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6. Electronics Design

This week I learned how to drew the circuit board, mill, solder and test the board.

The design rules

Basic electronic components & symbols

  • Capacitor To protect the board from damaging may be caused by the varies input power. Always connects to a resistor of 10 K.
  • Diode
    Please pay the attention to the direction.
  • LED (Light emitting diode) Always connects to a resistor to control the current, in case short circuit will break the LED. 1000 Ohm match the LED Red, and 500 Ohm match the LED Green. Always pay attention to the direction.
  • Transistor
    As the most important component of modern electronic, they can be used as a digital switch, eg 0001010. The transistor is necessary, especially the circuit has different power.
  • Crystal/Resonator
  • Micro-controller (IC, integrated circuit)
  • Switch Button The one side of switch connects to the GND, the other side connects to the VCC.
  • Resistor One resistor connect to the VCC and Reset Pin, which could tell the IC that you’re on. And resistor is needed for lower current.

How to draw the board beautifully?

  • VCC=Voltage, the board normally connect to 5 V powder.
  • By pass capacitor is necessary.
  • For the whole board, all the VCC and GND pad should be linked by the lines.
  • The width of the line in the design is normally 10 mil. Bigger line could be make the soldering IC process simple, such as 12 mil for the lines connected to the IC pad.
  • For 1/64’‘ endmill, the clearance around the traces should be 16 mil.
  • Capacitor & resistor & micro-controller are necessary components for each board, it’s better to put them close to each other.
  • Please check the circuit before export it as .png files.

PCB CAD software—Eagle

  • Install Eagle 9.6.2 version.
  • Copy the fab.lbr into the folder Eagle/libraries.
  • Open the Eagle, click File-Create-Sketch, add the components by click add part, click the SCH/BRD to switch.

  • The IC I use is ATTINY44-SSU, other commponnets can find the right sizeo in the fab libraries.

  • Set the design rule. Open Tool- DRCdiaglue, clearance change to 16 mil. Click ” sizes”, Minimum Width changes to 10 mil.

  • There are two ways to connect the different components. Firstly, use the net line to link them. Secondly, use Autorouter.

  • Autorouter can link the components according the name of each line. Different positions of components could led to different circuits. Keeping changing the positions of components to find a neat circuit and get a 100% connected circuit. The operation is simple, but the process really kills time.

  • After ” Autorouter “, we can change ” Grid ” to 5 mil to correct the lines and enlarge the space between lines.

  • There are three lines passing through the middle of micro-controllers, please keep the gap between traces big enough for end mill to pass through, more than 4 mm. The size of the board is 50 mm* 50 mm.

  • Check the design rules, to see whether there is erro lines or not.

  • Save as .png(Raster), check the size of board is no more than 50 mm * 50 mm, and create hello world trace image and hello world outline image by GIMP or PS. Pease notes that certain raster softwares may enlarge the size of pictures without asking you.

Mill the board

  • Open the images in the Fabmodules， chose image(.png)---hello world trace.pgn, click output format--Roland mill(.rml), process-PCB traces(1/64), “PCB outline endmill (1/32)” for “hello world outline.png”.
  • The machine we use is SRM-20, X0: 0, Y0: 0, Z0: 0, Zhome: at least 10. The cut depth is 15 mm or 2 mm, which is a little bigger than the thickness of the board.

  • Click calculate, you will get the .rml file.

  • Cut the board by SRM-20 Machine, choose 1/64 int end mill for the trace and 1/32 int end mill for the outline.

  • Get the circuit out of the copper board with a ruler, and polish the surface with the ruler gently.

Solder the board

  • Find the components for the board. Resistor—10 K Ohm * 2, 500 Ohm * 1 LED Green, Capacitor—0.1uF * 1 IC— ATtiny 44 a Switch Button or Push Button, its pins go through hole, and I cut part of them and make them flat. Resonator ISP 2 * 3 pin FTDI, the pins are a little bigger and I cut half.
  • Find the location of each component.
  • Also pay the attention to the direcation of IC and LED. The black dot of IC is close to the No.1 pin.
  • The pins of the IC and resonator is small and hardly to fix well. So I firstly fix one pin of them and solder the second pin, then solder the first pin again. To control the quantities of metal, I solder the line connect to the componnet and push the metal to cover the little pins.
  • After finish soldering, use alcohol and toothbrush to clean the board.

Test the board

  • The hello world board need a FabISP to communicate with the computer.

  • Open device manager and check the connection of FabISP.

  • Download Makefile file, rename it exactly as “Makefile”(no extension name), run it in the command board, it produces the new files on my computer. Open it and use the proper codes to build the firmware for the board.

  • Run make program-usbtiny-fuses in Git Bash.

  • Run make program-usbtiny

  • Input hello Alisa

Problems & Errors

  • I use GIMP to check the size of the image, I didn’t how to check and used the Inkscape instead. GIMP really spent times, next time I will use PS to check & create images.

  • When calculating the circuit, the lines traces that pass through the IC lost (as shown in the picture) , so the line was drawn again in the GIMP.

  • My first hello world board only works for first several hours and couldn’t program later. We use multimeter to test the circuit and attempt to find the problems and fail.

Update

As my first FabISP and hello world don’t work and checking the circuit by multimeter doesn’t give any help. In case the components don’t work, so I cut and solder my second FabISP and hello world this week, and use make. file to set the firmware for the second board.

  • Run make program-usbtiny-fuses in Git Bash.

  • Run make program-usbtiny in Git Bash.

The new hello world board works well means the components are OK.

Files

hello world.brd

hello world.sch

Last update: June 23, 2021