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Electronic Ignition spark advance signal boost

 
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yellowduckduo(at)gmail.co
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PostPosted: Sun Dec 17, 2017 8:34 am    Post subject: Electronic Ignition spark advance signal boost Reply with quote

Wade
A very good question.
If no one else replies I will do a little research this evening.
We want a single supply op amp that will run on 5 volts and is rail to
rail output (ie down to zero volts output).
Typically these are cmos type technology that run on a wide range of
voltage and consume negligible power in an application like this.
I will have to refresh my memory but I'm pretty sure down to .01 volts
is doable on a single supply op amp these days. Years ago an op amp
would be run on a dual +5 volt and -5 volt supply to do this. Someone
might offer to drop one in the mail and I will look around here. I'd
probably suggest initially trying more like 1K ohms for the input
resistor. Might need a bit higher if too low a value drags down the
input signal. A tiny adjustable resistor can always be used to tweak the
gain to precisely what you need.
Ken
On 17/12/2017 10:28 AM, Airdog77 wrote:
Quote:


Ken,

I think I've got the function of the non inverting op amp down.... pretty cool. Just a couple of questions before I pull the trigger on purchasing any.

I noticed on Mouser that the input voltage is usually 1.8, 2.7 or 4.5 volts. Am I reading this right that those are +/- input volt, so say -1.8V to +1.8V. May seem like a silly question, but just asking since I need 0V or 0.01 volts covered as a possible input voltage.

Also, I think I've got it right that the R1 and R2 resistors values are set simply as a ratio to provide the correct gain. Are the resistor values completely arbitrary, or any standards that I should be following? Right now I have R2 = 500 Ohm, R1 = 4.5K Ohm.

Again, thanks for the info on these op amps. Neat stuff.

Cheers,
Wade

--------
Airdog
Wade Parton
Building Long-EZ N916WP
www.longezpush.com


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PostPosted: Sun Dec 17, 2017 8:52 am    Post subject: Electronic Ignition spark advance signal boost Reply with quote

I'd consider running the op amp on 12V instead of 5V. Since you want the
max output to be so close to 5V to drive the instrument input on the
efis, using 12V should help keep the output linear.


On 12/17/2017 10:33 AM, C&K wrote:
Quote:


Wade
A very good question.
If no one else replies I will do a little research this evening.
We want a single supply op amp that will run on 5 volts and is rail to
rail output (ie down to zero volts output).
Typically these are cmos type technology that run on a wide range of
voltage and consume negligible power in an application like this.
I will have to refresh my memory but I'm pretty sure down to .01 volts
is doable on a single supply op amp these days. Years ago an op amp
would be run on a dual +5 volt and -5 volt supply to do this. Someone
might offer to drop one in the mail and I will look around here. I'd
probably suggest initially trying more like 1K ohms for the input
resistor. Might need a bit higher if too low a value drags down the
input signal. A tiny adjustable resistor can always be used to tweak
the gain to precisely what you need.
Ken
On 17/12/2017 10:28 AM, Airdog77 wrote:
>
>
> Ken,
>
> I think I've got the function of the non inverting op amp down....
> pretty cool.  Just a couple of questions before I pull the trigger on
> purchasing any.
>
> I noticed on Mouser that the input voltage is usually 1.8, 2.7 or 4.5
> volts.  Am I reading this right that those are +/- input volt, so say
> -1.8V to +1.8V.  May seem like a silly question, but just asking
> since I need 0V or 0.01 volts covered as a possible input voltage.
>
> Also, I think I've got it right that the R1 and R2 resistors values
> are set simply as a ratio to provide the correct gain. Are the
> resistor values completely arbitrary, or any standards that I should
> be following?  Right now I have R2 = 500 Ohm, R1 =  4.5K Ohm.
>
> Again, thanks for the info on these op amps.  Neat stuff.
>
> Cheers,
> Wade
>
> --------
> Airdog
> Wade Parton
> Building Long-EZ N916WP
> www.longezpush.com


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Airdog77



Joined: 24 Nov 2013
Posts: 80
Location: Northern Virginia

PostPosted: Mon Dec 18, 2017 9:10 am    Post subject: Re: Electronic Ignition spark advance signal boost Reply with quote

Ken, I would think these things (at least a version out there) would go down to 0.0 volts... Roger on using a higher resistor value.

Charlie, I think you're saying simply supply 12V power to the op amp (one rated for 12V) at the V+ and V- pins? Spark advance input is obviously unchanged (at +In). I guess the affect on the output being more linear is internal to the op amp?

Regards,
Wade


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PostPosted: Mon Dec 18, 2017 11:22 am    Post subject: Electronic Ignition spark advance signal boost Reply with quote

Wade

As you surmise, there has to be two wires to to get the signal to your
amplifier and on to the EIS. So pin 1 of the amplifier in Bob's diagram
has to be grounded.
The complication is that you can ground that pin to numerous places in
the aircraft and each of those places will typically give a slightly
different reading when dealing with millivolt sensor signals. This may
or may not be significant in your application. Grounding pin 1 to the
ignition unit which is the source of your signal will likely be the best
choice and we recommend that you try that.

If that is difficult in your particular aircraft, or it proves
unsatisfactory, the next choice would probably be to try grounding pin 1
at the EIS ground. The issue with that is that any voltage difference
between the ground at the ignition unit and the ground at the EIS will
be amplified by a factor of 10 by the AD626. That may or may not be
significant depending on exactly what currents are flowing and what the
resistance is between the two different physical ground points. That
difference can change when you turn on or off various electrical
circuits in the aircraft which might introduce measurement errors. If
this makes sense to you, congratulations, you now understand the concept
of a ground loop and you can appreciate why bringing most of our
aircraft grounds to the common "forest of tabs" makes sense. Even
grounding both the EIS and the ignition unit at a forest of tabs might
not totally eliminate these ground errors though as there may well be
millivolt differences in the wire between the forest of tabs and the
ignition unit. All wires and connections have some resistance and any
current through a resistance results in some voltage drop however small.
We are trying to avoid adding such a voltage drop to your millivolt
sensor signal. So again running a ground wire from pin 1 of your
amplifier all the way to a connection at the ignition unit can make sense.

I am not familiar with your ignition but if your ignition coils are
grounded through a remote ignitor on the engine side of the firewall, it
is more likely that it will not matter where you ground the amplifier
pin. Coil grounds pulse several amps and you don't want that running
through the same wire as your sensor ground.

Ken
On 18/12/2017 12:36 PM, Charlie England wrote:
Quote:


On Mon, Dec 18, 2017 at 11:10 AM, Airdog77 <Airdog77(at)gmail.com
<mailto:Airdog77(at)gmail.com>> wrote:


<Airdog77(at)gmail.com <mailto:Airdog77(at)gmail.com>>

Ken, I would think these things (at least a version out there)
would go down to 0.0 volts... Roger on using a higher resistor value.

Charlie, I think you're saying simply supply 12V power to the op
amp (one rated for 12V) at the V+ and V- pins? Spark advance input
is obviously unchanged (at +In). I guess the affect on the output
being more linear is internal to the op amp?

Regards,
Wade

--------
Airdog
Wade Parton
Building Long-EZ N916WP
www.longezpush.com <http://www.longezpush.com>

My comment was based on using one of the ancient op amp circuits,
most of which get a bit nonlinear when output approaches the
supply rail voltage. The much more modern instrumentation amp that
Bob referenced doesn't seem to have that issue, making it simple
to power it from the EFIS's 5V source.
On Bob's comment about ground references: I'm not up to speed on that
device, but I'd expect a differential amplifier to look at the voltage
difference between the two source voltages, and in this case, the <->
input would be the ground reference at the device you're measuring.
Since it's a differential amplifier, I'd expect it to be immune to
ground reference issues, but hey; you don't know until you test.

If I were setting it up, I'd start by hooking the <+> input to the
advance output, the <-> input to the ground terminal *on the ignition
module*. I'd supply power from the EFIS & ground from the same spot
the EFIS gets its ground. I wasn't sure what Bob meant in his previous
post, either, but he may have been saying to supply ground from the
ignition module; the same point that supplies 'reference' to the <->
input. (By 'ground', I'm talking about the power supply ground
terminal; not the <-> input to the amp.)


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Airdog77



Joined: 24 Nov 2013
Posts: 80
Location: Northern Virginia

PostPosted: Mon Dec 18, 2017 8:10 pm    Post subject: Re: Electronic Ignition spark advance signal boost Reply with quote

Hi Ken,

I talked with Electroair earlier today. They are taking a look at the AD6262 and the best place to tie in the ground. It doesn't show up in the manual and honestly I forgot about it, but on the experimental version there is a ground wire coming off the Electroair controller unit. Their initial thought is that would be the best place to tie in the A626 ground input.

I'll await Electoair's evaluation and press on from there.

Thanks a ton for all your advice.

Regards,
Wade


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