SSTV Tx/Rx with a Pi and an RTL-SDR

It turns out that transmitting and receiving SSTV signals is pretty easy, using just a raspberry pi as a transmitter and an RTL-SDR as a receiver. There are a few programs which you’ll need to install before you begin:

TI-BASIC Bejeweled

TI-BASIC is the unofficial name for the programming language included on the stock operating systems of the TI-83 and TI-84 Plus series of calculators. This includes a large set of calculators, the most popular these days being the 96x64 monochrome TI-84+SE, the 320x240 16 bit color TI-84+ Color SE (referred to as the “CSE”), and the newly released TI-84+CE which features a LCD which is significantly faster to access than the CSE and a processor upgrade from a z80 to an ez80.

Prelude of the Chambered in Dart

I was watching Notch write what was essentially a re-implementation of Doom in Dart recently, and it inspired me to port Prelude of the Chambered (PotC) to Dart.

z80 Assembly: Binary-Coded Decimal

One method for display numbers that take more than 16 bits is to convert it to Binary Coded Decimal (BCD) first, and display the result. BCD works by using four bits to store each decimal (base 10) digit of a number. The following code can convert a number to BCD, and display it. It’s currently written to convert a 24 bit number to a 10 digit BCD number, but can be modified to support anything really. It is memory ineffecient, because it uses one byte for each digit rather than storing two digits per byte. This is useful though because it makes the display routine simpler.

TI-84+CSE: Max Pixel Fill Speed with OTIR

One of the fastest practical ways to write arbitrary pixels (no 1-color rectangles) to the LCD is with an OTIR loop copying pixel data directly from memory. That being said, I was wondering how many pixels you could theoretically update per frame. As mentioned, this is theoretical. This does not take into account the overhead of adjusting the LCD window, or any of the other logic you may have. It also assumes that interrupts are disabled.

TI-84+CSE: Half Resolution Mode

Half res mode is an LCD mode which results in a halved horizontal resolution. This can also be used for double buffering, because one can write to the left side of the screen while displaying the right side or vice versa.