Can I add warning to D-180 for open canopy?

I think there are spare inputs on the D-180 and I?d like to add a switch to detect open canopy. I?d like the audible warning to be functional only if throttle is advanced above a set threshold - say 4000 RPM. The reason for the RPM stipulation is to allow taxing with the canopy partially open for increased ventilation. And of course the reason for the switch/warning is to prevent takeoff with canopy ajar. Does anybody know if this is possible with the D-180?

Not directly, no. The D180 only has two available switch inputs, and both are used in the RV12. One is used for the stall warning switch, the other for the spar pin warning.

I have come up with a simple retrofit that uses the spar pin warning for both that functuon and a canopy switch. It also watches the data from the EFIS serial port so that the spar pin warning is always active, but the canopy switch warning is only active if the engine RPM is above 3900.

I haven't had a chance to test it yet, and don't know how long it will be before I do. I have spent far too much time already with the plane torn apart, watching everyone else go flying! Plus... after leaving the canopy partly unlatched once, I highly doubt I'll make that mistake again.

Like Dale said, there are no spare inputs, but the Spar pin warning can be re-purposed. There is already an independent big red spar warning light on the panel. The D-180 provides a redundant warning. If concerned about the spar pins coming out, they could be safety-tied or bolted.
Here is one way to wire the canopy switch:

Aircraft Spruce sells an AIRSPEED SWITCH.
An electronic hobbyist might use LM2907 RPM Speed Switch.
A couple of mechanically inclined builders have installed a throttle position switch.

I like Joe?s suggestion to tie into the spar pin input on the D-180 so I can get both visual light and warning tone through headset.

If I can?t get RPM info from the D-180 then I guess maybe my best alternative is to sense physical throttle position with a limit switch. I?m thinking about adding a small microswitch mounted to one of the carburetors to sense full open throttle position. I?m interested to see if anyone has a slick way of doing this?

If a warning light is not installed, then a diode is not required either. When a pilot is concentrating on the takeoff, she might not notice a warning light.
The disadvantage of using an airspeed switch is that the plane is already 1/3 of the way down the runway by the time the pilot aborts the takeoff roll. Of course if the throttle is opened slowly, a throttle or RPM switch will have the same result.
Once a pilot has taken off with the canopy open and survived, the next time he tries to takeoff with the canopy open, he will recognize the wind in his face and abort. A canopy open switch is no longer required.

Mich48041 said:

Once a pilot has taken off with the canopy open and survived, the next time he tries to takeoff with the canopy open, he will recognize the wind in his face and abort. A canopy open switch is no longer required.

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That's true but I have two things working against me that counter that logic... I have flown a Cub for 23 years mostly with door/window open so wind in face is pretty much ingrained. Second strike against me is age related memory deficiency. Weather here is near 90F and I have attempted takeoff twice this past week with canopy raised for taxi - actually twice in two days. I have added canopy latch to the before TO checklist but I do my checks while engine is warming up instead of just before the TO roll. I think it best if D-180 gives me a slap to the head if throttle is advanced too far with canopy not latched.

Piper J3 said:

If I can?t get RPM info from the D-180 then I guess maybe my best alternative is to sense physical throttle position with a limit switch. I?m thinking about adding a small microswitch mounted to one of the carburetors to sense full open throttle position. I?m interested to see if anyone has a slick way of doing this?

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You can get RPM from the D180, just not in a convenient manner. The D180 spits serial data (including RPM) out on a port pin. So you have two choices that I can see. First, you could use a throttle position switch to sense when the throttle is opened past a certain point (like, more than you would use for taxi). It's more wiring and a mechanical installation, but relatively easy to do for normal people.

Second, and the easier path easier for slightly twisted nerds like me, is to grab the serial data stream from the D180 and use that. That means no mechanical installation or extra wiring. I designed it to fit into a short enclosure with a DB-25 on each end, so it just plugs between the D-180 and the cable - so no wiring hassle and it's easily removable.

So why go to all that trouble when it would be easier to just replace the spar warning input? I debated that. I think the D180 spar pin input is less that completely useful. If it alarms in flight, it means your switch is flaky... there's no way those pins are coming loose on their own, right? And if you haven't put the pins in right you'll know it when you try to start the engine - even if you miss the big red glowing light. Still, I try to do things like this with a thought to others using it. I didn't want to spend time having that discussion with every single person who might want one. I also wanted to leave the plane doing everything it did before -- even things that are of debatable value. Plus, adding RPM sensing required a microcontroller, and once that's in place it's two lousy lines of code to add the logic to merge the spar pin and canopy switch functions.

I can't say when I'll have a chance to install and test it. I am guessing it will take me a couple of tries to debug the firmware, since I have not dealt with the D180 data stream before... it's documented, but I have found that such documentation is often not completely accurate after a few years of software revisions. But, when I do have it working right I'll have several circuit boards left over in case anyone else wants to try it out.

Piper J3 said:

I think there are spare inputs on the D-180 and I?d like to add a switch to detect open canopy. I?d like the audible warning to be functional only if throttle is advanced above a set threshold - say 4000 RPM. The reason for the RPM stipulation is to allow taxing with the canopy partially open for increased ventilation. And of course the reason for the switch/warning is to prevent takeoff with canopy ajar. Does anybody know if this is possible with the D-180?

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I have installed micro switches on the canopy handle and throttle position wired in series with the spar pin switch. The throttle position is set to allow 4000 rpm before activating to allow for a run up without the warning activating.

2johns said:

I have installed micro switches on the canopy handle and throttle position wired in series with the spar pin switch. The throttle position is set to allow 4000 rpm before activating to allow for a run up without the warning activating.

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Any chance of some installation photos showing switch mounting?

Piper J3 said:

Any chance of some installation photos showing switch mounting?

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I used magnetic switches ala original spar pin switches purchased from Van,s. They work fine but were a hassle to get adjusted. If I had it to do again, I would use regular mechanical micro switches.

DaleB - I sent you a PM...