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Simplest way for a go/no-go 2-Stroke Engine Temperature Indi

 
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PostPosted: Tue Jan 02, 2018 7:28 am    Post subject: Simplest way for a go/no-go 2-Stroke Engine Temperature Indi Reply with quote

It's not good to initiate a takeoff with a 2-stroke engine that isn't warm enough, so I'd like to find or make a circuit that measures the temperature and extinguishes an LED when the temperature reaches a certain threshold. Preferably I'd like to adjust that threshold with software or a potentiometer. The result would be a "wait" light: start the engine, and don't take off until the LED is out. That would also function as a "you forgot to turn off the master" warning, after the flying is done.

My first thought was a type K thermocouple measuring CHT under the spark plug, feeding to a hobbyist micro controller like this:
https://learn.adafruit.com/introducing-trinket

with a thermocouple amplifier like this:
https://www.adafruit.com/product/1778

But since I'm only wanting a simple and binary wait/go indication rather than a readout in degrees, I wonder if the above plan is going a little overboard. The electrical system has an 18.5 volt battery for starting, with no onboard charging, so energy consumption is a minor consideration. Tiny size, durability, and reliability are high priorities.
Does anyone have an idea for a simpler design, or better yet, is someone already selling one?


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email(at)jaredyates.com
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PostPosted: Tue Jan 02, 2018 9:26 am    Post subject: Simplest way for a go/no-go 2-Stroke Engine Temperature Indi Reply with quote

Thanks Charlie, this is a foot launch ultralight with no panel, so pilot
viewing space is especially premium. Does the LM34 need to be in contact
with the cylinder? I wonder how to best accomplish that, mechanically speaking.
On January 2, 2018 11:37:25 Charlie England <ceengland7(at)gmail.com> wrote:

Quote:


On 1/2/2018 9:27 AM, Jared Yates wrote:
> It's not good to initiate a takeoff with a 2-stroke engine that isn't
> warm enough, so I'd like to find or make a circuit that measures the
> temperature and extinguishes an LED when the temperature reaches a
> certain threshold. Preferably I'd like to adjust that threshold with
> software or a potentiometer. The result would be a "wait" light: start
> the engine, and don't take off until the LED is out. That would also
> function as a "you forgot to turn off the master" warning, after the
> flying is done.
>
> My first thought was a type K thermocouple measuring CHT under the
> spark plug, feeding to a hobbyist micro controller like this:
> https://learn.adafruit.com/introducing-trinket
> with a thermocouple amplifier like this:
> https://www.adafruit.com/product/1778
>
> But since I'm only wanting a simple and binary wait/go indication
> rather than a readout in degrees, I wonder if the above plan is going
> a little overboard. The electrical system has an 18.5 volt battery for
> starting, with no onboard charging, so energy consumption is a minor
> consideration. Tiny size, durability, and reliability are high priorities.
>
> Does anyone have an idea for a simpler design, or better yet, is
> someone already selling one?
>
My 1st thought is that the 'forgot' mode probably won't be effective (at
least for me), since it takes time for the heads to cool down. I know
I'd be likely to walk away before the light came on.

2nd thought is that since I'd want CHT gauges anyway, why not just use
them? I'd be sitting in the plane with the engine running, looking at
the instruments, so why not just look at the CHT? No power required, no
extra instrument.

If you really want the light, an LM34 feeding a comparator circuit (op
amp and some resistors) would work.

Charlie

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