Low or High Density?

Preamble

I need some (4 x 4 GB) memory DDR2-800 (or DDR-667) PC2-6400u (or PC2-5300) UDIMMS Unbuffered Non-EEC for an AMD Althon Dual Core 4850e motherboard.

From DDR2 PC2-6400U 800Mhz, high density are not recommended.

If you google a particular memory stick identifier, you can end up with different looking sticks (126 or 32 ICs)

So how to tell low density from high density?

Continue reading Low or High Density?

Retro!

Preamble

After watching The Gigatron TTL Computer without a Microprocessor, I got to thinking about building an Apple I (or II). After a quick search I found the Wikipedia entry for the Replica 1 (see this Apple 1 kit page), and from there the Apple II section of ReactiveMicro’s site, and the apple-ii-rev-0 board.

Then I came across loads of retro teardowns from EEVblog

Continue reading Retro!

Noisey chips

Preamble

Following on from Banging noises…, I attempted to recreate the Noise Chip (U4) depicted in the LDB-1 schematic, from the article Anatomy of a drum machine. The noise chip creates both a white noise signal as well as four tuned square waves at different (unknown) frequencies. I have attempted to contact the author for more details but have not had a reply as yet.

It is using either PIC (which is likely seeing as the author states a preference for the PIC microcontrollers), or an ATtiny.  I will attempt to use a ATtiny/ATmega microcontroller (specifically ATmega48P/88P/168P/328P but the code should compile for most Arduinos).

Note that parts of this are a work in progress.

Note: The phase-correct 50% trick is possible with Timer0 on an ATtiny85, but it is not clear if it is possible with Timer1 (although Timer0 does have two channels). Atmel AVR ATtiny comparison chart

Continue reading Noisey chips

Messrs. Schmitt, Trigger and APC (and other stories)

Preamble

Just for the hell of it, I wondered if it was possible to substitute the 555 timers in an Atari Punk Console (APC) with some other component, or components.

After seeing some Schmitt-trigger inverters (CD40106) used in oscillator circuits, see Swingers, I thought that I would come up with an alternative design.

Continue reading Messrs. Schmitt, Trigger and APC (and other stories)