Cool Cap Engineer

Engineering by an anime nerd

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Projects: Face Tracking Turret Update #3


And you guys thought I forgot about this project! Oh no. I just been busy with school that I had to put the project on the back burner. However, I did buy the rocket turret from Here’s what I found from my dissection from this rocket turret.


Underneath the rocket turret was a couple of rubber stickers, which actually hid the screws for the base. After unscrewing the base, I found the main controller for the turret. I could not tell what was the microcontroller that was used, because I spent most of my time learning which wire controls the three motors inside the turret.


After I unscrewed the bottom of the base, I proceeded to  the top of the base. It seems like the rocket turret is able to move 0 degrees to 180 degrees due to the mechanical system shown above. The top base can also tell whether or not it will not exceed 0 or 180 degrees due to the switches inside the top of the base.


So I proceeded to tear apart  the bottom base some more.  Inside the base contains two motors. These motors are responsible for rotating the head of the turret as well as moving the head 0 to 180 degrees.


The final part I looked at was the main turret head. This was the part I ran into. The problem I was having was figuring out how the firing mechanism work. The firing mechanism uses a small dc motor, but there seems to be a certain sequence that must be achieved before the missile can be launched. Because of this, I’m changing the face tracker to use a small water pump I found on

Well, that’s all I have for you guys today. I’ll let you know any new developments I have for the project.

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Analog Discovery: An Electrical Engineer’s Best Friend


If there’s anything I learned in college, then it is this: you cannot solve a circuit related problem without having the proper debugging tools to do so.  There were numerous times in which I could not solve any problems in my circuit because I could not properly see a waveform, or could not measure the current correctly.  Then in my last semester of senior year, one of my professors gave to me Digilent’s Analog Discovery for free (I got a lot of free stuff during college).  After obtaining that piece of engineering beauty from my professor, I instantly fell in love with the device.

What is the Analog Discovery?

The Analog Discovery is a USB multitool to properly debug or power your circuit.  This little device has an oscilloscope, function generator, DC power supply, digital outputs, and logic analyzer in one package.  All you need to use the device is a computer with a good ole’ USB connection.  So what tools are available? I’ll talk about the tools I used on the Analog Discovery thus far.


1) Oscilloscope: You will find yourself working with signals that will not always output a simple square pulse. Sometimes, you’ll work with sinusoidal, triangular, and even sawtooth waveforms. To make sure the circuit is outputing the correct waveform, you need to see it. This is where an oscilloscope comes in. Although I saw waveforms moving at 1KHZ (as seen in my implementing PWM on PIC18F tutorial), the fastest signal you can see on the scope is 5MHZ.


2) Multimeter:  Although most electrical engineers should have at least a multimeter in their possession, the Analog Discovery includes a multimeter as well! Although the device claims it can measure up to 20V, I usually play it safe and measure up to 5V.

How do you use it?

Although I mentioned you need a USB micro cable, you also need to download Waveforms from Digilent’s website.  Underneath the Analog Discovery is a bunch of wires. Based on what tool you want to use, you’ll need to use a specified  wire. For example, if I wanted to use the tool’s oscilloscope, you need to connect Analog Discovery’s 1+ to your signal, and 1- to ground. Finally, if I wanted to use the 5V DC power supply, then I’ll connect my devices requiring 5V to V+ and my devices requiring ground to V-. If you want a more concrete look at Analog Discovery’s pinout diagram, then look at the picture below, which can also be found on Digilent’s website.


What’s The Bad News?

Unfortunately, I cannot say the device is free. Although I got this device for free……this device is quite expensive. Without a student discount, the Analog Discovery costs $200, which is enough to get you a really good oscilloscope, function generator, or logic analyzer for that price.If for you are a college student, then you can get a 50% student discount, which will make the Analog Discovery cost $100.

In my opinion, if you have $200 laying around, I rather get standard EE equipment. However, if you move alot, and do not want to carry EE equipment with you where you go, then buy the Analog Discovery. You buy the Analog Discovery from Digilent’s website.

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Controlling A Seven Segment Display Using Mojo


Remember a couple weeks ago when I said that I will be working on tutorials for the Mojo? Today’s post will be the first post that will be a Mojo tutorial. Although I originally planned to show you guys how to create a simple half adder with a 7 segment display, I realized we have to learn how to control the seven segment display first.  Today, I will show you not only how to connect your seven segment display to the Mojo, but how to implement a digital design to control the display on the Mojo.

What Are Seven Segment Displays?


A seven segment display is just seven LEDs arranged to display a number ranging from 0-9.  However, seven segment displays have two different connections: common anode and common cathode.Seven segment displays with a common anode connection means that all of the LEDs have their anodes connected together.  However, seven segment displays with common cathode connection means all of the LEDs cathodes are connected to each other. The picture on the bottom shows common anode and common cathode seven segment displays.

When you have a common anode display, you just need one current limiting resistor, but 7 devices to sink the current for each LED. A common cathode display requires multiple current limiting resistors, but one ground connection to sink the current for all of the LEDs. For today’s tutorial, we will use a common cathode seven segment display.

What Will You Need?

1) (1x) Mojo Board

2) (1x) LTS-4301JR 7 Segment Display

3) (7x) 330 ohm resistor

4) (1x) Micro USB cable

Wiring Connection

The picture below shows how to connect the 7 segment display to the Mojo.


How To Implement Your Digital Design Onto The Mojo?

For the next part, you’ll probably need to visit my getting started with FPGAs guide as alot of the steps from that tutorial can be applied for this one such as downloading the Xilnix Web ISE.
Afterwards, you’ll need to download the Mojo project base.

After downloading and extracting the Mojo project base, open Xilnix Web ISE. Once you open up the Xilnix ISE, go to file->open project. Navigate to your Mojo Project base and select the Xilnix ISE Project file inside the folder.

From the hierarchy menu in the Xilnix Web ISE, double click on the Mojo Top.v file, and edit it to look like this.

module mojo_top(
    input clk,
    input rst_n,
    input cclk,
    output spi_miso,
    input spi_ss,
    input spi_mosi,
    input spi_sck,
    output [3:0] spi_channel,
    input avr_tx,
    output avr_rx,
    input avr_rx_busy,
	 output [6:0] display

wire rst = ~rst_n;

assign spi_miso = 1'bz;
assign avr_rx = 1'bz;
assign spi_channel = 4'bzzzz;
assign led = 8'b0;

Don’t worry about line 24. We’re going to add the seven_segment_display_decoder module right now. Right click on Mojo Top.v and add a new verilog file. We’re going to call it “seven_segment_display_decoder.” After creating the file, add the following code to the file.

`timescale 1ns / 1ps
module seven_segment_display_decoder(clk,number,seven_segment_display_control_lines);
input clk;
input [8:0] number;
output reg [6:0] seven_segment_display_control_lines;

always @ (posedge clk)
	1:seven_segment_display_control_lines = 7'b0110000;
	2:seven_segment_display_control_lines = 7'b1101101;
	3:seven_segment_display_control_lines = 7'b1111001;
	4:seven_segment_display_control_lines = 7'b0110011;
	5:seven_segment_display_control_lines = 7'b1011011;
	6:seven_segment_display_control_lines = 7'b1011111;
	7:seven_segment_display_control_lines = 7'b1110000;
	8:seven_segment_display_control_lines = 7'b1111111;
	9:seven_segment_display_control_lines = 7'b1110011;
	default:seven_segment_display_control_lines = 7'b1111110;	

Finally, select your mojo.ucf file. Edit it to make sure it look like this.

#Created by Constraints Editor (xc6slx9-tqg144-3) - 2012/11/05
NET "clk" TNM_NET = clk;
TIMESPEC TS_clk = PERIOD "clk" 50 MHz HIGH 50%;

# PlanAhead Generated physical constraints 
NET "clk" LOC = P56;
NET "rst_n" LOC = P38;

NET "cclk" LOC = P70;

NET "led<0>" LOC = P134;
NET "led<1>" LOC = P133;
NET "led<2>" LOC = P132;
NET "led<3>" LOC = P131;
NET "led<4>" LOC = P127;
NET "led<5>" LOC = P126;
NET "led<6>" LOC = P124;
NET "led<7>" LOC = P123;

NET "spi_mosi" LOC = P44;
NET "spi_miso" LOC = P45;
NET "spi_ss" LOC = P48;
NET "spi_sck" LOC = P43;
NET "spi_channel<0>" LOC = P46;
NET "spi_channel<1>" LOC = P61;
NET "spi_channel<2>" LOC = P62;
NET "spi_channel<3>" LOC = P65;

NET "avr_tx" LOC = P55;
NET "avr_rx" LOC = P59;
NET "avr_rx_busy" LOC = P39;
NET "display<0>" LOC =P87;
NET "display<1>" LOC =P85;
NET "display<2>" LOC =P84;
NET "display<3>" LOC =P83;
NET "display<4>" LOC =P82;
NET "display<5>" LOC =P81;
NET "display<6>" LOC =P80;

So we finished all of the code for the Mojo. Now we need to create the bit file. Before we create the bit file, make sure you save everything. Once you save everything, select mojo_top.v. Underneath the hierarchy menu is the processes menu. Look for “Generate Programming File” in the Processes menu. Click on it. Xilnix will now try to create a bitfile aka your digital design.


Now we need to burn the bitfile onto the Mojo board. If you have not done so, download the Mojo Loader. Once your download and extract the mojo loader and configure your computer to recognize the Mojo, open the application file inside the Mojo Loader folder. From the Mojo Loader select “Open Bin File.” Navigate to your Mojo Project Base and then to Mojo-Base->syn. Select the mojo_top.bit file.

Finally, select load file. When the bit file is uploaded to your Mojo, you should see a 9 on the seven segment display.

Well that’s it for today you guys! I’ll leave you to figure out how to change the number displayed on the display. If you guys have any more questions or concerns, then please leave a comment!