Thread: Hedghog II
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Old 4th Jun 2019, 2:09 pm   #1
FRANK.C
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Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 601
Default Hedghog II

Hedghog II is mainly in response to the recent trouble with the EP2C5 FPGA boards.

Hedghog II for the most part it is the Same as Hedghog but with a few changes.
The biggest difference is the FPGA board is dispensed with. Now all the components are mounted on a single PCB.
The FPGA is changed to a more modern EP4CE6E22C8N.
The R2R DAC is changed from 9 bit to a 10 bit.
It now can be used in modulator only mode.
The video out socked is moved to the rear panel and an extra toggle switch is added to the front panel.
The DIP switch is now a 6 pole type.
It has a test mode that drives the Test card from the 50 MHz clock. This will allow the 405 side of the FPGA to be tested without the video clock been required and so should help to identify video decoder problems.

There are some circuit changes.
A 50 MHz oscillator feeds the FPGA. All other clocks are referenced from the 50 MHz clock. This includes a 14.31818 MHz clock for the video decoder which previously required it's own crystal.
The pull-up resistors for the switches have been removed and it now uses the weak pull-up's provided by the FPGA.
The unused section of the video amplifier chip is now used together with a analogue switch to enable it to be used in modulator only mode.
To provide all the required power rails there are now 5 voltage regulators 5V, 3.3V, 2.5V, 1.8V and 1.2V.
It still fits on a double sided PCB of the same dimensions as the Hedghog PCB and so will fit the same case.

All the files needed to build it can be downloaded here.

Frank
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