Computer Science, Crafty, Electronics, Engineering, Good Reads, Milestones, Simon's sketch book

Simon trying to build a 8-bit computer in circuit simulators

As some of you may know, Simon is working on building a real-life 8-bit computer from scratch, guided by Ben Eater’s tutorials (it’s a huge project that may takes months). He has also been enchanted by the idea to build the computer in a simulator as well, researching all virtual environments possible. The best simulator Simon has tried so far has been, although he did stumble upon a stack overflow error once, approximately half-way through (maybe the memory wasn’t big enough for such an elaborate circuit, Simon said). You can view Simon’s projects on Circuitverse here:

Link to the project that ended up having a stack overflow:

And here is a link to Simon’s new and more successful attempt to put together a SAP-1 (simple as possible) processor (work in progress), something he has been reading about in his new favourite book, the Digital Computer Electronics eBook (third edition):
the register
the RAM

Simon has also tried building an 8-bit computer in, but it was really difficult and time consuming:

Version in

The next hopeful candidate was the Virtual Breadboard desktop app for pc. Simon downloaded it about ten times from the Microsoft store but it somehow never arrived, most probably because our Windows version was slightly outdated but who knows.

And finally, Simon has also discovered, an environment for creating your own pcbs with a real-life look. He may attempt actually making a hardcopy SAP-1 via Fritzing after he’s done with the Ben Eater project. Conclusion: sticking with Circuitverse for the time being.

Computer Science, Electronics, Engineering, Good Reads, Notes on everyday life, Uncategorized

The Digital Computer Electronics book

Simon has been mesmerised by this book for a couple of days by now, the Digital Computer Electronics eBook (third edition). He has downloaded it online and has been reading about the so called “simple as possible” processors or the sap’s (he loves the name) one of which is like the 8-bit computer he is currently trying to build from scratch.

Simon reading the book in the playroom. I hearbhim laughing and reading aloud.
a screenshot of the book
Taking notes on SAP-2 instructions (and listening to a quiz show on YouTube at the same time) – his way of learning
Computer Science, Crafty, Logic, Math and Computer Science Everywhere, Murderous Maths, Simon teaching, Simon's sketch book, Together with sis

The Diffe-Hellman key exchange algorithm

This is Simon explaining Diffe-Hellman key exchange (also called DiffeHellman protocol). He first explained the algorithm mixing watercolours (a color representing a key/ number) and then mathematically. The algorithm allows two parties (marked “you” and “your friend” in Simon’s diagram) with no prior knowledge of each other to establish a shared secret key over an insecure channel (a public area or an “eavesdropper”). This key can then be used to encrypt subsequent communications using a symmetric keycipher. Simon calls it “a neat algorithm”). Later the same night, he also gave me a lecture on a similar but more complicated algorithm called the RSA. Simon first learned about this on Computerphile and then also saw a video about the topic on MajorPrep. And here is another MajorPrep video on modular arithmetic.

originally there are two private keys (a and b) and one public key g
Neva helping Simon to mix the colors representing each key
Mixing g and b to create the public key for b
Mixing the public and the private keys to create a unique shared key
Done!Both a and b have a unique shared key (purplish)
Simon now expressed the same in mathematical formulas
Simon explained that the ≡ symbol (three stripes) means congruence in its modular arithmetic meaning (if a and b are congruent modulo n, they have no difference in modular arithmetic under modulo n)
Computer Science, Electronics, Geometry Joys, Logic, Math and Computer Science Everywhere, Murderous Maths, Notes on everyday life, Simon's sketch book, Trips

Doing math and computer science everywhere

One more blog post with impressions from our vacation at the Cote d’Azur in France. Don’t even think of bringing Simon to the beach or the swimming pool without a sketchbook to do some math or computer science!

This is something Simon experimented with extensively last time we were in France. Also called the block-stacking or the book-stacking problem.
Simon wrote this from memory to teach another boy at the pool about ASCII binary. The boy actually seemed to find it interesting. A couple days later two older boys approached him at the local beach and told him that they knew who he was, that he was Simon who only talked about math. Then the boys ran away and Simon ran after them saying “Sorry!” We have explained to him that he doesn’t have to say sorry for loving math and for being the way he is.
Drinking a cocktail at the beach always comes with a little lecture. This time, the truth tables.
Community Projects, Computer Science, Group, Milestones, Murderous Maths, Notes on everyday life

Simon introducing himself for the World Science Scholars program

This is Simon’s introductory video for the World Science Scholars program (initiative of The World Science Festival). In May this year, Simon has been chosen as one of the 30 young students worldwide, joining the 2019 cohort for exceptional talents in mathematics. Most of the other students are 14 to 17 years old, age was not a factor in the selection process. To help the students and their future mentors to get to know one another, every World Science Scholar was asked to record an introductory video, no longer than 3 minutes, answering a few questions such as what is the biggest misconception about math, what your favourite branches of math and science are and who among the living mathematicians you’d like to meet.

Throughout the program, the students are given access to over a dozen unique interdisciplinary online courses and have the option to complete an applied math project, alone or as a team, consulting real experts in the field of their project. Simon has already started the first course module, on Special Relativity by Professor Brian Greene. The course has been specifically recorded for the World Science Scholars and reflects the program’s ethos: it’s self-paced, no grades, it relies on beautiful animations and visualizations, it’s full of subtle humour, is dynamic, thought-provoking and quite advanced (exactly in The Goldilocks Zone for Simon, as far as I could judge), yet broken up into easy-to-digest pieces. It’s difficult to predict how Simon’s path as a World Science Scholar will unfold (I’m afraid of making any predictions as he is extremely autodidact), but so far we have been very pleased with the nature of this program and it seems to match our non-coercive, self-directed learning style. I have especially liked one of the course’s main postulates: “Simultaneity is in the eye of the beholder”.

Simon watching Brian Greene’s Special Relativity course
Studying light clocks
Light clocks. Does the moving light clock tick slower?
Simon thinking about the question: Does the moving light clock tick slower?
Computer Science, Crafty, Electricity, Electronics, Engineering, Logic, Milestones, motor skills, Simon teaching

Simon building an 8-bit Computer from scratch. Parts 1 & 2.

Parts 1 and 2 in Simon’s new series showing him attempting to build an 8-bit computer from scratch, using the materials from Ben Eater’s Complete 8-bit breadboard computer kit bundle.

Simon is learning this from Ben Eater’s playlist about how to build an 8-bit computer.

In Part 1, Simon builds the clock for the computer
In Part 2, Simon builds the A register (more registers to follow).
these little black things are an inverter (6 in one pack), AND gate and OR gate (4 AND and OR gates in one pack)
this schematic represents the clock of the future 8-bit computer
Simon and Neva thought the register with its LED lights resembled a birthday cake
Coding, Computer Science, JavaScript, Simon teaching, Simon's Own Code, Simon's sketch book

Back to the sorting algorithms: Beadsort (and a short lecture about the generator function)

Link to the project:
Made my Beadsort step-by-step with a generator function! (Scroll down to see the “Next” button!) Code:
The video also contains a bonus tutorial about what a generator function is!
Coding, Computer Science, English and Text-Based Data, Python, Simon teaching

Encoding and Cracking Codes in Python

Had great fun learning how to crack codes using Python! Simon is currently following the Programming with Python course on and showed me how to see whether an encrypted piece is gibberish or a real text is hidden behind it.

Simon writes:

A Caesar Shift is a simple cipher, which was a standard in Roman times. It works like this: shift every character by some fixed amount in the alphabet. Something like this:

Example: Suppose some professor writes his name on his board:


It’s encoded with a caesar shift. Because it’s a professor’s name, it probably starts with “Dr.”, so it’s probably a shift that turns D into E, and R into S. So we can work backwards from that shift, and get:


That was an easy one, so let’s do something more complex with code.

One of the messages below is a real text, encoded using a Caesar Shift, the other one is just a random sequence of letters. Can you tell which one is which?

Text 1:
Text 2:

Simon has explained a way to see whether the encrypted piece contains meaningful (real) text: one can plot the frequency of each letter as it’s used in the encrypted piece. If all letters have generally similar frequency, it’s not a real text, because in real texts, certain letters are encountered much more often than others. Below are the frequency plots Simon made for the texts above, using a Python package called matplotlib:

Frequencies for text 1:

Frequencies for text 2:

As you can see, the second plot depicts a greater variety in frequencies. “For example, o appears the most, but g does not appear that much. And t does not appear at all!” Simon showed me.

As it turned out, we could actually use our knowledge about which letters naturally appear more frequently in English-language texts to crack the code! “Which letter is the most frequent one in English writing?” Simon asked me. “Letter e!” I guessed. “So now we know that the letter o in the encrypted text stands for e in the real text!” Simon exclaimed. “All we have to do to decode it now is simply shift the letters by 10 letters back, because e is 10 letters behind the o!”

Simon Writes:

So, what is the message about? Simon tweaked Brilliant’s code to make sure it shifted by the amount of 10…


…put the spaces and punctuation in appropriately…

I met a traveller from an antique land
Who said: “Two vast and trunkless legs of stone
Stand in the desert . . . Near them, on the sand,
Half sunk, a shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold command,
Tell that its sculptor well those passions read
Which yet survive, stamped on these lifeless things,
The hand that mocked them, and the heart that fed:
And on the pedestal these words appear:
‘My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!’
Nothing beside remains. Round the decay
Of that colossal wreck, boundless and bare
The lone and level sands stretch far away.”

So, it’s about Archeology! This is the poem Ozymandias by Percy Shelley (1818).

Source Code

Encoder / Decoder:

alphabet = "abcdefghijklmnopqrstuvwxyz"

# convert between letters and numbers up to 26
def number_to_letter(i):
    return alphabet[i%26]

def letter_to_number(l):
    return alphabet.find(l)

# How to encode a single character (letter or not)
def caesar_shift_single_character(l, amount):
    i = letter_to_number(l)
    if i == -1: # character not found in alphabet:
        return "" # remove it, it's spaces or punctuation
        return number_to_letter(i + amount) # Caesar shift

# How to encode a full text
def caesar_shift(text, amount):
    shifted_text = ""
    for char in text.lower(): # also convert uppercase letters to lowercase
        shifted_text += caesar_shift_single_character(char, amount)
    return shifted_text


message = """
paste the text here

code = caesar_shift(message, 2)

Code for Plots:

import matplotlib.pyplot as plt
alphabet = "abcdefghijklmnopqrstuvwxyz"

code = """
paste the text here

letter_counts = [code.count(l) for l in alphabet]
letter_colors =[0.8*i/max(letter_counts) for i in letter_counts]), letter_counts, color=letter_colors)
plt.xticks(range(26), alphabet) # letter labels on x-axis
plt.tick_params(axis="x", bottom=False) # no ticks, only labels on x-axis
plt.title("Frequency of each letter")