AVR NTP Clock

A web-synchronized clock/calendar based on the AVT2632 kit, ATtiny4313, and ENC28J60.

Description

This device is a typical clock based on 7-segment displays, with the following features:

• Time or date display
• Automatic synchronization with an NTP server
• Automatic network configuration using DHCP
• Configurable timezone and daylight saving time
• Rudimentary menu for adjusting settings

Background

This project is an upgrade of the AVT2632 clock kit which adds time synchronization over Ethernet networks, while minimizing the hardware changes to the kit. The largest AVR microcontroller pin-compatible with the kit is ATtiny4313 featuring 4KB of program memory and 256B of RAM. As such, the project became a challenge to fit a minimalistic network stack and other functionality within this constrained environment.

Warning: due to the size constraints, code readability and maintainability was often sacrificed to save a few bytes. Don't use it as reference for good coding practices.

Hardware

The clock is based on the AVT2632 kit. As far as I know it's no longer available for sale, but it should be easy to replicate based on the schematic. Additionally, you'll need an ATtiny4313 and an ENC28J60 module (preferably with a built-in 3.3V regulator).

A few modifications to the schematic are required:

• Replace U2 with ATtiny4313
• Solder a jumper across SW1
• Cut trace between K and K1
• Connect K1 to K2 (GND)
• Connect ENC28J60 module as follows:
  • K - CS
  • H1 - SCK
  • H2 - SO
  • H3 - SI (may be labelled ST)
  • H4 (GND) - GND
  • VCC (output of U1, e.g. left-hand side of ZW1) - 5V

If your ENC28J60 module doesn't have a 3.3V regulator, you'll need an external one to convert the 5V supply to 3.3V. Note that SPI lines don't need level shifters because ENC28J60 inputs are 5V tolerant.

The code also supports ATmega16 which I used for debugging, but I don't have a schematic for that.

Compilation

Compiled binary is available on the Releases page. The flash usage is 4080 bytes (99.6%) when compiled with AVR-GCC version 5.4.0. If you want to compile it yourself, follow the instructions:

• Windows: open AvrNtpClock.atsln in Microchip Studio 7.0 (formerly Atmel Studio 7.0) and compile the project. Make sure the Release configuration is selected.
• Linux: you can try as2make to generate a makefile from AvrNtpClock.cproj, but I haven't tested it.

To flash the MCU you need to use a breadboard as AVT2632 doesn't have an ISP socket. Remember to program the Flash, EEPROM, and Fuse Bits (see main.c for Fuse Bit settings).

Usage

After connecting the device to network, it obtains an IP automatically (provided that a DHCP server is available). Then, date and time is obtained from an NTP server (configurable in the settings).

By default, time is shown in the Hour-Minute-Second format. Blinking dots between hours and minutes indicate that a synchronization happened within the last hour. When SW2 is pressed, the current date is shown as Day-Month-DayOfWeek. When SW3 is pressed, the current year is shown along with network synchronization status code:

Code	Status
0	ENC28J60 not responding
1	Network cable disconnected
2	Waiting for DHCP offer
3	Waiting for DHCP ack
4	Waiting for DHCP ack (renew)
5	Waiting for ARP reply
6	Waiting for NTP reply
7	Synchronized

Settings can be accessed by pressing SW2 and SW3 at the same time. The interface is rather rudimentary as there are only two buttons available. There is a total of 50 configuration bytes. In the settings menu, the display shows DVVVBB. BB indicates which configuration byte is being edited (00-49). VVV is the value of that byte (000-255). D shows which digit of the current byte is being edited (1-3 or blank). Pressing SW3 cycles through D. If D is 1, 2, or 3, pressing SW2 increments the hundreds, tens, or ones respectively. If D is blank, pressing SW2 moves to the next byte (or exits the menu after the last byte). The configuration bytes are as follows:

Byte index	Setting	Unit	Range	Default
0	Manually set current UTC time	Year (within century)	0-99	0
1		Month	1-12	1
2		Day	1-31	1
3		Hour	0-23	0
4		Minute	0-59	0
5		Second	0-59	0
6	Timezone 1 UTC offset	1 - plus, 0 - minus	0-1	1
7		Hours	0-23	1
8		Minutes	0-59	0
9	Timezone 1 ends on	Month	1-12	3
10		Week within month (5 - last)	1-5	5
11		Day of week	1-7	7
12		Hour	0-23	2
13		Minute	0-59	0
14	Timezone 2 UTC offset	1 - plus, 0 - minus	0-1	1
15		Hours	0-23	2
16		Minutes	0-59	0
17	Timezone 2 ends on	Month	1-12	10
18		Week within month (5 - last)	1-5	5
19		Day of week	1-7	7
20		Hour	0-23	3
21		Minute	0-59	0
22	Daytime ends on	Hour	0-23	22
23		Minute	0-59	0
24	Daytime brightness	0 - blank, 9 - full	0-9	9
25	Nighttime ends on	Hour	0-23	7
26		Minute	0-59	0
27	Nighttime brightness	0 - blank, 9 - full	0-9	4
28	NTP server IP	Most significant byte	0-255	134
29		...	0-255	130
30		...	0-255	4
31		Least significant byte	0-255	17
32	Device IP (or 0 to use DHCP)	Most significant byte	0-255	0
33		...	0-255	0
34		...	0-255	0
35		Least significant byte	0-255	0
36	Gateway IP (or 0 to use DHCP)	Most significant byte	0-255	0
37		...	0-255	0
38		...	0-255	0
39		Least significant byte	0-255	0
40	Netmask (or 0 to use DHCP)	Most significant byte	0-255	0
41		...	0-255	0
42		...	0-255	0
43		Least significant byte	0-255	0
44	Device MAC	Most significant byte	0-255	78
45		...	0-255	84
46		...	0-255	80
47		...	0-255	99
48		...	0-255	108
49		Least significant byte	0-255	107

License

This project is released under the GPLv2 license. Some parts of the code are based on Procyon AVRlib by Pascal Stang and Tuxgraphics NTP clock by Guido Socher, both released under the GPLv2 license.