+
+
+
+ 
+
+ 
+
-### I2C Cable Twisting
+TFSLOT can be bought directly from us via our contact [email](https://www.thunderfly.cz/contact-us.html). The email can also be used if there are specific requirements for custom modifications or if the product will be inquired in large quantities. TFSLOT is also available for online purchase through the [Tindie store](https://www.tindie.com/products/thunderfly/tfslot01a-airspeed-sensor-with-integrated-imu/).
-To improve I2C bus reliability, the supplied cable is specifically twisted by following the scheme
-- 10 turns for each pair SCL/+5V and SDA/GND per 30cm cable length
-- The two pairs are turned again by 4 turns of pairs per 30cm cable length.
+## Support and Integration
-These special cable conductors' winding method greatly improves the signal integrity by minimizing the crosstalk between the SDA and SCL signals.
+### Drone avionics
+The TFSLOT01A sensor (PCB board [TFASPDIMU02A](https://github.com/ThunderFly-aerospace/TFASPDIMU02)) is currently supported by the PX4 autopilot, where it can be utilized both as an airspeed sensor and as an external IMU unit (external magnetometer). Instructions for integrating the sensor with the PX4 autopilot can be found in the official [PX4 documentation](http://docs.px4.io/master/en/sensor/airspeed.html#airspeed-sensors). The sensor is also hardware-compatible with other autopilots, such as Ardupilot, but currently lacks the computation code to convert differential pressure into airspeed.
-
-## Working Principle
-
-The sensor basically uses the [Venturi Effect](https://en.wikipedia.org/wiki/Venturi_effect#Instrumentation_and_measurement) to measure fly velocity in the air.
-
-The velocity and pressure of the fluid are required to meet [Bernoulli's principle](https://en.wikipedia.org/wiki/Bernoulli%27s_principle)
-
-
-
-
-
-Then the velocities are in relation to cross sections in the plane of pressure measurement ports
-
-
-
-
-
-Therefore equations for pressure difference and airspeed velocity could be derived.
-
-^2-1\right]\Rightarrow&space;&space;v_\infty=\sqrt{\frac{2\Delta&space;p}{\rho\left[\left(\frac{A_D}{A_d}\right)^2-1\right]}})
-
-
-
-Where
-
-| Symbol | Explanation |
-|--------|------------------|
-| | Measured pressure difference |
-|  | Air density |
-| | Free air velocity e.g. measured airspeed |
-|  | The velocity of air running through the sensor |
-|  | Cross-section area at the position of the outer pressure port |
-|  | Cross-section area at the position of internal pressure port |
-
-### Comparison to pitot-static tube
-
-In contrast to classical [Pitot tube](https://en.wikipedia.org/wiki/Pitot_tube), the TFSLOT design is the perfect choice for low airspeed measurement (generally below 10 m/s).
-The design has the following advantages compared to a pitot probe:
-
- * Better resolution on low airspeeds (where kinetic pressure is small)
- * Less tendency to clogging (due to the absence of stagnation point)
- * Direct differential pressure sensor integration without any additional tubing
-
-The improved resolution on low airspeeds is the principal difference from the pitot-static tube. This could be explained by comparing it with the classical equation for pitot-static tube:
-
-
-
-The equation for TFSLOT venturi-based sensor (see equations above) differs from it by a factor
-
-^2-1)
-
-That means the TFSLOT sensor is more sensitive (e.g. has a higher measurable pressure difference at the same airspeed) than the pitot-static tube (at the same air density) in every configuration where
-
-
-
-The advantage of the higher sensitivity results in increased drag, but it could be negligible at low airspeeds. The best use case of the sensor is the integration of the sensing device into the relatively massive fuselage or other construction geometry. The user is supposed to find the best mounting option for the device or adapt the TFSLOT 3D printed case to fit the specific application. From that perspective, the TFSLOT01 is a fully functional development kit that is able to cover specific user needs.
-
-# Usage
-
-TFSLOT is equipped with [TFASPDIMU](https://github.com/ThunderFly-aerospace/TFASPDIMU02) electronics, which contains the required differential pressure sensor and an IMU unit through which the pressure sensor is connected. To activate I2C access to it, it is necessary to set the pass-through mode in the IMU unit. The [TFASPDIMU02](https://github.com/ThunderFly-aerospace/TFASPDIMU02) has many options for how can be used, please look at its documentation for more details.
-
-## PX4 autopilot
-
-PX4 is able to initialize the sensor itself. All you have to do is add the following two lines to the [startup configuration file](https://docs.px4.io/master/en/concept/system_startup.html#replacing-the-system-startup) on the Autopilot's SD card.
-
-```
-icm20948_i2c_passthrough start -X -b 2 -a 0x68
-sdp3x start -X
-```
-
-The script assumes a connection to port _I2C 2_. This was set by the `-b` parameter in both commands. The correct bus has to be set by the user.
-
-> The model for converting to the airspeed from an air pressure is not yet in the stable version of the PX4 autopilot source code. Therefore the master upstream needs to be used with the sensor.
-
-Sensor requires firmware with modifications from the [`tf/aspdimu`](https://github.com/ThunderFly-aerospace/PX4Firmware/tree/tf/aspdimu) branch. The GitHub [pull-request](https://github.com/PX4/PX4-Autopilot/pull/18593) into the PX4 master is currently open to solve this issue. The airspeed recalculation model should be included in the next stable release. Alternatively, you can temporarily applicate [this PR changes](https://github.com/PX4/PX4-Autopilot/compare/master...ThunderFly-Aerospace:tf/aspdimu) or [apply patch](https://patch-diff.githubusercontent.com/raw/PX4/PX4-Autopilot/pull/18593.patch).
-
-### Configuration
-
-TFSLOT01 contains a specific aerodynamic profile. Therefore it requires a different converting model. This is done by setting the parameter `CAL_AIR_CMODEL` to 3 (Venturi effect-based airspeed sensor). Setting the wrong profile causes the measurement of negative airspeed values, which results in an `airspeed sensor failure` condition during the attempt to fly.
-
-### PX4 Calibration process
-
-
-
-The sensor itself is calibrated and the PX4 calibration process aims to verify that the sensor is properly mounted and connected. Thanks to the used sensor, this sensor is not sensitive to temperature changes and has zero offsets. It is enough to calibrate (verify) the sensor once it is mounted into the UAV. And there is no need to do it before each flight (as with other types of airspeed sensors).
-
-The procedure is performed with the help of a calibration tool in a few steps:
- 1. Place the calibration tool in the TFSLOT inlet
- 1. Press the tool against the sensor (green arrow) with your hand or rubber band and hold it there during the whole process.
- 1. Start the [callibration process](https://docs.px4.io/master/en/config/airspeed.html#performing-the-calibrationhttps://docs.px4.io/master/en/config/airspeed.html#performing-the-calibration) in PX4
- 1. Wait for the measure of static offset (no blowing)
- 1. PX4 will command you to blow into the airspeed sensor
- 1. Blow from the back of the sensor (blue arrow). If you blow too little, repeat the attempt.
- 1. PX4 calibration should now be completed, confirmed by a beep, and in the QGC.
-
-
+### Robotics and measurement
+For other applications, the sensor can be easily connected to any computer with an I2C interface, such as RaspberryPi or a generic desktop with a USB to I2C converter (e.g., [USBI2C02A](https://www.mlab.cz/module/USBI2C01/), [shop it on tindie](https://www.tindie.com/products/mlab-project/mlab-usbi2c01a-usb-to-smbusi2c-bridge/)), and the differential pressure values or values from the IMU unit can be read, for example, by a Python script.
# FAQ
Frequently asked questions are listed on [TFSLOT's documentation page](https://docs.thunderfly.cz/avionics/TFSLOT01#faq)