Joystick Controlled 8x8 Display

Group PI Parker Larsen Isaac Spanier

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Abstract:

The objective for this project was to control a single pixel on an 8x8 display using a joystick without the aid of a microcontroller. Multiple older style Integrated Circuits will be used to encode and decode the signals throughout the circuit. Both the X and Y directions have a potentiometer to output the current position of the Joystick. The 8x8 matrix contains 16 pins. Half of the pins are active low(ground) and half are active high allowing for control of all 64 LEDs. This circuit contains a 5-volt linear regulator to allow this circuit to be run off a single 9-volt battery. A clock will also be needed to control the speed that the LED moves across the display. This frequency will be determined based on what is visually appealing to the user.

Original Testing Plan:

The original testing plan involved 3 main elements. The first involved testing the power supply and confirming a constant 5-volt output coming from a 9-volt source. The second involved testing to find a lower operating voltage to allow for a smaller voltage source. Finally, the third objective was to find a build a clock source that provides both consistency and a visually appealing speed for the viewing user.

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Design Overview:

There is a variety of different the steps that the signals must go through from start to finish. Below is a more in-depth view of the signal transfer from component to component.

Breadboarding and Perfboarding:

Since this project involves a lot of small systems working together to solve a larger problem, we decided to break the problem down into smaller parts. The steps that we took are as follows:

1. Control the 8x8 using CMOS

2. Build clock using a 555 timer

3. Build comparators

4. Test the counters

5. Combine comparator, 555 timer and the counters

6. Add the decoder, display and the CMOS

Final testing plan:

Since our project involved a lot of components that either worked or did not, we decided that it would be more beneficial to break the project down into specifications and a series of testing steps. The testing steps are listed above under Breadboarding and Perf-Boarding and the final specifications are listed below.

-Clock Frequency: 3 Hz

-Input voltage: 9 volts

-Comparator cutoffs: Under 2 volts = Low, Over 4 volts = High

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Final Schematic:

Operational Amplifier Comparator Circuit Operational Amplifier Comparator Circuit and 555 Timer

CMOS Controlled 8x8 and Counters

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Completed Perf-Board:

Perf-Board Reflection:

The perf-board example of our circuit proved to be valuable in making sure that our circuit was correct. This allowed us to complete a circuit with many components without worrying about bumping and unplugging wires. It also gave us a sense of security knowing that we have a working model in case something happens to our final PCB.

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PCB Design:

PCB-Design Reflection:

Looking back on the PCB Design, I realized that a very helpful tip that the class had brought up during our presentation was to use a ground plane and a power plane. This take some big refactoring of how wires were set up and it really helped me get a better understanding of KiCad and so it made me understand my layout better as well. I think one big takeaway for me after multiple iterations of the board was to make sure that parts of the circuit were grouped together to provide clarity for both myself and anyone trying to understand the functionality of the circuit. It also made it easy to wire everything up because the proximity of certain aspects of the circuit were closer together.

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Completed-PCB:

PCB-Reflection:

Both of us were very excited to get the PCB back, the soldering was straight forward, and the only issue with the design that is apparent is the holes for the headers labeled J1-J4 were too small for the headers we planned. This error means that we cannot move the dot from its starting point in the bottom left corner. This is disappointing, but we know that the circuit works because of our perf-board prototype functioning flawlessly. One thing we were both pleased with was the symmetry and overall look of the board once it was all soldered up. It was very pleasing to see a semester’s worth of work come to life.

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Bill of Materials:

Conclusion:

We learned a lot during the course of this project. We picked a complex project and followed the design process from start to finish. The complexity and scale of the project was beyond anything that we had completed in the past on this digital logic level and this led to a miscalculation on the time needed to complete this project. The pen and pencil design, ordering parts and the breadboarding all went fairly quick. The perfboard replica put us behind schedule due to the number of connections that needed to be made. This eventually pushed us behind schedule and also forced us to create a 4-layer board. Due to delays in fabrication we were not able to get the PCB working in time for the demo, but we were able to show off our completed perfboard instead. If we were to complete this project in the future we would look into creating a scalable version to limit the prototyping needed, look into using leds rather than a matrix due to the messy pinout, and possibly look into surface mount due to the PCB size.