Question about setting up contact switch/gear

[8181C]

I would like to connect the EMS to monitor the state of my gear while using the existing microswitches and interconnect. My aircraft system is 28vdc and if I understand the manual correctly, I will have to convert this voltage to 12vdc in order to use as a gear input signal. Am I understanding this correct that the system can not use 28vdc for switch condition state? Thank you.
Larry :-/

 

[Pobb]

I have done this on my Glasair 2 RG, using three wires and three resistors for each gear unit. One lead is a ground lead, one the signal lead which goes to a contact on the EMS and the third wire is for a test lead. As well as giving gear indications, the signal lead also connects to a separate alarm circuit, independent of the EMS, in case the Dynon units go out.

The display shows indications for each gear unit, with green indicating down, red, gear in transit and black for gear up. The test lead applies ground to the gear down lead to show the gear in transit light and also sound an audible alarm.

Unfortunately, my main computer has just died, so I am unable to send you a circuit at the moment. Hopefully I will have a new computer by the end of the week.

 

[8181C]

Thank you. For simplicity, I wanted to tie into the existing gear light circuit (28vdc) so I can get the audio. If the system can only handle 12vdc max, I will need to put a voltage divider inline to the wire that goes to the EMS. Unless someone else has some great shinny idea instead of a voltage divider?

 

[8181C]

I see Dynon sells different D Sub connectors but I have not seen an reference to D Sub 37 pin connectors. Does Dynon also sell these 37 pin connector for custom harnesses?

 

[dynonsupport]

If you already have an engine monitor, you already have the D37 plugged into it. It comes with our engine monitor harness.

I'm assuming your wires are at 28V when the gear is down and 0V when it's up?

The contacts can only read 0-5V. Anything above 5V will just read as 5. They are only designed to handle up to 30V however, and a 28V plane can put 60V on the line during some load dumps.

You can fix this by putting a 4.7K ohm resistor in series with the input. The only downside to this is that when you switch grounds out, you'll see 1-2V on the input instead of ground because of the internal 10K pull up, but that's fine because you'll still get a swing from 2V to 5V when the switch changes state.

 

[Dynon]

We don't sell the D37 connectors separately, but if you give our tech support team a call at 425-402-0433 they might be able to help out.

 

[8181C]

I had a chance to speak with Mike at Tech support after reading the above suggestions. Because the written description in the manual does not align with the response on the board, I needed further explanation. It was confirmed that the contact switch output uses a pull up resistor and thereby provides a voltage to that output when not loaded. Secondly, I was notified that the input must be 5vdc to accommodate one of the two stages or voltage ranges for contact switches, no 15vdc max that the manual states. So that being said, one state must be 5vdc (up or down) and the other state must be a ground. An open will not bring the pull-up voltage below what the second state is required (0vdc to 2vdc). A single line diagram would be great to help explain some of these unique input requirements, as the manual is confusing and in this instant, if the above is correct, the manual is wrong. I will bench up my proposed solution and let you know how that works out.

 

[dynonsupport]

Spooky,
From above:

The contacts can only read 0-5V. Anything above 5V will just read as 5.

One state must be between 0V and 4.9V. The other state can be above 5V. As long as we can detect the difference in these states, we can trigger on it. This doesn't mean the input can't handle more than 5V without damage.

If you have a grounding switch hooked to a 24V light, just hook to the wire between the switch and the light. This wire will be 0V when the switch is closed and 24V when the switch is open. This will work perfect.

I do see that the manual doesn't make it clear in the contacts section that only changes within 0-5V can be detected. It is correct however that voltage up to 30V will not damage these inputs. So it's missing a limitation, but it's not "wrong" per se. We'll get that fixed.

 

[vlittle]

Thank you.  For simplicity, I wanted to tie into the existing gear light circuit (28vdc) so I can get the audio.  If the system can only handle 12vdc max, I will need to put a voltage divider inline to the wire that goes to the EMS.  Unless someone else has some great shinny idea instead of a voltage divider?

The most foolproof method is to put a diode in series with the input. Anode connected to the SV and the cathode to the gear light. This will block the high voltage and block any parasitic current flowing into the SV that could cause the light to glow when not activated.

A common 1N4007 diode will do, not critical.

A resistor divider may also cause the lamp to glow, so that's not ideal.

Vern