Jeti GPS-Sensor

To build the RCT Jeti GPS-sensor jump to the Ebay-world, components needed:

  • Arduino Pro Mini 3.3V 8Mhz Example link to Ebay here.
  • NEO-8M (or NEO-6M) GPS module Example link to Ebay here.
  • One 2.4kΩ to 4.7kΩ resistor
  • Some wires and shrink-wrap

Nothing else is needed, total cost just over 10€, not bad at all! If you want you can also use a NEO-8M with external antenna for those carbon-fuselages. Remember that the better “view” to sky GPS-module has the better it responds.

I have found the NEO-M8N to be quite more sensitive than NEO-6M, takes satellites better so NEO-M8N is highly recommended.

Note: This is totally new firmware version of RCT Jeti GPS, the old version can be updated without any changes to hardware! Old version still available HERE.

Features and operating modes

Features:

  • EX-Bus sensor (125kbps between sensor and receiver)
  • Really fast update of values
  • Possibility to reset home-position and altitude with a dedicated channel from transmitter
  • Hardware reset of Arduino

Note about EX-Bus: The port in receiver has to be set as “EX-Bus”, also note that Hardware Jetibox and Expanders do not work. Sensor has to be connected to receiver port.

I wanted some extra functionality and possibility for user to choose the working mode so I made two operating modes, basic and extended.

Basic mode sensor-values

  • Latitude
  • Longitude
  • Groundspeed
  • Relative altitude
  • Possibility to use “US” or “EU” units (km/h & meter vs. mph & feet)

Extended mode sensor-values

  • Latitude
  • Longitude
  • Groundspeed
  • Relative altitude
  • Altitude (Absolute, over the sea level)
  • Variometer (Vertical speed indicator)
  • Distance to model from start point
  • Heading (Model flying heading)
  • Course (Direction to model from start point)
  • Satellites count
  • HDOP (Horisontal dilution of precision)
  • Possibility to use “US” or “EU” units (km/h & meter vs. mph & feet)

Connections

Connection are simple:

  • NEO-8M VCC -> Arduino VCC
  • NEO-8M GND -> Arduino GND
  • NEO-8M RX -> Arduino 9
  • NEO-8M TX -> Arduino 8

You also need the connection to Jeti receiver:

  • Arduino TX0 -> 2.4kΩ to 4.7kΩ resistor AND receiver signal
  • Arduino RX1 -> 2.4kΩ to 4.7kΩ resistor
  • Arduino RAW -> Receiver positive
  • Arduino GND -> Receiver negative

NOTE: Some boards have GRN where my boards have GND. Do NOT use GRN for voltage GNS input, use GND!

Schematic

Connection schematic below says it all, really simple:

Physical dimensions

The whole setup is not that big at all, here’s a comparison between Arduino Pro Mini and NEO-6M:

That “disc” is the antenna and should not be covered with the Arduino-board. One neat feature of this NEO-6M board I chose is the USB-connector:

The USB on NEO-module can be used to connect NEO-8M module to PC and change settings like update speed etc with UBlox U-Center application. NEO-8M (or NEO-6M) has to be in 9600bps and to work with RCT GPS-sensor.

You can also see a tiny battery on the NEO-8M module, this is for the module to remember last position, helps for faster start when it’s been unpowered for a while, nice.

About other GPS-modules

While some other modules than NEO-8M and NEO-6M might work with this sensor they are not supported by me. The low-level speed settings included in RCT-GPS work only with NEO-modules, you will not necessarily get the faster update speed with other modules.

Pictures!

Here’s an idea of final installation (Not yet soldered) little heat-shrink and it’s perfect:

Update speed?

Refresh interval is fast, up to 5 times per second in basic mode seen from transmitter.

Programming Jeti GPS-Sensor

Download the zipped .hex file HERE. (Version for Arduino 5V is also available HERE, Note that I have not tested it)

Use RCT-Firmware uploader HERE to program the Arduino-board.

Hardware reset of Arduino

If you have used the Arduino board in some other applications where EEPROM might ave been overwritten you can do a hardware reset:

  1. Connect RCT-GPS to receiver for power
  2. Connect pin 10 (lower right corner in picture above) to GND, keep it connected
  3. Press reset-button on arduino, board restarts and led blinks a few times fast, then one longer blink
  4. Remove the short between pin 10 and GND
  5. Program the sensor as descibed below

If this does not fix your sensor replace the Arduino.

Using GPS-Sensor with Jeti

After connecting Jeti GPS-Sensor to your receiver you will find the Jeti GPS-Sensor defaulting in metric and basic mode. This means you have four values with metric units km/h and meters. If this is what you want’, fine, no need to do any setup.

Changing sensor settings

Go to Jetibox in your transmitter, here is the menu:

GPS Settings menu

When in a setting screen pressing DOWN will change the setting, moving RIGHT takes you to next sceen. After all settings are to your liking go to “Save settings”-screen and press DOWN, sensor stores the settings and restarts.

IMPORTANT: If you have changed units (meters / feet) or operating mode (Basic/Extended) you HAVE TO go to sensor-settings and do a re-scan of sensors. Jeti does not change these automatically!

Using Jeti GPS-Sensor with your transmitter

Using is simple: You have some new sensors, picture is from extended mode, basic has the four first sensors.

  

After this you can use them on your transmitter just as any other telemetry-values, here are the values:

RCT GPS RCT GPS

About altitude

There is two altitude-values available. “Altitude” is absolute altitude, this is the altitude GPS is sending. The “Rel. Altit” is relative altitude and is automatically set to zero after a GPS fix is got. This is the altitude you want to know when you ask “how high above ground my model is.”

Using voice announcement on these are also different, Jeti announces “Altitude” as “Absolute altitude nn meters” and “Relative Altitude” as “Altitude nn meters”.

Home position and altitude

Since GPS-sensor’s tend to “wander” a bit after start for some time the home altitude and -position can be reset to current position activating momentarily the reset channel. Set a channel (1 to 24) of your choice to have a value of +100% when activated.

What is HDOP?

HDOP is short of “Horizontal Dilution Of Precision”, meaning it’s horizontal accuracy. The value given by module is a multiplicator of sensor manufacturers announced accuracy. For NEO-6M it’s 2.5 meters. So, if you have a HDOP of 1.75 the accuracy of position is 1.75 x 2.5 and this results to 4.375 meters. This was the short explanation, there’s ton of this stuff in world wide wait if you are interested. (If i was wrong let me know!)

Version history

  • 2.b Initial release as beta-version
  • 2.0 Full release version, added hardware reset and separate 3.3V and 5V versions

Disclaimer

Always make sure everything works as it should. Do not use faulty devices. neither RC-Thoughts and/or me are in any way liable or responsible for anything you do with your equipment or to others with equipment used as described here. You should never use LUA-apps for operation-critical functions.

If you find something that is not working or is behaving strangely please let me know. I’m a car-mechanic by training, not a programmer-geek :)

Most important thing

Is to have fun building and using, this will not bankrupt you in any way :)