Stairway to Heaven Game
Abstract
The Stairway to Heaven game kit was purchased from Carl’s Electronics. Significant debugging was done on a breadboard and modifications were made to make the game work since the kit as shipped was faulty. The purpose of each component was described with explanations of any changes made. An updated schematic and PCB layout were made in DipTrace. The board was finally manufactured and assembled. Suggestions for the future include changing the value of resistors around the step LEDs.
Description
Design
A game kit found online at Carl’s Electronics was adapted for this project. This game blinks an LED between red and green. If a button is pressed while this LED is green, then a set of LEDs will light up, like a kind of speed game. The kit included a schematic (Figure 1).
Figure 1 This is the schematic that came with the kit. After being informed by Dr. Pan that in the past people have tried this without getting it to work, attempts were made to assemble this schematic on a breadboard. Bugs are highlighted in the diagram above.
Changes were made to the final design of the project based on a considerable amount of debugging. Here is a list of the changes with a brief explanation:
- The capacitor in the pink circle powered the LEDs and was charged itself through the resistor circled in green. The resistance appeared to be too high, making it very hard to charge the capacitor. This resistance was changed to 1.1K with two 2.2K resistors in parallel. The capacitor does leak a little over time, so the LEDs will eventually turn off if the game is not actively played.
- In addition, the resistor and transistor combo in red caused the LEDs to blink. This was very distracting and was removed from the system, so the LEDS were connected straight to the power.
- The resistors in purple and yellow were not provided with the kit. The yellow resistor appears to be a typo and is supposed to be a 4.7K resistor. There was also an extra 22K resistor and a variable resistor provided in the kit, which was placed in series to create the 33K resistance in purple. This resistance can also be changed with the variable resistor to change the speed of the blinking, changing the difficulty of the game.
- The switch provided was a single-pole-double-through switch. This type of switch has 3 prongs, not 2 as this schematic suggests. This was fixed so that the final schematic would match the PCB layout.
- Finally, the IC had 14 pins, where pin-7 has to be connected to ground and pin-14 needs to be connected to the power.
A video of the working breadboard can be found at http://youtu.be/DYnqKcyhkxA. The final schematic was drawn in Dip-Trace with the changes previously mentioned (Figure 2).
Figure 2 Schematic constructed in DipTrace with all the changes highlighted as before. The traces on the PCB were followed to confirm that the changes made were consistent with what had been intended.
| Component Type | Component Number | Purpose |
|---|---|---|
| R | 1-2 | Reduces current flow from power supply to protect bi-LED and IC. |
| 3-4 | Determines the speed of the bi-LED blinking. R4 can be adjusted to make the bi-LED blink slower or faster. Increases resistance makes the blinking slower | |
| 5-6 | Determines how quickly C3 charges. This value of 1.1K makes the LED light easily after a good hit. | |
| 7-18 | Biases transistors 2-7 to light LEDs to switch at a specific voltage level. | |
| 19 | Determines how quickly C3 discharges. This value was chosen to be lower than the charging value so that the LEDs will all turn off when the button is hit incorrectly. | |
| C | 1 | Decoupling capacitor that smooths voltage when powering up and down. |
| 2 | Determines speed of blinking with resistors 3-4 | |
| 3 | Powers the LEDs to remain on, when this capacitor is charged. The amount of charge it has determines how many of the LEDs will be on. | |
| D | 1 | Bi-LED that blinks between red and green depending on which way the current is flowing. |
| 2 | Prevents C3 from charging through the lower resistance of R19 | |
| 3-8 | Shows the progress of how many times the button has been pressed correctly as stairway LEDs. | |
| 9 | Sets minimum voltage for first LED. | |
| Q | 1 | Allows charge in C3 to drain slowly. If this transistor were not in the circuit, the charge would drain 6 times faster through Q2-7. |
| 2-7 | Acts as on/off switches for the LEDs until enough charge is collected in C3. | |
| S | 1 | Turns component on and off thereby connecting the power supply to the circuit. |
| 2 | Button that is correctly pressed when the bi-LED is green and incorrectly pressed when the bi-LED is red. If pressed correctly, the current will flow allowing C3 to charge. If pressed incorrectly, the current will flow allowing C3 to discharge. | |
| U | 1 | Group of Schmitt trigger inverters. Makes transition between on and off smooth. |
| J | 1 | Supplies power to the ciruit. If this power drops below 7V, the last LED will not light up. |
The PCB (printed circuit board) board was then designed (Figure 3). All the components were measured since the manufacturer specs were not included with the kit. The pads were made on the large side since there was little experience with soldering.
Figure 3 The PCB was designed to fit in the casing that was included with the kit. The layout was arranged landscape with the step LEDs on the left and the button on the right.
The PCB was designed differently form the board included with the kit. First the new board was designed to be landscape instead of portrait but with the same dimensions to still fit in the casing that was included with the kit. The step LEDs were also arranged in a straight line. The button was placed on the bottom right so it may be hit while being held in one hand. The bi-LED was placed near the button and far from the step LEDs to prevent distraction while playing. The variable resistor was placed in the center and the on/off switch was placed on the edge to be easily accessed.
Manufacture
The board layout was checked for manufacturability by an outside company and after passing was sent to Taiwan to manufacture. A week later the board was received.
Manufacturability specifications were as follows:
- Minimum copper trace width = 7mil
- Minimum copper trace spacing = 8mil
- Minimum hole size = 15mil
- Minimum annular ring = 10mil
A caliper was used to measure the components. Lead size was measured and a few mills were added to create the hole size. Annular rings were made large to allow for easy soldering. In addition, lead spacing was measured.
Assembly
Unfortunately, the IC was measured a little off, but was able to be connected to the board though an IC socket. This component came with the kits but was not planned on being used. Since leads had to be bent to fit the IC, the socket was used since it was thought to be easier to replace.
The resistors and diodes were placed after the IC, followed by the capacitors, transistors, switches, and step LEDs. The bi-LED was placed last to ensure that it was placed in the right direction. The power supply was connected to the bottom to allow the battery to be stored in the casing while playing the game.
After ensuring that the leads did not touch, the game was played to confirm that the circuit worked (Figure 4). Finally, the leads were cut leaving about 2mm from the board. The board was then attached to the casing.
Figure 4 Check that the game works after assembly. The top LED (D3) drains quickly. Watch the video.
Conclusions & Discussions
In conclusion, the game works, but needed adjustments from the original schematic. In the end, the game was a success and much was learned about PCB design and DipTrace software. In the future, different resistances can be tried to further improve the design.
A couple of issues remain. First, the red LEDs drain, go out without touching the board, quickly. The top red LED will only stay lit for about 15 seconds. It is possible that the capacitance of C3 or changing the value of the resistors will help this LED stay lit longer. The next two LEDs go out in about 2-3 minutes. It takes about an hour for the whole row to drain. Second, the last LED will not light when the battery voltage is below 7 volts. Improvements can be tried to increase battery life.
Downloads
- Presentation (PDF)
- BOM (PDF)
- Schematics (JPEG)
- Layouts (JPEG)
