# Modules Reference: Optical Flow (Driver)
## thoneflow
Source: [drivers/optical_flow/thoneflow](https://github.com/PX4/Firmware/tree/master/src/drivers/optical_flow/thoneflow)
### Description
Serial bus driver for the ThoneFlow-3901U optical flow sensor.
Most boards are configured to enable/start the driver on a specified UART using the SENS_TFLOW_CFG parameter.
Setup/usage information: https://docs.px4.io/en/sensor/thoneflow.html
### Examples
Attempt to start driver on a specified serial device.
```
thoneflow start -d /dev/ttyS1
```
Stop driver
```
thoneflow stop
```
### Usage
```
thoneflow [arguments...]
Commands:
start Start driver
-d Serial device
stop Stop driver
info Print driver information
```