VFD Approximate Clock using a Professional PCB


This is the "production" version of the Prototype Approximate Clock.

The features remain the same:

After considerable help from Nick deSmith with the board layout, I eventually placed an order with Olimex Ltd for a couple of manuafactured boards to build and fully test before looking to a larger order for gifts and for sale (these are now available).

Schematic and PCB

The Eagle schematic and layout editor files are available for download if you want to look for an alternative supplier or order from Olimex yourself. There are two components connected by wires and so not shown on the schematic a NORPS12 LDR to sense light level for setting the display brightness and a rotary encoder with a built in push button (I used an Alps encoder) - see the Parts List below.

The boards are in the photo gallery below.


The software was written entirely using C and compiled using the CodeVisionAVR version 2 compiler. The complete source code is available for downloaded here. Beware - C purists beware that my C is perhaps a bit idiosyncratic but I like it. However, I hope you will find the code well commented. I have included the required libraries and you may have to play with the various paths to suit your individual set up. This zip file includes the required fuse settings and compilled hex files.

With help for René Eickhoff I have a German language version available and adding more langauges is fairly straight forward. Croatian, Gaelic, French and Spanish are looking possible.

The clock software has three main modes:

  1. A scrolling text message displaying the time on as a 12 hour clock, pressing the push button displays a scrolling text message giving the date.
  2. A static "conventional" digit clock using numbers, pressing the button displays the date using numbers.
  3. A settings mode where the clock display parameters can be selected using a Clock Menu system. In brief:
    • Set Date and Time:
      • Set DST - can be off, on (+1hr), automatic to EU rules, automatic to US Federal rules.
      • Set year (2000-2099), month, day, hour, minute, second.
    • Set Scrolling parameters:
      • The Scroll lead-in and lead-out character (including none) as "*" is used in * * * FIVE MINUTES TO EIGHT * * *
      • The number of lead in/out character (3 in this example)
      • The scroll delay between character shifts in 10mS counts - basically "scroll speed"
    • Time Formating:
      • HH-MM-SS or HH-MM display
      • Select the separator character to use, "-" in this example
      • Whether the separator is flashed on and off each second (looks good in HH-MM format)
      • Whether spaces are added to use more of the display width: 18 - 16 - 23
      • Display the number digital clock in 12 or 24 hour mode: 01:30 or 13:30
      • Supress the leading 0 on the hours digits: 09:47 or 9:47
      • The "approximate" clock granularity 5, 10 or 15 minutes - the time steps taken between changes
    • Date formatting:
      • DMY, MDY, YMD formats
      • Show the day of week as well on the text display: * * * TUESDAY, JUNE 10, 2008 * * *
      • The separator character, spaces selection and leading 0 supression as for the time display above
    • PWM dimming controls:
      • Automatic or manually set.
      • Two parameters for the LDR sensitivity and two more for the VFD PWM limits for fine adjustments.
      • Turn off the VFD filament overnight timer (with a wake up function)

All of these parameters are stored on the NVRAM space on the clock chip and are saved and loaded as required.

Photo Gallery

For Sale

At the time of preparing this web page I have some spare boards and VFDs for sale for 15 GBP for a set (one board, one VFD) contact me if you are interested. I can also supply the A6810 and LM9022 chips and a programmed AVR - all for a price of course!


The menu exists as a tree with a "top menu" which is selected using the encoder and then pressing the push button. There are then 6 sub menus and a final "return" back to the top menu. Each sub menu has a sub-sub-menu. When an item to edit is eventually selected, rotating the encoder will show the possible values. Difficult to describe with words, but intuitive to use (IMHO).

VFD Clock Menu
sub-menu sub-sub-menu function range default
0. DATE&TIME 0.0 DST MODE Allows automatic adjustment for DST
  • 0. Off
  • 1. On
  • 2. Automatic EU rules
  • 3. Automatic USA federal rules
0.1 YEAR Adjust clock year 2000-2099 2000
0.2 MONTH Adjust clock month 1-12 1
0.3 DAY Adjust clock day 1-28,29,30,31
depends on month
0.4 HOUR Adjust clock hours 0-23 0
0.5 MINUTE Adjust clock minutes 0-59 0
0.6 SECOND Adjust clock seconds 0-59 0
0.7 ADJUST This number of seconds is added (or subtracted) from the time each Sunday midnight - use to fine tune clock accuracy ±120 seconds 0
0.8 RETURN Back to sub-menu
1. SCROLLING 1.0 CHARACTER Character use to to prefix and postfix the scrolling display
e.g. = in
= = = IT'S ABOUT SIX O'CLOCK = = =
Any valid character *
1.1 COUNT The number of prefix and post fix characters to use, such as 3 in the above example 0 - 20 3
1.2 TEMPO Adjust the speed of the scrolling text, low number = fast, high number = slow 1 - 255 30
1.3 DATE EVERY Show the time this count and then show the date once 0 - 20
0 = never
1.4 RETURN Back to sub-menu
2. TIME 2.0 CHARACTER Y = HHMM format
N = HHMMSS format
N - Y N
2.1 SEPARATOR Separator between HHMM and MMSS e.g.
23 = 01 = 56
Any valid chanarcter =
2.2 BLINK The separator can blink on and off every second N - character is steady
Y - character is blinking
2.3 SPACES Are the time numbers and separator characters spaced out e.g.
23 = 01 = 56 -or- 23=01=56
N - no spaces inserted
Y - spaces are inserted
2.4 12 HOUR clock is either 24 hour (0 - 23) or 12 hour (1 - 12) N - 24 hour clock
Y - 12 hour clock
2.5 LEADING 0 The leading 0 on the hour can be omitted
03 = 01 = 56 -or- 3 = 01 = 56
N - omit a leading 0
Y - show leading 0
2.6 GRANULARITY The approximation of time into 5 minute, 10 minute or 15 minute chunks for the scrolling display
  • 0. 5 minutes
  • 1. 10 minutes
  • 2. 15 minutes
2.7 RETURN Back to sub-menu
3. DATE 3.0 FORMAT Select the format for the date e.g. 23 May 2009 -or- May 23, 2009 -or- 2009 May 23 in the scrolling mode and 23/05/2009 -or- 05/23/2009 -or- 2009/05/23 in the non-scrolling mode
  • 0. DMY
  • 1. MDY
  • 2. YMD
3.1 DOW Select if the day of the week will preceed the date e.g. FRIDAY, 10 APRIL 2009 (etc) N - no DOW
Y - insert DOW
3.2 SEPARATOR Select the separator for the non-scrolling date e.g. / in the examples above Any valid character /
3.3 SPACES Are the date numbers and separator spaced out
e.g. 23/05/2009 -or- 23 / 05 / 2009
N - no spaces inserted
Y - spaces inserted
3.4 LEADING 0 The leading 0 on the day and month can be omitted
03/01/2009 -or- 3/1 /2009
N - omit a leading 0
Y - show leading 0
3.5 RETURN Back to sub-menu
4. DIMMING 4.0 UTILITY display the current value from the LDR ADC. Will show a lower number in a bright environment (300 typically) and a high value in a dark room (1000 typically) not a menu
4.1 AUTO Select if dimming control is manual or automatic (depends on room light level) N - manual
Y - auto
4.2 MANUAL PWM If manual control is set then the display brightness can be adjusted; low number gives a darker display (below about 40 the display can break up or disappear entirely) 0 - 255 255
4.3 DARK ADC The LDR ADC for a dark room (use the utility menu 4.0. to determine the value - not critica 0 - LIGHT ADC 300
4.4 LIGHT ADC The LDR ADC for a bright room DARK ADC - 1023 1000
4.5 DIM PWM The display brightness that will be used in a dark room 0 - BRIGHT PWM 40
4.6 BRIGHT PWM The display brihtness that will be used in a bright room DIM PWM - 255 255
4.7 BLANK START Time in decimal hours (e.g. 23.5 is 23:30) that the display will shutdown 0.0 - 23.9 23.5
4.8 BLANK END Time in decimal hours (e.g. 23.5 is 23:30) that the display will start up again (if start is set equal to end then the display will not shutdown) 0.0 - 23.9 5.5
4.9 WAKE UP If the encoder is moved or pressed the display will wakeup for this number of minutes 0 - 240 1
4.10 RETURN Back to sub-menu
5. RESET Reset to default settings (except clock date and time) Y - Restore
N - Don't restore
6. RETURN Back to top menu selector

Parts List

Although all listed here, many items were bought on Ebay or were selected as I already had them to hand for instance the SB160 diodes could be replaced by many other diodes with a lower voltage rating. Obviously the component sizes and shapes only become important if you are going to reproduce the Eagle PCB layout without change or if you are going to use the available PCB. Some components are critical, most of the ICs and crystals for example. The capacitors in the power supply a closely spaced so the table below includes the required dimensions. The microcontroller expects the pulse series for the encoder used (sequence and timing) substituting a very different encoder might require code changes. Otherwise most of the components can be substituted with other types and ratings.

The Mouser and Digi-Key BOM can be downloaded and an Excel Spreadsheet (with thanks to Mark Kaufman).

Parts List
Parts Value Farnell Code Rapid Code Digi-Key Code Mouser Code Dimensions
B1 CR2032 Cell
CR2032 Holder
flat style 24mm diameter
two pin - 20 mm spaced
C1, C12-C15
(see note 2)
08-0232 399-4150-ND 594-K103M15X7RF53H6 2.5mm leg spacing
C2, C10 1u 63V
radial electrolytic
11-0205 P13468-ND 140-XRL63V1.0-RC 2 mm lead spacing
5mm can diameter
(see note 1)
47u 35V
radial electrolytic
11-0345 P11232-ND 647-UPB1V470MED 2.5 mm lead spacing
6.3 mm can diameter
(see note 1)
100u 35V
radial electrolytic
11-0350 P10294-ND 647-URZ1V101MPD1TA 3.5 mm lead spacing
8 mm can diameter
C8 1000u 35V
radial electrolytic
11-0760 P10305-ND 647-UVZ1V102MHD 5 mm lead spacing
13 mm can diameter
C9 1000u 10V
radial electrolytic
11-0315 P10225-ND 647-UVZ1A102MPD 5 mm lead spacing
10 mm can diameter
C11,C16-C19 100n polyester 10-3260 495-2465-ND 80-R82DC3100AA50M 5mm lead spacing
C20, C21 22p ceramic 08-0046 495-1004-1-ND 140-50N2-220J-RC 2.5 mm lead spacing
L1 220 uH
radial minature
88-1037 811-1316-ND 580-18R224C 7.2 mm lead spacing
13 mm diameter
D1 - D5
(see note 1)
SB160 47-5316 MBR160-ND 863-MBR160G
(see note 6)
IN4001 47-3130 1N4001GDICT-ND 583-1N4001-B
D7 IN5820 47-2546 1N5820-TPMSCT-ND 844-1N5820
Encoder and switch Alps EC12E2424407 1520813 688-EC12E2424407
(see note 3)
LM2576-5 1564682 82-0664 LM2576T-5.0-ND 863-LM2576T-005G
IC2 LM9022 (SMD) 1286933 LM9022M-ND
IC3 DS1307 1188042 82-0567 DS1307+-ND
IC4 ATMEGA168-20 9171207 73-4276 ATMEGA168-20PU-ND 556-ATMEGA168-20PU
(see note 2)
A6810 1193489 620-1092-ND
Q1 32.768 kHz crystal
watch, radial
90-3052 300-8303-ND 695-CFS206-327KF-U 2.5 mm lead spacing
Q2 20MHz crystal
1469646 90-1084 300-8507-ND 695-HC49US-20-U
(see note 5)
NORPS12 58-0132 PDV-P9203-ND
R1, R2, R5, R6 10k 0.25W carbon 63-2344 10KQBK-ND 291-10K-RC
R3, R4 4k7 0.25W carbon 63-2340 4.7KQBK-ND
X1 VFD see above
4 off
(see note 2)
DIL18 sockets 22-0165 ED3318-ND 535-18-3518-10
1 off DIL28-3 socket 22-0175 ED3328-ND 535-28-3518-10
1 off DIL8 socket 22-0150 ED3308-ND 535-08-3518-10
JP1, JP2
(see note 7)
pin header jumper
J1 switch, LDR and encoder connection 7 pin header or wiring
ISP connector
6 way
(see note 4)


  1. If a 24VDC power supply is used then D1 - D5, C3 - C7 can be omitted. JP3 must be set accordingly.
  2. The current software version does not address the dot or comma display so IC8 and C15 can be omitted (it would not hurt to fit the socket and C15 as a low cost compromise).
  3. DC input voltage can be anywhere in the range 12 VDC to 40VDC, higher if the high voltage version of IC1 is used.
  4. ISP connector is arranged as a standard Atmel 6 pin - pins 1 and 6 are marked for correct orientation.
  5. The LDR can be omitted and the display brightness set manually.
  6. This diode is for accidental reverse polarity protection and is not intended as a rectifier.
  7. The current software does not use these jumpers, so they can both be omitted.