Donation machine result – success!

A more detailed version of this blog post has been featured on

This is a follow up to this blog post

It’s just over a year since the ‘donation machine’ was set up and it looks to have been a success as the index funds have increased in value by around 12% and has generated just over £30 in dividends.

So that’s been moved over from the brokerage to the bank account and then transferred to crisis. So if we use that £30 in their ‘societal return on investment‘ calculation (£30 * 3.3) this equates to an investment of £99.

Hooray! Humble beginnings but not a bad start at all. With the growth and adding some more funds to the pot, it should mean a larger round of dividends next time.

Comparing CRC32 to MD5 for use in Hash Tables

This is a follow on from the previous blog post about using a cyclic redundancy check (CRC32 in this case) to hash domain names to determine which database they should be stored on. More on that here.

Although CRC seems to work fine in the sense that it generated a completely unique hash codes it was not designed for that purpose. Instead, the focus of CRC is on error detection in data on storage devices and when transmitted over networks. I won’t go into it any further here as it’s explained very well elsewhere. On the other hand md5 was specifically designed as a hash function.

The question I had was whether MD5 was better at evenly distributing hashed values across a set of nodes. In a nutshell MD5 was better but not by a great deal and this was measured using a standard deviation and also by simply eyeballing the data (smaller min/max range in md5). If you look at the two graphs below, they each show 1 million domain names were distributed across a set of 64 databases and what you can see is that the groupings on the md5 graph are slightly more clustered around 15600 – 15700 but it’s nothing major and the crc32 does a reasonably good job.

MD5 Code

Both java and python implementations were made which are shown below and the larger repository can be found below.



Main repository with crc32 and md5 tests and results


I’ll be scrapping the CRC32 and using the md5 instead simply because that’s what MD5 was designed for and the distribution is slightly better. If you need any clarification or have any improvements to the code, please comment below.

Building a donation machine

A more detailed version of this blog post has been featured on

Please note that this is by no means a recommendation that you take this approach. It’s a method I have chosen to donate money.

While reading a part of American Psycho by Brett Ellis I took a break due to how grim it is. During that break, I started looking into homeless statistics and came across the Crisis website which is a charity that directly helps homeless people find a home and also campaigns for changes needed to solve homelessness altogether.

After browsing through the site and learning more, I spotted the Crisis investor page which discusses Social Return on Investment (SROI). This is a completely new to me but my understanding of it is that by donating money you are making an investment in society that yields dividends and/or savings. They have conducted research and are able to provide estimates on the savings a donation makes. It boils down to – for each £1 you invest, there is around £3.30 SROI.

This return on investment comes from the result of helping people find homes and providing them with support they need which makes it more likely that they will start paying taxes.

Conceiving the machine

This got me thinking of stocks and shares investments in relation to charities and after some thinking the idea of a set of shares that are dedicated to perpetually creating money for charity came to mind and is something I found very appealing.

How do shares generate money?

When you buy shares you are buying a piece of a business. Some companies distribute money to shareholders in the form of something called ‘dividends’. Dividends are usually paid out periodically (usually a few times a year). Although not all companies give dividends, many do and the dividend payout can fluctuate (just like the stock price) .

Building the core of the machine

Getting this off the ground with the basics involved:

  1. Opening a low cost brokerage account (just for charity donations)
  2. Deposit cash in the account
  3. Purchase some shares (UK Vanguard ETF’s)
  4. Set dividends to pay out to bank immediately
  5. Bank transfer them over to the charity once they arrive

I’m currently on step 4 so I’m just waiting for some dividends to be paid at the moment.

Why make this ‘machine’

It perpetually generates money

So the key benefit is that in theory it should perpetually generate money. Share prices go up and down but British companies are pretty good at paying out dividends and by buying an ETF (an ETF is like buying a share of a group of companies. So if you bought a FTSE 100 ETF, you would be buying a slice of every company in the FTSE 100. For more on ETF’s please read this) you are not relying on a single company continually dishes out dividends.

You can build on it

This simply means adding more cash to it. So by periodically buying more shares, the dividend payout should on average increase meaning there is more cash to donate.

You have a lump sum

There is a lump sum in the account that you can call upon if things go really really bad and you need cash. However, lets stay positive and go with the plan of never needing to touch it and letting it continue generating the cash for donation.

It should grow by itself

In addition to this share prices have historically increased over time so we should find that this machine generates more cash as time goes on.

Automating the machine

What I have so far is a good starting point, it gets the ball rolling and it is now only a matter of time before some dividends are paid, ready to be donated.

However, the end goal is to completely automate this whole process so that in a sense it is a truly automated machine that regularly makes and dispenses money to charitable causes with little if any involvement from me. So it behaves just like a direct debit but instead of a set amount each month, dividends are checked are paid out as soon as they arrive.

More on this next time.

Evenly distributing data on a group of MySQL databases

I recently read an article about the way pinterest save data. After some rapid growth, they experimented with a variety of setups (which did not work too well), they devised a simple (relatively speaking) system to save data across an array of MySQL databases. The idea behind this being that you could initially put all the databases on a single server and as demand grows, move these databases out to their own servers.

Part of this approach involved saving data for a specific URL. This involved doing a hash and running a modulus operation on a URL that returns a number between a certain value (e.g. 1 – 4096) to determine where the data would be stored for that URL. So for example, a hash would be ran on the string ‘’ and that would return 3 which would place it on db0003, ‘’ would return 2034 which would place it on ‘db2034’ and so forth. The idea around this being that data would be evenly distributed between the databases.

I’ve been thinking about a project involving saving large amounts of data in a distributed fashion and was quite taken by this because of it’s simple approach to sharding. However, how evenly data were distributed was something I wondered about. After some initial poking around, it seemed that crc32 was a good candidate due to it not being particularly resource intensive compared to md5 and sha*.

However, two questions sprang to mind:

* How evenly was distributed between the shards.
* Are there no discrepancies between the hash function

I was pretty sure the answers to the questions would be ‘quite well’, and ‘there are no discrepancies’ respectively but did some tests anyway. After all, the last thing we want is for one implementation to give a different result from another.

The test strings were ran on the majestic millions top domains and what the code does is create an array of all the shard id’s with each one initialized at 0. Then go through that majestic millions text file line by line and does a hash (and modulus) to get the shard id. Once the shard id is retrieved, iterate the array with the shard id’s by 1. The graph below shows the result of those hashes and shows how many domains each bucket has.

The x axis shows the shard id and the y axis shows the number of records in each shard. Click to embiggen

What we can see from eyeballing the graph it is that data are roughly evenly distributed between the shards. A few outliers here and there but most shards have between 100 and 140 items. Another script which compares the shard result of each implementation demonstrated there were no discrepancies either.

All code can be found here. Any questions, feel free to comment and I’ll get back asap.

Building a Clay Pigeon Remote (part 3): Precision cutting with milling machines

For the past few weeks I’ve considered purchasing a milling machine. These seem to be the best tool for modifying off the shelf enclosures in a non mass produced way. The primary reason for this is that they offer precision and allow for boring into metals and plastics in a variety of different ways.

They are relatively expensive tools for a hobby workshop, a typical pillar drill may cost around £100 (mine cost £120 and when matched up with a steppper drill bit it’s perfect for drilling button holes) but at a minimum a capable desktop milling machine is £800 which seemed quite surprising as my understanding of them is that they are essentially pillar drills with special drill bits and an adjustable base.

However, I’ve come to understand they are far heavier and sturdier machines. This is because a milling machine is required to apply pressure perpendicular to the drill rather than vertically is much more strenuous while at the same time maintain precision.I’m sure there is more to it than that and please feel free to comment and let me know.

I’ve bit the bullet and gone for the Draper variable speed mini mill as it should fit the purpose of cutting accurate shapes into enclosures for rectangular instruments such as lcd’s ad switches. and I look forward to putting it to the test. It should be here by mid April and at that point I’ll give the machine a try write up a review on here. I’m looking forward to it as it’s going to be quite an upgrade from a handheld Dremel!



Shutter Speed Tester

So first of all what is a shutter speed tester? It’s simply a tool that times how long a camera shutter (in the lens) is open for. This is not typically needed for newer cameras as they tend to be accurate. However, older film camera tend to loose their precision due to wear and tear, and exposure settings can be inaccurate. Using a shutter speed tester allows the photographer to gain a true measure of the shutter speed rather than using a trial and error process which can waste film.

The shutter speed tester has been quite a quick project primarily because it is relatively simple and and it was a case of making alterations to a project developed by c-s-1. These modifications essentially consisted of trimming it down and modifying it to work on a 2 x 16 screen and removing one of the buttons (an lcd light toggle).

The project is cased in a hammond stomp box enclosure (1590XX) and runs off a dc power supply. If you would like any further information about it to build your own, please get in touch and I’ll fill out the blog with further details.

Here are some potential questions and their corresponding answers

Q: Why is the tester is not picking anything up?

A: There are a few things that need to be checked.

  • Check the receiver and emitters are as close as they can be to the lens. If they are further than a few centimetres from each other the receiver may not pick anything up.
  • Check the wires are actually connected to the right sockets.

Q: The device is giving some random results and I have not used it yet.

A: After you have set it up, before actually using the device, click ‘reset’ it first. During setup the receiver and transmitter can get into contact and give off odd readings.


Links index


Building a Clay Pigeon Remote (part 2): Comparing 3D printed and premade enclosures

This blog post is essentially a recount of my experiences trying out 3d printing to make enclosures and may be useful to read if you’ve never made an enclosure before and are thinking about whether to take the 3d printed (printing a box) or ready made route (machining an existing metal box).

When I first started out working with enclosures I typically purchased a handheld enclosure and drilled or cut out each section for the buttons, cable gland, lcd or whaever else warrented the enclosure being cut into.

Due to having few tools and almost always having to make do, the end result always looked terrible with major flaws that really stuck out. Shortly after my first few initial attempts, 3d printers started coming into the mainstream and becoming affordable. I thought this was fantastic, I’d just have to do some CAD designs and the printer would magically produce the thing (I ended up going for the wanhao I3).

It ended up not being quite like that. The CAD software took a couple of weeks to get my head around (Freecad) which is fair. However, while I made some suitable enclosures, they took hours, sometimes days for the printer to produce and if there were any mistakes the whole thing needed to be redone.

This is the latest example – this is a rotatable model so you can use your mouse to zoom in and out.

The same problem found with enclosures arose again – the quality was not great and after messing up screw inlays multiple times I finally decided it was not suitable. The whole thing seemed too fragile and the amount the filament and electricity cost would come to the same price as a solid aluminum enclosure by Hammond which would be rock solid. That’s not even taking into account the time it takes to built the thing.

So, what next … do a 180 and go back to enclosures.

I knew the issue was precision so after browsing youtube it looked like the way to go was to either have it machined at a manufacturer (expensive and only worth it if you do 100+ enclosures) or draw a stencil, print it out and overlay it on the enclosure. I chose the latter

The next step is cutting out the sections now that the stencil is on. 90% of the sections to be cut were circles. I went all out and bought a pillar drill along with a step drill bit. The pillar drill combined with the stencil and a vice would give the most precision. The only thing better would be a cnc machine (low end models which drill into metal are a few thousand pounds from what I can gather) or sending it off to a fabrication company.

The only time I’d reccomend using a 3d printer is for for smaller components such as mounts. That is if you have a low to mid range printer.

Here’s the latest result which is a clay pigeon remote. As you can see, the sections drilled out are mostly circles (where the pillar drill and step drill bit come into play). Wheras a dremel with a ‘speedclic metal saw’ was used to drill out the square for the lcd.


Building a clay pigeon remote using open hardware (Intro)

A few years ago, myself and a friend purchased a trap from a shooting school that was closing down (North Yorkshire Shooting School).  It came with a basic button switch that released the traps which in essence did the trick in that it released the clays. Nice and simple.

However, we thought about a remote one which allowed for delays, preprogrammed sets and randomly thrown sets. After some searching online we quickly found out these were quite expensive which prompted me to look into alternatives.

As I’d had a play with Arduino microcontrollers before it seemed like the perfect project to learn more about the device and hopefully create a complete product that does the basics but has bells and whistles too.

It’s quite close to being complete now so I thought I’d do a few blogs about some of the key steps involved in its development to demonstrate the progression and hopefully knock out some useful information for anyone interested in developing their own devices. So stay tuned!

Move your projects out of the basement

Lets start off with keeping projects out of the *basement and by that I mean preventing projects from being hidden away and only accessible and used by yourself.Do read on if the following sounds familiar:
  • Start project
  • Finish it (get it to a state where it does what you want)
  • Start using it in some capacity for yourself.
  • Briefly contemplate promoting it but: make excuses that it needs more work, shrugging, hiding under your desk.
  • Start a completely new project

I have a few tips listed below which can help get the project out there. They’re all points I keep in mind personally too.

The project itself

Decent Readme

The first is to write a decent readme explaining what the software does and ideally has all the key stuff like how to contribute, how to ask for help and so forth.

Get them up and running as quickly

Ideally a standalone exe or a single command such as pip install example or apt-get install example. Go on the assumption that a user is mildly interested and may give an installation attempt a few minutes (if you’re lucky) and outline this with in a quickstart heading in the readme.

Getting it out in the open

Find forum posts where people are asking questions.

Think of what questions a user would ask that would lead them to your project. The more specific the better. For example, with the MRISA project I literally googled ‘reverse image search api’ found a user asking for one on stack overflow and popped. Basically all the traffic comes from that post and the project has around 80 stars and multiple contributions. Not bad for 5 mins of ‘marketing’!

The real trick though is to make sure what you are posting is genuinely helping. If you just randomly or insensitively plug your project, it’s going to upset people and backfire.

Submit your project to relevant sites

If your project uses an api, library or has any other dependancy, check the sites and see if they have a place to submit projects.For instance, digitalocean has a projects page which I recently had a project accepted on. The worse they can say is no (I say that as though it’s such a little thing!) and if they come back with suggestions it’s a win because you know what to improve.

I think those four points are particularly useful as they are quite fundamental, should be quickly and easily achievable but have the potential to provide high returns(plenty of visits and users) for minimal investment (takes relatively litte time to implement).

Agree/disagree, have something to add? Let me know in the comments section. Thanks for reading!

* I literally keep my projects on a 1u server in the basement running gogs. But I’m gradually starting to push things onto github

Monitoring your DNS records

Sometimes DNS servers just drop hostnames for a variety of reasons. Perhaps a customer forgets about a bill and their DNS records are wiped or there is an edit to a record, it’s not quite right and needs to be reverted and so on.

In an ideal world this would never happen but it does seem to every now and again. In most cases, this can be recovered but it can be a pain and also time consuming.This is where DNS Historian comes in – an applicaton which monitors and records DNS changes. It also provides an http api to new hostnames can be added and existing ones can be queried.  To find out more, check out: