Contacts & software updates

[Bob_B]

According to the install manual, the contact pins 9 & 10 on the D-120 will indicate a light color in the closed state (connected to ground). If I want to have an electric fuel pump indicate as on or off, how would I wire it? The fuel pump has a maximum load of 3 amps. Can the pump be grounded directly through pin 9/10 to complete the circuit so that it will show when turned on?
Would the load be too much for the D-120 ?

How is the D-120 connected to a PC for software updates?

 

[davemgill]

If it was me I would use a dual-pole switch for the fuel pump. Connect one side as normal to switch +12v for the pump and the other side to switch ground to the D-120

 

[dynonsupport]

You can't put current through these pins. They're not switches, they are detectors.

They will show closed when grounded and open when above about 1.5V or floating(how this displays on the EMS is up to you). They are safe up to 15V.

The easiest way to do this is to switch the positive side of the fuel pump, and hook the contact to the switched side of the pump. When the pump is off this side will be near ground because the resistance of the pump is low. When you switch it on, this side will be 12V and we'll read that as off. Since you can set up the colors on the EMS however you want, this should work fine.

The D120 connects via a serial cable to the PC to do firmware updates. If you don't have a serial port on your laptop, you can use a USB-serial converter.

 

[Bob_B]

So it is OK to put positive voltage on these contacts? With the alternator running, the voltage will be around 14.2 vdc. This will not damage the Dynon unit?

 

[dynonsupport]

They are safe up to 15V, though you don't want current flowing through these inputs.

 

[Bob_B]

I'm confused with the reply from Dynon support. The earilier post said to connect one of the contact pins to the + side of the fuel pump. The last post says you don't want current flowing through the contact inputs, but if the input is connected to the + side of the fuel pump, isn't that what will happen when the fuel pump is energized? 14 vdc flowing to the input from the pump connection?

 

[dynonsupport]

Yes, some current will flow as a basic rule of electronics. What we meant was that you can't use the inputs as a major current path. The contact inputs have thousands of ohms of resistance to ground. It's actually not possible to flow any current through them that will damage them unless you put lots of voltage on them.

Hook the fuel pump up as you normally would. Connect the contact input to the + side of the fuel pump. There will now be two connections there- one from the switch and one to the EMS / D180.

This will work fine and will not damage the EMS on a 12V airplane (which we are well aware often goes to 15V+)

 

[Simn_Smith]

Just to add another question to this, is it possible to use one of the contacts to detect if 12v is being supplied to something (the Turbo Control Unit on a rotax 914 in this case). I think from your answer to the fuel pump question above that I can do this but I just want to be sure.

What I want is for my D180 to give an alarm if there is no power to the TCU but be silent if there is 12v to it.

 

[dynonsupport]

Sure, this is possible. Just hook it up and define your alarm states as desired. You may need to install a resistor to ground if it doesn't show off when there's no power, but this will depend on how the TCU is designed inside.

 

[Simn_Smith]

Sure, this is possible. Just hook it up and define your alarm states as desired. You may need to install a resistor to ground if it doesn't show off when there's no power, but this will depend on how the TCU is designed inside.

I finally got round to wiring this today and have hit upon a problem.

I have connected pin 9 to the power supply to the TCU between the CB and the TCU. With the aircraft master switch on the contact1 is seeing closed regardless of CB position. With the Master switch off and the D180 running on internal power I get the correct on/off logic indication when the CB in pulled.

I guess that I need to insert a resistor. Can you give me an idea as to required ohm value and wattage and suggest how it should be wired?

Thanks

Simon

 

[dynonsupport]

Hmm. Closed on a contact means that it sees ground all the time. What that means is that when your master switch is on, the wire leading to the TCU is always near 0V. This doesn't really make any sense if it's the wire from the CB. If you said it was open all the time, that might make more sense, because that would be 2V+ all the time.

The first thing I would check is the voltage on that wire with a simple voltmeter. Check it with the CB on and off, and see what you read. Let us know and hopefully we can go from there.

In any case, any wattage resistor will work. There's no current here, so anything down to 1/16th watt would be fine.

 

[Simn_Smith]

I've got it set up to show OPEN/RED and CLOSED GREEN. With the master switch on the display remains green regardless of CB position. The voltage with the CB in is ~12v (battery could probably do with a charge as the aircraft has not flown for a month) and with the CB out is ~2v. This line is the only source of power to the TCU and the only other external connection is the RPM which is connected to pin 32 on the D180 but I doubt that the power is coming from there.

I'll be away now until next wednesday so I'll have another look then. Is it possible that there may be a capacitor or something in the TCU that is keeping up the voltage and stopping the D180 from seeing the change? As I mentioned before, the Dynon does correctly display the CB position when the master is off and the D180 working on internal power.

 

[dynonsupport]

Well, the issue is that it needs to go below 2V before we'll see it as "open." Seems like we might have open and closed reversed, but the problem is the same.

I think your best bet is to add a resistor to ground along that line. I'd start with a 1K and if that doesn't work, try 500 ohms. If you do go to a 500 ohm resistor, you'll need at least a 1/4 watt resistor.

 

[Simn_Smith]

I finally got to have a go at solving this yesterday. I only had a 2.2k resistor in my spares box and it works with that. Is it okay to stick with that or is there some reason to drop to 1k?

 

[dynonsupport]

Nope. If it works, it works. The values were all just gut level guesses, and apparently my gut was about 1200 ohms low