Introduction: Two-player Reaction Timer

About: A young innovator passionate about making an impact in the world

In this project, you will build a 2 player reaction timer. The reaction timer works on the premise that if one person presses their button, the other person has to press their button as soon as possible after the first button is pressed.

The 7-segment display will then show the time difference between the two presses and hence the reaction time of the second player. You can then press the reset button and the numbers displayed on the 7 segments will go back to 0.

The game is extremely fun when you are competing between two people. Each person will try and get a lower reaction time.


Check out the supplies from the table shown in the image.

Step 1: Designing the Housing and UI Panel

It is very important to ensure that you have thought carefully through the design of the product or project before going through with its production. There are a couple of differences between the 3D CAD model and the actual product however that is to happen with any project you work on.

Things will not work out the way they are supposed to and you will have to make some changes to your production plan.

Step 2: Designing the Circuitry

The circuit is powered by the NE555 IC in astable mode. The pulse generated by the IC is sent a 4026IC to control the 7 segments. There is a reset button connected to pin 15 of both 4026s and +5V to reset the 7 segments after one round. There is a pull-down resistor to remove any floating voltage.

Here is a good link describing the 555 astable circuit:

And for the 555IC's connection to a 4026 and 7 segments, you can find the link here:

The switch part of the circuitry, the button system, uses a thyristor, XOR gate, and transistor. When the first button is pressed thyristor 1 is activated and it sends a high value to one of the XOR gate's input. This causes the XOR gate's output to be also 1. The high XOR gate output activates a transistor that connects the output of the NE555 and clock pin of the 4026.

Alternatively, the activated transistor can also connect the positive rail to the NE555 IC to power the IC and start the pulse.

Once the second person presses the button, the second thyristor is activated and then both inputs for the XOR gate are high which causes the gate's output to be 0. This deactivates the transistor and the 555 circuits is powered off. Therefore the 4026IC stops receiving a pulse and the value on the 7 segment doesn't increase.

The schematic for the switch circuitry can be found in the images.

Step 3: Designing the PCB

It is a lot easier to design a PCB than to solder the components onto a perf board. Therefore I designed a PCB on Easyeda. Then I ordered the PCB to be manufactured by SEEED. It was about 10USD for the manufacturing along with delivery to Singapore.

The Gerber files for the PCB can be found here:

It is a link to a google drive folder with the zipper Gerber file.

Step 4: Testing UI Panel on Card

To help prevent wastage of acrylic which is a lot more expensive

Step 5: Laser Cutting the Front and Back Panels

Please do this under an adult's or teacher's supervision. Also continuously monitor the laser cutter for fires. Do not leave the laser cutter's side while it is operating.

Step 6: Spray Painting the Text (Finishing the UI Panel)

When you engrave a text onto an acrylic panel using a laser cutter, the top protective film is removed which exposes the acrylic. This allows you to color the engraved text using spray paint. Everything else except the engraved text will be covered by the protective film.

Make sure to wear a mask, goggles, and apron as spray paint is dangerous. Also if you are a child, please spray paint under a teacher's or adult's supervision. Additionally use newspaper as the base to help prevent the spray paint from messing up your workbench or table.

Step 7: Marking the Wood's Dimensions

In the above images you can find the orthographic models of the housing. It shows all the dimensions of the box and individual wood pieces.

For this step, use a pencil, set square, and a ruler to mark out the general dimensions of the wood pieces.

Details such as the 45 degrees cut for the miter joint as well as the 3mm notch for the UI panel will be marked and made later.

Step 8: Cutting the Wood to the Right Width and Height

I used 10mm thick teak wood for the sides of the box. The width of the wood is 37mm and the length of the wood is 240mm for the long side and 160mm for the short side.

I used a table saw to cut the wood to the right thickness and a circular saw to cut the wood to the right length.

Step 9: Using a Router to Cut the Groove for Acrylic Panel

Please refer to the orthographic images to get a better picture of the dimensions and shape.

A router blade was set 5 mm of the table. The router blade had a thickness of 4mm. This gave the acrylic panel a 0.5mm wiggle room on each side. Additionally, the groove was 3mm deep as per the dimensions shown in the orthographic.

I used scrap wood to test out the router before using my final pieces.

Tools used:

Ruler and pencil


Scrap wood


Step 10: Using Miter Cutter to Cut the Mitre Joint for the Box's Sides

The miter cutter is essentially a blade angled at 45 degrees that cuts miter joints for wood and metal.

I shaved the wood by small amounts repeatedly, until the cut was on the edge of the wood piece.

Safety check:
Kept fingers away from the blade

Used with teachers supervision Wore goggles

Step 11: Applying the Teak Oil

Using an old rag, I applied 3-4 coats of teak oil for the wood piece. I let the piece dry between the coats for about 5 minutes.

Step 12: Putting the Box Together

I used PVA glue to put together the sides of the of box.

I spread the glue evenly using the wooden stick

I dabbed off any excess glue leaking from edges using tissue.

Checked joints for gaps/ uneven joints before applying the glue.

Thick rubber bands were used to hold the structure together as it dried overnight.

The UI panel was slotted into the groove between the 4 sides and after the glue dried, it was held in place.

Step 13: Soldering Leads Onto the Buttons

Step 14: Soldering the Components Onto the PCB

Make sure to wear goggles and solder in a well-ventilated environment.

Have adult supervision if you are a student.

Quality controls:

Use soldering flux for clean joints

Use an IC chip holder. It is much easier to solder and there is no chance of the IC burning while soldering.

Pull-on any leads to make sure it is solid and there are no dry joints.

Tips for soldering:

Hold the soldering iron's tip on the join. After about 5 seconds the joint would be heated up. Feed the soldering wire into the pad or joint. Not onto the soldering iron tip. This will help you soldering quickly without overfeeding soldering wire and prevent overheating the components.

Step 15: Soldering the UI Components Onto the PCB.

The 7 segments, battery, switch, and potentiometer were soldered onto the PCB.

Do not solder the button onto the PCB as then it would be possible to secure the button to the UI panel as the wires have to go through the hole.

Step 16: ​Securing the Battery Pack in the Housing

I just used a hot glue gun to secure the battery pack.

When you are putting in a battery, make sure it is new. The circuit requires quite a high voltage to operate. If the battery's voltage drops below 7.5V, the circuit won't function proper.

Additionally, when you are holt gluing the battery holder to the frame, remove the battery from the battery holder to prevent overheating of the battery.

Step 17: Inserting the UI Components Into the UI

The potentiometer, use to change the pace of the counting, is secured using a nut tightening it onto the UI panel.

The 7 segments were secured using a bit of hot glue.

The reset button was secured using super glue. Make sure the superglue doesn't jam the motion of the button.

The buttons clipped in automatically into the laser-cut holes.

You may have to sand the holes down a bit to ensure the components fit.

Step 18: Securing the PCB Using Hot Glue

It was difficult to find PCB feet with my required dimensions. Therefore I used hot glue to secure the PCB onto the front UI panel.

Step 19: Securing the Back Panel and Peeling the Cover

I had left the protective film to prevent any scratches or marks on the acrylic.

The premade holes in the acrylic back panel during laser cutting were 3mm in diameter. I used 3mm screws to secure the back panel to the sides of the box.

The product is now done. Special thanks to Mr. Williams and the DT lab at UWCSEA East for their assistance with this project.