In this page I will explain the process I went through to design, build, and test the cirucits I made for my final project.

Page content:

Files:

1. Thigh circuit

1.1. First version

I have used 8-bit AVR ATmega328P SMD to create my own micro-controller circuit. First of all, I have checked its datasheet summary to get the important information about it and to know its pin configiration. Later, I have reviewed the full data sheet.

Pin Configurations:

I used Autodesk Eagle to draw my circuit by referring to the minimal circuit for Atmega328 processor desgin provided in this website. However, I added more components as I need for my project.

The following Eagle libraries were used in the design:

Schematic Design:

Circuit Routing:

I set all the routing widths to 16 mil, then I changed the routing width of the ATmega328P pads to 10 mil because it is mentioned in the datasheet that the miminum width of each leg is 0.30mm, which is equal to 11.811 mil.

PCB Design:

The Top and Pads layers routing were exported as an image:

Then the Dimension and Pads layers were exported also.

Dimension and Pads layers after editing with GIMP.

Prepeare for milling with Mods:

I used mods to geneeate the rml file for milling.

Circuit after milling:

As you can see in the following picture of my circuit, there are some traces not milled by the milling machine. So, I used a cutter to disconnect them. But, by accident I have removed the trace of pin 16 which is the AVR MISO pin. Therefore, I have decided to make some changes to my circit design in Eagle and mill it again.

1.2. Second version

I have re-designed my MCU circuit in a way that makes it as small as possiable with less traces and components. Changes made are as following:

Schematic Design:

Circuit Routing:

Export for milling:

Show only Top and Pads layers and export them as an image.

Export for cutting:

Then the Dimension and Pads layers were exported also. To do that, below steps were followed:

Edit cutting image with GIMP:

Open the exported image with GIMP. Then from the top bar menu, click on Image » Mode » RGB.

Click on Bucket Fill, select any color other than black and white, and click on the black space inside the holes.

Fill in the outer circle with black color.

Change Image Mode to Greyscale.

Fill in the inner circle with white color.

Export as png image.

Prepeare for milling with Mods:

I used mods to geneeate the rml file for milling.

You can download my design files from here:

1.3. Third version

I have re-designed the circuit based on my instructor suggestion. The previous version is also big in size to fit on the human thigh. So I changed the MCU used from ATmega328P to ATtiny84A. In addition, there are multiple seperate components to be connected to the board using connectors, which may result in loose connections when moving the leg. Therefore, I have added the bluetooth circuit on my microcontroller board using a surface mounted part RN4871.

Schematic Design:

Circuit Routing:

Export for milling:

Export for cutting:

After edit with GIMP:

Circuit milling:

Problem with cutting:

After cutting the outline, the circuit fly off the bed so I have stopped the machine immediately. The problem was due to that, there was not enough tape under the board to keep it stable.

Since the board was removed from its location on the machine bed, therefore I wasn't able to do the cutting for the holes using the milling machine. So I have drilled the holes I need as shown in the following image:

One of the traces was removed, so I have solved the issue by soldering a jumper wire.

Later, I have gathered all the components and soldered them on my printed circuit board.

Bill Of Materials (BOM):

Circuit after soldering:

Testing the board:

After soldering, I have tested my circuit by programming it using Arduino UNO. To do that:

First upload ArduinoISP example code to Arduino uno with the following settings:

Then connect my attiny84 board to Arduino UNO using SPI connection as following:

If you don’t have attiny84 library, go to week 7 to know the steps of adding attiny84 board library.

Set the following and click on Burn Bootloader.

Done burning bootloader

2. Shank circuit

The second circuit will be placed on the shank and connected with the microcontroller circuit (on the thigh) using ISP connector. This circuit contains two main components, which are mini vibrating motor and Inertial Measurement Unit (IMU) - MPU6050.

I have followed this tutorial to learn how to build a vibration motor circuit. It says that the vibration motor has 2 terminals, red and blue wire. The polarity does not matter for motors.

Based on the data sheet, this vibration motor has 2.5-3.8V operating voltage range; So, it will vibrate by supplying it with 3V. However, I want to control it using my microcontroller (ATtiny84) by coding to reduce the current draw/strength and turn it ON at some intervals. To do that, I have referred to the following circuit design from Learning about Electronics website.

Vibration Motor Circuit:

Circuit components:

When designing my circuit, some of the components shown in the previous schematic are not available in SMD (Surface Mounted) packaging. Therefore, I have replaced them with other alternatives.

Schematic Design:

Circuit Routing:

Export for milling:

Export for cutting:

Bill Of Materials (BOM):

Circuit after soldering:

3. Problems

I couldn't program my ATtiny84 circuit because there was a piece of copper between xtal and reset pin. After removing the extra copper and cleaning the circuit, it works.