diff --git a/lib/vfd.c b/lib/vfd.c
index 83b4bf2..3b56f5b 100644
--- a/lib/vfd.c
+++ b/lib/vfd.c
@@ -23,6 +23,8 @@
 /* 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/spi.h> // SPI library
+#include <libopencm3/cm3/nvic.h> // interrupt handler
 
 #include "vfd.h" // VFD definitions
 
@@ -254,8 +256,11 @@ static const uint8_t pict5x7[][5] = {
 	{0x00, 0x00, 0x00, 0x00, 0x00} // nothing
 };
 
-/* the three 32 bits values to be shifted out to the VFD driver */
-static uint32_t vfd_data[3] = {0};
+/* the 32 bits values to be shifted out to the VFD driver
+ * split into 16 bit for SPI transfer */
+static uint32_t vfd_data[VFD_DRIVERS] = {0};
+static uint16_t vfd_spi[VFD_DRIVERS*2] = {0};
+static volatile uint8_t vfd_spi_i = 0;
 
 char vfd_digits[VFD_DIGITS] = {0};
 char vfd_matrixs[VFD_MATRIX] = {0};
@@ -267,7 +272,12 @@ void vfd_digit(uint8_t nb, char c)
 	if (!(nb<VFD_DIGITS)) { // check the digit exists
 		return;
 	}
-	vfd_data[0] = 0;
+	
+	// clear data
+	for (uint8_t i=0; i<LENGTH(vfd_data); i++) {
+		vfd_data[i] = 0;
+	}
+	
 	vfd_data[1] = 1<<(4+(9-nb)); // select digit
 	/* encode segment
 	 * here the bit order (classic 7 segment + underline and dot)
@@ -293,25 +303,29 @@ void vfd_digit(uint8_t nb, char c)
 			vfd_data[1] |= (ascii_7segments[i]<<(17)); // add encoded segments to memory
 		}
 	}
-	
-	vfd_data[2] = 0; // last part is not used
 }
 
 /* set dot matrix <nb> to ASCII character <c>
  * non ASCII characters are used for pictures */
 void vfd_matrix(uint8_t nb, char c)
 {
-	if (!(nb<VFD_MATRIX)) { // check the matrix exists
+	// check the matrix exists
+	if (!(nb<VFD_MATRIX)) { 
 		return;
-	} else if (nb<4) {
-		vfd_data[0] = 0;
-		vfd_data[1] = 1<<(3-nb); // select matrix
-	} else {
-		vfd_data[0] = 1<<(35-nb); // select matrix
-		vfd_data[1] = 0;
+	} 
+	
+	// clear data
+	for (uint8_t i=0; i<LENGTH(vfd_data); i++) {
+		vfd_data[i] = 0;
+	}
+	
+	// select matrix
+	if (nb<4) {
+		vfd_data[1] = 1<<(3-nb); 
+	} else {
+		vfd_data[0] = 1<<(35-nb);
 	}
 	
-	vfd_data[2] = 0;
 	if ((c<0x80) && (c>=' ')) { // only take printable characters
 		uint8_t i = c-' '; // get index for character
 		if (i<LENGTH(font5x7)) {
@@ -336,6 +350,20 @@ void vfd_matrix(uint8_t nb, char c)
 /* shift out the VFD data */
 void vfd_shift(void)
 {
+
+	// prepare SPI data
+	for (uint8_t i=0; i<LENGTH(vfd_data) && (uint8_t)(i*2+1)<LENGTH(vfd_spi); i++) {
+		vfd_spi[i*2] = vfd_data[i];
+		vfd_spi[i*2+1] = vfd_data[i]>>16;
+	}
+	vfd_spi_i = 0;
+	
+	spi_enable(VFD_SPI); // enable SPI (the tx empty interrupt will trigger)
+	//while (true) {
+	//spi_send(VFD_SPI, vfd_spi[vfd_spi_i++]); // send first data (also enables latch)
+//}
+
+/*
 	gpio_clear(VFD_PORT, VFD_NLE); // do not latch data
 	gpio_set(VFD_PORT, VFD_CLK); // clock is idle high	
 	for (uint8_t i=0; i<sizeof(vfd_data)/sizeof(vfd_data[0]); i++) {
@@ -350,10 +378,9 @@ void vfd_shift(void)
 		}
 	}
 	
-	gpio_set(VFD_PORT, VFD_STR); // disable HV output
 	gpio_set(VFD_PORT, VFD_NLE); // latch data
-	gpio_clear(VFD_PORT, VFD_STR); // enable HV output
 	gpio_clear(VFD_PORT, VFD_NLE); // stop latching data
+	*/
 }
 
 /* transmit every digit and matrix */
@@ -413,18 +440,80 @@ void vfd_test(void)
 	}
 }
 
+/* switch VFD display on */
+void vfd_on(void)
+{
+	gpio_clear(VFD_PORT, VFD_STR); // enable HV output
+}
+
+/* switch VFD display off */
+void vfd_off(void)
+{
+	gpio_set(VFD_PORT, VFD_STR); // disable HV output
+}
+
 /* setup VFD */
 void vfd_setup(void)
 {
-	rcc_periph_clock_enable(VFD_RCC); //enable clock for VFD
+	rcc_periph_clock_enable(VFD_PORT_RCC); // enable clock for VFD GPIO
 	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_STR); // set VFD pin to 'output push-pull'
-	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_NLE); // set VFD pin to 'output push-pull'
-	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_CLK); // set VFD pin to 'output push-pull'
-	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_DIN); // set VFD pin to 'output push-pull'
+	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_NLE); // set VFD pin to alternative function push-pull
 	
-	vfd_clear(); // initialize values
+	//gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_DIN);
+	//gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, VFD_CLK);
 	
 	gpio_set(VFD_PORT, VFD_STR); // disable HV output
-	gpio_clear(VFD_PORT, VFD_NLE); // do not latch data
-	gpio_set(VFD_PORT, VFD_CLK); // clock is idle high
+	gpio_clear(VFD_PORT, VFD_NLE); // do not output latched data
+	//gpio_set(VFD_PORT, VFD_CLK); // clock is idle high
+	
+	rcc_periph_clock_enable(VFD_SPI_RCC); // enable SPI clock
+	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, VFD_CLK); // set VFD pin to alternative function push-pull
+	gpio_set_mode(VFD_PORT, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, VFD_DIN); // set VFD pin to alternative function push-pull
+	
+	spi_reset(VFD_SPI); // clear SPI values
+	/* set SPI:
+	 * - use VFD_SPI port
+	 * - divide clock by 8 for generating the baudrate (F_PCLK1 is 36MHz, max HV518 is 6MHz)
+	 * - clock idle high polarity
+	 * - data is valid on rising edge (second clock phase)
+	 * - send 16 bits at a time
+	 * - send least significant bit first (that's how I coded the data)
+	 */
+	spi_init_master(VFD_SPI, SPI_CR1_BAUDRATE_FPCLK_DIV_64, SPI_CR1_CPOL_CLK_TO_1_WHEN_IDLE, SPI_CR1_CPHA_CLK_TRANSITION_2, SPI_CR1_DFF_16BIT, SPI_CR1_LSBFIRST);
+	//spi_set_bidirectional_transmit_only_mode(VFD_SPI); // only use MOSI to transmit
+	//spi_set_unidirectional_mode(VFD_SPI); // MISO is unused
+	//spi_disable_software_slave_management(VFD_SPI); // use hardware NSS
+	spi_enable_software_slave_management(VFD_SPI); 
+	//spi_enable_ss_output(VFD_SPI); // allow slave select
+	spi_set_nss_high(VFD_SPI); // set NSS high
+	spi_enable_tx_buffer_empty_interrupt(VFD_SPI); // enable TX empty interrupt
+    nvic_enable_irq(VFD_SPI_IRQ); // enable SPI interrupt
+	
+	//spi_enable(VFD_SPI);
+	//SPI_CR1(VFD_SPI) &= ~SPI_CR1_SSM;
+	//SPI_CR2(VFD_SPI) |= SPI_CR2_SSOE;
+	
+	vfd_clear(); // initialize values
+}
+
+#if (VFD_SPI==SPI1)
+void spi1_isr(void)
+#elif (VFD_SPI==SPI2)
+void spi2_isr(void)
+#endif
+{
+	if (SPI_SR(VFD_SPI) & SPI_SR_TXE) { // transmission buffer empty
+		if (vfd_spi_i<LENGTH(vfd_spi)) { // check if data is available
+			gpio_clear(VFD_PORT, VFD_NLE); // slave select to latch data
+			spi_send(VFD_SPI, vfd_spi[vfd_spi_i++]); // send next data
+		} else { // all data transmitted
+			while (SPI_SR(VFD_SPI) & SPI_SR_BSY); // wait until transmission is complete (not sure it's a good idea in an isr)
+			gpio_set(VFD_PORT, VFD_NLE); // output latched data
+			//spi_set_nss_high(VFD_SPI); // set NSS high
+			spi_clean_disable(VFD_SPI); // disable latch to output data
+			//spi_set_nss_high(VFD_SPI); // set NSS high
+			gpio_set(GPIOA, GPIO1); // toggle LED
+			//gpio_set(VFD_PORT, VFD_NLE); // do not output latched data
+		}
+	}
 }
diff --git a/lib/vfd.h b/lib/vfd.h
index 2226402..81cca69 100644
--- a/lib/vfd.h
+++ b/lib/vfd.h
@@ -17,14 +17,37 @@
  * it used three chained supertex HV518P shift register VFD drivers */
 
 /* supertex HV518 VFD driver pins */
-#define VFD_RCC RCC_GPIOA
+/* port on which the pins to control the supertex HV518 VFD driver are
+ * we use port A because of the SPI interface */
 #define VFD_PORT GPIOA
-#define VFD_STR GPIO4
-#define VFD_NLE GPIO5
-#define VFD_CLK GPIO6
-#define VFD_DIN GPIO7
+#define VFD_PORT_RCC RCC_GPIOA
+/* SPI port to use */
+#define VFD_SPI SPI1
+#if (VFD_SPI==SPI1)
+#define VFD_SPI_RCC RCC_SPI1
+#define VFD_SPI_IRQ NVIC_SPI1_IRQ
+#elif (VFD_SPI==SPI2)
+#define VFD_SPI_RCC RCC_SPI2
+#define VFD_SPI_IRQ NVIC_SPI2_IRQ
+#endif
+/* strobe pin to enable high voltage output
+ * high voltage is output on low
+ * drive using a GPIO PA6 (normally MISO) */
+#define VFD_STR GPIO6
+/* latch enable pin
+ * store the shifted data on low
+ * output the parallel data on high
+ * use the SPI NSS (PA4) */
+#define VFD_NLE GPIO_SPI1_NSS
+/* clock signal
+ * drive using SPI SCK (PA5) */
+#define VFD_CLK GPIO_SPI1_SCK
+/* data input, where the data is shifted to
+ * drive using SPI MOSI (PA7) */
+#define VFD_DIN GPIO_SPI1_MOSI
 
 /* the number of blocks available on the VFD */
+#define VFD_DRIVERS 3
 #define VFD_DIGITS 10
 #define VFD_MATRIX 12
 
@@ -48,5 +71,9 @@ void vfd_clear(void);
 void vfd_test(void);
 /* transmit every digit and matrix */
 void vfd_transmit(void);
+/* switch VFD display on */
+void vfd_on(void);
+/* switch VFD display off */
+void vfd_off(void);
 /* setup VFD */
 void vfd_setup(void);
diff --git a/main.c b/main.c
index f534a9a..8b55bd1 100644
--- a/main.c
+++ b/main.c
@@ -27,6 +27,8 @@
 #include <libopencm3/cm3/scb.h> // vector table definition
 #include <libopencmsis/core_cm3.h> // Cortex M3 utilities
 
+#include <libopencm3/stm32/spi.h> // SPI library
+
 /* own libraries */
 #include "main.h" // board definitions
 #include "usart.h" // USART utilities
@@ -69,7 +71,7 @@ int main(void)
 
 	gpio_setup(); // setup main inputs/outputs
 	usart_setup(); // setup USART (for printing)
-	cdcacm_setup(); // setup USB CDC ACM (for printing)
+	cdcacm_setup(); // setup USB CDC ACM (for printing)	
 	vfd_setup(); // setup VFD
 	
 	setbuf(stdout, NULL); // set standard out buffer to NULL to immediately print	
@@ -77,6 +79,8 @@ int main(void)
 
 	printf("welcome to the STM32F1 CuVoodoo display driver\n");
 
+
+	vfd_on(); // switch on VFD
 	vfd_test();
 	vfd_shift();
 	for (uint32_t i = 0; i < 0x800000; i++) {
@@ -84,6 +88,8 @@ int main(void)
 	}
 	vfd_clear();
 	vfd_shift();
+	vfd_digit(0,'0');
+	vfd_shift();
 	
 	bool vfd_flag = false;
 	for (uint8_t i=0; i<LENGTH(vfd_digits); i++) {