EMS General Purpose Pin 9 and Canopy Contact

[brinzlee]

Dear Knowledgeable forum members
I wonder if somebody could help me with an issue I am having with the EMS 221. I am trying to set up a monitoring pin 9 on an open canopy contact which is wired through a 12v indicator as per my diagram. The issue I'm having is the way it is wired at present when the contact is closed the lamp is on but when the contact is open the lamp dims ever so slightly and doesn't turn off. I guess this is because it is sinking through pin 9. Is there a way to stop this.
Kind regards
Brinsley

 

[brinzlee]

Can anybody help me with this pretty pleeeeease ?

 

[Raymo]

Are you not using the built-in indicator that would normally be on the display for pitot heat but rather an external lamp? You can add the pitot heat indicator to your display and would not need the external lamp.

Regardless, you will need to power the lamp separately (e.g. pin 15 or external source), then use pin 9 for reading that voltage for display indication on your Skyview.

 

[brinzlee]

I have two doors, two switches, and two lights on the panel to indicate if the door is open. This works fine. The circuit diagram above is how I wired it, all very simple. I just wanted to have the sensors off the ems 221 flag this on the dynon as well. But the problem with the way it is wired, when then the door contact is open circuit the light doesn't go out it just goes dimmer suggesting the ems is sourcing to ground. I'm not sure how to resolve it.

 

[Raymo]

I must be blind. Having read Brinsley's response, I see that it is wired as I suggested with an external 12v source.

I agree, the EMS must be providing some amount of ground. A diode on the line to pin 9 should take care of the issue.

 

[mmarien]

The diode would work. But I think the logic is backwards. Wouldn't you want the light ON when the canopy is open. Lights usually come ON when there is an error condition. You also don't want a light in your eye when flying at night.

Use a small relay to reverse the logic:

The light is on when the Canopy is open. Closing the canopy turns the light off. The SV contact would be 2.5V-5.0V OPEN and 0V-2.5V CLOSED

 

[dynonsupport]

The light you have must be something like an LED? The EMS will look like about a 6K ohm resistor to ground if you put 12V on the pin, which won't show up at all on an incandescent bulb.

Three options:

1) Use a diode on the wire to the EMS. Point the cathode (ground band) of the diode away from the EMS. This works because the EMS has a pull-up resistor inside. If there was no resistor, it wouldn't work.

2) A resistor in line with the wire going to the EMS. Put 10K on that line and it will likely make the bulb so dim you never notice. It will change your trigger voltages seen by the EMS some, but that's fine as you can just adjust for that.

3) Reverse your schematic, so the switch is on the power leg, and the bulb on the ground leg.

 

[brinzlee]

Thanks very much for your suggestions. I will try with the diode first, cathode pointing towards the bulb from EMS pin 9, and let you know how I get on.

 

[brinzlee]

Tried your suggestion with the diodes and this solution worked an absolute treat...
Thank you very much for your help
Brinsley