FC.Duo is a two-lane slot car lap counter and timer with sensors that you install in the track. Once installed, it can count laps and show timing information without a computer. This manual walks you through sensor placement, the starting sequence, the displays, and basic troubleshooting.
FC.Duo and FC.Duo-HO use different sensor installations. FC.Duo has two wired sensors that sit in holes in the track; FC.Duo-HO uses a gantry placed over an HO track segment. Follow the instructions for the product you own.
Quick start
- Choose a timing point where each car will pass directly over its lane's sensor. Check the position with the types of cars you normally race.
- Drill one 5 mm hole per lane. Install each sensor facing upward, about 0.5 mm below the track surface, and route its cable underneath the track.
- Plug the sensor pair's white connector into the sensor port on the main unit. Hold the connector itself when plugging or unplugging it; do not pull on the wires.
- Provide steady light above both sensors. Position the cars so their starting noses are about one inch before the timing point, and keep shadows away from the sensors during startup.
- Connect USB-C power. Wait for the display check and start sequence to finish. The race begins when all displays turn off again.
- Drive each car over its sensor. The first pass in a lane displays 0 as the starting reference; later passes count completed laps.
What comes with the timing system?
The printed FC.Duo guide describes the main unit and a pair of wired light sensors ending in a white connector. Check your package or product listing for the accessories supplied with your particular order. You will also need an appropriate 5 mm drill bit and a suitable means of securing the sensors in the track.
Controls and displays
On the back of the main unit are the Restart button, the average/best selector switch, the USB-C port, and the sensor connector port. Each lane has three front display rows:
- Top: Lap count.
- Middle: Average lap time or best lap time, selected with the rear switch.
- Bottom: Last lap time.
You can switch the middle row between Average and Best at any time.
Install the sensors in the track
FC.Duo uses two light-dependent resistor (LDR) sensors, one for each lane. Under normal conditions, light reaches the sensor and when a car passes over it, the car briefly blocks some of that light and the system detects the crossing. The sensors need stable illumination and a clear change when a car passes.
1. Choose the sensor positions
Choose a location that each car will cover as it crosses the timing line. For an HO track, the printed guide places the sensor between the rails and the slot of each lane. For larger scales, it places the sensor to one side of the rails, as close to them as practical. Check the positions against the cars you actually race before drilling, particularly cars with different body widths or ride heights.
Place the timing point about one inch ahead of the cars' starting noses. At power-on or restart, the cars should not shade the sensors while the system establishes its light reference.
2. Drill and fit the sensors
- Mark one sensor position in each lane and drill a 5 mm hole at each mark.
- Fit each sensor with its light-sensitive face pointing upward, recessed approximately 0.5 mm below the track surface. It must not protrude into the path of the car.
- Secure the sensors by press-fit or a suitable adhesive without covering their light-sensitive faces.
- Route and secure both cables beneath the track, away from moving parts and places where they could be pulled or pinched.
- Place the main unit where drivers can read it and connect the white sensor plug to its rear sensor port. Hold the solid connector, never the wires, when connecting or disconnecting it.
A small, careful bend in a sensor lead can help it fit your track layout. Avoid repeated sharp bends or tension at the sensor or connector. Keep the sensor faces clean and free of dust.
For more installation detail and diagrams, see How to Install a Slot Car Lap Counter Sensor.
Power on and start a race
Before powering on or pressing Restart, make sure both sensors are well lit. Keep your head, hands, body, and the cars from casting shadows across them during startup.
- Connect USB-C power or press the rear Restart button.
- All displays briefly show 0000 and turn off. This is the display check.
- The top row shows 8888, followed by the middle row and then the bottom row, about 1.5 seconds apart.
- When all displays turn off again, the start sequence is complete and racing begins.
Crossing a sensor before the start sequence ends results in a one-lap jump-start penalty for that lane. Its starting 0 appears only after the sequence has finished. Press Restart to begin a new race.
Understand the lap count and times
On the first pass after the start sequence, a lane's lap display shows 0. That pass establishes the starting reference. The next pass completes its first measured lap, and each later pass updates that lane's count and timing displays.
The top row shows lap count; the middle row shows Average or Best according to the rear switch; and the bottom row shows Last Lap. The two lanes are tracked separately.
Optional USB connection to a computer
FC.Duo works as a standalone lap counter. Legacy units also send lane information over a USB serial connection as comma-separated values in this order: lane (1 or 2), lap count, average lap time, best lap time, last lap time. A program configured to read that serial connection is required; simply plugging the device into a computer or opening a spreadsheet does not automatically import the data.
FC.Platform 2.0 supports compatible FC.Duo and selected legacy circuit devices. Its setup depends on the firmware in your unit. For FC.Protocol devices, follow the FC.Platform 2.0 User Guide to identify the device, assign its Device ID if needed, and connect its sensors to track lanes. For a legacy unit, follow the legacy circuit instructions in that guide. If you are unsure which version you have, contact FC Slot-Cars before attempting a firmware change.
Troubleshooting
A car passes but its lap is missed
Check that its sensor faces upward, remains slightly below the track surface, and lies beneath a part of the car that casts a clear shadow. Clean the sensor and provide steady light above the track. Test with several representative cars at normal racing speed.
An empty lane counts laps
Check for changing shadows or nearby light sources reaching the empty lane's sensor. Restart with both sensors uncovered and test with no cars crossing the timing point. If the count continues changing under steady light, contact FC Slot-Cars with a short video of the installation and displays.
Detection changes after adjusting the track
Inspect the sensor position, cable routing, and white connector. Make sure a sensor has not been pushed out of its recessed position or covered by dust or adhesive. Restore stable lighting, then restart and test both lanes.
The first pass shows 0
This is normal. It establishes the starting reference; the following pass completes the first measured lap.
Restart takes several seconds
This is normal. Press the rear button once and wait through the 0000 display check and the three-row start sequence. Begin racing only when all displays turn off again.
Windows detects FC.Duo, but FC.Platform cannot communicate
If the unit works on its own but Windows shows a warning icon for its USB serial connection, the CH340 driver may be missing or incorrect. In Windows Device Manager, check Ports (COM & LPT) and, if needed, Other devices. Download the official WCH CH341SER.EXE driver, run its installer as Administrator, then disconnect and reconnect FC.Duo. Check that the warning icon disappears and a COM port appears before reopening FC.Platform. If communication still fails, contact us with the device and port information shown in Device Manager.
See also Why Slot Car Lap Counters Miss Laps for a broader explanation of sensor and lighting issues.
Frequently asked questions
Do I need a computer to use FC.Duo?
No. The unit counts laps and displays timing information on its own. A computer connection is optional.
Do I have to drill the track?
Yes. Standard FC.Duo uses two wired sensors installed in separate 5 mm holes in the track. FC.Duo-HO is a different model with a gantry installation that does not require sensor holes.
How far below the track surface should the sensors be?
About 0.5 mm, with their light-sensitive faces pointing upward. They should not protrude above the racing surface.
Can I switch between Average and Best during a race?
Yes. The rear selector changes the information shown in the middle display row at any time.
Why does the first pass show 0?
It establishes the starting reference. A complete measured lap is recorded on the next pass.
Care and support
Keep the sensors clean, the cables secured beneath the track, and the connectors free of tension. When unplugging the sensor pair, hold its solid white connector instead of pulling the wires. Race with steady light reaching both sensors.
If you need help, email fc.slotcars@gmail.com. Include your track scale, the cars you use, photos of both sensor positions, and a brief description or video of what happens. Your experience helps me improve the products and their documentation.
- How to Install a Slot Car Lap Counter Sensor
- FC.Platform 2.0 User Guide
- Standalone Lap Counter vs. Race Management Software
Fernán Castillo
FC Slot-Cars