diff --git a/project/dotmatrix.c b/project/dotmatrix.c
index 0c0d7e7..ce9e1ce 100644
--- a/project/dotmatrix.c
+++ b/project/dotmatrix.c
@@ -1,6 +1,7 @@
 #include "max2719.h"
 #include "dotmatrix.h"
 #include "malloc_safe.h"
+#include "com/debug.h"
 
 DotMatrix_Cfg* dmtx_init(DotMatrix_Init *init)
 {
@@ -37,6 +38,11 @@ void dmtx_show(DotMatrix_Cfg* dmtx)
 	}
 }
 
+void dmtx_clear(DotMatrix_Cfg* dmtx)
+{
+	memset(dmtx->screen, 0, dmtx->drv.chain_len*8);
+}
+
 void dmtx_intensity(DotMatrix_Cfg* dmtx, uint8_t intensity)
 {
 	max2719_cmd_all(&dmtx->drv, MAX2719_CMD_INTENSITY, intensity & 0x0F);
@@ -46,3 +52,26 @@ void dmtx_blank(DotMatrix_Cfg* dmtx, bool blank)
 {
 	max2719_cmd_all(&dmtx->drv, MAX2719_CMD_SHUTDOWN, blank & 0x01);
 }
+
+void dmtx_set(DotMatrix_Cfg* dmtx, int32_t x, int32_t y, bool bit)
+{
+	if (x < 0 || y < 0) return;
+	if ((uint32_t)x >= dmtx->cols*8 || (uint32_t)y >= dmtx->rows*8) return;
+
+	uint32_t cell_x = (uint32_t)x >> 3;
+	uint8_t xd = x & 7;
+
+	// resolve cell
+	uint32_t digit = y & 7;
+	cell_x += ((uint32_t)y >> 3) * dmtx->cols;
+
+	uint32_t cell_idx = (digit * dmtx->drv.chain_len) + cell_x;
+
+	uint8_t *cell = &dmtx->screen[cell_idx];
+
+	if (bit) {
+		*cell |= bit << xd;
+	} else {
+		*cell &= ~(bit << xd);
+	}
+}
diff --git a/project/dotmatrix.h b/project/dotmatrix.h
index bba0e66..3e02bee 100644
--- a/project/dotmatrix.h
+++ b/project/dotmatrix.h
@@ -34,4 +34,16 @@ void dmtx_intensity(DotMatrix_Cfg* dmtx, uint8_t intensity);
 /** Display on/off */
 void dmtx_blank(DotMatrix_Cfg* dmtx, bool blank);
 
+/**
+ * @brief Send a single bit
+ * @param dmtx : driver struct
+ * @param x : pixel X
+ * @param y : pixel Y
+ * @param bit : 1 or 0
+ */
+void dmtx_set(DotMatrix_Cfg* dmtx, int32_t x, int32_t y, bool bit);
+
+/** Clear the screen (not showing) */
+void dmtx_clear(DotMatrix_Cfg* dmtx);
+
 #endif // MATRIXDSP_H
diff --git a/project/main.c b/project/main.c
index 534b753..deae1c3 100644
--- a/project/main.c
+++ b/project/main.c
@@ -35,15 +35,12 @@ int main(void)
 	dmtx_cfg.CS_GPIOx = GPIOA;
 	dmtx_cfg.CS_PINx = GPIO_Pin_4;
 	dmtx_cfg.SPIx = SPI1;
-	dmtx_cfg.cols = 4;
-	dmtx_cfg.rows = 1;
+	dmtx_cfg.cols = 2;
+	dmtx_cfg.rows = 2;
 
 	dmtx = dmtx_init(&dmtx_cfg);
 
-	dmtx->screen[0] = 0xF0;
-	dmtx->screen[4] = 0x0F;
-
-	dmtx_show(dmtx);
+	dmtx_intensity(dmtx, 2);
 
 	ms_time_t last;
 	while (1) {
@@ -52,10 +49,27 @@ int main(void)
 		}
 		poll_subsystems();
 
-		dmtx_blank(dmtx, false);
-		delay_ms(250);
-		dmtx_blank(dmtx, true);
-		delay_ms(250);
+		// 1
+		dmtx_clear(dmtx);
+		for (int i = 0; i <= 15; i++) {
+			dmtx_set(dmtx, i, i, true);
+			dmtx_set(dmtx, i+2, i-2, true);
+			dmtx_set(dmtx, i-2, i+2, true);
+		}
+		dmtx_show(dmtx);
+
+		delay_ms(500);
+
+		// 2
+		dmtx_clear(dmtx);
+		for (int i = 0; i <= 15; i++) {
+			dmtx_set(dmtx, 15-i, i, true);
+			dmtx_set(dmtx, 15-(i+2), i-2, true);
+			dmtx_set(dmtx, 15-(i-2), i+2, true);
+		}
+		dmtx_show(dmtx);
+
+		delay_ms(500);
 	}
 }