I began this week by going through all the basics again. The last time was about what a PCB is, it's type and the components on the PCB. This week was how to use them create your own board, by drawing a schematic drawing for the same. The basics of PCB and components can be accessed from HERE

So before I begin drawing a PCB I need to know the basics of a circuit. What is a circuit, how electricity flows through different components? The following links explain all this in a very simple manner.

A particular IC is categorized as either linear (analog) or digital, depending on its intended application. From what I understand IC is the brain of a circuit and it controls all event happening on the board. The following link explaining all about IC's

Knowing the different type of IC’s is crucial as well.

Here's a very shallow breakdown of the micros in my world:

PIC - This is the classic micro form Microchip. Very simple, very proven, but it lacks many of the features that other mfg's are building into their chips. This is a big deal for me. I was a die-hard PIC person for years and I've started to see the limits of PICs and the benefits of other micros!

AVR - This is basically a direct competitor to PICs. They do everything a PIC does, but in my new opinion, better, faster, cheaper, and simpler.

MSP - These are very good micros by Texas Instruments (TI), not as beefy as AVR or PICs. However, they truly excel at low-power applications. More on this later, but imagine running a complete system on one AA battery for 5 years. This is in the realm of nano-amp current consumption. Crazy!

ARM - Why are all these three letters? I don't know actually… ARMs are the new kids on the block and they are huge. Very powerful, very low-cost, they are taking over the world but can be really intimidating if you've never played with a micro before.

8051 - The '8051 core' was the de facto standard in 8-bit (and 4-bit!) microcontrollers. Developed by Intel in the 1980s, it still seems to be the instruction set they love to teach you in college. They are based on archaic, but field proved instruction sets. Very old tech in my humble opinion, but these ICs have been significantly improved over the years (now Flash-based, ADC, SPI, etc.).

68HC08/11 - Another very common instruction set developed by Motorola. Extremely popular, and a micro commonly taught at university, it's the microcontroller I love to hate. These original micros often lack onboard RAM and flash-based memory.

Each one gets utilized as per requirement of the board. The cost of each varies depending on their function and capabilities.

To understand each component such as an IC the manufacturer of the same provides a DATASHEET.

Datasheet

A datasheet, data sheet, or spec sheet is a document that summarizes the performance and other technical characteristics of a product, machine, component (e.g., an electronic component), material, a subsystem (e.g., a power supply) or software in sufficient detail to be used by a design engineer to integrate the component into a system. Typically, a datasheet is created by the component/subsystem/software manufacturer and begins with an introductory page describing the rest of the document, followed by listings of specific characteristics, with further information on the connectivity of the devices. In cases where there is relevant source code to include, it is usually attached near the end of the document or separated into another file.

For example:

The Datasheet of a microcontroller will have the following:

-Description

-Configuration summary

-Block Diagram

-Pin Configuration

-I/O Multiplexing

-Resources

-Data Retention

-About code examples

-Capacitive Touch Sensing

-Packaging information

This provides a comprehensive data on how the MCU can be used.

To further understand how to read a datasheet, the following link is very useful

Understanding Pinout

In electronics, a pinout (sometimes written "pin-out") is a cross-reference between the contacts, or pins, of an electrical connector or electronic component, and their functions.

The functions of contacts in electrical connectors, be they power- or signaling-related, must be specified in order for connectors to be interchangeable. When connected, each contact of a connector must mate with the contact on the other connector that has the same function. If contacts of disparate functions are allowed to make contact, the connection may fail and damage may result. Therefore, pinouts are a vital reference when building and testing connectors, cables, and adapters.

The pdf provides basic information on how to read and understand a pinout. The pinout diagram for each IC is different and its specified in the datasheet for that particular IC. There are such well-designed pinouts that make reading them very easy. At least for me as a beginner was really helpful to have found one of these.

Hence to design a circuit its not just enough to understand the working of the circuit but also to understand in detail all its components and how to connect them. The following links are really good to read to understand the basics of a circuit.

Note:

From my personal experience in trying to understand electronics, Sparkfun was a really great website because it has all information and really great tutorials for beginners that are explained in simple language.

Eagle

Eagle is PCB designing software. Its a really powerful software with really great features. As post to manual designing, these software really help make life easy. The software is very easy to use and is merely drag and drop. The software can be download from here:

And the tutorials fro the same from here

Note the youtube tutorial is for an older version nonetheless the basics are the same. The second links explains all the new feature of eagle.

Scheme

The task is to redraw the Hello-Echo board. This is the scheme of the board

These are the list of components required to design this board

 Component list:

1x ATtiny44

1x 10kΩ resistors

1x 10uF Capacitor

1x FTDI Header

1x 6 pin AVRISP Header

1x 20Mhz Resonator

Additional components:

1x Red LED

1x 1kΩ resistors

1xPush button

Once all the connections are complete we can switch to board to see how we can arrange them. To do this click on file and switch to the board

All the components can be selected, drag and drop them into the dark black area.  Now arrange the components in the desired shape, but keep in mind that placing the components close to the components it's connected to helps avoid crossing of the line.

Then when the components are arranged in the desired format, its time to set design rules. The DRC(Design rule check) can be accessed from the tool menu. This opens a window where the rules need to be set by the user. The little graphic on the side gives an idea of what parameters you are changing. As a default, I set everything to 13mil which is approx. 0.3mm. Also from the sizes tab, I made my minimum width of the trace to 13mil

Now the rules are set. The next step is to route it. Meaning to connect all the components with traces. I used the auto route feature for this.

At the first attempt getting a 100% may not be always possible. From here on you can evaluate the design and make modification yourself or you can cancel the job and reorient the components again to a more effective position.

After a few attempts, I got a 100% routing. Yet the routing didn't seem efficient. So I modified them a little to suit my needs.

The designing was done. Now its time to export it for trace and cutting. To do this its necessary to switch off the unnecessary information. In the view, menu click on layer settings. This will bring up a window with layer settings. Here you can switch on only the top layer if it's an SMD board. This will show only the traces on the board.

Then file and export as image. Set the location and dpi and do not forget to click on monochrome. This gives a b/w image that's necessary for cutting and tracing.

Once I got the trace file. I took it to Krita cropped it and made the cut file from it.

Unfortunately, my lab was out of Attiny 44. So I was unable to solder the board.

But to understand more about pinouts and other processors I tried to redraw the same board but instead of using an Attiny44 (14 pins), I tried to do it with AtMega328 AU (32 pins).

To do this I need to understand the pinouts for both the boards. I think it is in this process I learned a lot about boards. Trying to find the right connections and why I would have to connect A-B and not to C. It was really a great learning experience.

Pin connection:

As seen in the picture the MISO MOSI AND SCK pins vary in the two MCU’s. The PA6 pin in attiny44 is MOSI where as the atmega doent even have a pin named PA6. When comparing two IC connections, its not right to match them using the port pin name . They have to be connected as per the pinout chart or the datasheet provided by the manufacturer. One post pin can be used for multiple uses like the PB3 pin in AtMega has IO, MOSI,OC2A and 12th Arduino pin. Depending on the connection to that pin the program needs to be specify its function.

I was successfully able to draw the scheme and take it to board.

Auto-routing was almost useless until I placed all my components far apart. So I partially autoroute it and started modifying the traces myself. But almost all the time I got stuck with the one or two traces. Here is the result of my last attempt, still one trace left.

TRI Board

So being unable to solder the hello echo board I decided to design my own board with an RGB led and a switch using AtTiny45. I took it eagle again to design my scheme.

Component list for TRI:

1x ATtiny45

1x 10kΩ resistors

1x 1kΩ resistors

1x 6 pin AVRISP Header

1x RGB LED

1x 1kΩ resistors

1xPush button

Having finished with the scheme I took it to the board to change the layout. I wanted to design in a way that has my processor in the middle with the switch and led to the extreme ends. Autorouting worked great for this board yes I made minor modifications and added text to name the board.

Having finished with the scheme I took it to the board to change the layout. I wanted to design in a way that has my processor in the middle with the switch and led to the extreme ends. Autorouting worked great for this board yes I made minor modifications and added text to name the board.

I exported the trace having finalized the design and began the milling.

During the milling week, I had used the local version of fab modules, but I tried using the online module to mill this board.

Using double-sided tape to secure the PCB on the milling machine

In addition to the last milling, I didn’t use a sacrificial board. So this time I used a sacrificial board, used another fr1 board.

Then went to fabmodules.org to access the module. To make the machine communicate with the computer I opened up the terminal and used the following command

Cd Desktop

Cd fabmodules

This gets me into the folder where I had cloned fabmodule. Detailed instruction for the same can be followed from here

https://github.com/FabModules/fabmodules-html5/wiki/How-to-install

Then I entered the following command to make my system talk to the machine

Npm start

Having established a connection I went back to the site to configure my input and output setting.

I selected png as input format, .rml as output format, 1/64 trace, and MDX-20 machine.

These are the parameter I used

Cut depth - 0.13mm

Tool diameter - 0.4mm

Offsets - 4

Offset overlap -50%

Path error 0

I calculated the path and began the milling process

The board looked absolutely fine. The traces did not overlap or touch each other. Having done with milling I went on to solder the board. Another important challenge I faced while soldering is having to identify the orientation of RGB led. Thanks to Gautam I was able to identify that.

This is TRI board after soldering.

Programming

As I didn't know programming I had a help of a friend to do so and also I kept referring this tutorial that was super useful.

To program the board I used Arduino. Arduino software can be downloaded from here. NOTE: To know how to program using the FabISP please click here Week 9

On opening the software this is what you are welcomed with

Arduino supports a number of boards but unfortunately, it doesn't come with Attiny family pre-installed. So I had to do that manually. The following link will help with that.

https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json

The URL has to be pasted in the preference menu in the location shown

Then when you open up the board manager in tools attiny will show up. I then installed it.

Now the first step is To make the Arduino talk to the ISP, a program had to be loaded first. The Arduino ISP program can be found in the File- Examples menu. I connected the Arduino board to my laptop and uploaded the code.

The next step is to connect the jumper cables to the ISP header in the board to the corresponding pins in the Arduino. This image was really helpful in doing that

After connecting it's important to select the correct board that needs to be programmed. I wanted to upload a simple blink program to check my circuit is working. To do this select blink program from the examples.

From the tools menu, the Board, Processor, Clock, and Port need to be configured. In my case its Attiny 45

The programmer has to be Arduino as ISP. This establishes a connection between both ISPs

Once everything was set I uploaded the program. I had an error while uploading the program. Having checked all parameters again and re-uploaded. The problem remained. I checked my circuit with a multimeter, the circuit seemed fine. I tried once more to upload the program but this time I held down the switch button and tried. The program got UPLOADED  !!! Though it worked something was definitely wrong with the board. That was not all the board did not behave the way it was supposed to. The following video explains the same.

Expected behavior.

The red and blue led must blink with the switching having no effect on them.

Reality

The blue and red LEDs blink but when I press the switch the blue alone blinks.

The same thing repeated with other combination of colors. So to correct the circuit I had to go online to check similar circuits/connections. The major problem I saw was that I did not connect the light or the switch to a and connection. Someone told me that its called voltage divider bias. Not sure what that meant, but I decided to connect the switch to the ground through a resistor of 1kOhm.

I Milled and soldered the board.

Went through all the programming procedures and actually this time to upload the program I didn’t have to hold down the switch. It worked like a charm.

The Led worked exactly how they were suppose to.

The following video shows the working of the board.

Update:

I have redesigned my board my adding a decoupling capacitor of 10mF. A decoupling capacitor is a capacitor used to decouple one part of an electrical network (circuit) from another. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect it has on the rest of the circuit. An alternative name is bypass capacitor as it is used to bypass the power supply or other high impedance component of a circuit.

I have connected a current-limiting resistors to each of the LED’s. You would usually want to have a current limiting resistor in series with your LED so that you can control the amount of current through the LED.

If too much current is going through your LED, it will burn out too fast. If too little current is going through it, it might not be enough to lit the LED. A red LED requires much lesser voltage to illuminate when compared to other LED’s. Looking at the data sheet I was able to understand the characteristics of my RGB LED.