I have a Gen 4 Jabiru 3300 and installed the Rotec alternator ( a story in itself) and a Rotec electronic ignition upgrade.  I also have the Dynon HDX SkyView system.

The only thing that the Rotec ignition installation manual says about the tachometer connection is the following;

” 10. Tachometer (optional):
a. The tachometer pulse signal is provided wire 7 of the ignition
module (see ​Figure 5.1). Pulses per revolution is as follows:
● Jabiru 2200 – 2 pulses per revolution
● Jabiru 3300 – 3 pulses per revolution
● Jabiru 5100 – 4 pulses per revolution”

The manual gives no explanation of where this wire would go or what to connect it to.

The Dynon EMS supplies a wire for the right tach and a wire for the left tach. However, the manual recommends running one wire to the EMS from the alternator wire. 

Since I no longer have the Jabiru alternator, I cannot do that. 

Is there another way that I can pick up both the left and right rpm using the wires from the Dynon EMS?

Does anyone have the Rotec ignition with the Dynon system?  If so, how did you connect your tach wires?


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I have a Gen 2 with the Rotec ignition and picked up the tack from the "magneto" switch. For the Rotec, this is the 12v power and for the Jabiru it's the grounding of the pickup coil...

I used both the right and left tach input to the EMS and I have left and right tack readout on the HDX display. If I recall correctly, there is some editing of the EMS settings file if you want both tach readouts with a single engine setup. I've have set warnings if either drop below 750 rpm indicating a bad ignition side...

It's my understanding that any impulse signal will work, doesn't have to be the alternator, might have to put a resistor inline, but I didn't. Also, I could look up my EMS settings if you're interested in going with the both L/R tach readout...

Thanks for the information.  
To make sure I understand you properly, you have attached one of the Dynon EMS tach input wires to your mag switch for the original Jabiru coil, and the second tach input wire from the Dynon to the power going to the Rotec ignition?

I will try attaching one of the Dynon wires to the grounding switch for the Jabiru coil, but as far as the Rotec ignition, I must have a newer version because it has a specific wire marked “tach output”.  My problem is that I don’t know what that output is (12 v+, ground, something else?), and Rotec supplies no information.  I have tried contacting them several times via email and their web support form but they have never replied.  I have no idea if I need a resistor and I don’t want to risk frying the Dynon…

I was hoping someone out there has already used the Rotec “tach output” wire and could tell me if a resister is necessary and if it’s safe to attach to the Dynon tach input wires.


No. I was wrong. You are correct. I used the Rotec tach wire. And yes, the grounding wire from the Jabiru ignition. My main goal was to get both tach readings on the Dynon so I could tell if the electronic one went bad in flight. If you just want a tach reading, then the Jabiru ignition option might be easier.

As far as the resistor, I didn't use one, but as I understand it, you might get erratic tach readings - in which case you would need a resistor. When I was installing my system, from the research I did it seemed like you just experiment with various resistors (20kohm to maybe 100-200 kohm) to get the reading to settle down. I don't "think" you'd fry the Dynon without the resistor.

As you said Rotec is not very helpful for specific installation questions, especially with the Dynon stuff, but Dynon has been very helpful for me in the past.

I received a reply from Rotec concerning their  “tach output” wire :

The Rotec "Tach" wire is  gentle 5 volt square wave form (digital output) and is perfect for a tach signal.  I'm sure your Dynon will accept it.”

Therefore when using the Rotec ignition as a tach input you would use the low voltage rpm input wires (pin 34 or pin 35) to attach to the Rotec ignition tach output wire.




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