Black and White

No not the game Black and White (although it was a good game), I'm talking black and white TV, the next evolution of my console. I'd give it a name but it's currently too close (almost identical ;) ) to the Pico to warrant it. Besides, choosing a name can be a difficult business, I'll probably just not give it a seconds thought and pick anything, how about the "me", the "you", the "them", the "we"... Wii thats the ticket. Wait what do you mean its already taken? Yes I know the joke has passed, but I couldn't resist. Besides, I'm quite looking forward to it :)

I spent the better part of last weekend reading up on nodal analysis to be able to calculate the voltage at each junction of the R-2R ladder that I've added. The calculations themselves are simple, just an application of Ohms law. Simplifying the network however took most of the time, at least until the method finally clicked.

The Pico uses an R-2R ladder to convert the digital signal of the SX28 into an analogue signal ready for sending to a TV. Four pins on the SX28 allow 16 different voltages to be transmitted to the TV. The voltage levels are interpreted as intensity, however since the signal the TV uses 0.0v to sync on and 0.3v as black, that leaves around 10 voltage levels to play with.

Since the previous blog entry, I've reshuffled the layout with the power regulator on its own in the top left of the image. Partially cut off is the main power switch (currently taped down :P).

Looking at the main part of the image to the right of the SX28 you can see the R-2R resistor network used to convert the 4 bit digital signal into an analogue voltage which is adjusted to a 0-1.4v range via the bottom red potentiometer. Above the SX28 is the main external oscillator socket, the 80MHz oscillator is currently in the XGS. Just to the right of this, taped to the breadboard is a switch to select between the external oscillator and the 4 pin SX-Key header.

The hardware above is still almost identical to the Pico, however it won't remain like this for long. The first divergance is probably going to come with the addition of joystick hardware. The Pico only supports a single joystick which is connected directly to the SX28. I'd like to have two ports (pong is two player afterall :P) so will be adding a serial interface for the joysticks.

The second area is either going to be interfacing with an SRAM chip or adding extra graphics hardware to take some pressure off of the SX28. I'm not sure which way to go with that yet, nor how problematic the pin count may be

To test the new hardware I created a quick test program that outputs a white bar at the top and bottom of the screen. The code used for signal generation is the "GID j - pixel in a day" code with the colour burst generation stripped out. Nothing fancy, but at least it's working :)

Schwassmann-Wachmann 3

Schwassmann-Wachmann 3 otherwise known as Comet 73P is on perhaps its final voyage around the sun. A recent hubble image shows the disitrigration quite clearly


With a good clear night on Monday, I took the opportunity to take a photograph of the comet. Yes I know, its not quite up to hubble standards ;)

Considering how little experience I have imaging, I'm quite happy with how this image turned out. I'm sure someone with more experience (read - any experience) at image reduction could improve on this.

In hindsight, I should have taken a lot more exposures for stacking and perhaps used a longer exposures time to help cut down on light pollution.

For anyone that cares, here are the image details:

• Exposure Time: 5 x 1.0s stacked
• Date: 2006-05-10 02:19:44 UTC
• CCD: Starlight XPress MX716
• Scope: LX90 8"
• Dark Frames: 5 x 1s median combined

I also managed to get an image of M57. 10x10s exposures stacked with 4 median combined dark frames. Comparing the image to my star charts, I've accounted for most of the brighter and dimmer stars but there's one star that shows quite brightly that isn't listed on my star chart, if anyone knows what it is please let me know.

The biggest problem I'm currently facing is the lack of accurate focus. I'm probably going to invest in a zero image shift microfocuser to help improve on that. I also think my scopes collimation is off, something to double check next time I get a clear sky. Fingers crossed I don't spend all night on it only to make it worse :P

Hopefully with more practice I'll get a little closer to getting the most out of the scope. In the hands of an experienced user, the LX90 and MX716 are capable of much much better images.