625 TO 405 LINE


Hedghog is a homebrew 625 to 405 line standards converter based around a EP2C5T144 FPGA development board. On this page you will find the files required to build it.

 All material including Downloads on these pages are provided 'as is' without warranty of any kind, either expressed or implied.



  • Aspect ratios of 4:3 and 5:4
  • Pedestal (lifts black level 50 mV above blanking level)
  • Normal broad pulses or broad pulses with equalising pulses
  • Soft, medium and sharp interpolation apertures 
  • Audio test tones of 400Hz and 1KHz
  • Test card and grey scale
  • 13 Channel RF out covering Band l and lll (system A)
  • 405 line video out (1VPP)
  • Requires 7.5 to 9 V DC at 250 mA




All Resistors, Capacitors and Inductors are 0805 size.

All Capacitors are ceramic multilayer types.

All Capacitors are rated at 6.3V or greater except C24 and C25

which must be 16V or greater.

Where given manufacturers part numbers are given as examples alternative parts may also suit.

I can no longer source the phono sockets that I originally used. The one's that I use instead are in the parts list and need to be modified so they will fit the PCB. A spar on the rear leg needs to be filed flat see photo below.


The PCB is double sided and measures 100 mm X 89.5 mm.

The PCB manufacturer I used was PCBWay.

Link to uploaded Gerber files on PCBWay.


The FPGA board is a EP2C5T144. It has no Makers name or model apart from "EP2C5/EP2C8 MINI BOARD" .

It is currently available from many sources and the photo below should help identify it.

Header P8 on the FPGA board supplies power (5V) to it. The FPGA board comes with this position empty so a male 2 pin 2.54mm header needs to be fitted. Header P8 can be seen in the top left corner in the photo below.

The FPGA board comes programed with a small program that makes the on board LED's D5, D4 and D2 flash in unison. When programed with the Hedghog program the three LED's flash but at different frequencies to each other. When installed in the Hedghog PCB this feature is disabled with the three LED's off.

If the Hedghog PCB is screwed into the Case don't attempt to insert or remove the FPGA board or the surface mounted components could get damaged.

The latest version of Altera's Quartus Prime does not support Cyclone II devices so an older version is required to program this FPGA board. I use Quartus II 13.0sp.


The converter has a built in test card loosely based on the Phillips PM5544. It has frequency gratings of 1, 1.5, 2, 2.5 and 3 MHz. In 5:4 mode the vertical castellations are cropped to keep the aspect ratio correct.


Hedghog is discussed on the Golborne Vintage Radio Forum.


 Hedghog discussion

 Hedghog review



Circuit diagram (.pdf)

Component list (.pdf)

Component layout (.pdf)

Front and rear panel legends (.pdf)

PCB Gerber files (.zip)

FPGA program file (.jic)