Creation of the Light Phaser to Atari 7800 adapter!
The Sega Light Phaser is my favorite home light gun. I recently discovered that you can build an adapter to use the light phaser on the Atari 7800! Even better than that, I happened to have all of the parts on hand! This Project was inspired by Willy of Arcade USA. He did the same build and posted a video – once I saw the light phaser working on atari, I had to give it a go!
Here is a link to my video showing my build:
Here is Arcade USA’s Video that inspired me:
Arcade USA Willy had linked to a blog post including a schematic that he based his build off of. Here is a link to the original blog:
Let’s get Started!
My first step was to print off the schematic and get all of my parts together.
Now, the schematic calls for a 2N2222, but all I had on hand were 2n3904. That should be close enough.
After I had all of the parts, I had to figure out the pins on the DB9 connectors. Fortunately the female end had them stamped into the plastic – so I was able to figure out the pins and clearly mark them.
As you can (barely) see, I used a sharpie to mark pins 1 and 9 on each connector. This made it a little more clear where I needed to actually run the wires.
I had to go back in verify that only 4 pins were being used for this circuit. Once I verified that – I realized how easy this build would be.
I attached the 4 wires to the male end of the adapter and I stripped the insulation where the resistor and transistor would be connecting to the circuit. Next I had to solder the components. The resistor was a really nice fit.
Once the resistor was in place I had to figure out how the transistor connected. I did a little research and figured out which leg was the Collector, Base, and Emitter. I then bent the legs so that they would fit nicely into the circuit. After I had soldered the transistor into place, all that was left was to solder on the female end of the adapter. It took some creative bending of wires, but everything fell into place nicely.
After a quick test – I made an enclosure out of a AAA battery holder. Everything works excellent and Crossbow is actually fun on the 7800 now 🙂
So, why was this needed and why does it work? The Sega Light Phaser and the Atari XE lightgun use the same basic method of determining where you are pointing at the moment that you pull the trigger. My understanding is that they blank the screen and then redraw it. The game waits for the sensor in the gun to detect an active pixel – based on how long it takes for the sensor to detect light, the game knows where on the screen you are pointing.
The transistor and resistor are needed to invert the trigger signal. Without that part of the circuit you would have to hold the trigger in and then quickly release it when you want to shoot.