[EE] Time difference between manual button pushes at "same" time.

[Gordon Williams]

Hi,

Hoping someone on the list may have some insight.

I have 3 LED clocks that need to be synchronized for a nordic ski race. 
They show the time to the second.

The way they are designed is they have a push button on the end that
starts the timing.  The plan is to have a count down (3,2,1,go) with a
person on each clock to push the button on "go".

They will be synchronized close enough for timing purposes, but I want
them visually synchronized as well so I don't get any complaints.

Question: If the clocks are all in the centre of your field of view, how
many milliseconds between the LED seconds digits changing can be
detected? In other words, if you had 2 LEDs, what would be the maximum
time difference between turning them on so you could say that LED A
turned on before LED B?

Thanks,

Gordon Williams

[David Van Horn]

24fps is good for motion pictures, that should put a ballpark on it.

-----Original Message-----
From: piclist-***@mit.edu <piclist-***@mit.edu> On Behalf Of Gordon Williams
Sent: Friday, October 12, 2018 3:05 PM
To: pic microcontroller discussion list <***@mit.edu>
Subject: [EE] Time difference between manual button pushes at "same" time.

Hi,

Hoping someone on the list may have some insight.

I have 3 LED clocks that need to be synchronized for a nordic ski race. They show the time to the second.

The way they are designed is they have a push button on the end that starts the timing.  The plan is to have a count down (3,2,1,go) with a person on each clock to push the button on "go".

They will be synchronized close enough for timing purposes, but I want them visually synchronized as well so I don't get any complaints.

Question: If the clocks are all in the centre of your field of view, how many milliseconds between the LED seconds digits changing can be detected? In other words, if you had 2 LEDs, what would be the maximum time difference between turning them on so you could say that LED A turned on before LED B?

Thanks,

Gordon Williams


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[Gordon Williams]

Many thanks for the replies and Denny for doing some tests.  That's
awesome.

Now I’m going to have to do some tests to make sure that I can get down
to that level of synchronization.

Regards,
Gordon Williams

[George Smith]

Post by Gordon Williams
The way they are designed is they have a push button on the end that
starts the timing. The plan is to have a count down (3,2,1,go) with a
person on each clock to push the button on "go".

I am obviously missing something here. Is it an AND gate - that all
three buttons have to be pressed before the three clocks start or does
each clock start when its pusher reacts to the "go"?

[Denny Esterline]

I suppose many of us are familiar with the concept of "Nerd Sniping"?
https://xkcd.com/356/
"Nerd sniping is a slang term that describes a particularly interesting
problem that is presented to a nerd, often a physicist, tech geek or
mathematician. The nerd stops all activity to devote attention to solving
the problem, often at his or her own peril."

So, I was totally in the middle of something else, stopped, broke out a
breadboard and wrote code to answer this question....
At about 15mS, I cannot tell they are out of sync.
By about 20mS, I can see that it's not "right" but it's hard to say which
is first.
At about 35mS, I can clearly see that they are out of sync and which one is
first.

My results are likely skewed by having one red and the other green, though
I did flip them and try again with about the same results.


Code attached below. Please note that I'm not claiming it's good code....
:-)



void setup() {
pinMode(D0, OUTPUT);
pinMode(D1, OUTPUT);
Serial.begin(115200);
}

int T1 ;
int T2;
int j;


void loop() {
j=analogRead(A0);
T2 = j/10;
T1 = 200 ;
Serial.println(j);

digitalWrite(D0, HIGH);
delay(T2);
digitalWrite(D1, HIGH);
delay(T1);
digitalWrite(D0, LOW);
delay(T2);
digitalWrite(D1, LOW);
delay(T1);
}

Post by Gordon Williams
Hi,
Hoping someone on the list may have some insight.
I have 3 LED clocks that need to be synchronized for a nordic ski race.
They show the time to the second.
The way they are designed is they have a push button on the end that
starts the timing. The plan is to have a count down (3,2,1,go) with a
person on each clock to push the button on "go".
They will be synchronized close enough for timing purposes, but I want
them visually synchronized as well so I don't get any complaints.
Question: If the clocks are all in the centre of your field of view, how
many milliseconds between the LED seconds digits changing can be
detected? In other words, if you had 2 LEDs, what would be the maximum
time difference between turning them on so you could say that LED A
turned on before LED B?
Thanks,
Gordon Williams
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[Harold Hallikainen]

Interesting! This reminds me of audio/video sync. We are very sensitive to
sound being early (before image), but very forgiving of sound being late
(up to a point) since in real life, sound always arrives a little late.

The two lights comparison is a little like "flicker fusion." In motion
pictures, with a peak white screen illumination of 48 cd/M^2, we do not
see the flicker with a flicker frequency of 48 Hz (two flashes per frame).
But, if the luminance is increased, we can see the flicker. The flicker
fusion frequency increases with luminance.

Another effect is we are more sensitive to flicker in our peripheral
vision. I can see the flicker in a multiplexed LED display if I am not
looking directly at it. If I look directly at it, the flicker is not
visible. I understand this is an evolutionary development. Those of us
(and other animals) that could see an attacker in the periphery survived.
Those that did not did not.

Perception is fascinating!

Harold

Post by Denny Esterline
I suppose many of us are familiar with the concept of "Nerd Sniping"?
https://xkcd.com/356/
"Nerd sniping is a slang term that describes a particularly interesting
problem that is presented to a nerd, often a physicist, tech geek or
mathematician. The nerd stops all activity to devote attention to solving
the problem, often at his or her own peril."
So, I was totally in the middle of something else, stopped, broke out a
breadboard and wrote code to answer this question....
At about 15mS, I cannot tell they are out of sync.
By about 20mS, I can see that it's not "right" but it's hard to say which
is first.
At about 35mS, I can clearly see that they are out of sync and which one is
first.
My results are likely skewed by having one red and the other green, though
I did flip them and try again with about the same results.
Code attached below. Please note that I'm not claiming it's good code....
:-)
void setup() {
pinMode(D0, OUTPUT);
pinMode(D1, OUTPUT);
Serial.begin(115200);
}
int T1 ;
int T2;
int j;
void loop() {
j=analogRead(A0);
T2 = j/10;
T1 = 200 ;
Serial.println(j);
digitalWrite(D0, HIGH);
delay(T2);
digitalWrite(D1, HIGH);
delay(T1);
digitalWrite(D0, LOW);
delay(T2);
digitalWrite(D1, LOW);
delay(T1);
}

Post by Gordon Williams
Hi,
Hoping someone on the list may have some insight.
I have 3 LED clocks that need to be synchronized for a nordic ski race.
They show the time to the second.
The way they are designed is they have a push button on the end that
starts the timing. The plan is to have a count down (3,2,1,go) with a
person on each clock to push the button on "go".
They will be synchronized close enough for timing purposes, but I want
them visually synchronized as well so I don't get any complaints.
Question: If the clocks are all in the centre of your field of view, how
many milliseconds between the LED seconds digits changing can be
detected? In other words, if you had 2 LEDs, what would be the maximum
time difference between turning them on so you could say that LED A
turned on before LED B?
Thanks,
Gordon Williams
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[Sean Breheny]

Isn't the sensitivity to flicker in the peripheral vision also related to
changing which receptors sense the light at the same time as the light is
turning on and off? For example, I find that I can often see the
multiplexing of LEDs if I just scan my eyes around their vicinity, as
opposed to trying to look straight at them or away from them.

On Fri, Oct 12, 2018 at 7:11 PM Harold Hallikainen <

Post by Harold Hallikainen
Interesting! This reminds me of audio/video sync. We are very sensitive to
sound being early (before image), but very forgiving of sound being late
(up to a point) since in real life, sound always arrives a little late.
The two lights comparison is a little like "flicker fusion." In motion
pictures, with a peak white screen illumination of 48 cd/M^2, we do not
see the flicker with a flicker frequency of 48 Hz (two flashes per frame).
But, if the luminance is increased, we can see the flicker. The flicker
fusion frequency increases with luminance.
Another effect is we are more sensitive to flicker in our peripheral
vision. I can see the flicker in a multiplexed LED display if I am not
looking directly at it. If I look directly at it, the flicker is not
visible. I understand this is an evolutionary development. Those of us
(and other animals) that could see an attacker in the periphery survived.
Those that did not did not.
Perception is fascinating!
Harold

Post by Denny Esterline
I suppose many of us are familiar with the concept of "Nerd Sniping"?
https://xkcd.com/356/
"Nerd sniping is a slang term that describes a particularly interesting
problem that is presented to a nerd, often a physicist, tech geek or
mathematician. The nerd stops all activity to devote attention to solving
the problem, often at his or her own peril."
So, I was totally in the middle of something else, stopped, broke out a
breadboard and wrote code to answer this question....
At about 15mS, I cannot tell they are out of sync.
By about 20mS, I can see that it's not "right" but it's hard to say which
is first.
At about 35mS, I can clearly see that they are out of sync and which one is
first.
My results are likely skewed by having one red and the other green,

though

Post by Denny Esterline
I did flip them and try again with about the same results.
Code attached below. Please note that I'm not claiming it's good

code....

Post by Denny Esterline
:-)
void setup() {
pinMode(D0, OUTPUT);
pinMode(D1, OUTPUT);
Serial.begin(115200);
}
int T1 ;
int T2;
int j;
void loop() {
j=analogRead(A0);
T2 = j/10;
T1 = 200 ;
Serial.println(j);
digitalWrite(D0, HIGH);
delay(T2);
digitalWrite(D1, HIGH);
delay(T1);
digitalWrite(D0, LOW);
delay(T2);
digitalWrite(D1, LOW);
delay(T1);
}

Post by Gordon Williams
Hi,
Hoping someone on the list may have some insight.
I have 3 LED clocks that need to be synchronized for a nordic ski race.
They show the time to the second.
The way they are designed is they have a push button on the end that
starts the timing. The plan is to have a count down (3,2,1,go) with a
person on each clock to push the button on "go".
They will be synchronized close enough for timing purposes, but I want
them visually synchronized as well so I don't get any complaints.
Question: If the clocks are all in the centre of your field of view, how
many milliseconds between the LED seconds digits changing can be
detected? In other words, if you had 2 LEDs, what would be the maximum
time difference between turning them on so you could say that LED A
turned on before LED B?
Thanks,
Gordon Williams
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