Ciro Santilli @cirosantilli 37

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Amplifier Updated 2025-07-16

Main implementations: the same as electronic switches: vacuum tubes in the past, and transistors in the second half of the 20th century.

Video 1.

How to make an LM386 audio amplifier circuit by Afrotechmods (2017)

Source. Builds the circuit on a breadboard from minimal components, including one discrete transistor. Then plays music from phone through headset cables into a speaker.

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Ciência sem Fronteiras Updated 2025-07-16

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Matthew Heaney Updated 2025-07-16

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github.com/matthewjheaney

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tcpdump Updated 2025-07-16

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To test it, let's get two computers on the same local area network, e.g. connected to Wi-Fi on the same home modem router.

On computer B:

find computer IP with the ip CLI tool. Suppose it is 192.168.1.102
then run Ciro's nc HTTP test server

On computer A, run on terminal 1:

sudo tcpdump ip src 192.168.1.102 or dst 192.168.1.102

Then on terminal 2 make a test request:

curl 192.168.1.102:8000

Output on terminal 1:

17:14:22.017001 IP ciro-p14s.55798 > 192.168.1.102.8000: Flags [S], seq 2563867413, win 64240, options [mss 1460,sackOK,TS val 303966323 ecr 0,nop,wscale 7], length 0
17:14:22.073957 IP 192.168.1.102.8000 > ciro-p14s.55798: Flags [S.], seq 1371418143, ack 2563867414, win 65160, options [mss 1460,sackOK,TS val 171832817 ecr 303966323,nop,wscale 7], length 0
17:14:22.074002 IP ciro-p14s.55798 > 192.168.1.102.8000: Flags [.], ack 1, win 502, options [nop,nop,TS val 303966380 ecr 171832817], length 0
17:14:22.074195 IP ciro-p14s.55798 > 192.168.1.102.8000: Flags [P.], seq 1:82, ack 1, win 502, options [nop,nop,TS val 303966380 ecr 171832817], length 81
17:14:22.076710 IP 192.168.1.102.8000 > ciro-p14s.55798: Flags [P.], seq 1:80, ack 1, win 510, options [nop,nop,TS val 171832821 ecr 303966380], length 79
17:14:22.076710 IP 192.168.1.102.8000 > ciro-p14s.55798: Flags [.], ack 82, win 510, options [nop,nop,TS val 171832821 ecr 303966380], length 0
17:14:22.076727 IP ciro-p14s.55798 > 192.168.1.102.8000: Flags [.], ack 80, win 502, options [nop,nop,TS val 303966383 ecr 171832821], length 0
17:14:22.077006 IP ciro-p14s.55798 > 192.168.1.102.8000: Flags [F.], seq 82, ack 80, win 502, options [nop,nop,TS val 303966383 ecr 171832821], length 0
17:14:22.077564 IP 192.168.1.102.8000 > ciro-p14s.55798: Flags [F.], seq 80, ack 82, win 510, options [nop,nop,TS val 171832821 ecr 303966380], length 0
17:14:22.077578 IP ciro-p14s.55798 > 192.168.1.102.8000: Flags [.], ack 81, win 502, options [nop,nop,TS val 303966384 ecr 171832821], length 0
17:14:22.079429 IP 192.168.1.102.8000 > ciro-p14s.55798: Flags [.], ack 83, win 510, options [nop,nop,TS val 171832824 ecr 303966383], length 0

TODO understand them all! Possibly correlate with Wireshark, or use -A option to dump content.

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Telomere Updated 2025-07-16

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grep Updated 2025-07-16

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If you are a programmer, grep becomes a verb: "to grep" means "to search text files", much like "to Google" means "to search random stuff online".

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Analog computer Updated 2025-07-16

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Some of the earlier computers of the 20th centure were analog computers, not digital.

At some point analog died however, and "computer" basically by default started meaning just "digital computer".

As of the 2010's and forward, with the limit of Moore's law and the rise of machine learning, people have started looking again into analog computing as a possile way forward. A key insight is that huge floating point precision is not that crucial in many deep learning applications, e.g. many new digital designs have tried 16-bit floating point as opposed to the more traditional 32-bit minium. Some papers are even looking into 8-bit: dl.acm.org/doi/10.5555/3327757.3327866

As an example, the Lightmatter company was trying to implement silicon photonics-based matrix multiplication.

A general intuition behind this type of development is that the human brain, the holy grail of machine learning, is itself an analog computer.

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Google BigQuery Updated 2025-07-16

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KEGG Updated 2025-07-16

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www.genome.jp/kegg/pathway.html

For a commented initial example, see: e. Coli K-12 MG1655 gene thrA.

KEGG does the visual maps well.

But BioCyc is generally better otherwise.

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