PCB Fabrication

Well after you have built your circuit. You need to realize that circuit to test or deploy. 

Single Layer Non-Commercial PCB Fabrication Process Sequence

  • Make Your Schematic in any EDA tool like KiCad, Eagle, Express PCB, Proteous.
    Note: These EDA tools are not inter compatible with each other so make sure to use the appropriate tools
  • Make the PCB Layout using EDA tools.
  • Now there are two type of output
    1. Graphic output (PDF, JPEG, BMP, SVG)
    2. CNC text output file or Gerber files
  • After you made you PCB layout. The base file consist of copper layer and silk layer.
    Copper Layer: This where all your traces (connecting wires) reside.
    Silk layer: This layer consist of the graphic layout. It for the accessibility of the user for easy insertion and Post production annotations. You can avoid this if want.
  • Two methods of etching
    1. Tonner transfer : In this method the plastic tonner of the laser printer is transfered to the PCB by the application of heat. 
    Heat can be applied by using the Laminator or the cloth iron.

    2. Photoresist method : This is an old method. It produce neat result but it takes a lot of step for understanding. 
    Three steps of photo resist development.
    a. Apply photoresist film
    b. Apply Mask
    c. expose the film under UV light : This can be done by placing the copper clad board into bright sunlight for a brief period of about 10 minute(try a test pcb for the correct exposure time) or you can place the board under a UV LAMP
    d. develop the photoresit by submerging the board into a solution of a sodium carbonate (1 gm of sodium carbonate into 500ml of water)
    e. etch the board by submerging the board into any one of the following solution.
     1. ferric chloride (dissolve ferric chloride into 200ml-300ml water till it becomes saturated)
    2. Muriactic Acid Solution (muriatic acid solution)
        (Old name for HCL)
    3. Copper sulfate + sulfuric acid
    4. Nitric Acid
    5. Hydrochloric acid + hydrogen peroxide
    f. rinse the board in water.
    g. photoresist removal : submerge in sodium hydroxide solution
    h. rinse the board in water.

Rewriting lfuse and hfuse of Atmel Atmega series

Atmel Atmega micro controller if set correctly will work fine. But when you tinker with its setting. Things get out of control. One such problem is when you set the wrong fuse setting of the device to use the external crystal oscillator.

  1. Connect the microcontroller with the USBASP programmer
  2. Open the command prompt 
  3. write the command
    avrdude -c usbasp -p m32 -t
  4. This will open a terminal where you will write
    read lfuse
  5. Note down the settings
  6. Then write 
    read hfuse
  7. Calculate the correct fuse setting and then write
    avrdude -c usbasp -p m32 -U lfuse:w:0xe1:m -U hfuse:w:0x99:m


These setting specified in the above post is incorrect. 
Calculate the fuse setting in advance
Also remember the JTAG pin will also be set correctly
Never Change SPI setting without reading document. Changing this setting will result in non-functioning of SPI and the programming can only be done with manufacturer programmer. 

The above said procedure is verfied on the follwing micrcontrollers:

  • ATMEGA16
  • ATMEGA32

Temperature Controlled Relay

This circuit uses very basic components. The use of mm74c922 integrated circuit makes it different from other. This hardware based scanning makes the code really simple. 

The use of Atmega16 can be avoided but this allows for complex coding structure to be stored. Due to cost associated with the micro controller. 

External crystals are avoided as the device will be used for low frequency of up to 100 Hz. Which can be used easily be handled by the internal clock. The deviation of clock timing should be taken into account when programming.

Schematic of Temperature controlled relay

The LM35 series are precision integrated-circuit temperature devices with an output voltage linearly-proportional to the Centigrade temperature