Wishful Coding

Didn't you ever wish your computer understood you?

Google Summer of Code is excluding half the world from participating

I recently came across someone who wanted to mentor a Yosys VHDL frontent as a Google Summer of Code project. This sounded fun, so I wrote a proposal, noting that GSoC starts before my summer holiday, and planning accordingly. Long story short, there are limited spots and my proposal was not accepted. I have confirmed with the mentoring organization that my availability was the primary factor in this.

While I understand their decision, it seems odd from an organizational viewpoint. Surely others would have the same problem? Indeed I heard from one person that they coped by just working ridiculous hours, while another said they never applied because of the mismatch. Google seems to be aware that this is an issue, stating in their FAQ:

Can the schedule be adjusted if my school ends late/starts early? No. We know that the schedule doesn’t work for some students, but it’s impossible to make a single timeline that works for everyone. Some organizations may allow a participant to start a little early or end a little late – but this is usually measured in days, not weeks. The monthly evaluation dates cannot be changed.

But how big is this problem, and where do accepted proposals come from? I decided to find out. Wikipedia has a long page of summer vacation dates for each country, and there is also this pdf which contains the following helpful graphic.

holidays holidays

Most summer vacations are from July to August, while GSoC runs from May 27 to August 19, excluding most of Europe and many other countries from participating. (unless you lie in your proposal or work 70 hours per week)

The next question is if this is reflected in accepted proposals. Since country of origin is not disclosed, this requires some digging. I scraped a few hundred names from the GSoC website, and scraped their location from a Linkedin search. This is of course not super reliable, but should give some indication.

      1 Argentina
      5 Australia
      1 Bangladesh
      6 Brazil
      1 Canada
      1 Chile
      7 China
      1 Denmark
      3 Egypt
      5 France
      9 Germany
      2 Ghana
      4 Greece
      2 Hong Kong
    212 India
      4 Indonesia
      1 Israel
      4 Italy
      2 Kazakhstan
      2 Kenya
      1 Lithuania
      2 Malaysia
      2 Mexico
      1 Nepal
      2 Nigeria
      1 Paraguay
      1 Peru
      3 Poland
      1 Portugal
      2 Qatar
      4 Romania
      4 Russian Federation
      1 Serbia
      4 Singapore
      1 South Africa
     10 Spain
      8 Sri Lanka
      2 Sweden
      2 Switzerland
      1 Tank
      2 Turkey
      4 Ukraine
      2 United Arab Emirates
      1 United Kingdom
     78 United States
     70 unknown
      1 Uruguay
      1 Uzbekistan
      3 Vietnam

Holy moly, so many Indians(212), followed by a large number of Americans(78), and then Spain(10), Germany(9), and the rest of the world. No Dutchies in this subset. For all European countries I counted a combined 51 participants, still a reasonable number. Even though Spain and Germany have the same holiday mismatch as the Netherlands. Tell me your secret! Interestingly, Wikipedia states that India has very short holidays, but special exceptions for summer programmes:

Summer vacation lasts for no more than six weeks in most schools. The duration may decrease to as little as three weeks for older students, with the exception of two month breaks being scheduled to allow some high school and university students to participate in internship and summer school programmes.

Anyway, I think a big international company like Google could try to be a bit more flexible, and for example let students work for a subset of the monthly evaluation periods that align with their holiday.


To scrape the names, I scrolled down on the project page until I got bored, and then entered some JS in the browser console.

Array.prototype.map.call(document.querySelectorAll(".project-card h2"), function(x) { return x.innerText })

I saved this to a file and wrote a Selenium script to search Linkedin. Likedin was being really annoying by serving me different versions of various pages with completely different html tags, so this only works half of the time.

from selenium import webdriver
from selenium.common.exceptions import NoSuchElementException
import json
import time
from urllib.parse import urlencode

with open('data.json') as f:
    data = json.load(f)

driver = webdriver.Firefox()

username = driver.find_element_by_id('login-email')
password = driver.find_element_by_id('login-password')
sign_in_button = driver.find_element_by_id('login-submit')

for name in data:
        first, last = name.split(' ', 1)
    except ValueError:
    if last.endswith('-1'):
        last = last[:-2]
    params = urlencode({"firstName": first, "lastName": last})
    driver.get("https://www.linkedin.com/search/results/people/?" + params)
        location = driver.find_element_by_css_selector('.search-result--person .subline-level-2').text
        print('"%s", "%s"' % (name, location))
    except NoSuchElementException:
        print('"%s", "%s"' % (name, 'unknown'))

And finally some quick Bash hax to count the countries. (All US locations only list their state)

cat output.csv | cut -d\" -f 4 | sed "s/Area$/Area, United States/i" | awk -F, '{print $NF}' | awk '{$1=$1};1' | sort | uniq -c
Pepijn de Vos

The only good open source software is for software developers

The rest is all inferior clones of commercial software.

When I think of really high-quality open source software, 90% of it are compilers, databases and libraries. Tools for software developers by software developers. There are exceptions (Firefox comes to mind), but as they say, the exception proves the rule.

Outside commercial projects that happen to be open source (Android comes to mind), open source software is largely driven by a “scratch your own itch” mentality. However, this poses a problem when software developers don’t have the itch, and people with the itch are not software developers.

I have recently begun to see the world from the perspective of academia and electrical engineering, and it came as a bit of a shock to me how many of the tools that are in common use are bloated commercial Windows GUI software, compared to nimble open source command-line tools I was used to.

Many of them cost hundreds if not thousands of Euros, take up gigabytes of RAM and storage, are a pain to use, and are still the best or only option available. I can only imagine the horrors of working in a non-tech industry.

I don’t think there is an easy solution. If I’m solving a problem for someone else, I probably want to get paid. So it seems the only plausible model is commercial software that happens to be open source.

The other option is either teaching people with an itch to code, or make people who code have the itch. Broaden your interests, y’all!!! </rant>

Pepijn de Vos

LM13700: Voltage Controlled Everything

When making a modular synth, everything has to be voltage controlled. So how do you make a voltage controlled amplifier, a voltage controlled oscillator, or a voltage controlled filter? One way is with an operational transconductance amplifier.

The LM13700 is like a swiss army knife of voltage control. Its datasheet is completely packed with refference circuits for voltage controlled everything. To get familiar with its operation, I built a few of the circuits on breadboard.

Voltage controlled amplifier

Basically an OTA is like an opamp with current output, but it’s frequently used without feedback. To make the differential pair more linear, biasing diodes are used at the input. But the linear range is still limited to a few dozen millivolt. What makes it voltage controlled is that the current gain is controlled by IABC, which is the tail current of the differential pair.

For my test circuit I hooked the current gain up to a button with an RC network connected to it, so it does a nice attack and decay when pressed and released.

State variable filter

Then I fed the output of my VCA into this beautiful state variable filter. What is cool about state variable filters is that they can have low-pass, high-pass and band-pass outputs from the same signal. Each OTA basically forms a Gm-C filter. Put simply, a resistor’s current depends on the voltage you put on it, and so does the current of the OTA depend on its input voltage.

For the above video, I output white noise and a low-frequency sine from the MyDAQ. The white noise goes through the VCA controlled by my RC button envelope, and through the band-pass output of the state variable filter, controlled by the slow sine wave.

Pepijn de Vos