Two months ago i set out on this project which was mostly executed on weekends or after office hours.
The more i worked on this project, the more it evolved. At the end, i was supremely proud of what i had made.
When i gifted it to reema, her feet were barely touching the ground. She has christened the moodlamp as “Reema’s Wonderlamp” and so it is…
I wanted to share the concept of Reema’s Wonderlamp so i shot a video and narrated a few internal ideas.
Hope you(yes, you – random-reader-who-stumbled-across-this-tumbleweed-of-a-blog!) like it…

Since then, i always wanted to work on a pottery wheel. As i grew up, i also became interested in making machines. Last month, i decided to make a Potter’s wheel.
I didn’t spend much time researching the actual potter’s wheel. I just went with my gut feeling about how it works and decided to make a disc that rotates at a decent speed.

I started with a motor. The exhaust fan motor seemed an obvious choice. It comes with a stand, very silent running, not too fast not too slow. After a 10 minute negotiation with the quite-reasonable electrician, i bought a 2nd hand motor for 300/- (I am sure it is cheaper but i was too exited to start the project!)

Exhaust Fan Motor

My 1st step was to add a speed regulator in the motor circuit. This way i can control the speed of the motor.

Then i fit an aluminium plate directly on top of the motor. (pic not available)

I bought a kilo of putty clay and started to work on my pottery in my bathroom. Within 15 minutes, the 4 walls of my bathroom were covered in clay. Since then, while bathing, my roommate curses everytime he steps on a lump of clay, thinking it was a lizard.

The problem was oxymoronic. Too fast and too slow.
When you put the blob of clay at the center of the plate and start the motor, it takes a while for the plate to gain speed. When it does, it accelerates so fast, that the clay starts shooting off in all directions.(Dear Centrifugal force, sometimes, i hate you).
And when you slow down the speed with the speed regulator, the motor absolutely stops when you touch the clay to shape it. Low torque.

It was clear i had to increase torque and reduce speed. So i found a kids bicycle wheel and made a belt drive.

Motor, coupling and bicycle wheel

This is what i came up with:

Potter's wheel without the belt

I am happy with this attempt. But i sure need to work on a real potter’s wheel to experience perfection. Potter’s wheel version 2 is destined for me. and i’ll attempt is someday.

Meanwhile here’s the video of ver 1

I’m not a music addict but yes, some particular tunes are a part of my routine.
Point being, like everyone else, headphones are now an indispensable accessory to me too.

Last week, while exploring some experiment ideas for our science section, my colleague Sandeep made a great paper speaker. But it somehow didn’t give a very nice sound output.  We made some changes in the materials used, and it gave birth to a fantastic balloon speaker

What is sound? Vibrations, right? (Actually pressure waves, but let’s not get into that)
If you are hearing a sound, it means something is vibrating somewhere.
The frequency of the vibration decides the tone of the sound and the amplitude decides the volume of the sound.

The string of the guitar vibrates faster than the diaphragm of a drum. Hence, the tone is different.

So this is what we did, we wanted to make a speaker. Simply put, we wanted to create vibrations of the frequency of the electrical signal that we get from the iPod speaker jack.

Let me take you through the making:
This is what you need:
1> Big Baloon
2> Something to stretch the balloon on. (I used a section of a PVC Pipe)
3> A magnet: this has to be a small and strong magnet. A cylindrical neodymium magnet is the best choice. There are not many vendors around. So you may try to hack some from magnetic key-chains. Or just use a strong ferrite magnet
4> 35 gauge laminated copper wire.
5> Foamboard/ cardboard

Step 1:
Cut the balloon and stretch it over the PVC pipe

Step 2:
Find a thin tub that can ‘just’ cover the magnet. I Cut a 5ml Syringe for this. The size happened to be perfect to ‘just’ cover the magnet. Now make a solenoid out of the tube by winding the 35 gauge wire around it. I don’t remember how many turns i did. But i stopped when it looked like this:

Step 3: Fit this coil at the center of the balloon diaphragm

Step 4: Cut a foam board piece of about the same size (not really necessary but looks good!) Keep the magnet at the center of the board. Drill 2 holes in the PVC pipe to get the terminals of the solenoid out

Step 5: Now keep the diaphragm on top of this such that the solenoid comes around the magnet. Connect a salvaged Audio Jack to these terminals

The Whole assembly looks like this:

Okay, so this is what is going to happen:
When i connect the Audio Jack to my iPod and play music, electrical signals will be transmitted and they will pass through the solenoid coil. This solenoid, thus, will become an electromagnet when the signal strength is high.
In other words, the solenoid is activated at the same frequency of the audio signal.
When the solenoid is activated, it will be attracted towards the magnet and so, the balloon diaphragm will be stretched downwards. When the solenoid is deactivated, the diaphragm will come back up.
All this happens at the frequency of the sound signal. Which means, that the balloon is vibrating with the frequency of the signal. What does that mean?

Check the Video:

And this one

Deepak, Sandeep and Arnav, we made it!

Extra Info:

http://electronics.howstuffworks.com/speaker5.htm

I kinda wanted an RC servo type characteristic in a DC motor. Or to put in other words i wanted a RC servo motor capable of spinning continuously. (For those who are unaware, an RC servo can move from 0-180 degrees only. It is generally used in robotic arms, humanoids etc)

As i realized, it is not difficult to modify an RC servo into a DC motor.
The video below explains it

It is based on a really simple, basic fact (which is the reason why I liked it). All colours can be resolved into their R, G, and B components.

Let’s say the intensity of the R, G and B colours varies from 0 to 255. Based on the weightage of Red, Green and Blue components, the resultant colour can be

• Yellow(R = 241, G = 251, B = 60)
• Pink (R = 233, G = 44, B = 228)
• White (R = 255, G = 255, B = 255)
• Or any other colour… I got this data from the colour editor of Paint.

So if I get hold of red, green and blue LEDs and modulate their intensity, I could make different colours! When your office is the R&D centre of ThinkLABs, you don’t even have the stretch you arm to find LEDs(That was metaphorical, of course. I had to cut through Harshad, Harish, Thomson and a pile of undefined junk to get to the workstation…).

I found Ultra bright LEDs of all 3 colours.

Then I got hold of AVR Prostik – a small ATmega16 development board, and started programming…

My agenda:

1>    Keep all three LEDs close together, connect them to 3 different PWM outputs of AVR(The concept behind changing the intensity of LED is to change the Duty Cycle of a high frequency PWM signal. More ON-time = More Bright).

2>    Program the AVR such that the Intensities of the LEDs vary.

3>    Project the beam of the LEDs on a white paper so that they overlap. This is how I’ll see the resultant colour.

I glided through the programming part. But there was a problem with the arrangement of the LEDs. There was an overlapping part, but it was too small as compared to the Beams coming from all the 3 LEDs. As a result, you couldn’t really see the colour as you expected to.

I tried another arrangement in which the LEDs were upright and a bottle with a milky white texture on top of them. The milky white texture helped in mixing the sharp beams. Now I saw Colours!

My next step was to program a sequence of changing colours. So I opened the colour editor of paint, moved my cursor across the different colours and observed the pattern in which the R-G-B composition changed.

I figured, to change colours from Red to Yellow to Green to Blue to Pink to Red again, I had to change the R-G-B composition as follows:

Keep Red at 255, Green at 0 and Blue at 0,

Increase Green keeping others constant,

Decrease Red keeping others constant,

Increase Blue keeping others constant,

Decrease Green keeping others constant,

Increase Red keeping others constant,

Decrease Blue keeping others constant… and so on…

Here’s how it looks…

The Making…

The Good: I had to make a small Solar Bot

The Bad: It had to be designed in just one week!

The Ugly: I didn’t have enough component samples…

So I went online and did what any self-respecting hobbyist would do, logon to solarbotics.net

Since I really had a week to design, I didn’t count on spending time on optimizing my bot for a better performance. So I promised myself that I would improvise the bot later and went on to copy the circuits in the resources section. The circuits that you design for running the bot, are called ‘Solar Engines’.

The working principle of these engines is more or less the same: Charge a big capacitor through a solar panel and when you think the cap is charged enough, release all the energy through the motor in one go. Then again wait for the capacitor to be charged.

The Engines are broadly defined in to 3 types:

1>     Time Controlled: The charge is boosted from the cap in periodic intervals. It doesn’t wait to check whether the cap is actually charged or not.

2>     Charge Curve Controlled:  The charge is boosted to the motor when the charge curve slows down. i.e we assume the when the curve becomes flat, the cap is charged and release the power.

3>     The voltage controlled: when the voltage across the cap rises above a specified level, the power is given to the motor. These types of engines are the most common.

I, of course, chose to go with my fellow robotists and started working on the Voltage controlled Circuits.

The major components that you might need for this type of Solar Engines are:

A Voltage detecting IC:

a transistor:

a super capacitor (i.e. a capacitor with a big value)

and a solar panel:

Although I knew I didn’t have much time, I wanted to try all the voltage controlled circuits explained on different websites. Solarbotics.net seemed to satisfy me with most of my requirements.

So I tried the following circuits: (I wouldn’t want to steal credits deserved by solarbotics.net So instead of explaining them here, I’ll direct you to their link)

1>Zener diode based SE (Solar Engine): http://solarbotics.net/library/circuits/se_t1_zener.html

2>1381 based SE: http://solarbotics.net/library/circuits/se_t1_1381.html

3> Miller Engine SE: http://solarbotics.net/library/circuits/se_t1_mse.html

Whew!!… 3 days up building debugging and tweaking the circuits. Now I had to fix one engine and I chose the last one.. the Miller Engine. It seemed to bee a pretty efficient engine.

(BTW, I was building these circuits on a breadboard and testing them with a 200W bulb. The Miller Engine worked pretty well. Even after I turn the bulb off, the motor worked for around 20-30 seconds, which is pretty cool. But now I had to get it out on a field run…)

So then I built 1,2,3 PCBs as prototypes and the 3^rd one worked just fine. The motor, now acting on load, did not run as much as it did when it was on a breadboard. But I was happy with it.

What I soon realized was that, by changing the contact area of the motor, I could make it run for longer,

i.e, if the motor is inclined such that more of its shaft is in contact with the ground, it runs faster, but since the load is more, it doesn’t run as long when the bulb source is removed. If I change this inclination such that lesser area is in contact with the ground, the motor runs for a longer time comparatively.

Have a look at the videos; the bot is kept in direct sunlight falling from the window of my room.

Among different communication interfaces, i chose the serial interface for the obvious reason that it’s ‘the’ most easiest port to work with. (Actually i really feel sad that it is now termed as a legacy port and now even some desktop manufacturers choose to exclude it.. )

The reason why i wanted to write a bootloader was that i wanted to interface avrstudio to one of our avr development boards.  AVRSTUDIO has programmer interfaces like STK500 and AVRprog.  The idea of writing a program and burning it using the same software is appealing and easy for my students (as i have mentioned earlier, i conduct workshops)

So i went about reading the protocol of both the interfaces AVRprog and STK500.. At first the AVRprog protocol seemed way easier than stk500.. So i went about writing the code for it.. The protocol is explained in the avr109 application note..

It’s really nothing different.. you recieve some command bytes via USART, decode those commands and execute the appropriate operation. Some standard operations are Page erase, Page load, Page write, Page read etc.. The datasheet of the device explains clearly how to accomplish all of these tasks..

now, i finished this code in very less time and after some debugging, it worked perfectly well with winavr’s avrdude utility..  B-)

Now as went off to boast about it in the avrfreaks forum,  i learnt that avrprog is no more supported(or something to that effect). :’(

i needed some work to do in order to make my bootloader compatible to avrprog. But i scraped the idea and thought of writing a stk500v2 compatible bootloader.

After a long break, i started doing that. No new concepts are needed here, just the protocol is a little long..

It is described in the avr 068 app note

I have almost finished it but there is still a problem.. It does not work perfectly at the baud rate of 115200.. i’ve tried baudrates lower than that and it works fine..  B-)  B-)

So here’s the story till now.. Although i’m in a fix, i think some of you who are going to attempt writting bootloaders might get some kind of idea what they are about to do.. Its great fun doing it.. and when you finish, you’ll want to boast.. comment on this post if i’m wrong..

But i’m tired( and very hungry) so, i’ll mention the details tomo.. But ya, though “writing a boot loader” seems an intimidating task, its actually very easy…

btw: i have started programming in assembly again and i feel nostalgic..

also, i have developed this code from scratch(well, with help of couple of scratches from here and there!) in 3 days.

The idea is to change the perception of remote controls. As of now, remote controls are cool, small, crisp handheld gadgets which can control tons of machines. They have different coloured, shaped, textured buttons which can command machines. Well, I just removed the buttons..

Say, how would it feel to control a racing robot with gestures instead of buttons? Just wear this glove thingy which has a sensor thingy, which can understand your hand gestures. This sensor thingy will transmit an appropriate command to the bot and, well, the bot behaves accordingly..

The Sensor thingy, of course, is the accelerometer. It measures the change in acceleration. Details later..

So what I present is the most crude form of the Gesture controlled Robot. It understands only 4 commands: Go Forward, Reverse, Left and Right. Attached below are some videos.

Before I start the tutorial, let me introduce you the accelerometer.

Accelerometer is an example of MEMS. MicroelectroMechanical Systems. Which simply means, micro dimensional mechanical moving parts in small packages like ICs. So an accelerometer has moving parts inside it!

This is how big an accelerometer is.
Basically, the most common types of accelerometers are of capacitive type.

If you want more details of the inside working of the accelerometer, refer to this: http://www.ett.bme.hu/memsedu/

So accelerometers sense accelerations right? Which means it senses acceleration due to gravity too..

When I tilt the sensor, I don’t change the magnitude of the acceleration acting on the accelerometer. But I change the direction. I have used the MMA7260Q accelerometer from Freescale. This is a capacitive sensors and gives an analog voltage proportional to the acceleration.

Most of the sensors can sense acceleration along all 3 axis. Mine does. So I have 3 analog voltage outputs.

Here are some considerations to make while choosing an accelerometer:

Sensitivity: The sensitivity of accelerometers can be programmable. The unit is generally G. 1G means the acceleration due to gravity. The highest sensitivity I have seen is 1.5 G. So a slight movement can be detected with this G setting. To sense sudden shocks, we will have to use the 10G setting.

Output: Many sensors can communicate in a protocol like I2C/SPI. Use them if u plan to use more than one sensors. Otherwise, simple analog voltage outputs are ideal for small projects.

My MMA7260 has the following values:

Sensitivity: Selectable 1.5g/2g/4g/6g

Output: 3 Analog output channels (for 3 axis)

They way an accelerometer is used is like this. When no acceleration is applied on the accelerometer (or equal acceleration from both sides), it gives a voltage output which is at the mid point. Since MMA7260 works on 3.3V, this value will be 1.65V.

When u tilt the Accelerometer on one side, the reading will increase from 1.65V to 3.3V.

When u tilt it on the other side, the reading will decrease from 1.65 to 0V.

Same for the other axes..

Now, all that said, here we go….

Things u’ll need:

A robot chassis with 2 DC motors.

An accelerometer circuit.

A motor driver circuit (I used TRI’s Motor Driver Board)

A microcontroller circuit. (Try to use a microcontroller with inbuilt ADC, this will simplify the circuit. I have used TRI’s miniAVR iBoard which has an ATmega8)

mini iBoard with accelerometer

Power Source. Batteries sound better.

Interface between Microcontroller and Motor Driver. The microcontroller-Accelerometer circuit will be in your hand and the motor driver will be on the robot. The interface can be wired/wireless. I made wired coz at that time I did not have a reliable RF-Module, plus wired remote control really simplifies the project.

I could give you the circuit for each component but it really won’t help a lot coz mini iBoard is really a general purpose development board and Accelerometer and motor driver circuits are well explained in respective datasheets.

The motor driver circuit was assembled on the bot as shown. The accelerometer circuit fits directly on the mini iBoard. An FRC Cable sends signals to the motor driver board on the bot.

The reason why every thing looks so compatible is because I had designed this for a workshop on advanced sensors. But, hobbyists can do this on a breadboard itself.

Here’s the algorithm for the code I burned in the microcontroller.

Flowchart

The reading I get from ADC is a value between 0 and 255 which is proportionally scaled between 0V and 5V.

I have compared the X axis value with X-reference +10 and X-reference-10 on purpose. This gap of 20 will not be in the active region. Meaning, the bot will do nothing in when the X-axis value is near Xref. This adds a little control to the robot. Otherwise the robot will constantly be moving, making it difficult to control.

I think I have given a feel of the gesture bot and fairly proved that it is as easy as making an obstacle avoider or line follower.. I may improvise my bot with speed control and wireless interface..

Am I missing anything? Lemme know..

Today i was preparing a demo for my students about ¨PCB etching process¨.

Figured, it might be useful here as well..

This is a simple (and actually, a widely documented) method of etching PCBs at home.

More than the application value, its the fun value that appeals to me..

The materials you´ll need are:

1. A single sided copper clad board – Find it in electronics/hobby shops. 20-25Rs per piece.

2. A4 size Photo Paper Computer shops sell papers like this. 10Rs per Paper.

3. Ferric Chloride Powder. This Pack, i got from one Gala Electronics in Mumbai.

FeCl is a traditional ingredient. There are other solutions such as this, http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!–A-better-etc/ which is more modern..

1. An Iron. Yeah, even I don´t have it. I borrowed my room mates iron.

2. A PCB Hand drill (Not in the Picture)

Step 1:

Create a schematic on your PCB Software (mine is Eagle). And create its PCB Layout.

The one i´ve shown here is the layout for our line sensor modules.

Now, to take a print of this layout, select only bottom layer and pads.

Take a monochrome ()Black and White) printout and edit it in your favorite graphics software. Ex- CorelDraw.

Take a mirror Print on a Photo paper. Why mirror? Youĺl find out later.

Note that the print should only be with a laser printer. The ink used in laser printer sticks to copper.

So, do not use anything but laser printer.

Paste this paper, printed side down, in the copper clad. Use clips/tapes/feviquicks anything to make sure that the paper doesn´t slide over the copper clad.

Now, turn on your iron at full heat and press it from the backside of the paper. Hold it in position for around 8-10 Minutes.

By now, the paper should be stuck to the PCB. Let it cool down.

Immerse this apparatus in water. Add a little detergent for better results

Delicately, remove the paper from the PCB. This is how it should look. Since I was in a hurry, I did not hold the iron long enough. So, the last 2 Pictures were not printed on the PCB.

In some tracks, the ink doesn´t stick completely. Use a permanent marker to touch up in these parts. The marker should be alcohol based. Just to play safe, I traced the whole PCB with the marker.

Now take some water in a plastic bowl and add the ferric chloride powder to make a solution. This solution is acidic. So don´t touch it. Also, do not use any metal container. Plastic is inert to FeCl.

You may add 2-3 drops of Hcl to catalyse the reaction.

Immerse this PCB in the solution and keep rocking the bowl.

After some time, youĺl notice the copper dissolving in the solution. If you feel this reaction is happening a little too slow, you may add more FeCl.

When you see that there is no copper on the board, remove it an wash it in water. Now the copper beneath the track is intact and the exposed copper is washed off.

The PCB is complete. Remove the Ink using an alcohol based solution (I used Xylene). A fine sand paper or ¨Scotch Bright¨ will also do.

Make the holes using a PCB Hand Drill.

Thats it, mount the components and start soldering..

As to my PCB, I´ve made better PCBs so I´m not satisfied with this one..

Learn from my mistakes.. Don´t hurry…

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