ring buffer, indexes, and available memory */
+static volatile uint8_t tx_buffer[64] = {0}; /**< ring buffer for data to transmit */
+static volatile uint8_t tx_i = 0; /**< current position of transmitted data */
+static volatile uint8_t tx_used = 0; /**< how much data needs to be transmitted */
+
+void spp_tx_setup(void)
+{
+	/* enable UART I/O peripheral */
+	rcc_periph_clock_enable(RCC_USART_PORT(SPP_TX_UART_ID)); // enable clock for UART port peripheral
+	rcc_periph_clock_enable(RCC_USART(SPP_TX_UART_ID)); // enable clock for UART peripheral
+	rcc_periph_clock_enable(RCC_AFIO); // enable pin alternate function (UART)
+	gpio_set_mode(USART_TX_PORT(SPP_TX_UART_ID), GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, USART_TX_PIN(SPP_TX_UART_ID)); // setup GPIO pin UART transmit
+
+	/* setup UART parameters */
+	usart_set_baudrate(USART(SPP_TX_UART_ID), UART_BAUDRATE);
+	usart_set_databits(USART(SPP_TX_UART_ID), 8);
+	usart_set_stopbits(USART(SPP_TX_UART_ID), USART_STOPBITS_1);
+	usart_set_mode(USART(SPP_TX_UART_ID), USART_MODE_TX);
+	usart_set_parity(USART(SPP_TX_UART_ID), USART_PARITY_NONE);
+	usart_set_flow_control(USART(SPP_TX_UART_ID), USART_FLOWCONTROL_NONE);
+
+	nvic_enable_irq(USART_IRQ(SPP_TX_UART_ID)); // enable the UART interrupt
+	usart_enable(USART(SPP_TX_UART_ID)); // enable UART
+
+	/* reset buffer states */
+	tx_i = 0;
+	tx_used = 0;
+}
+
+void spp_tx_putchar_blocking(char c)
+{
+	spp_tx_flush(); // empty buffer first
+	usart_send_blocking(USART(SPP_TX_UART_ID), c); // send character
+}
+
+void spp_tx_flush(void)
+{
+	while (tx_used) { // idle until buffer is empty
+		__WFI(); // sleep until interrupt
+	}
+	usart_wait_send_ready(USART(SPP_TX_UART_ID)); // wait until transmit register is empty (transmission might not be complete)
+}
+
+void spp_tx_putchar_nonblocking(char c)
+{
+	while (tx_used>=LENGTH(tx_buffer)) { // idle until buffer has some space
+		usart_enable_tx_interrupt(USART(SPP_TX_UART_ID)); // enable transmit interrupt
+		// don't go to sleep since this might prevent an interrupt
+	}
+	usart_disable_tx_interrupt(USART(SPP_TX_UART_ID)); // disable transmit interrupt to prevent index corruption
+	tx_buffer[(tx_i + tx_used) % LENGTH(tx_buffer)] = c; // put character in buffer
+	tx_used++; // update used buffer
+	usart_enable_tx_interrupt(USART(SPP_TX_UART_ID)); // enable transmit interrupt
+}
+
+/** UART interrupt service routine called when data has been transmitted or received */
+void USART_ISR(SPP_TX_UART_ID)(void)
+{
+	if (usart_get_flag(USART(SPP_TX_UART_ID), USART_SR_TXE)) { // data has been transmitted
+		if (!tx_used) { // no data in the buffer to transmit
+			usart_disable_tx_interrupt(USART(SPP_TX_UART_ID)); // disable transmit interrupt
+		} else {
+			usart_send(USART(SPP_TX_UART_ID),tx_buffer[tx_i]); // put data in transmit register
+			tx_i = (tx_i + 1) % LENGTH(tx_buffer); // update location on buffer
+			tx_used--; // update used size
+		}
+	}
+}
diff --git a/lib/spp_tx.h b/lib/spp_tx.h
new file mode 100644
index 0000000..cfecefb
--- /dev/null
+++ b/lib/spp_tx.h
@@ -0,0 +1,37 @@
+/* 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 for UART communication to tje Blutooth module
+ *  @file
+ *  @author King Kévin <kingkevin@cuvoodoo.info>
+ *  @date 2016-2020
+ *  @note peripherals used: USART @ref spp_tx_uart
+ */
+#pragma once
+
+/** setup UART peripheral */
+void spp_tx_setup(void);
+/** send character over UART (blocking)
+ *  @param[in] c character to send
+ *  @note blocks until character transmission started */
+void spp_tx_putchar_blocking(char c);
+/** ensure all data has been transmitted (blocking)
+ *  @note block until all data has been transmitted
+ */
+void spp_tx_flush(void);
+/** send character over UART (non-blocking)
+ *  @param[in] c character to send
+ *  @note blocks if transmit buffer is full, else puts in buffer and returns
+ */
+void spp_tx_putchar_nonblocking(char c);