## Posts

### We as a society need to start wearing masks or this won't stop

Things will not start getting better until the infection slows down. That won't happen until either most people are infected or people start wearing protection in the limited social interaction: grocery shopping, essential working, etc.

For various reasons, the CDC has recommended people to not wearing masks. However, things are changing and there are more evidence now that masks helps:
Masks can reduce the amount of droplets you inhale and contact with your mouth and nose. It is never one virus that get you sick, it is the amount of virus that matters, reducing the amount of droplets will reduce the risk.There are more people infected every minutes and it grows exponentially, and most of infected people are asymptomatic. That means everyone, me and you, or anyone you come to contact remotely, however healthy one looks, can actually be infected and contagious. Masks protect others.Masks shows you care, and can be a sign of safety. If you have to take take-outs or food delivered, do…

### How many Starlink satellites will you see?

How many Starlink satellites will you see?

According to the current plan, there will be ~12000 satellites on 3 orbital shells on height 340km, 550km and 1150 km.

For estimation, it is good enough to assume the satellites will more or less evenly spread on each orbital shells.

We need to calculate how many will be visible to one point on the ground for satellites on each shells.

In the diagram left, the inner circle is the Earth. For all the satellites on the orbital shell h away from the ground, a person on the ground can see all the ones from the blue cap.

So the ratio of visible to all satellites are the ratio of area of the blue cap to the area of the sphere.

With  $h =\text{height of orbit}$ and $r = R_{earth} + h$

We have the ratio of visible satellites to all satellites on the same orbital shell:

$=\frac{2\pi r h}{4\pi r^2}=\frac{h}{2 r} = \frac{1}{2}\frac{h}{R_{Earth} + h}$

With the number from the current plan:

orbital shellHeight#% visible# visible155016003.97%642115028007.65…

### 5 secs fact check: does data center use more electricity for cooling than for computing?

No.

Let's assume the energy used in datacenter are from 2 parts: computing(including all the power from the servers) and cooling.

We know that for a cooling system(at least a decent one), the energy need to move the amount of heat:

$W = qQ = T_{low} / (T_{high} - T_{low}) Q$

where q is the efficiency of the system, and almost always > 1 (only if the outside temp$T_{high}$ is extremely high already or we want to cool the system to super low temperature($T_{low}$); neither is true for data center)

so no, for all the electricity we use for computing, it all turns into heat, and to move that heat out, we always use less than that energy.

Go to your Tesla account at https://www.tesla.com/teslaaccount/settings

Click contact, it will expand and you can set your secondary contact.

Click edit, fill the form including the email address and you can see a new checkbox "Give access to secondary contact"

Check that and save, you will receive an email for setting up your account!

After click reset password and reset it, you can now log in with the new email and have the same access!

You can use my referral link to get 1,000 free Supercharger miles on a new Tesla: https://ts.la/bingyan18312

### The realistic guide to safer Autopilot, with model and back-of-envelope calculation.

TL;DR1: for people new with Autopilot: how to use it safer.
TL;DR2: for Autopilot safety: One argument is that Autopilot gives people false sense of safety, leading people to be less attentive, which may make it less safe than without. Let's see if that stands by check how much less attentive people can be with Autopilot to get the same accident rate.
Intro One reason Tesla owners are spoiled and never want to go back to non-Tesla car is Autopilot. It is such a great experience to drive with Autopilot. It can make daily commute way more enjoyable, and make long road trip relaxing instead of tiring.

I got my Long Range RWD Model 3 May 2018 and have driven it for more than 13k miles. My commute is around 25 miles each day, 90% of them on crowded US-101. Autopilot make it extremely relaxing. All I have to do it drive on the highway, get onto the carpool lane, turn on Autopilot and then relax till the car move it self to the highway exit and slows down, then take over. …

### Tesla Autonomous day, from a AI engineers' perspective

TL;DR Great progress from Tesla. Tesla is probably in par or even ahead of other self-driving company. However, L5/RobotTaxi is still very far away.
Summary Tesla's Autonomous Investor day talk is very interesting, to say the least. A weird ~1 hour loop video, followed by 2 amazing talks full of tech details about AI chip design and deep learning system from Pete Bannon and Andrej Karpathy, then one hour of unrealistically ambitious RoboTaxi picture from Elon.

The stock market sunk significantly in the following days, partially because of the recent fire in Shanghai, which is totally unnecessary, and partially because of the disappointing financial report, and in my understanding, partially because of the revenge from the investors who feel stupid of themselves after attending an unexpected tech talk they probably understand only 1%.

Jokes aside, the tech talks are awesome. It shade lights on lots of details and progress about Tesla's self driving work, and probably place Tes…

### Tesla new Browser capabilities!

Tesla updated the in car web browser in update 2019.12.11.1. Overall, the impression has been great from the owners. People start to try to do crazy things on it, trying out video conferences, remote desktop, you name it.

Today, I will look into the tech details of it, and its API and capabilities!

First thing first, here is the UserAgent string of the browser.

Mozilla/5.0 (X11; GNU/Linux) AppleWebKit/537.36 (KHTML, like Gecko) Chromium/73.0.3683.101 Chrome/73.0.3683.101 Safari/537.36 Tesla QtCarBrowser
This is a Chrome(Chromium to be more precise), and it is pretty recent 73. BTW, looks like Tesla's UI is based on QT framework!

Next thing, we checked the HTML5 features this browser support. Here is the result.

TL;DR is, this is better score than Chrome on Mac OS!

The significant missing ones are:

MPEG4, H264, H265 codecs. This is why Youtube/Netflix is not working, and we are seeing the no-codec error code on Tesla on YoutubeWeb Authentication / FIDO 2ObjectRTC API for WebRTCWeb N…