SHOWALL FUN PRANKS HIGH VOLTAGE LAZARUS-64 PHOTOGRAPHY SPY GADGETS VIDEO GAME
Figure 4 - This is the mother of all solderless breadboards
Figure 4 - This is the mother of all solderless breadboards

I knew the prototype would occupy a huge chunk of breadboard real estate, so rather than attempt to string six or more smaller breadboards together, I decided to create one massive breadboard to hold the entire design as well as the host microcontroller. Normally, I would just stick the components through some perforated board and solder all of the wires on the underside, but the Lazarus-64 project was going to be a massive circuit with many hundreds of wires, so a design flaw would be a monumental mess if it were hard wired. I purchased 10 small solderless breadboard blocks and then bolted them all down to a steel baking tray to make a good grounding base. All power and ground lines were interconnected and decoupled using .1uF capacitors for good noise immunity. The massive breadboard was also wired with composite video jacks, a 5 volt power supply, power switch, and even an analog VGA port in case I wanted to build a different version.



Figure 5 - Making an analog nanosecond delay chain
Figure 5 - Making an analog nanosecond delay chain

With the 216 square inch breadboard ready to use, the fun task of converting several hundred hand drawn schematic fragments into a fully working retro game console could begin. The large order of various 74HC logic chips, static memory, oscillators, microcontrollers and a new Atmel AVR programmer had just arrived, so I began to build The Lazarus-64 Retro Game System one small block at a time.

The first part of the project to be made will be the chroma phase delay unit, which takes a 3.579MHz pulse and delays it up to 240 nanoseconds in 16 somewhat even steps. It may seem odd to be using digital gates (74HC245 Buffers) to create an analog delay, but the propagation time from input to output of each gate is highly predictable, giving about 7 nanoseconds per gate. By feeding these 16 gate delay taps into a pair of 74HC4051 multiplexers, a 4 bit chroma selector is made, allowing half of the 8 bit output from video memory to select 16 colors. Actually, one of the 16 selections will be grounded in order to create 16 shades of grey, so there are actually 15 colors plus black. By using the other 4 bits of video data to drive a luminance DAC, 256 colors are possible (16 shades of grey plus 240 colors). The final color space will be 16 shades of grey plus 15 shades of different colors, giving a very complete and flexible palette that spans the entire NTSC color wheel. Game graphics as well as photo realistic images will be possible.

The color phase delay unit consists of four 74HC745 buffers to create the 16 taps, a pair of 74HC4051 multiplexers to allow selection of 16 taps using 4 bits, and a 74HC4040 12 bit counter that will only be used to divide the 14.318 MHz master clock by four in order to output the required 3.579 MHz color burst frequency. 14.318 MHz was needed in order to drive the AVR sync generator, which requires a 4.77 MHz pixel clock in order to achieve 224 horizontal pixels.

Back Home Last Next
You are Viewing... Page 3 of 15
Lucid Science Electronics from the Fringe AtomicZombie Hack-a-day SparkFun