In the previous blog we introduced the various types of signals present in a digital control system and highlighted the pros and cons. In this blog we take a a closer look at the digital control system.
A digital control system, can only cope with digital signals. That is because it is inherently discrete in time and space. This is caused by the processors clock rate and due to the finite word length of a digital system. For instance, a 32 [bit] computer which runs at 4 [GHz] has a time resolution of 0.25 [ns] and the value of an unsigned integer can only range from 0 to 232 − 1.
Figure 1 shows the digital control system in its most elementary form. Herein is the sampler. The sampler converts the analog output signal of the plant at time to a digital measurement signal at discrete-time . As mentioned in the previous blog, the digital signal is obtained by sampling and quantization of the analog signal. In final, denotes the recronstructor, also known as a digital-analog convertor (DAC), it converts the digital control signal provided by the controller to an analog control signal .
Figure 2 shows that the sampler exists out of two devices namely; i) a sample and hold (SH) device and ii) a analog-digtal convertor (ADC).
The SH device knows two different states. The first state is called the track state at which the analog input signal is tracked by the SH device. The track state is also refereed to as sample state. However because of the ambiguous meaning of the word sample we will use the track, which is also commonly used in literature. The second state is called the hold state at which the analog input signal is being kept constant for a short period of time. The hold state is activated when the hold command is given. During the hold state the ADC is able to process and digitize the signal. The hold command can be triggered by any logic device. While there are many more aspects and subtleties to be considered with a SH device this gives a summarized overview of its functionality.
Various different strategies exists at what time instance the hold command is triggered. These are called sampling strategies.
Periodic sampling; the sampling instances are equally spaced, that is to say with and , given in [s], being the sampling period. See also Figure 2(a). The sampling period is often also denoted as the sampling rate or sampling frequency , given in [Hz]. It is related to the sampling period by .
Multi-order sampling; a pattern of sampling instances are repeated periodically, as a result . See Figure 2(b).
Event-based sampling; the sampling instances are generated based on a event in the system. For instance, when a certain measurement threshold has been crossed. See Figure 2(c) in which the signal is sampled at every value.
Random sampling; the sampling time instances are chosen at random, see Figure 2(d).
Periodic sampling is the most common in industry. That is because of several reason; i) most deterministic behavior, ii) extensively been researched, iii) easiest to model and iv) easiest to obtain key performance indicators, for instance, in time- and frequency domain. Finally, proofing stability for the other sampling strategies is much harder then for periodic sampling.
Digital control systems never did get enough attention during my Master System & Control in my opinion. In the various courses which I was taught, continuous-time control systems were always examined, but almost never digital control systems. For most courses this is also perfectly fine. However, you would expect that there would be also a more in-depth course about digital control systems into the curriculum. Especially, since almost all control systems are a digital control system.
I remember a course in which each group had to program a robot to convey pizza’s from one cabinet to another. A group mentioned, during their presentation, that they used a PID controller to control the various axis of the robot. I knew all the groups had designed their control algorithms in the continuous-time domain, therefore I asked; i) what discretization method(s) they had used, ii) if they had check the stability and iii) if they had checked the robustness (phase, gain and modulus margin) of their digital control system with respect to the continuous-time domain controller. Unfortunately none of my questions were answered. This disappointed me and was an acknowledgement of my opinion that not enough attention was given to digital control systems. Since this was one of the last courses given before one started their internship and graduation.
For the above reason, I will do a couple of blogs about digital control systems. I will try to focus on a single topic each blog and keep it clear and easy to understand; “If you can’t explain it simply, you don’t understand it well enough.”. In this first blog I will briefly go into the pros and cons of digital control systems and its analog counterpart. Followed by the introduction of the various type of signals that are present in a digital control system.
Pros and cons of digital control systems
Below is a list of pros and cons for both digital as well as analog control systems. Remark that there might be many more and that some pros or cons are subject to opinion, experience or interpretation.
Robust; do not (often) break down
Continuous processing; no inherent bandwidth limits
Hard to modify; time-consuming, hardware needs to be rebuilt
Flexible; ability to create complicated controllers, easy to modify and fast to develop, less susceptible to aging and environmental variations
Robust; performance or safety can be monitored, errors can be dealt with appropriately
Diagnostics; on-the-fly testing, parameters can be adjusted, measurement signals can be stored
Slow development; difficult to develop accurate designs due to tolerances in components
Complex: difficult to create complicated controllers, also hard to modify, testing alternatives is difficult, hard to build in intelligence, difficult to do multi-input-multi-output control
Discrete; signal might be inaccurate due to finite word length, time delays in control loop, discrete controller, stability might be an issue
Complex; complicated controllers, difficult to obtain a high bandwidth
While analog control systems have considerable disadvantages the flexibility of digital control systems stands-out. The latter made sure that companies adopted digital over their counterpart because it opened multiply doors. For instance, the rapid development of a complex controllers which incorporated optimization algorithms to maximize performance and profit. All created at the tenth of the costs for the same analog control system.
Types of signals in a digital control systems
The main disadvantage of digital control systems is found in the fact that one has to deal with discrete variables instead of continuous ones. Consequently, let us define the different types of signals. A Continuous-time signal is a signal for which every point in the time domain, this can be infinitely, an amplitude is defined. Similarly, a discrete-time signal is a signal for which only a sequence of points in time an amplitude is defined. Note that these points in time do necessarily have to be equidistant. In case it is, the signal has an associated periodic interval. Likewise to the domain, signals may also be continuous or discrete with respect to their range, i.e., amplitude.
Summarized; in general signals can either be continuous or discrete with respect to their domain or range. Herein, the domain is in general time, in case of control systems and the range can be anything; Voltage, Amperes, Newtons, meter per second, et cetera. Figure 1 shows the four possible combinations.
In Figure 1(a) an analog signal is displayed, which is both continuous in time and amplitude. Figure 1(b) shows a sampled signal; continuous in amplitude and discrete in time; Figure 1(c) the quantized signal, discrete in amplitude and continuous in time. Finally Figure 1(d), the digital signal. This signal is both discrete in time and amplitude. Remark: the exact definition of a quantized signal and sampled signal are often ambiguous. Often it is implicitly assumed that a quantized signal is also sampled, e.g., discrete in time. Likewise, the sampled signal is sometimes in explicitly assumed to be quantized as well. Lastly, the digital signal can be obtained by sampling and quantization of the analog signal.
We have read about the pros and con, and defined the different signal types present in a digital control system. Conclusively, I want you to point to the books in the references below, these are the best literature references in this field. I also use them as a reference for these blogs, and will try to point or refer to a chapter or section from the book when addressing a certain topic. In the next blog we will focus on the different system components of a digital control system.
 Levine, William S., ed. “The Control Handbook: Control System Fundamentals”. CRC press, 2010.
 Åström, Karl J., and Björn Wittenmark. “Computer-controlled systems: theory and design”. Courier Corporation, 2013.
 Franklin, Gene F., et al. “Feedback control of dynamic systems”. Vol. 3. Reading, MA: Addison-Wesley, 1994.
 Wittenmark, Björn, Karl Johan Åström, and Karl-Erik Årzén. “Computer control: An overview”. IFAC Professional Brief, 2002.
 Ogata, K. “Discrete-Time Control Systems”. Pearson Education, 1995.
At some point one you will want to keep track of your expenses to gain insight where you can save money. There are many websites and programs which offer insight into your expenses, for instance, YouNeedABudget, MoneyDashboard, GNUCash. However, for following three main reasons I decided to simply create my own expenses spreadsheet using Microsoft Excel.
The programs often have a learning curve and you have to adapt to their way of working.
I wanted to use a tool of which I can be almost certain that it will still exist in +20 years.
Sometimes you will find yourself in the spot in which you want to have insight into some details. But, unfortunately these are not (directly) provided by the tool. Therefor I wanted to be able to program myself to gain insight. However, this still should be fairly simple to do.
Now let me tell you what my spreadsheet provides. Since I wanted to categorize my expenses I created one sheet with categories and subcategories. To keep track of all the transactions, a table was created in which all main transactions details are logged. The table has the following fields: bank account, type of account (saving or payment?), date, type (income or expense?), amount, currency, kind (variabel or fixed?), category, subcategory and remarks. While there is a currency field, it is not used yet. The with main reason for this is because fortunately I do not have to deal with money different currency types. To gain insight into the data from the table, three pivot tables and charts were created. Using the pivot tables and charts, which are semi-interactive, one is able to, for instance, zoom-in in a particular category or time stamp. To finalize, I created a kind of dashboard in which all income and expenses data is summarized per month. First details are displayed about my balance of my payment and savings account. Followed by all the expenses details, sorted by category. Using the outline group functionality one is able to open the category and list the subcategories for that month. For each category and subcategory I show its portion (in percentage) with respect to all expenses, the median per month and the average per month. Using conditional formatting this data is also visualized to give a overview, such that you are able to identify the ratios and relationships quickly. sparklines are being used to show the trend of the expenses through out the year. Concluding, the dashboard sheet makes sure that all the data and details are visible at one glance but still manages to dive into details.
Codenames is played between two teams, red and blue on a set of twenty-five codenames. Each team consists of a single spymaster who knows the secret identity behind each codename, with the remaining players as field operatives who will contact the codenames. On each turn of the game, the spymaster provides a clue to their field operatives. The field operatives will then attempt to contact at least one of their aligned agents based on the codenames clued. The first team to activate all of their agents wins the game!
Codenames is an interesting game since it can be adapted to a variaty of themes. For instance, it can be themed to Harry Potter. As such it is also a very good game to be played with children. Therefor, I created an excel file(Update 2017-04-30: I updated and added two additional word lists to the file; i) the official word list and ii) an extensive noun word list. Download here) from the original game which includes all the necessary items for the basic game:
Codenames (two categories, general and Harry Potter)
You can print these on sheets of paper and cut them out. Now follows a set of detailed instructions for playing the game.
Players are divided into two teams, Red and Blue. Each team consists of one spymaster, with the remaining players as field operatives. All players observe a set of twenty-five words, representing codenames for agents aligned with each team. While field operatives do not observe the identities of each of the codenames, the spymasters each get to see the identity of all codenames on the map card.
There are four different agent identities: red agent, blue agent, bystander, and assassin. One of the teams will have nine of their-colored agents in the set of codenames, while the other team will have eight agents. The team with nine agents will take the starting turn in the game. Among the eight codenames not aligned with either team, there are seven Bystanders and one Assassin. Effects for contacting these agents are described in the following section.
On a team’s turn, their spymaster must start by providing their field operatives with a clue for the identities for their own agents. A clue consists of a single word and a number. The word should be related to the codenames that are aligned with the acting spymaster’s team, while the number represents how many codenames are related to the clue word. Further guidelines, including two special number rules, follow in the section below.
Once a clue has been given, the field operatives are free to discuss which codename(s) should be contacted. When the field operatives have decided on a guess, they may register their guess by touching the codename. The host or spymaster will reveal the identity of the codename by putting an identity card (Red Agent, Blue Agent, Bystander or Assasin) on top of it.
If the revealed agent is of the same team as the operatives, then they may continue making guesses. A maximum number of guesses may be made equal to the number given in the spymaster’s clue, plus one. Alternatively, the field operatives may pass to end their turn, so long as they have made at least one guess already on their turn. If the revealed agent is not of the same team, then the turn ends. In the special case that the assassin was revealed, then the team that performed the reveal immediately loses the game.
Spymaster Clue Guidelines
Spymaster clues consist of a single word and a number, with the following guidelines:
Words must be related to the meaning of the codenames being clued.
The number following the word cannot be used as a clue itself.
Clues may not include codenames or related forms of codenames. For compound codenames, this includes the constituent words that comprise the compound word. Once a codename has been guessed, it can be used in clues.
Overall, be reasonable about rules; spymasters may consult with their opposing spymaster and the host for the validity of a clue. If an invalid clue is provided, then the turn immediately ends and the opposing spymaster may declare an agent of their own color before making their own clue.
Spymasters have two special options for numbers associated with their clue words. First, spymasters may declare zero (0) as their clue, suggesting that none of the codenames are related to their declared word. In the case that zero is declared, the field operatives do not have a limit to the number of guesses that they may make before passing. The second special option is to declare “unlimited” as their clue, suggesting at least one codename is related to the declared word. As with zero, the number of guesses that may be made by field operatives before passing is unlimited.
The United States navy developed in the 1950’s a program evaluation research task (PERT). It was designed to analyze the duration of a project and the tasks within the project. Each task in the project is given the following properties:
Name of the task
Predecessor, the list of tasks that have to be completed before the task can start.
The amount of time it will take for a task to be finished.
The duration of a task is often not fixed. It can vary between a minimum and maximum. The PERT distribution was created to give a good estimate of what the probability is of the duration of a task. It uses the same three parameters as the Triangular distribution, namely, the minimum (), the most likely () and the maximum (). The probability density function (PDF) is given by
being the mean.
An additional shape parameter might be added, in which case we are dealing with the modified PERT (MPERT) distribution. The parameter influences the peakness of the distribution. The only difference with PERT is the definition of and . These are namely defined as:
I created some Matlab code which includes functions for the PDF, the (inverse) cumulative distribution function (CDF). The inverse CDF is important for when you want to generate random numbers. The code can be download from here.
Finally, below is an interactive example of the PDF of PERT (blue) and MPERT (red) distribution.
During and after my Master thesis I authored and co-authored three articles. Two for a scientific journals (IEEE) and one for a Dutch professional magazine (Mechatronica & Machinebouw). While it took me a lot of time writing these articles and I do think that the current publish or perfish system is completly wrong – can write a whole blog about this or maybe read this article – I am glad I took up the challenge to write them next to my thesis.
Writing a scientific article is completely different compared to writing your thesis. For your thesis you have numerous pages to explain your story for a scientific article you only have a few. As a result, you will have to be very precise in your writing and choose the words carefully. It has to be very clear, precise and short. This can be very challenging when your story touches a lot of subjects from different fields. Angel Borja wrote a three articles on writing your article and I would like to share these with you:
Finally, without further ado, the three articles I have written.
Frequency-domain analysis of real-time and networked control systems with stochastic delays and data drops
Abstract—We present a novel frequency-domain analysis framework for a closed-loop model capturing a wide range of real-time and networked control systems with stochastic delays and packet drops. Our results allow for inferring the mean and variance of the output response to deterministic inputs, based on a new frequency response plot. We illustrate the usefulness of our results in the context of real-time control systems with input-to-output delays resulting from the use of a shared processor.
Keywords—Frequency-domain analysis, networked control systems, real-time systems, stochastic systems, data losses, delays
The impact of deadline misses on the control performance of high-end motion control systems
Abstract—In high-end motion control systems the real-time computational platform must execute tasks from multiple control loops operating at high sampling rates. In recent years traditional special-purpose platforms have been replaced by general purpose multi-processor platforms, which introduce significant fluctuations in execution times. While considering worst-case execution times would severely reduce the sampling rates, accepting deadline misses and assuring that the control system still meets the desired specifications is challenging. In this paper, we provide a framework to model and assert the impact of deadline misses in a real-time control loop. We consider stochastic models for deadline misses and characterize the mean and the variance of closed-loop output variables based on a time-domain analysis. We illustrate the usefulness of our framework in the control of a benchmark motion control experimental setup and in the control of a wafer stage in a lithographic machine.
Keywords—Deadline misses, data losses, packet drops, performance analysis, stochastic analysis, industrial case study, hybrid systems, cyber-physical systems, real-time systems
Smarter balancing between performance and costs in control systems
Abstract—In order to ensure the performance of control systems, the digital platforms on which they are executed are often over-dimensioned, which are unnecessary costly. State-of-the-art model based techniques make it possible to create cheaper control systems, without performance degradation.
Keywords—Deadline misses, data losses, packet drops, performance analysis, stochastic analysis, industrial case study, hybrid systems, cyber-physical systems, real-time systems
A few weeks ago I saw the following tweet by Bo Marit. I really liked how the quote and the symbol reference stand out in front of the text in the frame. Since, I liked them so much I decided to be a copy-cat. However, I added also another frame with a reference to Game of Thrones.
The font that she uses for the quote is called Darleston. It is a really elegant calligraphic font created by Youssef Habchi. For the book page text I used Garamond, a standard font on most computers. I chose this font because it has an oldish style to it. While this could easily be created in Photoshop or any other graphics editor, I simply recreated it with Microsoft Word, which is maybe even easier! I simply created a two column layout, added two textboxes for the quotes and the symbol image. You can download the word file here (note: you will need the fonts Darleston and Garamond) or a pdf file here. As an frame I would recommend a simple wooden frame as Bo Marit uses, I think it gives adds elegance and makes it look more humble. Furthermore, I would not use regular A4 paper to print this on. I searched for the same type of paper you often see used in books. Most likely you will find this type of paper in your local hobby store.
Finally, my result:
I plan the hang the Harry Potter frame near to a light switch, the Lord of the Rings frame near to the clock and the Game of Thrones frame near to the thermostat.
From 28th of May to the 1st of June GEMOLD14 takes place. GEMOLD14 is the GEWIS version of the popular Dutch television program wie is de mol?, literally translated who is the mole?. The program is about 10 candidates who have to complete several assignments with which they can earn money. However, one of the candidates is the mole, it is his solely purpose to make sure that assignments fail and the team of candidates earn as less money as possible. At the end of each episode there is an execution, the candidates have to answer a number of questions about the identity of the mole. The candidate who answers the least amount of questions correct has to leave. Candidates can earn jokers, which turns a falsely answered question into a correct one, or free-cards with which they do not have to do the answer the questions at all and guarantees continuation to the next episode. At the end of the program there are only three candidates left, the mole and two candidates. The winner is the candidate, who is not the mole of course, who answers the most correct questions about the identity of the mole.
On the 23rd of February I got an e-mail from the GEMOLD14 committee with the message I was selected to participate as a candidate. Together with the e-mail I received a questionnaire which I immediately filled in. You can download it here, however, it is in Dutch. I also had to write a small introduction about myself for the website, which you can view here, also in Dutch. After that it was just waiting for the 28th of May.
On the 28th of May all 14 candidates gathered at GEWIS in the Metaforum at the university. Before I went to GEWIS I made a visit to the bathroom where I wrote mole on mirror with soap just as a tease for the other male candidates who might had to go to the bathroom after I went. Later we were delegated to come to balcony of the Metaforum. After a group picture with all the candidates GEMOLD14 was finally about to start. Tim the host of GEMOLD14 showed up and welcomed us. He explained some organizational matters and how jokers and free cards looked like. We handed in our mobile phones, wallets and everything else that we were not allowed to have in our possession during the weekend. Afterwards, he told us to prepare ourselves for execution! With only the questions from questionnaire someone was already going to leave the group. Everyone was in shock, while I only had an eye for the joker and free card which Tim showed us as an example and left on a small table. With an easy pace I walked up to the table and grabbed them while everyone was gasping and watching me. Unfortunately however, one of the other organizers came up to me and told me to give them back. As polite as I am, I gave them back. Very stupid afterwards since they really lay in the open and the organizers were only to blame themselves to leave them so in the open. In the meantime the monitor was placed. Ruben, the host who did the executions, called the first name: Rik — who I think is the mole by the way — got a green screen. He was followed by Celine, Mark, Jos, Arno and Levi who all got a green screen. Then it was Wout’s turn, he was one of the finalist of GEMOLD13. Unfortunately for him he got a red screen and we were left with 13 candidates.
Wout was executed and the remaining candidates and myself gathered between the Metaforum and the Main building. Tim showed up. He asked for two volunteers who were lazy, Jos and Annebel presented themselves after which they were escorted away from the rest. Tim asked for someone who still had to recover from the shock, Mike presented himself and he was also escorted. At the end Tim needed two more volunteers who would enjoy a little walk, Ingmar and Leroy presented themselves. The rest had to fetch our bicycles and were escorted by two people from the organisation, Merel and Serge. For clearance here a list of the people:
Two volunteers who were lazy: Jos and Annebel.
One volunteer who still had to recover from the shock: Mike
Two volunteers who enjoyed a walk: Ingmar and Leroy
The rest who were gonna travel by bicycle: Wouter (me), Jorik, Celine, Wim, Levi, Rik (mole!), Patricia and Arno.
We drove to the Opwettense Watermill. Tim was waiting for us, after we parked our bicycles Tim explained us the assignment. Two people would arrive at the Watermill in approximate 10 minutes. From there on we had to guide them within one hour to the camp location were we would spend the night. We were to act as a traffic signpost and were not allowed to communicate by any other means than that. We were given three maps in which not all roads were clearly visible. On the left side the street directions were given in plain text. After the instructions of Tim we gathered in a circle around one of the maps, discussing which positions were best to post someone as a signpost. In this discussing Levi took the lead. Celine also got hold of one of the maps, I asked her if I could have a look at it. She gave me the map, but not before saying that she wanted it back afterwards, of course I never gave it back. At the first point were we had to leave someone behind I told the group we had to leave Celine as a signpost, I took the lead in this discussion since I did not suspect her. Celine was left at the first street crossing and the rest bicycled further. During the road there was some discussion whether or not someone had to be left at a street junction however of course our logic kicked in and we decided to post no-one as long as the directions was straight ahead. Jorik was left next at a roundabout. Then Patricia was left at a crossing. After that there was some discussion if we took the correct turn. I quickly ended that discussion because from reading the map and street names I knew we were correct. It was very funny and suspicious to see that no one seemed to be bothered to actually look at the street names and the ones on the map. The discussions were more like — when you look at the scale of the map and the distance from this crossing to this crossing, this had to be the correct crossing. At the next crossing I told the group which was left, that I want to act as a signpost and to be left behind. Levi did not like that and wanted to leave someone else behind — I guess he did not trust me. Rik (mole!) however told Levi however that we could keep discussing but that it was useless and he should accept the situation as it was. I was left behind as a signpost and the rest continued. However at the end of the road they stopped and were discussing. Later I learned that there was confusion about the map since there should have been a straight clear road ahead but there was not. However during their discussion Ingmar and Leroy arrived at my location, quickly I acted as a signpost and pointed them to the correct direction. Ingmar and Leroy were gaining upon the rest of the bicyclists, since they were still discussing. Suddenly they saw them and drove of, however, leaving Wim behind as a signpost. From this point on I could only guess and learn from others what happened further on. Suddenly however Mike arrived, I was kind of surprised and without thinking I pointed him in the correct direction, very foolish of me so it appeared afterwards.
While I was waiting to be picked up by one of the organizers I started to write in my mole booklet. After a while the group reappeared and we drove back to the starting point to pick up everyone after which we drove straight to the camp location. At the camp location we had to step off from our bicycles and one by one we had to go to the gates from the encampment. Jorik went first, he however came back and told us that he did not get in. He told us that we were getting a yes or no question about if we wanted to get into the encampment for -500 mole money. In the meantime Arno did went to the gate and got in. At first I thought he told yes. Then Wim and Celine got in as well. I got to the gate and got the question which Jorik told me I would get, I clearly said no and got in. From what I learned afterwards Jorik told not clearly no but said “euh no“. Inside the main building of the encampment I learned that while there was some confusion on the road, after I was left behind, we succeeded with the assignment. When every candidate was inside Tim greeted us. He told us that Ingmar and Leroy were inside the encampment in time with which we earned 500 mole money. However, Mike also made it also into the encampment with which he earned a free-card. This did however cost -1000 mole money. So actually we did fail with the assignment, since we got -500 mole money in the end. The mole had succeeded and we went to sleep.
The next morning all candidates gathered in a small room. Tim joined and explained the lie and cheat assignment. The moles of the three previous editions of GEMOLD would join us they would act as a jury. Tim would then ask each candidate two questions, one had to be answered truthfully the other with a lie. The jury would then try to guess which answer was a lie. Each candidate could earn mole money when the jury did not manage to find out which answer was a lie. When a previously candidate managed to fool the jury the next candidate could choose to call. The mole money earned by the previous candidate would then be safe. If he continued and the jury would guess correctly which answer was a lie then the previously earned mole money would be gone. The amount of mole money earned would raise by:
First Ingmar and Patrice who both did not manage to fool the jury. Then other candidates told me I had to go, I resisted a bit but gave in to the pressure. Tim asked me two questions, if I had a part-time job and what my favorite book was. Since I did not quiet understand the game at that moment, I was wondering if the question which were asked stood in the questionnaire, I decided to answer the first question falsely and the second truthfully. The jury then guessed wrong. The next candidate did not decide to call and unfortunately he did not fool the jury. The 10 mole earned by me were gone. After my question, I gave the assignment some more thought and I believed that we could have lied always regardless what type of question we were asked because the questions did not actually come from the questionnaire. Hence it could never be checked if the candidate was actually lying towards the jury. After I got executed, I looked it up and indeed both questions which I was asked were not in the questionnaire. As such I think I was correct during the game and we could all just have lied towards the jury. Unfortunately everyone was to truthfully towards the jury and we only managed to obtain 100 mole. We could have earned a lot of mole money very easily. This time the mole was not clever, we were dumb.
After the next assignment, I unfortunately got executed. I wrote this blog almost immediately after I was executed. However, I did not describe the events during the last assignment, I did plan to finish it at a later stage. However, as you can see that never happened. Because the episodes are being aired now, I decided not describe these events anymore from my point of view.
Simyo is a mobile virtual network operator (MVNO), which is active in several countries. Namely, Netherlands, Belgium, Germany, France and Spain. Simyo, as a MVNO, does not own any network infrastructure. In the Netherlands it uses the infrastructure of KPN. KPN is namely its parent company. Furthermore the company has no offices and solely operates by using the internet.
I joined Simyo in august 2013. Because I wanted to switch to a SIM-only subscription, since my phone, from my previous subscription, was still working fine. From my invoices I figured out that I did not call or text that much. I spent around +/-70 minutes calling or texting and around +/- 600 MB of internet traffic. For this reason I decided that I only needed a subscription which could offer 100 min/sms with 1000 MB internet traffic for a reasonable price. After searching and searching for a subscription, I came across Simyo. I then decided to join Simyo for the following reasons.
It was the cheapest (it really was, my subscription is 13 euro’s, I should note however that it nowadays is 14 euro’s)
It was already at that time, called one of the best providers in the Netherlands by a non-profit organization which promotes consumer protection, the “consumentenbond“.
It uses the KPN network, which, by reputation, is know to be very reliable
A while ago my parents told me that they needed a new mobile subscription and they asked me if I could be of help. Since I am a happy Simyo customer, I advised to go for a subscription at Simyo. At the same time Simyo had started an advertising campaign, called the “Vriendendeal” or in English “Offer for friends”. This campaign was about getting existing customers to tell friends to join Simyo. As an existing Simyo customer it was made possible to start your own shop. If people would then register for a Simyo subscription, using your shop, both the shop owner and the subscriber would earn 10 euro discount on theirs subscription fee.
Naturally my parents did obtain a Simyo subscription using my shop. A few days later my brother also called me, if I could be of help with his mobile subscription. Again, I pointed him to my Simyo shop. Because of these three subscriptions my shop, apparently, was one of the best in attracting new customers towards Simyo. For this reason Simyo asked me, as well as a few others, who also ranked high in selling subscriptions, if they could put a link to my Simyo shop on their main website. I replied that I did not had any objection, however I was skeptical since I thought “oh well, I guess my link just appears somewhere at the bottom of the webpage, but everything is better than nothing.”. The nice thing was, was that I was completely wrong. Namely on Sunday, the 13th of September, the Simyo website looked as follows.
They actually had removed the links to their own subscription form and replaced it with a link to my Simyo shop. When I saw it I was really exited. At the end of the day a total of 36 people ordered a subscription at Simyo using my shop. Of those 36, 12 people also activated their SIM card which did boil down to 120 euro’s in discount. As you can imagine I was, and am still, very happy because of this. It is for this reason and the fact that I am just a happy customer at Simyo, I wrote this blog. To thank them for putting my shop on their main website.
In the end I managed to obtain 160 euro’s in discount. Below is the list, I removed the names for privacy reasons.