Beginning of the Competition

On the first day of the competition, there was a work day for all the teams to use to get their robots ready again after a long flight to Canada.  As the current mechanical team lead for the Thunderbots, I too had to get our own robots ready to play.  The mechanical systems had already been completed some weeks ago, but unfortunately, even now, the electrical board testing and firmware coding still had not been completed yet and some parts that we needed were still not in.  For the next day and a half, the team was scrambling to get everything finished in preparation for the first game on Sunday.  Because, the only critical tasks remaining were the electrical testing and coding, only the electrical team had the know-how to tackle those tasks.  The mechanical and software teams could only wait for results.  As the electrical team worked, everybody else on the team became more and more stressed.  We all kept wondering whether the team would have working robots for the first game.  We were all helpless in this situation.  The electrical team worked throughout the day and night trying to finish.  Some of the other team members stayed in anticipation while others went home to rest hoping for results in the morning.

Throughout this work day, the Chinese team continued testing their robots on the field.  They seemed like the most ready team.  The German team however, had lots of work to do as well.  Their flight to London from Germany was delayed and as a result, they missed their flight from London to Vancouver.  They arrived in Vancouver on Saturday night.  They  had even less time than we did to get their robots working.  When each team set up their work space, they each made sure to put up their mascots.  For the Chinese team, they had a panda plush of about 1.5 ft tall and the Germans had a full size German flag.

Game Days

On the game day, I woke at up 5:30 AM and arrived bright and early on campus at 8 AM.  When I arrived, the electrical team was still at it and seemingly not even close to finishing.  This led to a change in the team’s strategy to the competition.  We would try to repair the electrical boards from last year’s robots.  These old boards had a different size than the new ones and had different mounting holes, but luckily, somebody on the team had the great idea of including mounting holes for these old boards for this year’s robots.  Otherwise, we would have had a really hard time hacking that together.  Given only the few hours we had to hack this set up together, the mech team and I worked as fast as we could to finish.  We each probably ran up and down the stairs at the UBC Engineering Design Center about 20 times that day looking for tools and delivering robots.

The first game was supposed to be at 9:30 AM, but my team certainly was not ready.  It seemed like the other teams weren’t completely ready either, so the game was postponed until the afternoon.  The Thunderbots was supposed to play the first game, but due to our lack of readiness, China and Germany played each other instead.  When it became our turn we play, we managed to get three robots out of six on the field.  None of these robots had a working break beam sensor (the sensor on the robot that is designed to detect ball possession).  Without break beams, the robots did not know they could kick the ball, since it would never know if it had ball possession.  The robots did not have a controller that worked well either (the controller determines how much voltage to apply to each of the motors such that the robot can move smoothly from A to B).  A controller that didn’t work well meant the robots drove about on the field seemingly confused.  “Derp” is probably the best word to describe it.  Despite the shortcomings of these three robots, they played their best against ZJUNLIct from China and the Thunderbots were defeated 10-0.

On the following few days, the mech team tried to help the electrical team the best they could with tasks such as building extra connectors.  We also tried to get the old break beam sensors working again.  It was something that had to be on the robot if it were to ever kick the ball properly.  After toiling for a few hours, we managed to get two out of three of them working.  We probably could have gotten more if we knew more about the electrical design.  There was little to go on in terms of the wiring schematic and spare parts.  It was also hard to troubleshoot since ambient lighting largely affected the sensor.  If it worked upstairs in our work space, it wouldn’t work downstairs on the playing field.  It took us a while to figure that out.

In our second game, we played against ER-Force from Deutschland.  For this game, we still only had three robots, but this time they were a little bit better equipped.  Even then, the robots still had trouble kicking because the lights being used on the field emitted too much infrared light, which obstructed the break beam sensors.  It was very frustrating to see the robots not knowing when to kick even though they were handling the ball perfectly. But somehow, we still managed to score a goal.  In the end we lost the game 6 to 1.

In the final game between China’s ZJUNLict and Germany’s ER-Force, the Chinese team was victorious.  Both teams had a full fleet of robots to play six on six.  A modest crowd of spectators also watched the whole game being played and in general people were quite impressed at this engineering feat.

Team Social

To allow the teams to better know one another, there was a social event planned by the organizers of the North American Open.  There, I met a lot of the members of the German and Chinese teams.  It was nice that that I could talk to each team in their native languages.  Although my German wasn’t that good to keep up a conversation for a long time, it was enough to get the Germans wondering how I knew it at all.  The last thing they’d expect is for a Chinese guy to start speaking German to them.  My Mandarin was at a level that I could talk to people in it, but there were still some occasions where I didn’t understand what they said.  It was probably because of me not having a lot of practice with Mandarin (I speak Cantonese normally) and them having an accent from their region that I didn’t recognize.

Press Conference

The organizers made sure to invite as much of the press as they could.  More publicity meant that the team could potentially get more money in sponsorship.  More money means better robots.  The administrative members of the team were in the spotlight and talked to most of the people from the press, while the technical members of the team continued to do their work.  The team leads from mech, software and electrical also had a brief interview with the 24 Hours Vancouver newspaper.  The team was also featured in the Ubbyssey here and on MacLean’s magazine here.

The Chinese team also put on a show for the press by putting all 12 of their robots on the field so they could they play against themselves six on six.  The performance went quite smoothly as there were not random break downs and the press were very impressed.

Engineering Failures

As with these student projects, an accident was bound to happen.  This one was with a battery.  There was have been a defective battery that the Chinese team unknowingly brought and when they charged it, the battery started puffing up – not a good sign for a battery.  One of our team members was quick to notice and instantly dunked it in soap water and disposed of it.

For our team, we had problems where the solenoid kicker would get stuck after being used repetitively.  Heat from the power dissipation in the solenoid windings would heat up the whole assembly and cause the solenoid housing to permanently deform.  The solenoid was produced out of stacked layers of poly-carbonate sheets.  This stacking of layers allowed each layer to deform individually.  To fix this problem, we printed out new housings made of ABS plastic.  By having one solid solenoid housing, it was more difficult for it to deform.

The German team had some problems with the turf getting dug out of the carpet and getting everywhere inside the problem and also with their robot shells not staying on properly.  The turf inside the robot meant that gears could get stuck intermittently and could also get in the way of other mechanical components.  Their solution solution for now was to clean it all out every game.  During games, the shells of the robot would pop out randomly whenever there was an intense impact with a ball or another robot.

Getting Ready for Mexico

On the Friday before all three teams left for Mexico City, everybody had to pack up all of their things.  The German and Chinese teams could pack everything easily since they had packed everything once before when they had to fly to Vancouver.  For us, our tools were scattered all over the place.  It took us about 4 hours to find all tools to pack into the the luggage containers.  The approach to packing was that we would pack any tool that was ours and was already lying out on the table.  This is because if we took it out of the tool closet, it meant that the team used it for something.  Naturally all of the hex keys, screw drivers and the like were packed.  All spare parts were packed.  Every tool that we had sitting around was packed.  Even electrical equipment like a power supply and an oscilloscope was packed.  We had everything we needed for RoboCup 2012 in Mexico City.  Even though not everything was done in time for this competition, everybody was confident that things would be better in the competition in Mexico.

More photos here

1.0 Motors

The chosen motors are:

• Finger grasping – Cytron IG32E-264K at a cost of USD $57.03 from RobotShop
• Finger sliding – Cytron MO-SPG-30E-20K at a cost of USD $22.58 from RobotShop

Both motors meet the torque speed requirements for this project.

1.1 Finger Grasping Actuation

From the initial budget, the budget set for actuators was set at $325.  The torque requirement needed for gripping was also calculated and each finger would require 4 Nm at its output to lift a 4 kg object using only the fingertips.  The evaluation criteria states that the device grasp as fast as possible and that the client would have the highest satisfaction if the device cost was less than $700.

Looking on several websites that sold motors, the following DC motor was chosen: Cytron IG32E-264K at a cost of USD $57.03 from RobotShop.  The specifications are as follows:

At 12 V with gearing included, the stall torque would be 20.7 Nm (without consideration of mechanical efficiency).  A motor with a high stall torque is also beneficial because it lowers the gear ratio required, which leads to the use of less space for gearing.  The motor also comes with its gearing, which contributes to its high torque.  Given the high stall torque of this motor addition gear reduction is not required.  During grasping, the motor will be exerting high torque at low speeds and therefore, the motor will be operating near the stall torque.  The torque here is more than sufficient even with mechanical efficiency losses accounted for.

For finger actuation before grasping occurs, there is a low load and therefore the motor will be operating closer to the no load speed.  The no load speed with gear reduction is 27.7 rpm (without consideration of mechanical efficiency).  Split among three output shafts, the speed would be 9.21 rpm.  Even with the load of the fingers accounted for, this is still acceptable. based on requirements and evaluation criteria.

While the torque is a lot higher than required, this motor was only more expensive than a motor of one size smaller by less than three dollars.  The electrical characteristics were also identical.  With a higher motor torque, the grasper would be comfortable in lifting objects even heavier than 4 kg, which is another benefit based on the evaluation criteria.

1.2 Finger Sliding Actuation

The motor required here does not require a large torque since motion in this degree of freedom is not expected to handle heavy loads.  This motor only requires enough torque to overcome the friction of the finger on the power screw that it is mounted on.  Therefore, a low-cost motor (relative to the grasping motor) will suffice.  The DC motor of choice is the Cytron MO-SPG-30E-20K at a cost of USD $22.58 from RobotShop.

The specifications are as follows:

The consistency of the stated specifications do not match the previous motor because the information that was provided by the manufacturer was not consistent.

An initial estimate of two 200 g fingers sliding on a 1/2” diameter power screw with a steel-steel sliding interface (friction coefficient of 0.8) shows that only 20 mNm of torque is required.  Therefore, this motor meets the requirement.  The power screw also has 13 threads per inch, and at the rated 185 rpm, the power screw would slide linearly at 6 mm/s.

1.3 Motor Type

DC and servo motors are motors that are suitable for the project.  An investigation between DC and servo motors showed that many manufacturers of motors did not provide the necessary specifications for choosing a servo motor in terms of the values of the no load, stall torque, and stall current.  While servos generate a lot of torque relative to their size when compared to DC motors, it is not feasible to use a servo motor because of the unknowns in the specifications.  It is possible to buy several servos and test them, but this is costly and time consuming.  At this stage in the project, the team is not able to commit the time to investigate further.

Comparison of the cost of the grasping motor relative to motors from Maxon Motor, a supplier of motors for UBC Thunderbots, shows that the price of a motor of the same power output costs approximately the same amount.  However, a fundamental difference is that the motor from Maxon does not include a gearbox, while the chosen motor for this project does.

2.0 Microcontroller

The microcontroller of choice is the Arduino Diecimila.  The primary motivator for using this board is because the UBC Thunderbots team already has this board and is currently unused.  The Thunderbots team has generously provided the board for use on this project.

The MCU will allow the turning the motors on and off, changing motor direction, changing motor speed, and reading encoder feedback.

3.0 Voltage Regulation for Encoders

Since the power supply is likely going to be run at 12 V, the encoders will require voltage regulation down to 5 V (the operating voltage of the encoder for the motors).  The chosen voltage regulator is the MC78L05A at a cost of USD from Digikey.  According to the typical application diagram of the datasheet, two capacitors will also be required (0.33 μF and 0.1 μF).  The cost of these are less than $1.

The voltage regulator will be wired up in this way as the datasheet shows:

The input will be from the 12 V source, and the output will be to the encoders.

4.0 Motor Driver

To control the motors, an H-Bridge is to be used.  However, due to the different current flows for each motor, one motor driver will require a high current capacity while the other one will not.  The high current capacity motor driver consists of a driving circuit using two half-bridges.  The low current capacity motor driver is made up of 1 IC.

4.1 Finger Grasping Motor Driver

To design the H-Bridge for controlling the motor, an L6205 motor driver will be used.  Each of them costs USD $11.36 from Digikey and can withstand a continuous current of 2.8 A and a peak current of 5.8 A and can be interfaced with the microcontroller with PWM inputs.  The driver can also be run in a parallel mode to double the current ratings by using both of its full bridges together.  The datasheet provides an application circuit as follows:

Output pins from the Arduino can turn the motor on and off through the enable pins.  Direction is controlled by adjusting the voltage polarity between IN1 and IN2.

There are also two output pins for current sensing.  By using it to measure the current draw, the microcontroller program can determine what the torque is through the use of the motor curves provided in the motor specifications.

4.2 Finger Sliding Motor Driver

The motor driver of choice is the L293D and each one costs $2.50 from Digikey.  Bidirectional control of a DC motor can be achieved by adapting the application circuit from the datasheet:

The 1A and 2A pins determine the direction of the motor or the motor deceleration.  A truth table is provided in the datasheet.

5.0 Power Supply

To power the grasper, a power supply plugged into the wall will be used.  It is expected that the future robot will have a power source of its own which will power the hand as well.  Therefore, for the purposes of testing the grasper for this project only a wall power supply will be required.

Looking at the maximum electrical power consumption of the two motors, the total comes to ~65 W (12 V * 5 A + 12 V * 0.41 A).  The other components also consume power and so the final power consumption will be higher.  To compensate, a 12 V power supply with a maximum wattage and current of 84 W and 7 A was selected.  The part number is CENB1090 and each costs USD $70.48 from Digikey.

6.0 Power Supply Connector

The power supply chosen has one port that uses a Molex Mini-Fit Jr. Receptacle.  Therefore, a proper receptacle must be used so that proper wire routing can power all the circuitry.  This also means that the future robot will also require a matching plug for this receptacle.

7.0 Fuses

Fuses will also be used as a redundant mechanism to stop the motor in case the current draw is too high.  The primary method of stopping the motor is through the current sense pins on the motor driver.

As one of the largest port cities in Europe, we got a chance to go to Hamburg to see its beauty.  We went there by car and saw much of the historical part of the city as well as took a ferry ride along the coast of the Elbe River and walked along the city’s canals.  The weather was pretty much raining for the whole time we were there.  As my friend put it, “when you go to Hamburg, plan for rain”.

The Drive

We left work at around noon to pick up our rental car.  It took us a bit longer than we expected because we had to go grocery shopping so we could have lunch and dinner in the car on the way there for our 6 hour drive (or so we thought).  The drive ended up taking 8 hours because of a stau (traffic jam).

The car we got from the rental company was a Mercedes-Benz C220.  When we got into the car, it smelled like new and being in such a new car for a road trip was undoubtedly awesome. We only got this car because it was the cheapest car with automatic transmission available.  I guess the Renault that we got last time was booked for today.  I wish that I got the chance to drive it though.

On the way there, we got to see a lot of the German countryside (as anyone typically does when going from one major city to another).  On the grass plains and knolls, we saw countless villages, farms, vineyards, and the like.  We even saw farms of wind turbines and solar panels.

After a few hours of driving, we stopped a few times.  We stopped at a rest area and at this middle-of-nowhere village.  The GPS guided us off the highway and into this village just to avoid the traffic jam.  For the first third of the trip, I sat in the front while three of my friends had to squish together in the back.  When it was my turn to sit in the back, I didn’t really feel the discomfort while I was reading on my friend’s Kindle.  I ended up going through about 90 pages of Band of Brothers.  Maybe the book was so interesting that I just completely zoned out of the real world for a little bit.

We reached our hostel at around 9 at night and parked the car.  After moving our stuff into our room, we began our sightseeing tour of Hamburg.

Reeperbahn

Our first destination was the Reeperbahn street.  Similar to Amsterdam, this area is one of the most famous red light districts in the world.  The whole area was full of sex shops, strip clubs, and brothels.  On the street corner, many women wearing fanny packs kept trying to approach tourists and we figured that these women were all prostitutes (that stuff is legal in Germany).

One of the more peculiar things was that there was a church that stood pretty much in the core of the whole area.  Really convenient for people to go to confess their sins I guess.

We meant to find a bar here for a drink, but pretty much all of the places reeked with pungent cigarette smoke or was way too loud.  Two of my biggest pet peeves in one place.  We ended up just going back to the hostel instead.

In order to keep up my “try-as-much-kinds-of-beer-as-possible mentality”, I tried a type of beer called Astra Urtyp.  It tasted horrible – too much of hops flavour.  Some of the others drank a few more beers and got tequila shots before heading out again.  As usual, I went to sleep.  The next morning, I found that they returned at around 5:30 in the morning.

The Rathaus

At around 11, on a cloudy day with a large and persistent ocean breeze (it was super cold even with my jacket on), we showed up at the meeting point for the walking tour – a Starbucks.  This tour company receives some sort of sponsorship from them.  Our tour guide, didn’t look like a German, and when he spoke, a clear Northern USA accent came about – apparently, he had been living in Germany for some time.  He led us to the first destination of the tour – the Rathaus (city hall).

Located by the Alster River, this rathaus replaced the old one that was destroyed in the fire of 1842.  This building looked quite similar in form to other city halls, like the one in Munich and Vienna, with a clock tower-like structure that extended directly above the main entrance.  Right above the gate of the main entrance, the Hamburgers proudly displayed their coat of arms that depicted the old fortress of Hammaburg (where the city got its name) that used to exist in the area before its destruction by the Vikings.  Once more this coat of arms was displayed on the clock tower of the rathaus, just beneath a large antiquated mechanical clock.  Statues of German Kaisers decorated the side of the building as each one stood in a line just beneath the rooftop.

In front of the building was a giant courtyard and during World War II, a bomb landed here, but didn’t explode.  If it had, the rathaus would have been badly damaged.  The bomb was defused and the timing mechanism removed from the bomb is now on display in the rathaus.  In the courtyard, the Hamburgers held the Stuttgart Wine Festival, which apparently coincided with the Hamburg Fish Market in Stuttgart.  Here, people set up tents selling South German cuisine – the kind of German food that I’m always used to eating. 

Along the Alster River stood a giant stone plaque engraved with a message saying that 40000 sons of the city gave their life for us all.  Everyday, people going to the rathaus are reminded of the tragedy that befell the country.  Beside it, swans, ducks and other birds frolicked about and went on with their day to day lives.

Buildings on the other side of the river formed a canal much like in Amsterdam.  Canals could be seen throughout much of the city and in fact, the city holds the world record for having the most amount of bridges.  At first I thought Amsterdam’s 900 bridges was a lot, but apparently Hamburg has around 2300.

St. Peter’s Church

Although, not so significant as a work of architecture, many believe this place to be the site of where the old Hammaburg fortress once existed.  When we stood at the entrance of this church, the tour guide said, “welcome to the highest point of Hamburg!”  I looked around and just saw a gentle slope and nothing more.  I guess Hamburg must not have any mountains! 

Besides being a church, this building once served as a stables for Napoleon’s forces.  Not long after the Napoleonic Wars, the church was destroyed in the fire of 1842.  Despite the fire, much of the art in the building was saved including the lion shaped door knocker – the oldest artifact in the city.  At the back of the church, vegetation grew along the brick walls over the years and not far beside it, a wooden sign stood with directions to various places for pilgrimages.

Expressionist Architecture

During the height of Hamburg’s power in sea trade, many firms set up offices in the city.  Many of these firms had buildings resembling the architecture style of the expressionists – elements of the building’s exterior would reflect the purpose of the building.  For example, in one of the accounting houses for sea trade, one could see elements of the building protruding from its side in the shape of a caravel or an anchor.

In another building, known as the Chilehaus, held the shape of a ship and above the front entrance, there were various objects representing the country of Chile.  Similarly, in the Afrikahaus, there was a giant statue of a tribesman wielding a spear and behind the statue on the gate, was a sculpture of a plant indigenous to Africa.

We also visited the Patriotische Gesellschaft (no idea what that is in English), but this building too had examples of the expressionist art.  Statues of caravels and Poseidon stood on the roof.

World War II Stuff

While on the tour, the guide pointed out a plaque on the side of a building and on it was information saying that the building was once the location of the firm that manufactured the Zyklon B gas that killed millions of people in the death camps.  This plaque used to be located at the main entrance of the building, but the building owners and people working there did not want a daily reminder of those atrocities.  To counteract this, they used a different entrance as the main one instead.

Another destination, the Church of Saint Nicholas was one of the many buildings destroyed during the instead bombing raids on Hamburg.  The church did not get a complete repair after the war, but instead it now stands as a memorial – another reminder of the devastation of World War II.

Deichstrasse

Located near a large network of canals, this area of the city is the oldest part of Hamburg.  Undoubtedly, this area was filled with old architecture and complete with the cobblestone roads that are so prevalent in Europe.  The building style also resembled a lot of 18th and 19th century architecture. 

There would have been more buildings in this area, but through several fires and bombings, much of it was destroyed.  In fact, one of the buildings here was where the fire of 1842 started.  It must have been reconstructed since then.

Speicherstadt

Literally translated, the title means a “city of warehouses”, which indeed is what the area was for – storing cargo.  Back in the day, this area used to be where the Hamburgers traded without having to deal with customs tariffs.

As the size of cargo ships got larger, these buildings began to be obsoleted as many of these cargo ships could not fit in the narrow city canals.

HafenCity

Probably the most modern part of the city, this district serves as a playground for architects.  Much of the buildings here don’t follow any sort of mainstream design ideas – lots of buildings here looked really bizarre.

One building to note though, is the concert house under construction.  It has the shape of ocean waves to represent the city’s rich history of sea trade.  Originally budgeted for 100 million euros, due to construction delays and other unfortunate events, the cost of the building is now nearing 500 million euros.

Before this area became popular, the city had trouble getting people to move here, so they rented out flats here for as low as 500 euros a month, but now people can’t rent a flat here for anything less than 3000 euros a month.

Shopping and Food

After our tour, some of my friends couldn’t stand the freezing ocean wind anymore and decided they had to go buy a hoodie.  The wind was so strong that the clouds weren’t just floating across anymore.  There was like a wind speed of about 20 km/h.  We walked around the old town and found an H&M.  I looked around inside and to my surprise, I found that the prices at this H&M seemed to be a lot higher than Stuttgart.  Otherwise, I most probably would have bought something there.

Later on, we went back to the old part of Hamburg for traditional Hamburg cuisine.  We entered a restaurant that had a theme of sailing.  The wall had on display some schematics and black and white photos of various types of ships.  The color scheme of the place even coincided with the stereotypical blue and white colour combination of sailors. We went to eat at around 3, so it was kind of empty at the time.

The food I tried here was Labskaus – a dish typically served in Northern Germany and according to Wiki, “the main ingredients are salted meat or corned beef, potatoes, and onion. Some – non-traditional – recipes put beetroot, pickled gherkin, or even herring into it.”  Mine was served with beetroot and pickled herring, which was typical of the Hamburg style.

Hamburg Hafen

After our meal, we went to the harbour for a ferry ride along the Elbe River.  The ferry drove along the coastline and gave us a really good view of the city.  We rode the ferry from HafenCity all the way to the beach near the Elbtunnel.  In addition to the city scape, we even saw a docked submarine and a cruise ship about to begin its journey.  The travellers on the ship happened to be doing their lifeboat safety drill as we passed by so the people on the two ships happily waved to each other.

The ocean wind we felt on the ship was so strong that I probably needed a winter coat to keep warm.  The wind even caused the waves to be strong enough such that water splashed onto the deck of the boat and onto everyone standing on it.

On the other side of the river, miles of cranes lined up the shore, ready to unload any cargo on ships that docked.  What we were seeing was the second largest port in Europe, the largest being the one in Rotterdam.

Bar District

Supposedly, this area is known as the bar district (at least that’s what we called it).  Despite its name though, there was a really tight concentration of bars here, but the cost of beer was even more than Stuttgart.

At the bar/restaurant, I ordered an apple strudel to help combat my hunger from walking around all day instead of going for beer like everyone else did (although I did have a little bit).  The apple strudel I got wasn’t that expensive and it looked and tasted amazing.

Fish Market

The next morning, we went to the fish market – Hamburg is famous for it.  However, we got there a little late, so by the time we got there, a lot of the places were closing down.  As a last ditch attempt to sell more stuff, a lot of shops there started giving people really good deals on food like selling a whole box of fruit for only 1 euro.  I would have bought it if I could eat all of that.  A pile of garbage behind all these people went to show how much food they sold that day.

Although the market by named says “fish”, people sold all sorts of things in addition to fish.  Many sold bread, cheese, and various types of meat.  I wondered if I’d see something similar to the wurst man I saw a while back, but I didn’t.

The market even had an indoor beer garden with a live band playing.  It was quite a nice place.  If only we were there early enough.

Driving Home

As I probably should have known, I could not resist the urge to drive.  I ended up taking the wheel for about half an hour and managed to get the Benz up to 200 km/h.  While driving at that speed though, the steering wheel was really shaky.  I felt that if the car ran over a pebble or something like that, the car would just plunge into the side of the road.  If it wasn’t for that, I would have reached the car’s top speed.

Before I started driving though, we stopped at a rest area.  When we took a good look at the back seat of the car and noticed a giant mess of crumbs from all our snacking during the trip.  I don’t think I had any to do with that since I never considered myself to be a messy eater.  Just as we finished commenting about the messiness of the car, one of my friends had apparently stepped on dog poop and got it in the car.  It smelled horrible.  He even got it onto another friend’s pants.  He cleaned it up right away, but a faint smell of the poop lingered in the car for the rest of the journey.  It’s a shame that the car rental company gave us a car smelling like new just so we’d give it back with a bad smell.

In another rest area near Frankfurt, we stopped for a bite to eat and went up to the observation tower there to look at the Frankfurt skyline.  That was a nice sight except for the giant high voltage line that blocked part of the view.  By then we were already pretty much 3/4 of the way home.  I continued reading Band of Brothers on the Kindle and managed to get through about 65% of the book in total.  We got back into Stuttgart at around 7:30 in the evening, returned the car, and went home.

More photos here

According to the writer of the guide, undervolting simply reduces the voltage applied to the processor.  Since all processors have a different voltage requirement, they all use one standardized value which is most likely higher than the amount that the processor itself requires.  By reducing this excess voltage, the power dissipated by the processor will decrease, and thus reduce heat and increase battery life.  It should also be noted that this process will not impact performance since the performance of a processor is governed by its clock speed.

By doing this, I’ve reduced the temperature of my laptop by about 12-15 degrees Celcius.  The laptop’s keyboard and touchpad are no longer warm to the touch and the side heat vent no longer feels like burning.  Definitely a major improvement!

Link: http://forum.notebookreview.com/hardware-components-aftermarket-upgrades/235824-undervolting-guide.html

Concept

I was given the circuit shown below (from Microelectronic Circuits 6th Edition by Sedra and Smith):

I was asked for the voltage of the output terminal and the current flowing through the diode.  Finding the current was easy, but I didn’t quite get the voltage.  I thought to myself, “from what two points do I measure the potential difference?”, because after all, voltage measurements are always taken relative to two points.  It took me the longest time before I could just use ANY two points and the measure the voltage.

What I figured is that, for part a, since the diode is in forward bias, the diode will act as a short circuit.  I then can say that V – (-5) = 0, since the voltage difference along a short is 0.  From there, I can easily determine that V = -5.  I can apply that same logic to the other three.

Nodal Analysis

I was given the circuit shown below (from Microelectronic Circuits 6th Edition by Sedra and Smith):

From class, I remember the professor saying that since we cannot tell right away which diodes are on and off, we can only make an assumption about the states of the diodes and then apply the usual analytical techniques.  In the event that the result is unreasonable, we know that our assumption wrong.  I made my assumptions, but afterward, I didn’t know where to go next.  I had forgotten how to analyze these circuits.

Later, I realized that I could use nodal analysis.  Since I assumed the two diodes in part a were both on, I replaced them with short circuits.  I used the intersection right before the current splits as my node.  For part a, the current into the node was 3 V/5 kΩ = 0.6 mA.  The current leaving was some unknown current for diode 1, and a current for diode 2.  I could determine the current of diode 2 by taking the potential difference between the node and the -3 V output and dividing that by the resistance in the path.  The result was (0 – (-3))/ 10 kΩ = 0.3 mA.  From the nodal analysis equation 0.6 mA = current from diode 1 + 0.3 mA, the current from diode 1 is 0.3 mA.  And as for the voltage V, the potential difference between V and the -3 V output is equal to the voltage across the resistor, (0.3 mA)(10 kΩ) = V – (-3).  Therefore, V = 0.  Alternatively, I can use the potential difference between the node and the output, which equals zero, thus yielding the same result.

Boolean Logic

The next issue I had was determining the Boolean outputs of a diode logic circuit.  Again, the picture below is from Electronic Circuits 6th Edition by Sedra and Smith.

The issue I had here is that I did not know current sources have no voltage if there is no current running through them.  Looking back that sounded pretty intuitive.  Finding all possible combinations of inputs A and B for this logic circuit, we get the truth table below:

A B X Y
0 0 0 0
1 0 0 1
0 1 0 1
1 1 1 1

The outputs of X reveal an AND gate.  Setting A or B to a logic 0 in (a) will cause current to flow through that path.  The potential difference X – A or X – B (depending which one was set to 0), will yield 0, thus the output X will be zero as well.  When A and B are both set to logic 1, it causes the diodes to go into reverse bias, and node X will be powered by the current source.

The outputs of Y reveal an OR gate.  Setting A or B in (b) to have different inputs, either 1,0 or 0,1, will cause the diode to be in forward bias for the input that has the logic 1.  For the input with logic 0, the diode will in reverse bias.  Since one of the diodes is on, current will flow and output Y will yield a logic 1.  In the case of both diodes being off, no current will flow, thus causing output Y to yield logic 0.

Other Notes

In the case of multiple parallel diodes in the same direction, if one of them is on, chances are they are all on (provided that the voltage across them is positive).  However, there may be a case where one parallel diode will want to flow into the other because of a greater voltage difference.  For example, if there were two parallel diodes, one with a 3V input and the other with a 2 V input both going to the same node, current from the 3 V input will want to flow into the diode connected to the 2 V input.  This will cause a reverse bias in the diode connected to the 2 V input, thus turning it off.

There is also another case where there are parallel diodes with different output voltages.  If current is flowing toward it, they will all be on, so they will all be a short circuit.  Which path will the current go to?  The path with the larger current.