7. Electronics design¶

Assginments¶

Redraw the echo hello-world board, add (at least) a button and LED (with a current-limiting resistor) check the design rules, make it, and test it.
Use the test equipment in your lab to observe the operation of a microcontroller circuit board

Let’s Start¶

I started with basic electronics. The default hello world is here.

I needed to add a push button and an LED to this existing design and resistor to ensure only the right amount of current passes through the LED. The Microcontroller( Attiny44) already has an 8Mhz internal clock. But we are adding an extra 20Mhz resonator for more accuracy and precise clock applications.

Pull Up and Pull Down Resistor

I read about pull-down resistors from this article. A pull up or pull-down resistor is used to remove the floating voltages and ensuring higher or lower states in the microcontroller pins so that it can read the values accurately. A pull-up resistor ensures a high state and a pull-down ensures a low state.

Eagle
To redraw the schematic and board I used Autodesk Eagle software. It is free for students and startups. It can be downloaded from here.

One advantage of this software is that the schematic can be realized in parallel to the board, so all the components that are inserted in the schematic are also inserted “physically” in the board. The same goes for the connections between the components.
By default, Eagle does not have a component library, so I downloaded eaglefab library and loaded it into the control panel window. The library contains the information of some components which include in addition to the technical characteristics, also the physical dimensions and the dimensions of the footprints.

Steps to add library

Download the Eagle Library Fab.lbr
Save it in the Eagle’s library folder.
Click on Options-> Library manager.
Click on the “available” tab and search for the saved library. Then click “use”

Adding components¶

To add components to your schematic, select add tool.
Now in the popped-up window, search for the required component and click OK.

After adding all the components, place them at the correct position using the move and rotate tools.
Next, wire all of your schematic symbols together with nets and add values and part names.
Final schematic