Beam interruption / time measurement

[Robert Barr]

It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes. (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption
of a light beam. Extreme accuracy isn't necessary -- 0.01 seconds would
be fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as
slowly as possible, for perhaps 20 feet. In other words, a 'slow race'.
You'll see these at various biker events, and it's a whole lot tougher
than it looks. Here's the best I've seen in a long time:

http://www.youtube.com/watch?v=HrJvv_L8WBw

I'm thinking of two pair of tripods, one for the start line and one for
the end, with each pair holding an opto-electric device and a reflector.

The cheapest opto-electric devices I can think of are the safety units
that automatically reverse a garage door opener. I have a pair (from an
old dead opener), and they're pretty cheap on eBay. The problem with
these is, I can't find any source of information about how these
operate. Perhaps it's deliberately arcane knowledge, so that it's
difficult to defeat their purpose.

Does anyone have a link or source of info on how I could use these
critters to my purpose? Or, for that matter, a simpler, cheaper way to
do the job accurately? I've seen timing kits specially made for racing,
but they're asking about $600 and up. I'm thinking of a small fraction
of that.

I also found these, after about an hour of web searching:
http://www.goldmine-elec-products.com/prodinfo.asp?number=B00002&variation=

.... but it's hard to tell how much useful information they'd come with.

I haven't decided on what to use for the actual timer & output, but that
might be the simplest part.

(One guy suggested pneumatic switches. Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station. They had
these antiquities called 'attendants' who would come out and put gas in
your car. Honest. Then they'd clean your windows. Nobody believes me,
but it was very common back when 6GH8A's were about $3.50 a copy...)

 

[BobW]

"Robert Barr" <not@for.harvest> wrote in message
news:mnICj.1144$LV5.560@newssvr19.news.prodigy.net...

It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes. (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption of
a light beam. Extreme accuracy isn't necessary -- 0.01 seconds would be
fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as slowly
as possible, for perhaps 20 feet. In other words, a 'slow race'. You'll
see these at various biker events, and it's a whole lot tougher than it
looks. Here's the best I've seen in a long time:

http://www.youtube.com/watch?v=HrJvv_L8WBw

I'm thinking of two pair of tripods, one for the start line and one for
the end, with each pair holding an opto-electric device and a reflector.

The cheapest opto-electric devices I can think of are the safety units
that automatically reverse a garage door opener. I have a pair (from an
old dead opener), and they're pretty cheap on eBay. The problem with
these is, I can't find any source of information about how these operate.
Perhaps it's deliberately arcane knowledge, so that it's difficult to
defeat their purpose.

Does anyone have a link or source of info on how I could use these
critters to my purpose? Or, for that matter, a simpler, cheaper way to do
the job accurately? I've seen timing kits specially made for racing, but
they're asking about $600 and up. I'm thinking of a small fraction of
that.

I also found these, after about an hour of web searching:
http://www.goldmine-elec-products.com/prodinfo.asp?number=B00002&variation=

... but it's hard to tell how much useful information they'd come with.

I haven't decided on what to use for the actual timer & output, but that
might be the simplest part.

(One guy suggested pneumatic switches. Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station. They had these
antiquities called 'attendants' who would come out and put gas in your
car. Honest. Then they'd clean your windows. Nobody believes me, but it
was very common back when 6GH8A's were about $3.50 a copy...)

Robert,

I'll do some thinking about this. I've learned how important slow and
controlled riding is on a motorcycle using the "friction zone" and rear
brake techniques.

If I were building it, I would use a little micro controller, lcd, and
associated switches and/or optical sensors. However, I'll see if I can come
up with something simpler and more off-the-shelf.

Bob

 

[BobW]

"BobW" <nimby_NEEDSPAM@roadrunner.com> wrote in message
news:JLedneeRO6d980banZ2dnUVZ_remnZ2d@giganews.com...

"Robert Barr" <not@for.harvest> wrote in message
news:mnICj.1144$LV5.560@newssvr19.news.prodigy.net...
It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes. (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption of
a light beam. Extreme accuracy isn't necessary -- 0.01 seconds would be
fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as
slowly as possible, for perhaps 20 feet. In other words, a 'slow race'.
You'll see these at various biker events, and it's a whole lot tougher
than it looks. Here's the best I've seen in a long time:

http://www.youtube.com/watch?v=HrJvv_L8WBw

I'm thinking of two pair of tripods, one for the start line and one for
the end, with each pair holding an opto-electric device and a reflector.

The cheapest opto-electric devices I can think of are the safety units
that automatically reverse a garage door opener. I have a pair (from an
old dead opener), and they're pretty cheap on eBay. The problem with
these is, I can't find any source of information about how these operate.
Perhaps it's deliberately arcane knowledge, so that it's difficult to
defeat their purpose.

Does anyone have a link or source of info on how I could use these
critters to my purpose? Or, for that matter, a simpler, cheaper way to
do the job accurately? I've seen timing kits specially made for racing,
but they're asking about $600 and up. I'm thinking of a small fraction
of that.

I also found these, after about an hour of web searching:
http://www.goldmine-elec-products.com/prodinfo.asp?number=B00002&variation=

... but it's hard to tell how much useful information they'd come with.

I haven't decided on what to use for the actual timer & output, but that
might be the simplest part.

(One guy suggested pneumatic switches. Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station. They had these
antiquities called 'attendants' who would come out and put gas in your
car. Honest. Then they'd clean your windows. Nobody believes me, but
it was very common back when 6GH8A's were about $3.50 a copy...)

Robert,

I'll do some thinking about this. I've learned how important slow and
controlled riding is on a motorcycle using the "friction zone" and rear
brake techniques.

If I were building it, I would use a little micro controller, lcd, and
associated switches and/or optical sensors. However, I'll see if I can
come up with something simpler and more off-the-shelf.

Bob

In thinking a little bit more about this, your pneumatic hose sensor (yes,
I'm old enough to remember those, too) sounds like the most reliable and
accurate solution to determining the start and stop points.

That guy in your video is amazing. I can't ride that slowly, yet. There is
no doubt, in my mind, that the motor officers are the best riders on the
planet. I have learned most of my techniques from a guy named Jerry
Palladino and his videos at www.ridelikeapro.com .

Still thinking....

Bob

 

[John Fields]

On Sat, 15 Mar 2008 07:49:33 -0700 (PDT), gearhead
<nospam@billburg.com> wrote:

On Mar 14, 9:36 pm, Robert Barr <n...@for.harvest> wrote:
It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes.  (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption
of a light beam.  Extreme accuracy isn't necessary -- 0.01 seconds would
be fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as
slowly as possible, for perhaps 20 feet.  In other words, a 'slow race'.
  You'll see these at various biker events, and it's a whole lot tougher
than it looks.  

(One guy suggested pneumatic switches.  Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station.  They had
these antiquities called 'attendants' who would come out and put gas in
your car.  Honest.  Then they'd clean your windows.  Nobody believes me,
but it was very common back when 6GH8A's were about $3.50 a copy...)

One thing about pneumatic tubes you ought to consider. In a slow race
an obstacle like a rubber hose could tip your bike. In that video the
cop comes to a dead stop every couple feet and turns the handlebars to
keep balance. What happens if you try to make a maneuver like that
with a rubber hose under your front tire? Bummer to tip over right at
the finish line.

---
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GFRC,GFRC:2006-50,GFRC:en&q=tape+switch

--
JF

 

[gearhead]

On Mar 14, 9:36 pm, Robert Barr <n...@for.harvest> wrote:

It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes.  (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption
of a light beam.  Extreme accuracy isn't necessary -- 0.01 seconds would
be fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as
slowly as possible, for perhaps 20 feet.  In other words, a 'slow race'.
  You'll see these at various biker events, and it's a whole lot tougher
than it looks.  

(One guy suggested pneumatic switches.  Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station.  They had
these antiquities called 'attendants' who would come out and put gas in
your car.  Honest.  Then they'd clean your windows.  Nobody believes me,
but it was very common back when 6GH8A's were about $3.50 a copy...)

One thing about pneumatic tubes you ought to consider. In a slow race
an obstacle like a rubber hose could tip your bike. In that video the
cop comes to a dead stop every couple feet and turns the handlebars to
keep balance. What happens if you try to make a maneuver like that
with a rubber hose under your front tire? Bummer to tip over right at
the finish line.

 

[Robert Barr]

One thing about pneumatic tubes you ought to consider. In a slow race
an obstacle like a rubber hose could tip your bike. In that video the
cop comes to a dead stop every couple feet and turns the handlebars to
keep balance. What happens if you try to make a maneuver like that
with a rubber hose under your front tire? Bummer to tip over right at
the finish line.

Yes, I'm sure you're right. I think the touch-less approach is best.

Even if it had no impact on the rider's performance, this will be used
on poker runs (Formula = bikes + alcohol + god-knows-whatelse +
bravado), so riders who don't do so well will be looking for excuses, no
matter how lame. No sense providing one.

I'm trying to avoid re-inventing the wheel here. Interesting suggestion
about the switch tape, but all the links lead to firearm-related
articles. (?). I need to search on this some more.

In keeping with 'keeping it basic', I found this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110232868846

How's that for pedestrian? I'd need a pair of them. Not sure how long
ago they were available in the stores, but that would do it.

 

[robb]

"Robert Barr" <not@for.harvest> wrote in message
news:iAWCj.20735$Ej5.13923@newssvr29.news.prodigy.net...

In keeping with 'keeping it basic', I found this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110232868846

How's that for pedestrian? I'd need a pair of them. Not sure
how long
ago they were available in the stores, but that would do it.

If your going with that solution then maybe you could consider
a "garage door safety beam" ?

they should be easily found and cheap

htiw
robb

 

[Robert Barr]

If your going with that solution then maybe you could consider
a "garage door safety beam" ?

they should be easily found and cheap

htiw
robb

This is cut & pasted from my original post:


"The cheapest opto-electric devices I can think of are the safety units
that automatically reverse a garage door opener. I have a pair (from an
old dead opener), and they're pretty cheap on eBay. The problem with
these is, I can't find any source of information about how these
operate. Perhaps it's deliberately arcane knowledge, so that it's
difficult to defeat their purpose."

If anyone knows where to find information about these things, I'd love
to see it. Perhaps my search skills have aged, but about all I can come
up with are consumer-oriented items. Nobody seems to know how these
work or how to use them for any purpose other then their original use.

 

[John Fields]

On Sat, 15 Mar 2008 20:46:06 GMT, Robert Barr <not@for.harvest>
wrote:

One thing about pneumatic tubes you ought to consider. In a slow race
an obstacle like a rubber hose could tip your bike. In that video the
cop comes to a dead stop every couple feet and turns the handlebars to
keep balance. What happens if you try to make a maneuver like that
with a rubber hose under your front tire? Bummer to tip over right at
the finish line.

Yes, I'm sure you're right. I think the touch-less approach is best.

Even if it had no impact on the rider's performance, this will be used
on poker runs (Formula = bikes + alcohol + god-knows-whatelse +
bravado), so riders who don't do so well will be looking for excuses, no
matter how lame. No sense providing one.

I'm trying to avoid re-inventing the wheel here. Interesting suggestion
about the switch tape, but all the links lead to firearm-related
articles. (?). I need to search on this some more.

---
Start here:

http://www.tapeswitch.com/

--
JF

 

[Robert Barr]

---
Start here:

http://www.tapeswitch.com/

Interesting stuff, but did you check their prices? The 131A ribbon
switch, the common type, is $21 per foot! I'd need about six feet, to
give the rider a 4' target at the end, and a 2' starting line.

 

[gearhead]

On Mar 15, 1:46 pm, Robert Barr <n...@for.harvest> wrote:

One thing about pneumatic tubes you ought to consider.  In a slow race
an obstacle like a rubber hose could tip your bike.  In that video the
cop comes to a dead stop every couple feet and turns the handlebars to
keep balance.  What happens if you try to make a maneuver like that
with a rubber hose under your front tire?  Bummer to tip over right at
the finish line.

Yes, I'm sure you're right.  I think the touch-less approach is best.

  Even if it had no impact on the rider's performance, this will be used
on poker runs (Formula = bikes + alcohol + god-knows-whatelse +
bravado), so riders who don't do so well will be looking for excuses, no
matter how lame.  No sense providing one.

I'm trying to avoid re-inventing the wheel here.  Interesting suggestion
about the switch tape, but all the links lead to firearm-related
articles.  (?).  I need to search on this some more.

In keeping with 'keeping it basic', I found this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=110232868846

How's that for pedestrian?  I'd need a pair of them.  Not sure how long
ago they were available in the stores, but that would do it.

Sure, keep it simple. Have a guy click a stopwatch when the alarm
sounds.

 

[Bob Monsen]

"Robert Barr" <not@for.harvest> wrote in message
news:mnICj.1144$LV5.560@newssvr19.news.prodigy.net...

It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes. (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption of
a light beam. Extreme accuracy isn't necessary -- 0.01 seconds would be
fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as slowly
as possible, for perhaps 20 feet. In other words, a 'slow race'. You'll
see these at various biker events, and it's a whole lot tougher than it
looks. Here's the best I've seen in a long time:

http://www.youtube.com/watch?v=HrJvv_L8WBw

I'm thinking of two pair of tripods, one for the start line and one for
the end, with each pair holding an opto-electric device and a reflector.

The cheapest opto-electric devices I can think of are the safety units
that automatically reverse a garage door opener. I have a pair (from an
old dead opener), and they're pretty cheap on eBay. The problem with
these is, I can't find any source of information about how these operate.
Perhaps it's deliberately arcane knowledge, so that it's difficult to
defeat their purpose.

Does anyone have a link or source of info on how I could use these
critters to my purpose? Or, for that matter, a simpler, cheaper way to do
the job accurately? I've seen timing kits specially made for racing, but
they're asking about $600 and up. I'm thinking of a small fraction of
that.

I also found these, after about an hour of web searching:
http://www.goldmine-elec-products.com/prodinfo.asp?number=B00002&variation=

... but it's hard to tell how much useful information they'd come with.

I haven't decided on what to use for the actual timer & output, but that
might be the simplest part.

(One guy suggested pneumatic switches. Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station. They had these
antiquities called 'attendants' who would come out and put gas in your
car. Honest. Then they'd clean your windows. Nobody believes me, but it
was very common back when 6GH8A's were about $3.50 a copy...)

You can get cheapo laser pointers for about $3 on ebay. Get two. Have them
laying on the ground at the start and the finish, pointing into a little
elongated box with a photodiode at the end. Build a sensor driver that gives
you a pulse when the beam is interrupted by building this:


10 MEG
___
.----------|___|--------.
| |
| |
| |
| |\ |
o---------|-\ | |\
| | >----------'----------|-\
| .-|+/ | >------.-- A
Photo - | |/ 9V .----|+/ |
diode ^ | | | |/ |
| | .-. | ___ |
o-------' 10k | |<--'-----|___|----'
| | |
| adj '-' 100k
| for |
| sensitivity
| |
| |
GND ----o------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The opamp used in leftmost part is a TLC251C (page 227 of AOE, 2nd Edition,
Hardcover) However, I suspect that an LM324 will work just as well, and will
be obtainable at RadioShack. The rightmost opamp is hooked up as a
comparator, and will compare the input voltage to the reference provided by
the potentiometer. You adjust the potentiometer so that the output at A is
off when the laser pointer is pointing at the photodiode, but on when it is
not. You may have to play with it onsite to make sure it is right, so you
can also add an LED to the output so you can see if it is on or off without
measuring it. The LED should go from A to a 1k resistor, and the other side
of the resistor should go to ground. If you have a multimeter, you can use
that to calibrate it onsite.

It will give you a positive pulse when the beam is interrupted. Try to buy a
photodiode that has good response at the laser frequency. However, if you
are just trying it out, you could probably just scrape the paint off of any
old diode, and give that a try. All diodes have a response to light, which
is why they paint them.

Put the photodiode at the end of a little 'tunnel' about 6 inches long to
prevent ambient light from affecting it. The smaller the opening, the more
likely it will be to work.

Tape it all to the ground with duct tape.

Once you have two of these, you can get pulses out of each output. For each
output, attach a twisted pair to the output and ground of the circuit, and
run it to a central place where you want to do the timing. Put a 1k resistor
between the output and the cable. On the other end, hook up each of the
twisted pairs to an optoisolator. This will give you two open collector
'active low' signals.

1.5V
|
.-.
| | 1k
optoisolator | |
.------------. '-'
___ Twisted | | |
A -|___|---- ------|-. -|--------o--- B
1k \ / | | | |
\ / | | |/ |
\/ | V -> | |
/\ | - |> |
/ \ | | | |
GND ---------/ \-------|-' -|--------.
Pair '------------' |
|
|
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Now, you need a display. If you connect both of the outputs to the same
wire, you have a 'wired or' signal. Now, pull the wire up to some voltage,
and you'll get downwards pulses when the lasers are interrupted.

Connect this up with a 1nF capacitor to your sound input on your laptop,
through a 100k resistor:


1nF 100k
|| ___
B -----||----|___|--------o tip (left channel)
||
NC o ring (right channel)

GND ------------------------o sleeve

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

(See http://en.wikipedia.org/wiki/Tip_ring_sleeve for info on cables)

You could also attach the 'start sensor' to tip, and the end sensor to ring
to get the different timing pulses on different stereo channels.

Then, download a copy of Audacity (freeware). You should be able to see the
pulses when you record from the line input, and measure the distance between
them very accurately.

If you have a Java hacker around, you could write a program that listens to
the audio port, measures the input, and reports the results. They could make
it as elaborate as they wanted, perhaps showing a moving clock until the
final pulse. It would be a simple program to write, I suspect.

I haven not built this circuit, so there may be issues I have not forseen.
Some of the more experienced guys may care to comment.

Have fun!

Regards,
Bob Monsen

 

[Bob Monsen]

"Bob Monsen" <rcmonsen@gmail.com> wrote in message
news:AH%Cj.14273$5K1.3954@newssvr12.news.prodigy.net...

"Robert Barr" <not@for.harvest> wrote in message
news:mnICj.1144$LV5.560@newssvr19.news.prodigy.net...
It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes. (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption of
a light beam. Extreme accuracy isn't necessary -- 0.01 seconds would be
fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as
slowly as possible, for perhaps 20 feet. In other words, a 'slow race'.
You'll see these at various biker events, and it's a whole lot tougher
than it looks. Here's the best I've seen in a long time:

http://www.youtube.com/watch?v=HrJvv_L8WBw

I'm thinking of two pair of tripods, one for the start line and one for
the end, with each pair holding an opto-electric device and a reflector.

The cheapest opto-electric devices I can think of are the safety units
that automatically reverse a garage door opener. I have a pair (from an
old dead opener), and they're pretty cheap on eBay. The problem with
these is, I can't find any source of information about how these operate.
Perhaps it's deliberately arcane knowledge, so that it's difficult to
defeat their purpose.

Does anyone have a link or source of info on how I could use these
critters to my purpose? Or, for that matter, a simpler, cheaper way to
do the job accurately? I've seen timing kits specially made for racing,
but they're asking about $600 and up. I'm thinking of a small fraction
of that.

I also found these, after about an hour of web searching:
http://www.goldmine-elec-products.com/prodinfo.asp?number=B00002&variation=

... but it's hard to tell how much useful information they'd come with.

I haven't decided on what to use for the actual timer & output, but that
might be the simplest part.

(One guy suggested pneumatic switches. Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station. They had these
antiquities called 'attendants' who would come out and put gas in your
car. Honest. Then they'd clean your windows. Nobody believes me, but
it was very common back when 6GH8A's were about $3.50 a copy...)


You can get cheapo laser pointers for about $3 on ebay. Get two. Have them
laying on the ground at the start and the finish, pointing into a little
elongated box with a photodiode at the end. Build a sensor driver that
gives you a pulse when the beam is interrupted by building this:


10 MEG
___
.----------|___|--------.
| |
| |
| |
| |\ |
o---------|-\ | |\
| | >----------'----------|-\
| .-|+/ | >------.-- A
Photo - | |/ 9V .----|+/ |
diode ^ | | | |/ |
| | .-. | ___ |
o-------' 10k | |<--'-----|___|----'
| | |
| adj '-' 100k
| for |
| sensitivity
| |
| |
GND ----o------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Slight correction. I built the circuit above and tried it out, and it works
ok, but the sense is inverted from what you want. So, use this instead:

Use a 9V battery, and connect the 9V to Vcc on the opamps

10 MEG
___
.----------|___|---.
| | 100k
| | ___
| | .--|___|----.
| |\ | 10k | |
o--------o|-\ | ___ | |\ |
| | >-----o---|___|--o----|+\ |
| .-|+/ | >---o---- Out
Photo - | |/ 9V .---o|-/
diode ^ | | | |/
| | .-. |
o-------' 100k | |<--'
| | |
| adj '-'
| for |
| sensitivity
| |
| |
GND ----o------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

That way, you won't be wasting your battery powering the output except when
the
beam is broken. So, the battery will last longer.

The opamp used in leftmost part is a TLC251C (page 227 of AOE, 2nd
Edition, Hardcover) However, I suspect that an LM324 will work just as
well, and will be obtainable at RadioShack. The rightmost opamp is hooked
up as a comparator, and will compare the input voltage to the reference
provided by the potentiometer. You adjust the potentiometer so that the
output at A is off when the laser pointer is pointing at the photodiode,
but on when it is not. You may have to play with it onsite to make sure it
is right, so you can also add an LED to the output so you can see if it is
on or off without measuring it. The LED should go from A to a 1k resistor,
and the other side of the resistor should go to ground. If you have a
multimeter, you can use that to calibrate it onsite.

It will give you a positive pulse when the beam is interrupted. Try to buy
a photodiode that has good response at the laser frequency. However, if
you are just trying it out, you could probably just scrape the paint off
of any old diode, and give that a try. All diodes have a response to
light, which is why they paint them.

Put the photodiode at the end of a little 'tunnel' about 6 inches long to
prevent ambient light from affecting it. The smaller the opening, the more
likely it will be to work.

Tape it all to the ground with duct tape.

Once you have two of these, you can get pulses out of each output. For
each output, attach a twisted pair to the output and ground of the
circuit, and run it to a central place where you want to do the timing.
Put a 1k resistor between the output and the cable. On the other end, hook
up each of the twisted pairs to an optoisolator. This will give you two
open collector 'active low' signals.

1.5V
|
.-.
| | 1k
optoisolator | |
.------------. '-'
___ Twisted | | |
A -|___|---- ------|-. -|--------o--- B
1k \ / | | | |
\ / | | |/ |
\/ | V -> | |
/\ | - |> |
/ \ | | | |
GND ---------/ \-------|-' -|--------.
Pair '------------' |
|
|
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Now, you need a display. If you connect both of the outputs to the same
wire, you have a 'wired or' signal. Now, pull the wire up to some voltage,
and you'll get downwards pulses when the lasers are interrupted.

Connect this up with a 1nF capacitor to your sound input on your laptop,
through a 100k resistor:


1nF 100k
|| ___
B -----||----|___|--------o tip (left channel)
||
NC o ring (right channel)

GND ------------------------o sleeve

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

(See http://en.wikipedia.org/wiki/Tip_ring_sleeve for info on cables)

You could also attach the 'start sensor' to tip, and the end sensor to
ring to get the different timing pulses on different stereo channels.

Then, download a copy of Audacity (freeware). You should be able to see
the pulses when you record from the line input, and measure the distance
between them very accurately.

If you have a Java hacker around, you could write a program that listens
to the audio port, measures the input, and reports the results. They could
make it as elaborate as they wanted, perhaps showing a moving clock until
the final pulse. It would be a simple program to write, I suspect.

I haven not built this circuit, so there may be issues I have not forseen.
Some of the more experienced guys may care to comment.

Have fun!

Regards,
Bob Monsen

 

[whit3rd]

On Mar 14, 9:36 pm, Robert Barr <n...@for.harvest> wrote:

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption
of a light beam.  Extreme accuracy isn't necessary

Outdoors optoelectronics can be difficult, but does it
really have to be optical? Could you use a taut thread
holding a springloaded switch open? Run through
the thread, it snaps and the switch closes.

 

[Bob Masta]

On Sun, 16 Mar 2008 04:56:10 GMT, "Bob Monsen" <rcmonsen@gmail.com>
wrote:

"Bob Monsen" <rcmonsen@gmail.com> wrote in message
news:AH%Cj.14273$5K1.3954@newssvr12.news.prodigy.net...
"Robert Barr" <not@for.harvest> wrote in message
news:mnICj.1144$LV5.560@newssvr19.news.prodigy.net...
It's been many a year since I've messed with electronics -- back when a
nice color television used maybe a dozen 6GH8A vacuum tubes. (Good
riddance!)

Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption of
a light beam. Extreme accuracy isn't necessary -- 0.01 seconds would be
fine, so no high-speed industrial stuff needed.

I want to measure the amount of time a motorcycle rider uses (without
touching a foot to the ground) to cover a fixed distance, riding as
slowly as possible, for perhaps 20 feet. In other words, a 'slow race'.
You'll see these at various biker events, and it's a whole lot tougher
than it looks. Here's the best I've seen in a long time:

http://www.youtube.com/watch?v=HrJvv_L8WBw

I'm thinking of two pair of tripods, one for the start line and one for
the end, with each pair holding an opto-electric device and a reflector.

The cheapest opto-electric devices I can think of are the safety units
that automatically reverse a garage door opener. I have a pair (from an
old dead opener), and they're pretty cheap on eBay. The problem with
these is, I can't find any source of information about how these operate.
Perhaps it's deliberately arcane knowledge, so that it's difficult to
defeat their purpose.

Does anyone have a link or source of info on how I could use these
critters to my purpose? Or, for that matter, a simpler, cheaper way to
do the job accurately? I've seen timing kits specially made for racing,
but they're asking about $600 and up. I'm thinking of a small fraction
of that.

I also found these, after about an hour of web searching:
http://www.goldmine-elec-products.com/prodinfo.asp?number=B00002&variation=

... but it's hard to tell how much useful information they'd come with.

I haven't decided on what to use for the actual timer & output, but that
might be the simplest part.

(One guy suggested pneumatic switches. Old-timers like me can remember
when gas stations had hoses draped across the pump lanes which, when run
over by a car tire, would ring a bell inside the station. They had these
antiquities called 'attendants' who would come out and put gas in your
car. Honest. Then they'd clean your windows. Nobody believes me, but
it was very common back when 6GH8A's were about $3.50 a copy...)


You can get cheapo laser pointers for about $3 on ebay. Get two. Have them
laying on the ground at the start and the finish, pointing into a little
elongated box with a photodiode at the end. Build a sensor driver that
gives you a pulse when the beam is interrupted by building this:


10 MEG
___
.----------|___|--------.
| |
| |
| |
| |\ |
o---------|-\ | |\
| | >----------'----------|-\
| .-|+/ | >------.-- A
Photo - | |/ 9V .----|+/ |
diode ^ | | | |/ |
| | .-. | ___ |
o-------' 10k | |<--'-----|___|----'
| | |
| adj '-' 100k
| for |
| sensitivity
| |
| |
GND ----o------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


Slight correction. I built the circuit above and tried it out, and it works
ok, but the sense is inverted from what you want. So, use this instead:

Use a 9V battery, and connect the 9V to Vcc on the opamps

10 MEG
___
.----------|___|---.
| | 100k
| | ___
| | .--|___|----.
| |\ | 10k | |
o--------o|-\ | ___ | |\ |
| | >-----o---|___|--o----|+\ |
| .-|+/ | >---o---- Out
Photo - | |/ 9V .---o|-/
diode ^ | | | |/
| | .-. |
o-------' 100k | |<--'
| | |
| adj '-'
| for |
| sensitivity
| |
| |
GND ----o------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

That way, you won't be wasting your battery powering the output except when
the
beam is broken. So, the battery will last longer.

The opamp used in leftmost part is a TLC251C (page 227 of AOE, 2nd
Edition, Hardcover) However, I suspect that an LM324 will work just as
well, and will be obtainable at RadioShack. The rightmost opamp is hooked
up as a comparator, and will compare the input voltage to the reference
provided by the potentiometer. You adjust the potentiometer so that the
output at A is off when the laser pointer is pointing at the photodiode,
but on when it is not. You may have to play with it onsite to make sure it
is right, so you can also add an LED to the output so you can see if it is
on or off without measuring it. The LED should go from A to a 1k resistor,
and the other side of the resistor should go to ground. If you have a
multimeter, you can use that to calibrate it onsite.

It will give you a positive pulse when the beam is interrupted. Try to buy
a photodiode that has good response at the laser frequency. However, if
you are just trying it out, you could probably just scrape the paint off
of any old diode, and give that a try. All diodes have a response to
light, which is why they paint them.

Put the photodiode at the end of a little 'tunnel' about 6 inches long to
prevent ambient light from affecting it. The smaller the opening, the more
likely it will be to work.

Tape it all to the ground with duct tape.

Once you have two of these, you can get pulses out of each output. For
each output, attach a twisted pair to the output and ground of the
circuit, and run it to a central place where you want to do the timing.
Put a 1k resistor between the output and the cable. On the other end, hook
up each of the twisted pairs to an optoisolator. This will give you two
open collector 'active low' signals.

1.5V
|
.-.
| | 1k
optoisolator | |
.------------. '-'
___ Twisted | | |
A -|___|---- ------|-. -|--------o--- B
1k \ / | | | |
\ / | | |/ |
\/ | V -> | |
/\ | - |> |
/ \ | | | |
GND ---------/ \-------|-' -|--------.
Pair '------------' |
|
|
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Now, you need a display. If you connect both of the outputs to the same
wire, you have a 'wired or' signal. Now, pull the wire up to some voltage,
and you'll get downwards pulses when the lasers are interrupted.

Connect this up with a 1nF capacitor to your sound input on your laptop,
through a 100k resistor:


1nF 100k
|| ___
B -----||----|___|--------o tip (left channel)
||
NC o ring (right channel)

GND ------------------------o sleeve

(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

(See http://en.wikipedia.org/wiki/Tip_ring_sleeve for info on cables)

You could also attach the 'start sensor' to tip, and the end sensor to
ring to get the different timing pulses on different stereo channels.

Then, download a copy of Audacity (freeware). You should be able to see
the pulses when you record from the line input, and measure the distance
between them very accurately.

If you have a Java hacker around, you could write a program that listens
to the audio port, measures the input, and reports the results. They could
make it as elaborate as they wanted, perhaps showing a moving clock until
the final pulse. It would be a simple program to write, I suspect.

I haven not built this circuit, so there may be issues I have not forseen.
Some of the more experienced guys may care to comment.

Have fun!

Regards,
Bob Monsen

If you want a digital readout without having to measure
pulse distances manually, check out the Frequency Counter option in
Daqarta. You can make it as big as you want, and it has a period mode
that will read out the time in msec directly. Its accuracy is
determined by the crystal that controls your sound card sample rate,
which is massive overkill for this application.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!

 

[Bob Monsen]

"whit3rd" <whit3rd@gmail.com> wrote in message
news:5d660049-1d1d-45e3-bf72-0dd5ca4f1b39@a23g2000hsc.googlegroups.com...
On Mar 14, 9:36 pm, Robert Barr <n...@for.harvest> wrote:
Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption
of a light beam. Extreme accuracy isn't necessary

Outdoors optoelectronics can be difficult, but does it
really have to be optical? Could you use a taut thread
holding a springloaded switch open? Run through
the thread, it snaps and the switch closes.

You could do that as well, but getting everything just right might be
painful. I personally like the idea of using lasers, since they won't break
when people trip on them.

My experiments last night with a $5 laser pointer show that a photodiode and
a laser pointer gives me a huge voltage difference with the posted circuit,
which is very easy to deal with. Right under a fluorescent light with 2
tubes, the opamp outputs about 200mV. If I point the laser at it, I get 2
volts. This is with a 9V supply. I have not taken it outside, however, so I
don't really know how sunlight will affect it.

I suspect that if he uses a tunnel made out of non-reflective material
(actually, a piece of hose or pipe as the tunnel would work well), then the
ambient light should not affect the photodiode at all.

On the other hand, one point to consider is the life of the laser pointer
cartridge. Cheap laser pointers don't generally have a feedback pin, and may
fade after a few hours of use. I'd say to limit the current into the laser
cartridge to the minimum required using a constant current scheme of some
kind.

Regards,
Bob Monsen

 

On 3ÔÂ17ČŐ, ÉĎÎç6Ęą54ˇÖ, "Bob Monsen" <rcmon...@gmail.com> wrote:

"whit3rd" <whit...@gmail.com> wrote in message
news:5d660049-1d1d-45e3-bf72-0dd5ca4f1b39@a23g2000hsc.googlegroups.com...
On Mar 14, 9:36 pm, Robert Barr <n...@for.harvest> wrote:
Anyhow, what I have in mind is a low-cost timing setup, used to measure
the time between two events -- both of which would be the interruption
of a light beam. Extreme accuracy isn't necessary

Outdoors optoelectronics can be difficult, but does it
really have to be optical? Could you use a taut thread
holding a springloaded switch open? Run through
the thread, it snaps and the switch closes.

You could do that as well, but getting everything just right might be
painful. I personally like the idea of using lasers, since they won't break
when people trip on them.

My experiments last night with a $5 laser pointer show that a photodiode and
a laser pointer gives me a huge voltage difference with the posted circuit,
which is very easy to deal with. Right under a fluorescent light with 2
tubes, the opamp outputs about 200mV. If I point the laser at it, I get 2
volts. This is with a 9V supply. I have not taken it outside, however, so I
don't really know how sunlight will affect it.

I suspect that if he uses a tunnel made out of non-reflective material
(actually, a piece of hose or pipe as the tunnel would work well), then the
ambient light should not affect the photodiode at all.

On the other hand, one point to consider is the life of the laser pointer
cartridge. Cheap laser pointers don't generally have a feedback pin, and may
fade after a few hours of use. I'd say to limit the current into the laser
cartridge to the minimum required using a constant current scheme of some
kind.

Regards,
Bob Monsen

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