FC.Duo-HO is a two-lane HO slot car lap counter and timer. It works on its own: install it over your track, connect USB-C power, and race. This guide explains how to position the track, what the displays mean, how the starting sequence works, and what to check if a car is not detected consistently.
If your cars or lighting call for a small sensor adjustment, the procedure below will help you make it one lane at a time.
Quick start
- Place a segment of your two-lane HO track on top of the thin plate that connects the gantry’s legs at the bottom. The plate positions the track at the intended height beneath the sensors.
- Check that both sensors face their respective lanes and receive light from the central white LED. Position the cars about one inch before the gantry, keeping the sensors free of shadows during startup.
- Connect the USB-C cable to power the unit. Wait for the display check and starting sequence to finish. Racing begins when all displays turn off again.
- Drive each car through its lane. On its first pass, the lap display shows 0, establishing the starting reference. Subsequent passes count laps and update the times.
- Use the switch on the back to choose average lap time or best lap time for the middle display row. The lower row shows the last lap time.
Get to know your FC.Duo-HO
On the back of the unit, you will find the Restart button, the average/best selector switch, the USB-C port, and a sensitivity adjustment for each lane.
On the front, each lane has three display rows:
- Top row: Lap count.
- Middle row: Average lap time or best lap time, depending on the position of the rear switch.
- Bottom row: Last lap time.
Install the gantry over your track
The FC.Duo-HO gantry has a thin plate connecting its two legs at the bottom. Place a segment of track directly on top of this plate. The plate establishes the track height intended for reliable detection. The track runs through the gantry, beneath the sensors and central white LED.
FC.Duo-HO uses light-dependent resistor (LDR) sensors. A passing car briefly reduces the light reaching its lane’s sensor, allowing the system to detect the pass. The central white LED is the sensors’ primary light source.
- Make sure the track segment rests on the lower plate, rather than beside or below it.
- Check that each sensor is positioned over its corresponding lane and receives light from the central LED.
- Do not raise the gantry or move the sensors to change their height. The plate provides the intended track position.
- Leave the sensors in their original positions. Each unit is assembled and tested with its sensor placement.
- Remove the protective film from the displays before use.
You do not need to drill holes in the track for FC.Duo-HO’s sensors. To learn how other slot car timing systems position their sensors, read How to Install a Slot Car Lap Counter Sensor.
Power on and understand the start sequence
Before connecting power or pressing Restart, make sure the track is resting on the gantry’s lower plate and both sensors receive unobstructed light from the central LED. Avoid covering them with a hand, finger, or car. Starting the cars about one inch before the gantry helps keep the light reference clear.
- At power-on or after pressing Restart, the displays briefly show 0000 and turn off. This is a display check.
- The top row then shows 8888, followed by the middle row and then the bottom row. Each stage is about 1.5 seconds apart.
- When the displays turn off again, the starting sequence is complete and the race begins.
If a car crosses its sensor before the start sequence ends, that lane receives a one-lap jump-start penalty. Its initial 0 appears only after the sequence has finished. To start over, press the Restart button on the back.
How lap counting works
After the start sequence, the first pass in a lane shows 0. It establishes the reference from which the system measures complete laps. Each later pass through that lane registers a lap and updates its displayed times. Both lanes are detected separately.
You can change the middle-row selector at any time. Average helps you judge consistent pace; Best shows the quickest recorded lap. The bottom row continues to show the last lap measurement.
Adjust sensor sensitivity if passes are missed
The factory sensitivity value is 15. Under normal conditions, you should not need to change it. Open-wheel or very low-profile cars may call for an adjustment. First make sure the track rests on the gantry’s lower plate and check the lighting. Then adjust only the lane that misses passes.
The sensitivity controls are the small blue components on the back with a gray screw in the center. Use a small screwdriver. Turning a screw clockwise increases sensitivity; turning it counterclockwise decreases sensitivity. The adjustment range is 0–30.
- Power on the unit or press Restart.
- Let the entire start sequence finish and wait until the displays turn off.
- Turn one lane’s sensitivity screw slowly. Its top display shows the value as you adjust it. If an increase is needed, try 20–22 as an initial setting.
- Stop adjusting and leave the unit untouched for about 10 seconds. A brief animation of zeros on the first display indicates that the value has been saved.
- Restart and drive several test laps in both lanes. If passes are still missed, repeat in small increments, up to the maximum value of 30.
Adjust one control at a time so you can tell which change helped. Do not move the sensors themselves.
Optional computer connection
FC.Duo-HO does not need a computer for lap counting and timing. Legacy units send comma-separated data over their USB serial connection in this order: lane (1 or 2), lap count, average lap time, best lap time, last lap time. Software configured to read the serial connection is required to display that stream; simply connecting the unit to a spreadsheet does not automatically import it.
Units released after August 2026 can be used with FC.Platform 2.0 on a Windows PC. The software provides driver and car records, circuit races, tournaments, and race history. Follow its user guide to identify your device and configure its track and sensor assignments.
If you are unsure which firmware is installed in your unit, contact FC Slot-Cars with your purchase details before attempting a firmware change.
Troubleshooting
A lane misses some cars
Confirm that the track segment rests on the plate beneath the gantry. Check that the affected sensor receives light from the central LED and test with steady lighting. If passes are still missed, increase that lane’s sensitivity gradually using the procedure above.
The first pass shows 0
This is expected. The first pass establishes the starting reference. A later pass completes the first counted lap.
The lap count is lower after a start
A car that crossed before the light sequence ended receives a one-lap penalty. Restart and wait until every display turns off before racing.
Detection changes after moving the unit
Check that the track segment is once again resting on the gantry’s lower plate. Make sure both sensors receive unobstructed light, then restart the unit.
A sensitivity change seems to disappear
After adjusting, wait about 10 seconds for the save animation before restarting.
FC.Platform does not communicate with the unit: check the CH340 Windows driver
If the FC.Duo-HO powers on and works normally by itself, but FC.Platform cannot communicate with it, Windows may not have the correct USB serial driver installed. This can occur on Windows 10 or Windows 11.
Possible signs include:
- Windows plays its connection sound when you plug in the unit.
- FC.Duo-HO powers on and operates normally as a standalone lap counter.
- FC.Platform shows “USB reset started”, but the device does not restart or respond.
- Device Manager shows a yellow warning icon beside the USB serial device.
To check and install the driver:
- Connect FC.Duo-HO to the computer and open Device Manager in Windows.
- Look under Ports (COM & LPT) for the USB serial device. If it does not appear there, also check Other devices for an entry with a yellow warning icon.
- If Windows indicates a driver problem, download the official WCH CH341SER.EXE Windows driver.
- Run the installer as Administrator and follow its instructions.
- Disconnect and reconnect FC.Duo-HO. Return to Device Manager and confirm that the warning icon is gone and a COM port appears under Ports (COM & LPT).
- Open FC.Platform again and check whether it recognizes the device.
If the warning icon is gone but communication still fails, confirm that FC.Platform is using the intended device and USB connection. Contact FC Slot-Cars if you need help identifying your unit or firmware.
For a deeper explanation of missed detections, read Why Slot Car Lap Counters Miss Laps.
Frequently asked questions
Does FC.Duo-HO need a computer?
No. It counts laps and displays timing data as a standalone system. A computer connection is optional for compatible data and race management workflows.
Do I need to drill holes in the track?
No. Place a segment of HO track on the plate connecting the gantry’s legs. This positions the track beneath the sensors without drilling.
Why does the first car pass show 0 instead of 1?
That first pass establishes the lap reference. The next pass completes the first full measured lap.
Can I change between average and best lap time during a race?
Yes. Use the rear selector switch at any time. It changes what the middle display row shows.
What should I do if a low-profile car is not counted?
First check that the track is on the gantry’s lower plate and that the sensor receives light. If it still misses passes, adjust that lane’s sensitivity after the start sequence, let the new value save, restart, and test again.
Can I install FC.Duo-HO over a track piece with a mechanical lap counter?
Use a regular track segment whenever possible. Place it on top of the thin plate connecting the gantry’s legs. Some track pieces with built-in mechanical counters are thicker than regular track, which can change the distance between the cars and the sensors. If you are using one of those pieces, move FC.Duo-HO to a regular straight or curved segment and test it again.
Why does an empty lane count laps?
An empty lane should not count laps. FC.Duo-HO detects a car through a change in the light reaching that lane’s sensor. A moving shadow or another light source near the track may sometimes produce a change that resembles a passing car.
First confirm that the track rests on the gantry’s lower plate and that the central white LED illuminates both sensors. Restart the unit with the sensors uncovered, then leave both lanes empty for a short test. If a lane counts without a car, check whether nearby lamps, windows, people, or cars on adjacent track sections cast changing light or shadows across its sensor. Try the test again with those sources removed or repositioned.
Do not increase sensitivity to address false counts. If the lane continues counting with no car nearby under stable lighting, contact FC Slot-Cars and include a short video of the setup and displays.
What should I do if the counter works for several laps and then stops registering cars?
That is not expected behavior. Check whether the affected sensor remains clearly illuminated when no car is above it. For another lap to be detected, the sensor must see the lane clear again after each car passes. A changing external light or a persistent shadow may interfere with that sequence, although the cause cannot be determined from the display alone.
Test the unit on a regular track segment resting on the gantry’s lower plate, with steady lighting and one car running at a time. Note whether the problem occurs in one lane or both, and whether an empty lane also counts laps. If the behavior repeats, please send FC Slot-Cars a video showing the entire gantry, nearby track and lights, and all six displays before and after the problem occurs.
Is it normal for Restart to take several seconds?
Yes. Press the Restart button on the back once. The displays briefly show 0000, turn off, and then run the starting-light sequence row by row. Wait until all displays turn off again before driving through the sensors. That sequence is part of a normal restart.
What if Windows detects the unit but FC.Platform cannot communicate with it?
Check Device Manager for a warning icon or a missing COM port. If Windows reports a driver problem, install the official WCH CH341SER.EXE driver and reconnect the unit, following the steps above.
Help and further reading
Questions or suggestions are welcome at FC.Slotcars@gmail.com. Tell me which lane is affected, what car you are using, the sensitivity value, and what happens during a few test passes. For computer connection problems, include what Windows shows in Device Manager.
Fernán Castillo
FC Slot-Cars