Dual Concentric Encoder Add-on (Optional)

What is a Dual Concentric Encoder? #

While the name may sound confusing, the operating principles of a Dual Concentric encoder are simple:

  • DC Encoders have an ‘inner’ and an ‘outer’ knob, which are aligned with each other through the center shaft – hence the ‘concentric’ nature of the device.
  • The ‘inner’ knob is smaller than the ‘outer’ knob.
  • Each Knob has it’s own functions – it is essentially two encoders in one!

Which Dual Concentric Encoders does the Class Echo Support? #

The Class Echo supports the ‘Elma E-37’ model of Dual Concentric encoder. This model can be bought directly from Leo Bodnar:
Click to Visit Leo Bodnar’s Elma E-37 Listing

IMPORTANT: The Elma E-37 kit requires assembly (Soldering the encoder to the included breakout board).

IMPORTANT: You must purchase a knob with your Elma E-37 from Leo Bodnar. Please choose your knob under the “accessories” dropdown over the buy button. You can also choose a more premium “Soft Touch” rubber knob from Leo Bodnar as well.

The base kit comes with:
– Dual Concentric Encoder
– Breakout Board
– Header Pins

All you need to purchase is the E-37 with a knob.

**Unfortunately, the PropWashSim DC Encoder is not supported.

Leo Bodnar Elma E-37 Kit Contents #

The Elma E-37 kit and knob is pictured. One again, the knob assembly is sold as an accessory and must be selected over the buy button when adding the encoder to your cart.

The Encoder Kit Contents:
– Dual Concentric Encoder Body
– Pin headers
– Breakout Board
– Encoder Nut

Pictured to the right is the knob, which comes in three pieces:
– Inner Knob
– Outer Knob
– Inner Knob Cap

i. Properly Aligning The Breakout Board / Pins #

Orient the breakout board and the encoder body in the way show in the photo. Note the following:

  • The text stamped on the side of the encoder body is facing the side of the breakout board that says ‘BTN’ and ‘OUTER’
  • The breakout board is flipped so that the words ‘OUTER’, ‘INNER’, and the pin labels are facing out and away from the bottom of the encoder.
  • Ensure the breakout board is flush with the bottom of the encoder.

ii. Solder The Encoder Pins #

Start with a light application of flux on the pins, then apply solder:

  • Typically a temperature of 400-425 celcius works well.
  • Take care not to leave the iron on the pins too long – a second or two maximum to prevent overheating.
  • Ensure the solder flows down the hole and encapsulates the pins.

iii. Solder The Header Pins #

Apply a light coat of flux to the header pin holes – this should help hold the header pins in place before you solder them.

IMPORTANT: solder the header pins so that they stick out the BACK of the encoder, not toward the front where the spinny bits are!

iv. Disassemble The Echo / Cut Existing Zip Ties #

v. Arduino Wiring Setup #

  • EXISTING ECHO: Remove the white wire from the ‘VIN’ pin and the black ground beside it (leave the ground and power wires for the display in place)
  • Plug the white wire into digital pin 5, and the green (spare) wire that comes with your echo into digital pin 6.
  • Plug the black ground wire into the ‘GND’ terminal on the same pin rail as pictured.

vi. Bodnar Wiring Setup #

  • Remove the old encoder from the hole and screw in the new Dual Concentric Encoder
  • Install the Outer knob, Inner Knob and place the plastic knob cap on the Inner Knob


Pin 2Inner B
Pin 3 Inner A
Pin 4 Button
Pin 5Outer B
Pin 6 Outer A

vii. Enabling Dual Encoder Support In The Firmware #

  • In the settings tab, toggle the “Dual Concentric Encoder Support” switch.
  • Finding Settings: Navigate to the ‘Flight Info’ tab, click the gear in the top left hand corner.

Enjoy your dual concentric encoder! Here are some features you can use it for:

  • Outer knob adjusts Alt by 1000s
  • Outer knob adjusts Hdg, Crs, Spd by 10s
  • FMS knob on the GPS units work with inner and outer knobs as you would expect in real life (such as on the G1000).

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