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Schematic

Parts

R1 - R6, R21, R24 390k IC1 89S2051 programmed with 2D3 firmware
R7 2 x 8K2 in parallel IC2 K155ID1 (74141)
R8 - R11 82K IC3 24LC00** or DS1307***
R12, R13, R15, R16 4K7 IC4 78L05
R14*, R26* 10K IC5 741
R22 1K8 IC6 555
R23 560R

R25 11K D1*, D3 1N4148


D2 1N4001
C1, C2 33pF D4 BA157
C3, C7, C10 100nF

C4, C5, C8 1uF axial TR1 - TR6 MPSA92
C6 470uF 25V radial TR7 - TR14 MPSA42
C9 4n7 TR15* BC548
C11 2u2 250V axial TR16 STD2NC45-1




L1 220uH (ELC08D221E) V1 - V6 IN-14 Nixie tube
X1 6Mhz 20ppm crystal (fit an insulator) N1 - N4 neon lamp as required
X2 ***
32.768Khz watch crystal CL=12.5pF






PSU 12V 300mA (min) regulated 2.1mm plug SK1 2.1mm power


SK2* 3.5mm stereo jack
Battery ***
CR1225 Lithium cell

Breakaway pin header (2x10 + 1x3 way)
***
Surface mount holder for CR1225

Breakaway SIL socket (2x10 + 1x3 way)

*      omit if the PC synchronisation option is not required.
**    not required if RTC option is fitted.
***  RTC option only

Layout

Construction

Construction using my PCB is quite straightforward but there are a few points worth a mention. If  the  RTC chip option has been bought as part of a kit it is best fitted before any other construction, details are here.

  1. The two boards are supplied joined together. They can be separated by flexing them along the scored line. As you bend the board you will hear a tearing sound as the glass fibres break. continue to flex the board back and forth until the two halves separate.
  2. The board is finished in standard PbSn. It is not lead free. Use lead/tin solder.
  3. The MOSFET's tab should be soldered to the board. For best heatsinking try to get the solder to flow right underneath the whole of the tab. This is best done before soldering the leads.
  4. The crystal MUST be fitted with an insulator or spaced 1-2 mm from the board.
  5. The easiest way to fit the tubes is to slide the insulator to the ends of the leads leaving only 1-2 mm showing. The tube can then be fitted making sure the anode lead is in the hole closest to the rear of the board. The anode can be identified by the white insulation inside the tube.
    Bruce Nadig who built one of my kits suggested an alternative method: "What I did was leave the anode wire at its full length. I then cut the wires immediately adjacent on either side about 2 to 3 mm shorter. The wires next in the circle were then cut about 2 to 3 mm shorter than the first two wires that I cut. I continued on in this pattern until I reached the wires at the front of the tube. These wires would be the shortest. I then installed the longest wire (the anode wire) into its hole. Following that, I installed the two next longest wires. I continued this until all wires were installed. I found this to be easiest for me."