Microcontroller and Embedded System Design

Introduction to my microcontroller and Embedded System Design Blog
For last two years I am working on microcontroller and embedded system design. I have worked with 8051, Atmega16/32, PIC 18F4550 (for USB) and will be working on ARM. I have little experiance on CPLD and will learn FPGA in this semester only. So I decided to start this new blog series related to microcontroller. For the starting I will use 8051. Architecture and assemble programming. After that I will switch to embedded C. Once we are done with 8051 we will move on to more complex microcontroller. Learning microcontroller is great fun. You can see the fruits of your labor. I hope that I will be able to give something which will benefit someone.

Home made C-V measurment system

My dual degree project is fixed and I am going to work on Nano devices. So surely I will be doing some HEMT fabrication and there characterization. Most common of electrical characterization is C-V measurement at different frequencies. So first challenge is measuring Capacitance (C) of the device. We had C-V measurement system in our lab but unfortunately it is shifted to electrical department and I am not in mood to go to EE department every time I want to do my measurements. Setting up a new CV setup is costly, A LCR meter from Agilent itself cost Rs 9 Lakh and we are not in mood of spending money on it. So I decided to make our own C-V measurement setup. Now I know some of methods which are used to measure capacitance.

1. Charge the capacitor with constant current source and then see how the voltage changes across the capacitor. Assuming ideal capacitor we can find capacitance equal to current / (time rate of change of voltage ). Well this method is simple but not accurate and many multimeter uses this method and there are very cheap so I am not going to this method.
   
2. Apply an AC signal across the RC circuit. Measure the voltage across the resistor or capacitor. The phase shift , amplitude difference between these signals will give as value of the capacitance. This is the method which is widely used in the more sophisticated instruments which cost lakhs. So I am going to use this method.

Now after deciding my method I am going to need some instruments. I made some circuits for both signal generator and aquaring data of voltage drop across the resistor. But since I need more sophisticated instrument I decided to use the Tektronix AFG3000 signal generator and Tetronix TDS1012B oscilloscope both of the instrument is available in my lab. I am going to use matlab for the data controlling the signal generator and acquiring the data from the oscilloscope. A Graphical user Interface will be made so that user can choose range of capacitance measurement and other tasks. This is what I have done so far , I will update the blog as I will go through the project

Home Made PCB using Toner Transfer Method

Making a circuit , soldering all components connecting them using wires etc are always been very painfull to me. So I came up with this solution of making PCB in home. In india it is really very difficult to find some shops from where you can get ready made PCB. Even if you find some shop (like i found one ) it will be very time taking ( you have to give order and then wait till it get ready and usually take one week or so ) and costly. So here we go.

Check list before you start.

1. Glossy paper (the one used for photoprinting and can be bought from any photostudio).
2. Blank copper PCB.
3. Ferric Chloride.
4. Acetone and Isopropenol (optional)
   
5. Liquid tin

Steps to follow-

1. First clean the PCB inorder to remove dust and oxides. You can clean it with VIM. (optionally you can clean it with iso proply alchohol).
2. Design you layout using the eagle software (you can download the free version just google it).
3. Take the printout of the circuit layout (mirror image) in the glossy paper.
4. Now heat up the iron, put the PCB on table and pre heat up it with iron and printed glossy paper on top of it heated PCB, be careful because the glossy paper will stick on the PCB so you have got only one chance to place the paper carefully.
5. Now put normal paper on top of the glossy paper and use iron to further heat. Put pressure so that the print get transfer to the PCB.
6. Once done with above step , let the PCB cool for some time to normal temperature and then put it in the water. Glossy paper will can now easy be removed from PCB just using thumb. After removing the glossy paper you can clearly see the Print on PCB.
7. Now take some Ferric chloride solution, heat it to 70 degree and then put the PCB in the solution and stair it for some time. (handle with care it is dangerous , avoid direct contact with skin - use mask and gloves).
8. You will see that the copper where the print is not there is been removed. Use window cleaner or nail polish cleaner to remove the remaining black print in PCB. (optionally you can use acetone or ask the printer guy the solution he uses when his clothes get dirty with the colors ).
9. Now you are left with the clean PCB with circuit treks in it. To avoid oxidation and good soldering use dip the PCB in liquid tin