This guide explains how to build the current recommended version of the KOTH Timer.
KOTH Timer is a DIY King of the Hill timer for Nerf, foam flinging, and other objective-based hobby games. It uses an Arduino Nano ESP32, two large team buttons, four TM1637 display modules, LED feedback, a battery display, and a local Wi-Fi web interface for controlling the game.
This guide is based on KOTH Timer v0.3.1, which keeps the event-tested v0.3 gameplay and referee UI while adding fixes for the web-interface setup controls.
Important: This is still a hobby project. Check the schematic, BOM, firmware, and photos before soldering. Builders should test their own wiring carefully before using the timer at an event.
This Build guide is in place for use ONLY if you plan to build the timer using prototype boards instead of the PCB. There is currently no updated build guide for the manufactured PCB. However, I designed the PCB to be as self explanatory (with a bit of context) as possible. It relies on headers/terminals for most major components so it is PNP for the most part.
This tested PCB revision is also available as a PCBWay shared project:
Order / view the KOTH Timer PCB v0.2 project on PCBWay
This link is useful for builders who want to order the tested PCB without manually uploading the Gerber files.
The timer has two teams.
Each team has:
- One large arcade button
- One LED output for button feedback
- Two 4-digit TM1637 display modules showing that team’s remaining time
The timer also has:
- An Arduino Nano ESP32 controller
- A single 18650 battery power system
- A 5 V boost converter
- A rocker power switch
- A fuse
- A 5-segment battery indicator
- A small battery-check button
- A local Wi-Fi web interface hosted by the ESP32
The game logic is simple:
- If Team A holds their button, Team A’s timer counts down.
- If Team B holds their button, Team B’s timer counts down.
- If both buttons are held, the point is contested and neither timer counts down.
- If no button is held, neither timer counts down.
- The match ends when one team’s timer reaches zero.
The current recommended firmware release is v0.3.1.
v0.3.1 keeps the tested v0.3 phone/referee UI and adds small UI input fixes for the setup controls.
The current recommended PCB revision is PCB v0.2.
PCB v0.2 has been manufactured, assembled, and tested with no known faults.
New builders should use:
Firmware/KOTH_Timer_v0_3_1/KOTH_Timer_v0_3_1.ino
PCB/v0.2-tested/
Main v0.3.1 improvements include:
- Phone-friendly referee/admin web interface
- More reliable phone connection using
http://10.10.10.1 - Open Wi-Fi network by default for quick event setup
- Optional Wi-Fi password support if the builder wants it
- Live time adjustment during gameplay
- Ref/admin can add or remove time from either team without resetting the match
- Larger touch-friendly controls
- Cleaner match status display
/pingtest page for connection troubleshooting/statefallback endpoint for UI updates
The older v0.2 firmware is still available for reference, but new builders should use v0.3.1.
The BOM includes:
| Qty | Part | Notes |
|---|---|---|
| 1 | Arduino Nano ESP32 | Arduino-branded Nano ESP32 |
| 1 | 18650 Li-ion cell | Single-cell battery |
| 1 | 18650 battery holder | Holds the battery |
| 1 | 5 V step-up converter | Boosts the 18650 voltage to 5 V |
| 1 | 1 A fuse | Use with a suitable fuse holder |
| 1 | Rocker switch | Main power switch |
| 2 | Large arcade buttons with LEDs | One for each team |
| 4 | TM1637 4-digit display modules | Two displays per team |
| 1 | 5-segment LED bar graph | Battery level display |
| 1 | Small push button | Battery display button |
| 2 | 100 kΩ resistors | Battery voltage divider |
| 7 | 220 Ω resistors | LED current limiting |
| 1 | 470 µF electrolytic capacitor | Power smoothing |
| 1 | 100 nF ceramic capacitor | Power smoothing/decoupling |
| As needed | Prototyping PCB | For soldering |
| As needed | Wire | 22 AWG was used in the original build |
| As needed | Heat shrink | For insulation |
| As needed | Terminal blocks | Optional, but useful |
| 1 | Enclosure | 3D printed or custom housing |
You will need:
- Soldering iron
- Solder
- Wire cutters
- Wire strippers
- Heat shrink or electrical tape
- Small screwdrivers
- Multimeter
- USB cable for the Arduino Nano ESP32
- Computer with Arduino IDE installed
A multimeter is strongly recommended. Do not skip voltage checks.
The timer is powered from a single 18650 cell.
Basic power path:
18650 battery
-> fuse
-> rocker power switch
-> 5 V boost converter
-> Arduino Nano ESP32 VIN / 5 V rail
All grounds must be connected together.
Battery GND
Boost converter GND
Arduino GND
Display GND
Button LED GND
Battery indicator GND
Important: Do not connect the 18650 battery directly to the Arduino 5 V or VIN pin without the boost converter/power circuit.
Li-ion safety: Use care when working with 18650 cells. Avoid shorts, use a fuse, and do not use damaged cells.
The v0.3.1 firmware uses the following pin assignments.
The team buttons are wired to ground and use the ESP32 internal pull-up resistors.
| Function | Arduino Pin | Wiring |
|---|---|---|
| Team A button | D2 | Button between D2 and GND |
| Team B button | D3 | Button between D3 and GND |
| Battery display button | D4 | Button between D4 and GND |
Button logic:
Pressed = LOW
Released = HIGH
The arcade button LEDs are driven from GPIO pins.
| Function | Arduino Pin | Wiring |
|---|---|---|
| Team A button LED | D5 | D5 -> resistor -> LED -> GND |
| Team B button LED | D7 | D7 -> resistor -> LED -> GND |
LED logic:
HIGH = LED on
LOW = LED off
Use suitable resistors for your LEDs. The BOM lists 220 Ω resistors.
The timer uses four TM1637 4-digit displays.
All four displays share the same clock pin, but each display has its own data pin.
| Display | Clock Pin | Data Pin |
|---|---|---|
| Team A display 1 | D8 | D9 |
| Team A display 2 | D8 | D10 |
| Team B display 1 | D8 | D11 |
| Team B display 2 | D8 | D6 |
Typical TM1637 wiring:
TM1637 VCC -> 5 V / VIN rail
TM1637 GND -> GND
TM1637 CLK -> D8
TM1637 DIO -> display data pin
The two displays for the same team show the same time. This lets the timer be visible from more than one angle.
The battery voltage is measured through a resistor divider.
| Function | Arduino Pin |
|---|---|
| Battery voltage divider midpoint | A0 |
The timer uses:
R1 = 100 kΩ
R2 = 100 kΩ
Basic divider:
Battery +
-> R1
-> A0
-> R2
-> GND
Important: Do not connect the battery directly to A0. The battery voltage must go through the resistor divider.
The firmware includes battery calibration values. If the displayed battery voltage is wrong, measure the battery with a multimeter and adjust the calibration values in the firmware.
The battery indicator uses five GPIO outputs.
| Segment | Arduino Pin |
|---|---|
| Red segment | A1 |
| Yellow segment | A2 |
| Green segment 1 | A3 |
| Green segment 2 | A4 |
| Green segment 3 | A5 |
The firmware assumes:
GPIO HIGH = segment on
GPIO LOW = segment off
Each LED segment should have current limiting.
The battery bar display turns on temporarily when the battery display button is pressed.
Before soldering everything permanently, build and test in sections.
Check:
- Fuse is installed
- Rocker switch controls power
- Boost converter outputs 5 V
- Arduino powers up from the 5 V supply
- Ground is common everywhere
Use a multimeter before plugging in the Arduino.
Wire:
Team A button -> D2 and GND
Team B button -> D3 and GND
Battery button -> D4 and GND
No external pull-up resistor is needed for these buttons because the firmware uses INPUT_PULLUP.
Wire:
D5 -> resistor -> Team A LED -> GND
D7 -> resistor -> Team B LED -> GND
If your arcade buttons have built-in LEDs, check their voltage and polarity before wiring.
Wire all TM1637 modules to power and ground.
Then connect:
All display CLK pins -> D8
Team A display 1 DIO -> D9
Team A display 2 DIO -> D10
Team B display 1 DIO -> D11
Team B display 2 DIO -> D6
If one display does not work, swap it with a known working one to check whether the issue is the display module or the wiring.
Wire the 5-segment bar graph using the schematic.
Firmware pin order:
A1 = red
A2 = yellow
A3 = green 1
A4 = green 2
A5 = green 3
Pressing the battery display button should show the battery level for a few seconds.
The firmware is written for the Arduino Nano ESP32 using the Arduino IDE.
Install Arduino IDE 2.x.
In Arduino IDE, install the board support needed for the Arduino Nano ESP32.
Select the Arduino Nano ESP32 board before compiling.
The firmware uses:
- Wi-Fi support for the ESP32
- Web server support
- WebSockets support
- TM1637 display support
- Preferences storage
- DNS server support for connection handling
If the code fails to compile because a library is missing, install the missing library through:
Arduino IDE -> Library Manager
Search for the missing library name shown in the compile error.
Open the .ino file from the Firmware folder.
For Arduino IDE compatibility, the sketch should be inside a folder with the same name as the .ino file.
Example:
Firmware/
KOTH_Timer_v0_3_1/
KOTH_Timer_v0_3_1.ino
Connect the Arduino Nano ESP32 over USB.
Then click:
Upload
After uploading, the ESP32 should start its local Wi-Fi access point.
Before closing the enclosure, test everything on the bench.
On boot, the TM1637 displays should show the starting game time.
If the displays are blank:
- Check 5 V and GND
- Check D8 clock wiring
- Check each display’s DIO pin
- Check display orientation
- Check the firmware uploaded correctly
The ESP32 creates a local Wi-Fi network:
SSID: KOTH-Timer
Password: none / open network
Connect to it with a phone or laptop.
There is no internet through this network. That is normal.
Open a browser and go to:
http://10.10.10.1
The KOTH Timer web interface should load.
If the main page does not load, test the connection page:
http://10.10.10.1/ping
If /ping loads but the main page does not, the Wi-Fi connection is working and the issue is likely with the web interface loading or browser caching.
Some phones may warn that the network has no internet. Choose the option to stay connected or use the network anyway.
By default, the KOTH Timer Wi-Fi network is open so referees can connect quickly during events.
If you want to add a password, edit the firmware Wi-Fi settings near the top of the code.
Find:
static const char* AP_PASS = "";Change it to something with at least 8 characters:
static const char* AP_PASS = "kothtimer";Then upload the firmware again.
After that, users will need to connect with:
SSID: KOTH-Timer
Password: kothtimer
The password must be at least 8 characters long. If the password is left blank, the timer will use an open network.
Start a test game from the web interface.
Then test:
- Hold Team A button: Team A timer should count down.
- Hold Team B button: Team B timer should count down.
- Hold both buttons: contested state, no timer should count down.
- Hold no buttons: idle state, no timer should count down.
During a running game:
- Team A capturing should light Team A LED.
- Team B capturing should light Team B LED.
- Contested should light both LEDs.
- Idle should turn both LEDs off.
Press the battery display button.
The 5-segment bar graph should light briefly to show the approximate battery level.
If the displayed battery level is wrong, measure the battery voltage with a multimeter and calibrate the firmware.
The web interface allows the referee/admin to:
- Start the game
- Pause the game
- Resume the game
- Reset the game
- Set match duration
- Set team colours
- Identify teams
- View battery voltage
- View current game state
- See the winner when the match ends
- Add or remove time from either team during gameplay
The reset button is only intended to work when the game is paused or when the match has finished.
The live time adjustment controls are intended for referee/admin corrections during a match. They can be used to fix timing issues without resetting the whole game.
The current firmware uses hold-to-capture logic.
| Button State | Result |
|---|---|
| Team A held only | Team A timer counts down |
| Team B held only | Team B timer counts down |
| Both buttons held | Contested, no timer counts down |
| No buttons held | Idle, no timer counts down |
| A timer reaches zero | Match ends |
This makes the timer useful for King of the Hill games where teams must physically hold the objective.
The original build uses a custom enclosure, but you can use any suitable housing.
When laying out the enclosure, consider:
- Buttons should be large and easy to hit during games.
- Displays should be visible from a distance.
- The power switch should be protected from accidental bumps.
- The USB port should still be accessible if possible.
- The battery should be secure and not able to rattle around.
- Wires should be strain-relieved.
- Solder joints should be insulated.
- The fuse should be accessible.
Do not leave bare battery connections exposed.
Before using the timer at an event:
- Battery fully charged
- Fuse installed
- Power switch working
- Displays visible
- Both team buttons working
- Both team LEDs working
- Battery indicator working
- Phone/laptop can connect to
KOTH-Timer - Web interface loads at
http://10.10.10.1 /pingtest page works- Start/pause/resume/reset tested
- Live time adjustment tested
- Match duration set correctly
- Enclosure closed and secure
Check:
- Battery voltage
- Fuse
- Rocker switch
- Boost converter output
- 5 V connection to the Arduino
- Ground wiring
Check:
- Firmware uploaded correctly
- Correct board selected in Arduino IDE
- Arduino is actually powered
- Try pressing reset on the board
- Try powering from USB first
Check:
- Your phone/laptop is connected to
KOTH-Timer - Your phone has chosen to stay connected to the no-internet Wi-Fi network
- Mobile data is not interfering
- Disable any VPNs
- Try opening
http://10.10.10.1 - Try opening
http://10.10.10.1/ping - Try another browser
- Restart the timer
Check:
- One side of the button goes to the correct GPIO
- The other side goes to GND
- You used D2 for Team A and D3 for Team B
- The button is normally open
- The wire has not broken off the terminal
The firmware expects the buttons to connect the pin to GND when pressed.
Use the normally open contacts on the arcade button.
Check:
- VCC
- GND
- CLK wire to D8
- DIO wire to the correct pin
- Display module orientation
- Solder joints
- Try swapping with a known working display
Check the data pins for that team:
Team A display 1 -> D9
Team A display 2 -> D10
Team B display 1 -> D11
Team B display 2 -> D6
Check:
- The resistor divider is wired correctly
- R1 and R2 are both 100 kΩ
- The divider midpoint goes to A0
- Battery ground and Arduino ground are common
- The firmware calibration value matches your real measured battery voltage
Use a multimeter to compare the real battery voltage against the web interface reading.
Check:
- Battery display button wiring
- Bar graph common pin wiring
- Segment polarity
- Current-limiting resistors
- Pins A1 to A5
- Ground connection
Check:
- Game has been started from the web interface
- Game is not paused
- Only one team button is being held
- The button wiring is correct
- The web interface state is not showing contested or idle
Check:
- You are using the v0.3.1 firmware
- The web interface is loaded properly
- The phone is still connected to the timer Wi-Fi
- Try refreshing the page
- Try opening
http://10.10.10.1/ping
The live time adjustment controls are included in the v0.3.1 web interface.
This is not a polished commercial product. It is a hobby project based on a working event-tested build.
Expect to do some testing and troubleshooting.
You can modify:
- Team colours
- Enclosure design
- Button style
- Display colours
- Battery setup
- Match rules
- Firmware behaviour
If you improve the design, consider sharing your changes back with the project.
v0.3.1 is the current recommended firmware release.
Planned future work may include:
- Improving the PCB assembly documentation
- Making the hardware documentation clearer for new builders
- Adding more photos and diagrams to the build guide
- Adding extra game modes beyond King of the Hill
- Improving the referee/admin interface further based on event feedback
- Exploring a Bluetooth or app-based version if there is enough interest
PCB v0.2 has been manufactured, assembled, and tested with no known faults. It is the recommended PCB revision for new PCB-based builds.
- Be careful with Li-ion batteries.
- Use a fuse.
- Do not short the battery.
- Insulate exposed solder joints.
- Do not leave loose wires inside the enclosure.
- Check polarity before powering the device.
- Do not use damaged cells.
- Do not charge the battery unattended unless your charging setup is designed for safe unattended use.
Guide written for:
KOTH Timer v0.3.1
v0.3.1 is the current recommended firmware release.