Mini Project: Guitar Amplifier (old!)

Playing guitar and electronics have been two of my favourite things for a long time now. When I was about 14, I combined these two for the first time and built a pretty simply 32W amplifier. While the design is super simple, it actually has a really nice clean tone and does not distort the sound at all. It’s capable of diving an 8 ohm or 4 ohm load. Today I decided to give it a bit of a clean and check if it still worked.

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Project: CRT Oscilloscope LCD Mod – Calculating Video Timing

The video format in the HP 1662AS logic analyser/oscilloscope is similar to a VGA a signal – it has an h-sync signal, a v-sync signal and a video signal (mono-chrome). However, it is not the same as VGA as the timings are completely different. It is therefore important to find out if a normal VGA monitor will accept the signal. To do so, we need to figure out what the timings are so that I can simulate the signals and see if the monitor locks onto them.

Project: Nixie Clock (upgrade) – Final Code

The clock is controlled by an ATTiny87 which has three main jobs:

1. Counting the pulses from the Maxim DS32kHz
2. Controlling the display via the shift registers (read more)
3. Interacting with the user via the reed switches to produce a user interface

Each of these jobs will be discussed separately below as well as the main code to bring it all together in a power efficient way. Full code can be found at my GitHub.

Amazon Echo Dot: Attempts at a Power Line Attack

The Amazon Echo Dot is a popular home voice assistant, often trusted to control heating, lighting, music and even door locks. Personally, I use mine for trivial tasks such as controlling Spotify and setting alarms but you can see that it would make an obvious target for an attack.

Project: Nixie Clock (upgrade) – SPI Bus Chip Select/GPIO Contention

As discussed in the previous article, the display is controlled by a number of shift registers. Shift registers can be controlled directly by a SPI bus, which is useful as most microcontrollers (including our ATtiny87) have a built in SPI bus peripheral. This means that writing a byte to the shift register is almost as easy as just writing a byte to a register.

Project: Nixie Clock (upgrade) – Using 74HC595 Shift Registers

My Nixie tubes have 11 active pins each: a common anode and one cathode per digit (ten in total). The anode is connected to +180V via a 47k current-limiting resistor and each cathode is connected to the collector of a high voltage bipolar transistor (MPSA42) so that current can be controlled through each of them via the base of the transistor. This gives a total of 29 transistors that need to be individually controlled (24 hour clock requires 3 possible numbers for the first digit, 10 for the second, 6 for the third and 10 for the fourth). I chose to do this by using four 8-bit shift registers, connected in series to make one, 32-bit shift register.

An Intuitive Derivation/Proof of the Sum of an Infinite Geometric Series based on Zeno’s Paradox

A geometric series is a series of numbers where each number in the series is equal to the previous number multiplied by a constant multiplication factor. For example: 2, 4, 6, 8, 16… is a geometric series with a constant multiplication factor of 2.

The sum to infinity of such a sequence, then, can be represented as: