Difference between revisions of "F13: LED Display"

Revision as of 16:27, 23 November 2013

Grading Criteria

Project Title

A Moderately Fancy LED Display

Abstract

This project will control several strings of household LED lights (i.e. Christmas lights) via a microcontroller. The LED display will be synced to a song playback.

Objectives & Introduction

This project will need to be able to control several relays with the microcontroller. The development board's GPIO header pins (P2.0 - P2.7) will be used to bias the gate of a FET, which will in turn drive the relay coil. The ADC will sync up the playback of the song to the LED display. The ADC will wait for the first beat of the song, and then begin the program. The LED timing and channel useage will be manually programmed to make a visually appealing show.

Team Members & Responsibilities

Mike Mellman

• Project Management
• Hardware Design and Build
• Parts Procurement
• Software Design
• Test
• Project Documentation

Schedule

Bill of Materials & Cost

Design & Implementation

The design section can go over your hardware and software design. Organize this section using sub-sections that go over your design and implementation.

Hardware Design

The system schematic is shown below in Figure 1 (with Bill of Material references).Each GPIO pin biases the gate of a transistor on the relay board. The voltage source on the relay board then has a conductive path to power the relay coil. The voltage sources use linear voltage regulators which control each output voltage. Each regulator's output voltage is set by the equation V_OUT = V_REF (1 + R_L / R_H).

For the LM317, V_REF is a fixed voltage of 1.25Vdc, and R_L is typically chosen to be 240Ω. The output voltage V_OUT is fixed by the choice of R_H.

Figure 1: Electrical schematic

Hardware Fabrication Steps

A piece of 1/2" Delrin sheet was obtained to hold the two boards and to give the AC wiring some strain relief. Holes for standoffs were drilled and tapped (see Figure 2).

The boards were then mounted (see Figure 3) to the Delrin with Aluminum standoffs. The relay board was screwed down, since it would not need to be removed. The development board was held on with set screws for easy removal during the fabrication process.

Figure 2: Drilled and tapped holes

Figure 3: Mounted boards

To attach the signal wires to the development board's header pins, a connector block was tried (to plug in all the signals at once). However, the correct contacts could not be obtained. Instead, each wire was terminated in a Molex-type contact that fit the header pins well. Each contact was then covered in white shrink tube to prevent shorting and to label each wire (see Figure 4). Each wire end that plugs into the relay board's screw terminal block was terminated in a Wago ferrule (see Figure 5). This wiring is shown in Figure 6. It should be noted that the 3.3V and ground wires were removed later due to higher voltage requirements.

Figure 4: Dev board contacts

Figure 5: Relay board contacts

Figure 6: Board wiring

Per the vendor's datasheet, the Omron solid state relays require a control voltage of 4-6Vdc to switch. The use of the development board's 3.3Vdc bus voltage was unsuccessfully attempted in the chance that the relays might switch at a lower voltage than specified. If it had it worked, this would have eliminated the need for a second voltage source. As a result, a dual voltage source was designed and built. Using a 9V alkaline battery and two linear regulators, a 3.3Vdc and 5Vdc source was constructed (see Figure 7). The 5Vdc voltage source connected to the relay board with 2 wires. The 3.3Vdc source connected to the development board through a modified USB cable.

Figure 7: Dual voltage source

Extension cords were modified instead of the LED cords. This would allow the LEDs to be used in a more conventional fashion by the author's spouse upon the completion of this project. The AC line wire was carefully separated from the cord with an exacto blade and then cut. A piece of 14AWG wire was soldered to the exposed AC line wire to allow easier connection to the relay board's screw terminals. Each extension cord was mounted to the Delrin sheet using cable ties (see Figure 8). The voltage source box was attached to the Delrin sheet using velcro tape. The voltage wires were then hooked up to each board. The project hardware was complete, with the two boards powered by a battery only (see Figures 9 and 10). It should be noted that the 8 AC plugs are connected to 110Vac power by a power strip for convenience.

Figure 8: AC wiring

Figure 9: Completed system

Figure 10: Completed system

Hardware Interface

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Software Design

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Implementation

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Testing & Technical Challenges

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Wifi Connection Issues

Many wifi connection issues were encountered. To solve this problem, a dedicated task was created to re-connect to wifi if the connection was ever lost.

Conclusion

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Project Video

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Project Source Code

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References

Acknowledgement

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References Used

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Appendix

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