diff --git a/Libraries/aprs/ax25.c b/Libraries/aprs/ax25.c
new file mode 100644
--- /dev/null
+++ b/Libraries/aprs/ax25.c
@@ -0,0 +1,156 @@
+/*
+ * FeatherHAB 
+ *
+ * This file is part of FeatherHAB.
+ *
+ * FeatherHab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * FeatherHab 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with FeatherHAB. If not, see <http://www.gnu.org/licenses/>.
+ * 
+ * Ethan Zonca
+ *
+ */
+
+#include "config.h"
+#include "ax25.h"
+#include "afsk.h"
+
+// Module globals
+static uint16_t crc;
+static uint8_t ones_in_a_row;
+static uint8_t packet[MAX_PACKET_LEN];
+static unsigned int packet_size;
+
+// Module functions
+void update_crc(uint8_t a_bit)
+{
+	crc ^= a_bit;
+	if (crc & 1)
+	crc = (crc >> 1) ^ 0x8408;  // X-modem CRC poly
+	else
+	crc = crc >> 1;
+}
+
+void send_byte(uint8_t a_byte)
+{
+	uint8_t i = 0;
+	while (i++ < 8) 
+	{
+		uint8_t a_bit = a_byte & 1;
+		a_byte >>= 1;
+		update_crc(a_bit);
+		if (a_bit) 
+		{
+			// Next bit is a '1'
+			if (packet_size >= MAX_PACKET_LEN * 8)  // Prevent buffer overrun
+			return;
+			packet[packet_size >> 3] |= (1 << (packet_size & 7));
+			packet_size++;
+			if (++ones_in_a_row < 5) continue;
+		}
+		// Next bit is a '0' or a zero padding after 5 ones in a row
+		if (packet_size >= MAX_PACKET_LEN * 8)    // Prevent buffer overrun
+		return;
+		packet[packet_size >> 3] &= ~(1 << (packet_size & 7));
+		packet_size++;
+		ones_in_a_row = 0;
+	}
+}
+
+// Exported functions
+void ax25_send_byte(uint8_t a_byte)
+{
+	// Wrap around send_byte, but prints debug info
+	send_byte(a_byte);
+}
+
+void ax25_send_flag()
+{
+	uint8_t flag = 0x7e;
+	int i;
+	for (i = 0; i < 8; i++, packet_size++) 
+	{
+		if (packet_size >= MAX_PACKET_LEN * 8)  // Prevent buffer overrun
+		return;
+		if ((flag >> i) & 1)
+		packet[packet_size >> 3] |= (1 << (packet_size & 7));
+		else
+		packet[packet_size >> 3] &= ~(1 << (packet_size & 7));
+	}
+}
+
+void ax25_send_string(const char *string)
+{
+	int i;
+	for (i = 0; string[i]; i++) 
+	{
+		ax25_send_byte(string[i]);
+	}
+}
+
+void ax25_send_header(const struct s_address *addresses, uint16_t num_addresses)
+{
+	int i, j;
+	packet_size = 0;
+	ones_in_a_row = 0;
+	crc = 0xffff;
+	
+	// Send flags during TX_DELAY milliseconds (8 bit-flag = 8000/1200 ms)
+	for (i = 0; i < TX_DELAY * 3 / 20; i++) 
+	{
+		ax25_send_flag();
+	}
+	
+	for (i = 0; i < num_addresses; i++) 
+	{
+		// Transmit callsign
+		for (j = 0; addresses[i].callsign[j]; j++)
+		send_byte(addresses[i].callsign[j] << 1);
+		// Transmit pad
+		for ( ; j < 6; j++)
+		send_byte(' ' << 1);
+		// Transmit SSID. Termination signaled with last bit = 1
+		if (i == num_addresses - 1)
+		send_byte(('0' + addresses[i].ssid) << 1 | 1);
+		else
+		send_byte(('0' + addresses[i].ssid) << 1);
+	}
+	
+	// Control field: 3 = APRS-UI frame
+	send_byte(0x03);
+	
+	// Protocol ID: 0xf0 = no layer 3 data
+	send_byte(0xf0);
+}
+
+void ax25_send_footer()
+{
+	// Save the crc so that it can be treated it atomically
+	uint16_t final_crc = crc;
+	
+	// Send the CRC
+	send_byte(~(final_crc & 0xff));
+	final_crc >>= 8;
+	send_byte(~(final_crc & 0xff));
+	
+	// Signal the end of frame
+	ax25_send_flag();
+}
+
+void ax25_flush_frame()
+{
+	// Key the transmitter and send the frame
+	afsk_send(packet, packet_size);
+	afsk_start();
+}
+
+// vim:softtabstop=4 shiftwidth=4 expandtab