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Computer Nerd Kev
Guest

Mon Jul 11, 2016 7:30 am   



Phil Allison <pallison49_at_gmail.com> wrote:
Quote:
Computer Nerd Kev wrote:


The circuit from ETI should take the place of a filter, and be more
adjustable. It detects peaks in the sound wave and measures the period
between them to determine the frequency. If the frequency is within a
certain range, it produces a constant HIGH output.


** Most cars have two horns with slightly different frequencies - so the
combined sound is a dual tone chord with rapid amplitude modulation.


As long as there's a pair of peaks in the waveform with a fixed period,
the circuit should be able to detect them. It effectively ANDs the peak
detector with a signal from a monostable which goes high for a period
(determined by how wide the desired range of frequency acceptance is),
after waiting for a time after the first peak is detected (the period
of the desired response frequency).

Quote:
I have no info on that old ETI circuit so cannot say if it is compatible
with a car horn sound.

Electret mics have more output than dynamic capsules so that would be my
pic for the task - with some pre-amplification and filtering of low
frequencies by careful choice of coupling caps.


At the microphone, would a cone or something attached to the Electret mic
be an advantage to picking up the sound?

> Good luck.

Thanks.

--
__ __
#_ < |\| |< _#

Computer Nerd Kev
Guest

Mon Jul 11, 2016 7:30 am   



Phil Allison <pallison49_at_gmail.com> wrote:
Quote:
Trevor Wilson wrote:



**There are a large number of far better schemes which can be employed,
very inexpensively. AT the low end, you could buy a movement sensor lamp
assembly. These things are pretty much plug and play.



** The OP has asked for a light switch system that works over a 20m range
and without necessarily a direct line of sight and preferably only when
he operates his car horn.


Yes, although the 20m was for turning the light off after I'd got to the
end of the drive, which would happen after a fixed delay with a PIR device.

Quote:
A PIR detector unit will fail on all counts - cos its lacks range and the
ability to see around corners plus triggers any time of day to any moving
object, like a tree blowing in the wind.


This last point is my paricular problem. I've never found these sensor lights
very reliable to trigger on the right movement, and not trigger on whatever
rabbit decides to bound past, or magpie flys by (and they often fly around
that area). Actually I'm rather dead set against them, I'm sure there are
plenty of people who any happy with them, but I've seen far too many
set-ups where they don't work properly. They annoy me.

I also slightly dislike the time delay aspect of them, though this is also
present in Sylvia's suggestion which I'll probably go with. Probably more
of a phycological thing, I like to be in control of my machines. Even
though in practice I'd always have a manual switch in the house as well.

Quote:
His idea can work well, a car horn is a loud and distinctive sound
particularly in a rural environment.

But designing and building it will take a tad more engineering than
he presently imagines.


I might end up doing both, building the horn sensor after the light
sensor is working, then I can experiment with it to work out the
limitations. However my past record shows that I'll probably never
get around to the horn sensor in that case.

--
__ __
#_ < |\| |< _#

Sylvia Else
Guest

Mon Jul 11, 2016 7:30 am   



On 11/07/2016 10:43 AM, Trevor Wilson wrote:
Quote:
On 10/07/2016 11:18 PM, Computer Nerd Kev wrote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 9:26 PM, Computer Nerd Kev wrote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 6:19 PM, Computer Nerd Kev wrote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 4:38 PM, Computer Nerd Kev wrote:
THE SHORT STORY:
^^^^^^^^^^^^^^^^
I want to know what sort of microphone would be suitable for
picking up the sound of a car horn from around 10-20m away.
It would be mounted outdoors and the signal used to detect
the sound of the horn and turn on/off an exterior light.

THE LONG STORY:
^^^^^^^^^^^^^^^
I'm hopefully soon to receive a new headlight to replace the
cracked one that's in my car currently, and I had the thought
yesterday that it might be handy to set it up inside a box. Then
locate it where it can illuminate a part of my driveway which
can be difficult to reverse down at night.

That should be easy enough, though I will be assuming that halogen
car headlight bulbs work OK on 12VAC, unless someone here wishes to
advise me otherwise. The issue is having the light turn off once
I have reached the point of the drive where my car can be returned
to it's rightful forward orientation.

Not liking the horn solution, (though I note your comment about the
neighbour's distance), I'm wondering whether a sensor to detect your
headlights while you're reversing would do the job. While headlights
detected, illuminate driveway.

Nice idea, but unfortunately the driveway has a bend in it, which is
the main reason I would like the extra light to make sure I don't
find myself against the power pole that the bend is placed to avoid.

It's possible that my ignorance of microphone capabilities is the
reason I think the horn idea will work. Do you have any reason
to suggest it wouldn't?

Not really, but you'd need an amplifier and a filter to separate the
horn from other noises (unless spurious triggering doesn't bother
you).
If you want to use the horn to turn it off, you'd also need to
implement
a toggle.

The circuit from ETI should take the place of a filter, and be more
adjustable. It detects peaks in the sound wave and measures the period
between them to determine the frequency. If the frequency is within a
certain range, it produces a constant HIGH output.

You might find that it triggers in heavy rain (the noise of which
has a
wide spectrum). If you're using the horn to turn off as well, then
heavy
rain might cause spurious turn-offs. No doubt some effort could be
expended to detect the wide spectrum, and ignore it, but you'd then
want
to make sure it still responds to the horn even in heavy rain - it all
starts to get rather complicated.

Yes, perhaps. I hadn't thought of rain, but one other issue will be
wind. There aren't many wind breaks around and, looking at the local
forcast, it would have to work in winds at (very) least up to 50Km/h.
You'd have both the wind noise and the effect of the wind blowing
away the sound of the horn (although it would be rare for a strong
wind to be blowing from the bearing directly behind the microphone).
I wouldn't be surprised if I had trouble myself hearing a car horn
15m away while standing in a 100+Km/h wind gust, and there are a lot
of other noises introduced by surrounding structures in those
conditions as well.

The wind, if it were to blow near parallel with the line between the
car and the microphone would also distort the frequency due to the
doppler effect. Well I think that's right anyway...

No, the Doppler effect only depends on the difference in speed between
the sender and the receiver - the effects of the wind speed cancel out.
The speed of the vehicle has an effect, but I gather you'll not be going
very fast at that point.

Ah, I understand. Thanks for that.

Actually, a light sensor and a time delay might work. I dismissed
a manually triggered time delay because I'm not very consistent
in the time it takes for me to go from leaving the house to begining
down the drive. But the headlights would enevitably be pointed at
the sensor until the bend, and the time taken to negotiate the bend
is much easier to determine. There will have to be an ambient light
sensor as well, to disable it during the day.


I might stay with the horn idea for the moment unless someone
educates on why it won't work. My worry with the light sensor is
that I'd have to fiddle with it to make sure light from the house
and reflected light from the driveway light itself didn't trigger
it. It would probably also mean that I couldn't leave the carport
light on for when I got back, if desired.

Putting the sensor inside a tube (painted matt black inside) pointed
down the driveway should eliminate spurious operation - headlights are
pretty bright, so the sensor need not be so sensitive. You may even
find
that you don't need daytime suppression.

The problem is that the drive isn't very level (it's gravel), so
the headlight beam will move vertically as pot-holes and pot-hole
repairs are encountered. There should be a middle ground where a
tube or box will allow enough light in, I just fear it might take
a fair bit of tinkering in the dark of night.

From what I gathered, this solution requires a delay timer anyway, to
deal with the bend in the driveway. Just be sure that it gets reset
every time the sensor detects the headlights. Then as long as the sensor
is not outside the beam for a very extended period, it will work.

Yes, that's true. I'll probably set a decent time of three minutes or
so as there's no great rush to turn the light off, so it should be
fine even if it's only triggered when the vehicle first takes off.

OK, I'll go with this solution unless someone convinces me that most
of your and my worries about the microphone are false.

Thanks for the advise.


**Even better, would be some of these:

http://www.ebay.com/itm/Waterproof-14LED-Dual-Head-Solar-Powered-Yard-Lights-PIR-Motion-Sensor-Spotlight-/121957783746?hash=item1c654018c2:g:2iQAAOSwubRXEbBU


No wiring, no hassle. I use one for my driveway.


How long does the rechargeable battery last before the thing has to be
replaced? I've had nothing but hassle with things that contain
rechargeable batteries.

Sylvia.

Trevor Wilson
Guest

Mon Jul 11, 2016 7:30 am   



On 11/07/2016 1:04 PM, Sylvia Else wrote:
Quote:
On 11/07/2016 10:43 AM, Trevor Wilson wrote:
On 10/07/2016 11:18 PM, Computer Nerd Kev wrote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 9:26 PM, Computer Nerd Kev wrote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 6:19 PM, Computer Nerd Kev wrote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 4:38 PM, Computer Nerd Kev wrote:
THE SHORT STORY:
^^^^^^^^^^^^^^^^
I want to know what sort of microphone would be suitable for
picking up the sound of a car horn from around 10-20m away.
It would be mounted outdoors and the signal used to detect
the sound of the horn and turn on/off an exterior light.

THE LONG STORY:
^^^^^^^^^^^^^^^
I'm hopefully soon to receive a new headlight to replace the
cracked one that's in my car currently, and I had the thought
yesterday that it might be handy to set it up inside a box. Then
locate it where it can illuminate a part of my driveway which
can be difficult to reverse down at night.

That should be easy enough, though I will be assuming that halogen
car headlight bulbs work OK on 12VAC, unless someone here
wishes to
advise me otherwise. The issue is having the light turn off once
I have reached the point of the drive where my car can be returned
to it's rightful forward orientation.

Not liking the horn solution, (though I note your comment about the
neighbour's distance), I'm wondering whether a sensor to detect
your
headlights while you're reversing would do the job. While
headlights
detected, illuminate driveway.

Nice idea, but unfortunately the driveway has a bend in it, which is
the main reason I would like the extra light to make sure I don't
find myself against the power pole that the bend is placed to avoid.

It's possible that my ignorance of microphone capabilities is the
reason I think the horn idea will work. Do you have any reason
to suggest it wouldn't?

Not really, but you'd need an amplifier and a filter to separate the
horn from other noises (unless spurious triggering doesn't bother
you).
If you want to use the horn to turn it off, you'd also need to
implement
a toggle.

The circuit from ETI should take the place of a filter, and be more
adjustable. It detects peaks in the sound wave and measures the period
between them to determine the frequency. If the frequency is within a
certain range, it produces a constant HIGH output.

You might find that it triggers in heavy rain (the noise of which
has a
wide spectrum). If you're using the horn to turn off as well, then
heavy
rain might cause spurious turn-offs. No doubt some effort could be
expended to detect the wide spectrum, and ignore it, but you'd then
want
to make sure it still responds to the horn even in heavy rain - it
all
starts to get rather complicated.

Yes, perhaps. I hadn't thought of rain, but one other issue will be
wind. There aren't many wind breaks around and, looking at the local
forcast, it would have to work in winds at (very) least up to 50Km/h.
You'd have both the wind noise and the effect of the wind blowing
away the sound of the horn (although it would be rare for a strong
wind to be blowing from the bearing directly behind the microphone).
I wouldn't be surprised if I had trouble myself hearing a car horn
15m away while standing in a 100+Km/h wind gust, and there are a lot
of other noises introduced by surrounding structures in those
conditions as well.

The wind, if it were to blow near parallel with the line between the
car and the microphone would also distort the frequency due to the
doppler effect. Well I think that's right anyway...

No, the Doppler effect only depends on the difference in speed between
the sender and the receiver - the effects of the wind speed cancel out.
The speed of the vehicle has an effect, but I gather you'll not be
going
very fast at that point.

Ah, I understand. Thanks for that.

Actually, a light sensor and a time delay might work. I dismissed
a manually triggered time delay because I'm not very consistent
in the time it takes for me to go from leaving the house to begining
down the drive. But the headlights would enevitably be pointed at
the sensor until the bend, and the time taken to negotiate the bend
is much easier to determine. There will have to be an ambient light
sensor as well, to disable it during the day.


I might stay with the horn idea for the moment unless someone
educates on why it won't work. My worry with the light sensor is
that I'd have to fiddle with it to make sure light from the house
and reflected light from the driveway light itself didn't trigger
it. It would probably also mean that I couldn't leave the carport
light on for when I got back, if desired.

Putting the sensor inside a tube (painted matt black inside) pointed
down the driveway should eliminate spurious operation - headlights
are
pretty bright, so the sensor need not be so sensitive. You may even
find
that you don't need daytime suppression.

The problem is that the drive isn't very level (it's gravel), so
the headlight beam will move vertically as pot-holes and pot-hole
repairs are encountered. There should be a middle ground where a
tube or box will allow enough light in, I just fear it might take
a fair bit of tinkering in the dark of night.

From what I gathered, this solution requires a delay timer anyway, to
deal with the bend in the driveway. Just be sure that it gets reset
every time the sensor detects the headlights. Then as long as the
sensor
is not outside the beam for a very extended period, it will work.

Yes, that's true. I'll probably set a decent time of three minutes or
so as there's no great rush to turn the light off, so it should be
fine even if it's only triggered when the vehicle first takes off.

OK, I'll go with this solution unless someone convinces me that most
of your and my worries about the microphone are false.

Thanks for the advise.


**Even better, would be some of these:

http://www.ebay.com/itm/Waterproof-14LED-Dual-Head-Solar-Powered-Yard-Lights-PIR-Motion-Sensor-Spotlight-/121957783746?hash=item1c654018c2:g:2iQAAOSwubRXEbBU



No wiring, no hassle. I use one for my driveway.


How long does the rechargeable battery last before the thing has to be
replaced? I've had nothing but hassle with things that contain
rechargeable batteries.


**No idea. Mine has Li-Ion batteries and has been up for about 2 years.
No problems yet. My experience with rechargable batteries goes back
quite a few years. Problems have been few and far between. Even in the
old NiCad days. My old Bosch screwdriver NiCad battery lasted almost a
decade. It's mostly down to the quality of the charging system used. The
Bosch charger is a very sophisticated pulse charger. Li-Ion chargers are
quite good nowadays.


--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

Phil Allison
Guest

Mon Jul 11, 2016 9:35 am   



Trevor Wilson wrote:

Quote:



**There are a large number of far better schemes which can be
employed, very inexpensively. AT the low end, you could buy a
movement sensor lamp assembly. These things are pretty much plug
and play.



** The OP has asked for a light switch system that works over a 20m
range and without necessarily a direct line of sight and preferably
only when he operates his car horn.

A PIR detector unit will fail on all counts - cos its lacks range and
the ability to see around corners plus triggers any time of day to
any moving object, like a tree blowing in the wind.


**Nonsense.



** Not it isn't - a "movement sensor lamp assembly" as you suggested is not suitable.


> PIRs can be sited remotely to lights.

** That is a new suggestion.

So now the OP needs a PIR sensor with ambient light inhibit, mounted where it can reliably sense his car approach at night while driving backwards and then power a mains voltage supply to a remote light which must stay on for a few minutes.


..... Phil

Phil Allison
Guest

Mon Jul 11, 2016 9:41 am   



Computer Nerd Kev wrote:

Quote:


At the microphone, would a cone or something attached to the Electret mic
be an advantage to picking up the sound?



** Car horns are loud, picking up the sound at 20m should not be a problem.


.... Phil

Trevor Wilson
Guest

Mon Jul 11, 2016 12:33 pm   



On 11/07/2016 2:25 PM, Phil Allison wrote:
Quote:
Trevor Wilson wrote:



**There are a large number of far better schemes which can be
employed, very inexpensively. AT the low end, you could buy a
movement sensor lamp assembly. These things are pretty much plug
and play.



** The OP has asked for a light switch system that works over a 20m
range and without necessarily a direct line of sight and preferably
only when he operates his car horn.

A PIR detector unit will fail on all counts - cos its lacks range and
the ability to see around corners plus triggers any time of day to
any moving object, like a tree blowing in the wind.


**Nonsense. PIRs can be sited remotely to lights. It costs a little
more, but not much. Depending on the PIR used, quite narrow, long ranges
can be managed. I use a PIR in my workshop, which switches a light on 6
Metres away. It would be a trivial exercise to site it 100 Metres away,
should I wish to do so.

Quote:

His idea can work well, a car horn is a loud and distinctive sound
particularly in a rural environment.


**It is a dumb idea on so many counts. The idea of using a PIR is MUCH
easier, more reliable and cheap. Everything is available off the shelf.

This is another alternative, though not Solar powered:

http://www.ebay.com/itm/10W-20W-30W-50W-LED-Flood-Light-IP65-PIR-Motion-Sensor-Security-Spot-Lamp-Bulbs-/271860310597?var=&hash=item3f4c232245:m:mpsLnVMUtZ4xuA5wNtKLF5Q



Quote:

But designing and building it will take a tad more engineering than
he presently imagines.


**Of course. It is a really dumb idea on so many levels.

--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
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Computer Nerd Kev
Guest

Mon Jul 11, 2016 3:19 pm   



Phil Allison <pallison49_at_gmail.com> wrote:
Quote:
Trevor Wilson wrote:

PIRs can be sited remotely to lights.

** That is a new suggestion.

So now the OP needs a PIR sensor with ambient light inhibit,
mounted where it can reliably sense his car approach at night
while driving backwards and then power a mains voltage supply
to a remote light which must stay on for a few minutes.


But it may still be difficult to avoid it triggering on
other nighttime movements. They've always seemed very
unreliable to me. Heck, even the automatic doors on
shops tend to ignore me unless I have the foresight to
wildly wave a limb at them (alright they're probably just
poorly set up, but I stubbornly dislike PIR sensors).

I think the light sensor would be better, of the options that
have me using a time delay, and I have no problem building it.
An LDR in the end of some poly pipe, connected in a voltage
divider on pin 2 of an NE555 IC in monostable configuration,
which drives a relay which turns on the light. Easy.

--
__ __
#_ < |\| |< _#

Jasen Betts
Guest

Mon Jul 11, 2016 3:27 pm   



On 2016-07-10, Computer Nerd Kev <not_at_telling.you.invalid> wrote:
Quote:

This leaves me with the problem of what kind of microphone I should
use to detect the sound of the car horn, and unfortunately this is
an area where I am not very knowledgeable.


Anyting suited to recording voice should give acceptable results.
if you've got any song birds around be aware that they learn to mimic
repeated sounds, dinner calls, crossing signals, ringtones, car alarms
, probably car horns too.

Quote:
For those worried about me disturbing the peace of my
neighbours, the nearest other residence is over half a
Kilometer away!


Good to know.

--
This email has not been checked by half-arsed antivirus software

Jasen Betts
Guest

Mon Jul 11, 2016 3:38 pm   



On 2016-07-10, Computer Nerd Kev <not_at_telling.you.invalid> wrote:
Quote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 6:19 PM, Computer Nerd Kev wrote:
Sylvia Else <sylvia_at_not.at.this.address> wrote:
On 10/07/2016 4:38 PM, Computer Nerd Kev wrote:
THE SHORT STORY:
^^^^^^^^^^^^^^^^
I want to know what sort of microphone would be suitable for
picking up the sound of a car horn from around 10-20m away.
It would be mounted outdoors and the signal used to detect
the sound of the horn and turn on/off an exterior light.

THE LONG STORY:
^^^^^^^^^^^^^^^
I'm hopefully soon to receive a new headlight to replace the
cracked one that's in my car currently, and I had the thought
yesterday that it might be handy to set it up inside a box. Then
locate it where it can illuminate a part of my driveway which
can be difficult to reverse down at night.

That should be easy enough, though I will be assuming that halogen
car headlight bulbs work OK on 12VAC, unless someone here wishes to
advise me otherwise. The issue is having the light turn off once
I have reached the point of the drive where my car can be returned
to it's rightful forward orientation.

Not liking the horn solution, (though I note your comment about the
neighbour's distance), I'm wondering whether a sensor to detect your
headlights while you're reversing would do the job. While headlights
detected, illuminate driveway.

Nice idea, but unfortunately the driveway has a bend in it, which is
the main reason I would like the extra light to make sure I don't
find myself against the power pole that the bend is placed to avoid.

It's possible that my ignorance of microphone capabilities is the
reason I think the horn idea will work. Do you have any reason
to suggest it wouldn't?

Not really, but you'd need an amplifier and a filter to separate the
horn from other noises (unless spurious triggering doesn't bother you).
If you want to use the horn to turn it off, you'd also need to implement
a toggle.

The circuit from ETI should take the place of a filter, and be more
adjustable. It detects peaks in the sound wave and measures the period
between them to determine the frequency. If the frequency is within a
certain range, it produces a constant HIGH output.

You might find that it triggers in heavy rain (the noise of which has a
wide spectrum). If you're using the horn to turn off as well, then heavy
rain might cause spurious turn-offs. No doubt some effort could be
expended to detect the wide spectrum, and ignore it, but you'd then want
to make sure it still responds to the horn even in heavy rain - it all
starts to get rather complicated.

Yes, perhaps. I hadn't thought of rain, but one other issue will be
wind. There aren't many wind breaks around and, looking at the local
forcast, it would have to work in winds at (very) least up to 50Km/h.
You'd have both the wind noise and the effect of the wind blowing
away the sound of the horn (although it would be rare for a strong
wind to be blowing from the bearing directly behind the microphone).
I wouldn't be surprised if I had trouble myself hearing a car horn
15m away while standing in a 100+Km/h wind gust, and there are a lot
of other noises introduced by surrounding structures in those
conditions as well.

The wind, if it were to blow near parallel with the line between the
car and the microphone would also distort the frequency due to the
doppler effect. Well I think that's right anyway...


only when the wind changes speed will the frequency vary from the
source frequency (as this changes the length of the delay),
but the wind speed will modulate amplitude.

--
This email has not been checked by half-arsed antivirus software

Computer Nerd Kev
Guest

Tue Jul 12, 2016 12:34 am   



Phil Allison <pallison49_at_gmail.com> wrote:
Quote:
Computer Nerd Kev wrote:



At the microphone, would a cone or something attached to the Electret mic
be an advantage to picking up the sound?

** Car horns are loud, picking up the sound at 20m should not be a problem.


Great!

--
__ __
#_ < |\| |< _#

Computer Nerd Kev
Guest

Tue Jul 12, 2016 12:43 am   



Jasen Betts <jasen_at_xnet.co.nz> wrote:
Quote:
On 2016-07-10, Computer Nerd Kev <not_at_telling.you.invalid> wrote:

This leaves me with the problem of what kind of microphone I should
use to detect the sound of the car horn, and unfortunately this is
an area where I am not very knowledgeable.

Anyting suited to recording voice should give acceptable results.
if you've got any song birds around be aware that they learn to mimic
repeated sounds, dinner calls, crossing signals, ringtones, car alarms
, probably car horns too.


I haven't heard any such behaviour from the local birdlife so far.
If it were a problem, I could hopefully set the sound amplification
so that only the loud car horn could trigger the circuit.

--
__ __
#_ < |\| |< _#

Computer Nerd Kev
Guest

Tue Jul 12, 2016 4:29 am   



Computer Nerd Kev <not_at_telling.you.invalid> wrote:
Quote:
Phil Allison <pallison49_at_gmail.com> wrote:
Trevor Wilson wrote:

PIRs can be sited remotely to lights.

** That is a new suggestion.

So now the OP needs a PIR sensor with ambient light inhibit,
mounted where it can reliably sense his car approach at night
while driving backwards and then power a mains voltage supply
to a remote light which must stay on for a few minutes.

But it may still be difficult to avoid it triggering on
other nighttime movements. They've always seemed very
unreliable to me. Heck, even the automatic doors on
shops tend to ignore me unless I have the foresight to
wildly wave a limb at them (alright they're probably just
poorly set up, but I stubbornly dislike PIR sensors).


Although I don't really need any more reasons not to go
with a PIR sensor, it has occoured to me that the cold
rear of a car that's just been started wouldn't likely
be significantly visible in infrared compared to the cold
ground. The exhaust fumes would be warm, however I
imagine they would have quite a weak infrared signature,
and they would be easily affected by wind.

Turning up the sensitivity would much increase the
(already high) likelihood of false triggering.

I may want to spend some time in the car before setting
off, so triggering on my presence wouldn't be convenient.

--
__ __
#_ < |\| |< _#

Phil Allison
Guest

Tue Jul 12, 2016 4:51 am   



Computer Nerd Kev wrote:

Quote:



Although I don't really need any more reasons not to go
with a PIR sensor, it has occoured to me that the cold
rear of a car that's just been started wouldn't likely
be significantly visible in infrared compared to the cold
ground. The exhaust fumes would be warm, however I
imagine they would have quite a weak infrared signature,
and they would be easily affected by wind.


** Your tail and brake lights would be picked up though - long as they are not LEDs !


..... Phil

Computer Nerd Kev
Guest

Tue Jul 12, 2016 9:49 am   



Phil Allison <pallison49_at_gmail.com> wrote:
Quote:
Computer Nerd Kev wrote:


Although I don't really need any more reasons not to go
with a PIR sensor, it has occoured to me that the cold
rear of a car that's just been started wouldn't likely
be significantly visible in infrared compared to the cold
ground. The exhaust fumes would be warm, however I
imagine they would have quite a weak infrared signature,
and they would be easily affected by wind.


** Your tail and brake lights would be picked up though
- long as they are not LEDs !


Ah yes, I forgot about that, and they're not LEDs (yet).

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