Looking for a pulse switch? Does such a thing exist?

[[email protected]]

Hi all,

I have a battery-based application powering a 12V light. I want to
pulse the light on and off automatically (similar to a strobe). The
duty cycle will probably be around 10%, but I'd accept just about
anything if the solution is simple enough.

I want to avoid use of PIC or other microcontrollers, as that would
likely require power regulators...recall, I'm using a 12V "dirty"
source. Not only that, but the intended use is in a somewhat harsh
environment (severe vibration, moisture) and I have very little space
(the 'switch' must be attached to the light itself).

So, does anyone know if there any ready made products (or simple
solutions) to pulse a light on/off?

Cheers,
Dave

 

[martin griffith]

Hi all,

I have a battery-based application powering a 12V light. I want to
pulse the light on and off automatically (similar to a strobe). The
duty cycle will probably be around 10%, but I'd accept just about
anything if the solution is simple enough.

I want to avoid use of PIC or other microcontrollers, as that would
likely require power regulators...recall, I'm using a 12V "dirty"
source. Not only that, but the intended use is in a somewhat harsh
environment (severe vibration, moisture) and I have very little space
(the 'switch' must be attached to the light itself).

So, does anyone know if there any ready made products (or simple
solutions) to pulse a light on/off?

Cheers,
Dave

An LM555 from national semiconductor, sounds ideal for this sort of
thing


martin

 

[Jamie]

Hi all,

I have a battery-based application powering a 12V light. I want to
pulse the light on and off automatically (similar to a strobe). The
duty cycle will probably be around 10%, but I'd accept just about
anything if the solution is simple enough.

I want to avoid use of PIC or other microcontrollers, as that would
likely require power regulators...recall, I'm using a 12V "dirty"
source. Not only that, but the intended use is in a somewhat harsh
environment (severe vibration, moisture) and I have very little space
(the 'switch' must be attached to the light itself).

So, does anyone know if there any ready made products (or simple
solutions) to pulse a light on/off?

Cheers,
Dave

go to your auto part store and ask for a
bimetal flasher. you will need to know the
approximate current your lamp/load is.
they also have flasher modules for 12
operations.

 

[ehsjr]

Hi all,

I have a battery-based application powering a 12V light. I want to
pulse the light on and off automatically (similar to a strobe). The
duty cycle will probably be around 10%, but I'd accept just about
anything if the solution is simple enough.

I want to avoid use of PIC or other microcontrollers, as that would
likely require power regulators...recall, I'm using a 12V "dirty"
source. Not only that, but the intended use is in a somewhat harsh
environment (severe vibration, moisture) and I have very little space
(the 'switch' must be attached to the light itself).

So, does anyone know if there any ready made products (or simple
solutions) to pulse a light on/off?

Cheers,
Dave

If you use the 555, you'll probably need to drive an FET
with it. You did not mention the current requirement of
your light, but the 555 is limited to no more than 200 mA.

If you just need something that blinks, not that particular
light, there are blinking LEDs you could use.

Ed

 

[[email protected]]

OP here,

I had a look at an LM555 datasheet, and it indicated that the max.
output current was around 200 mA. The light I'm driving is an
off-the-shelf LED automotive taillight which *may* come under 200 mA,
but I haven't tested it (there were no ratings on it). Since the light
isn't at my desk I can't check right now (I wouldn't be surprised if it
was up in the 0.5 A - 0.8 A range). In all likelihood I would end up
using a FET of some sort; for my application, it needs to be on the
high side of the load.

I have tried the LED blinking lights (generally they run on 3V = 2 x
1.5V batteries). However, IMO they just aren't bright enough for my
application...they have enough intensity from directly behind the
light, but trail off dramatically when you move to the side.

The application is a bicycle taillight. I found a 12V LED light that
has excellent visibility from all relevant angles. Traffic in my area
is generally ignorant of cyclists, so anything to grab their attention
is a good thing (ignorant != malicious). I already run a 20W halogen
up front, so powering the light is not an issue. The taillight has a
low- and high-intensity mode...so I want to be able to run the light
constantly 'low' and strobe the high-intensity light for approx 0.1
second at a frequency of around 2 Hz. This would hopefully serve to
make me more noticeable, drain less power, and keep me legal (the light
is constantly on).

Someone mentioned the use of a bimetal flasher...this sounds
interesting, I will check it out. I may not find one with the flash
frequency/duration that I am looking for, and even if I do the size
and/or cost of the device may be prohibitive.

Cheers,
Dave

 

[martin griffith]

OP here,

I had a look at an LM555 datasheet, and it indicated that the max.
output current was around 200 mA. The light I'm driving is an
off-the-shelf LED automotive taillight which *may* come under 200 mA,
but I haven't tested it (there were no ratings on it). Since the light
isn't at my desk I can't check right now (I wouldn't be surprised if it
was up in the 0.5 A - 0.8 A range). In all likelihood I would end up
using a FET of some sort; for my application, it needs to be on the
high side of the load.

I have tried the LED blinking lights (generally they run on 3V = 2 x
1.5V batteries). However, IMO they just aren't bright enough for my
application...they have enough intensity from directly behind the
light, but trail off dramatically when you move to the side.

The application is a bicycle taillight. I found a 12V LED light that
has excellent visibility from all relevant angles. Traffic in my area
is generally ignorant of cyclists, so anything to grab their attention
is a good thing (ignorant != malicious). I already run a 20W halogen
up front, so powering the light is not an issue. The taillight has a
low- and high-intensity mode...so I want to be able to run the light
constantly 'low' and strobe the high-intensity light for approx 0.1
second at a frequency of around 2 Hz. This would hopefully serve to
make me more noticeable, drain less power, and keep me legal (the light
is constantly on).

Someone mentioned the use of a bimetal flasher...this sounds
interesting, I will check it out. I may not find one with the flash
frequency/duration that I am looking for, and even if I do the size
and/or cost of the device may be prohibitive.

Cheers,
Dave

Hi Dave, I must buy a new bike. But have a look at this
http://www.linear.com/pc/downloadDocument.do?navId=H0,C2,C1543,C1683,D9039
its all about led drivers, and efficiency, also look at luxeon LEDs.
I have my doubts about a bimetal thingy, it will waste power heating
up, which is bad news for a bike application


martin

 

[Fred Bloggs]

OP here,

I had a look at an LM555 datasheet, and it indicated that the max.
output current was around 200 mA. The light I'm driving is an
off-the-shelf LED automotive taillight which *may* come under 200 mA,
but I haven't tested it (there were no ratings on it). Since the light
isn't at my desk I can't check right now (I wouldn't be surprised if it
was up in the 0.5 A - 0.8 A range). In all likelihood I would end up
using a FET of some sort; for my application, it needs to be on the
high side of the load.

I have tried the LED blinking lights (generally they run on 3V = 2 x
1.5V batteries). However, IMO they just aren't bright enough for my
application...they have enough intensity from directly behind the
light, but trail off dramatically when you move to the side.

The application is a bicycle taillight. I found a 12V LED light that
has excellent visibility from all relevant angles. Traffic in my area
is generally ignorant of cyclists, so anything to grab their attention
is a good thing (ignorant != malicious). I already run a 20W halogen
up front, so powering the light is not an issue. The taillight has a
low- and high-intensity mode...so I want to be able to run the light
constantly 'low' and strobe the high-intensity light for approx 0.1
second at a frequency of around 2 Hz. This would hopefully serve to
make me more noticeable, drain less power, and keep me legal (the light
is constantly on).

Someone mentioned the use of a bimetal flasher...this sounds
interesting, I will check it out. I may not find one with the flash
frequency/duration that I am looking for, and even if I do the size
and/or cost of the device may be prohibitive.

What is your power source for the 20W halogen? The LED tail light may
not be so spectacular at marginal voltages under 13V. The 12V rating is
more of a descriptive indicating 12V automotive system and really means
the best performance is at 13.5V or above. Unlike the halogen
technology, the LED output will fade fast below a certain threshold.
This means that a small switching boost regulator to maintain 13.5V may
be required. I take it the LED assembly is a two wire with case grounded
to the frame. There are any number of ways to strobe the high intensity
cheaply, but the question is can both the high intensity and low
intensity leads receive voltage simultaneously or does the lamp require
that only one at a time be used. Your most readily available timing
source is probably an existing reed switch pickup on a rear wheel spoke
or pedal.

 

[Rich Grise]

Hi all,

I have a battery-based application powering a 12V light. I want to
pulse the light on and off automatically (similar to a strobe). The
duty cycle will probably be around 10%, but I'd accept just about
anything if the solution is simple enough.

I want to avoid use of PIC or other microcontrollers, as that would
likely require power regulators...recall, I'm using a 12V "dirty"
source. Not only that, but the intended use is in a somewhat harsh
environment (severe vibration, moisture) and I have very little space
(the 'switch' must be attached to the light itself).

So, does anyone know if there any ready made products (or simple
solutions) to pulse a light on/off?

Cheers,
Dave

I'm guessing that there's one ground on your light, and two leads which
are "low beam 1" and "low beam 2", where both "low"s to +12 is high
beam, right?

I'd do a 555 with your duty cycle, but upside-down, i.e., low for the
..1 second and high for 1.9. Put about a 4.7K pullup to +12V, and get
some P-channel power MOSFET; put its source to +12, its gate to the
output of the 555, and its drain to the section of the light that's
not always on.

Good Luck!
Rich

 

[[email protected]]

The source is currently a 12V SLA battery. Effectively equivalent to a
(really) small car battery. I may migrate to a NiMH battery pack, but
it's not in the near future due to cost.

The LED assembly is DOT approved and intended for use in automotive
applications, i.e. running off a 12V lead acid battery. When I first
tried plugging the light in, I used a spare battery that I'd estimate
was at 60%...and the light output was pretty damn bright. I don't have
access to the internals of the light (it's a sealed unit) but I expect
that the circuit regulates the input appropriately.

The assembly has three terminals: ground and two +12V lines (lo and
hi). Hi and Lo can be simultaneously connected to +12. So for
flashing operation, the lo line will be always connected and the hi
line will simply be pulsed at the required frequency/duration.

I will also be requiring the off, steady-low, and steady-high modes.
One of the reasons the pulsing needs to be done on the positive side of
the load.

Cheers,
Dave

 

[Rich Grise]

The source is currently a 12V SLA battery. Effectively equivalent to a
(really) small car battery. I may migrate to a NiMH battery pack, but
it's not in the near future due to cost.

The LED assembly is DOT approved and intended for use in automotive
applications, i.e. running off a 12V lead acid battery. When I first
tried plugging the light in, I used a spare battery that I'd estimate
was at 60%...and the light output was pretty damn bright. I don't have
access to the internals of the light (it's a sealed unit) but I expect
that the circuit regulates the input appropriately.

The assembly has three terminals: ground and two +12V lines (lo and
hi). Hi and Lo can be simultaneously connected to +12. So for
flashing operation, the lo line will be always connected and the hi
line will simply be pulsed at the required frequency/duration.

I will also be requiring the off, steady-low, and steady-high modes.
One of the reasons the pulsing needs to be done on the positive side of
the load.

I answered this for you about an hour ago. A 555 and a P-channel high-side
driver. With the new "steady on" requirement, a rotary switch.

Good Luck!
Rich

 

[Fred Bloggs]

The source is currently a 12V SLA battery. Effectively equivalent to a
(really) small car battery. I may migrate to a NiMH battery pack, but
it's not in the near future due to cost.

The LED assembly is DOT approved and intended for use in automotive
applications, i.e. running off a 12V lead acid battery. When I first
tried plugging the light in, I used a spare battery that I'd estimate
was at 60%...and the light output was pretty damn bright. I don't have
access to the internals of the light (it's a sealed unit) but I expect
that the circuit regulates the input appropriately.

The assembly has three terminals: ground and two +12V lines (lo and
hi). Hi and Lo can be simultaneously connected to +12. So for
flashing operation, the lo line will be always connected and the hi
line will simply be pulsed at the required frequency/duration.

I will also be requiring the off, steady-low, and steady-high modes.
One of the reasons the pulsing needs to be done on the positive side of
the load.

Cheers,
Dave

If you're concerned about size and durability, then a ready-made product
is the way to go. There are some suggestions here:
http://nordicgroup.us/s78/taillights.html which advocates the xenon
strobe as the best light to use.
These products give you the light source and electronics all in one. You
could make something from Radio Shack parts, but it would fairly big,
and run $20 or more before you're finished with it. Was that AA battery
powered job something like this CatEye TL-LD1000 from Agee's. They say
50 hours continuous so that at approximately 3000 mA-Hour capacity, and
the batteries probably in series for net 3V, the LED light draws about
60mA. It would be far simpler to make a small regulator to adapt this
product to a 12V system. That would be a LM317, series power resistor,
some filter caps, and small voltage setting resistors- all available
from Radio Shack. You can find out how to use the LM317 by going to
http://www.national.com and entering -LM317- in the part number search box.

 

[[email protected]]

I answered this for you about an hour ago. A 555 and a P-channel high-side
driver. With the new "steady on" requirement, a rotary switch.

Good Luck!
Rich

Rich,

Yes, you did answer my question, for which I am thankful (sorry if I
didn't acknowledge). I'll probably avoid the rotary switch and opt for
a dual micro switch...one to turn the light on (low), the other
on-off-on switch to control high/strobe/low modes. Perhaps the most
compelling reason is the size of the project box (actually just a spare
anti-static container from Maxim, which was smaller than any 'real'
project box I could find). Rotary switches aren't terribly common in
my area. I only found a couple locally, and neither was well suited to
the application.

BTW, the 3V LED I was using was indeed a Cateye LD1000. I was very
disappointed with the light output from this thing (especially at
$30+). Again, very bright from directly behind, but light output was
miserable once you move a few degrees either side (even with the
dedicated side-facing LEDs). I have a number of similar CatEye
products which seem to perform just as well, but only cost $8...so I'll
continue to use these as backup.

Referring to a post about reduced voltage levels, I hooked up a nearly
discharged battery, and only the central bank of LED's lit up in low
mode (while high mode managed to illuminate all of the LED's).

I have a prototype built, and will be field-testing shortly. Thanks
all!

 

[Rich Grise]

Rich,

Yes, you did answer my question, for which I am thankful (sorry if I
didn't acknowledge). I'll probably avoid the rotary switch and opt for
a dual micro switch...one to turn the light on (low), the other
on-off-on switch to control high/strobe/low modes. Perhaps the most
compelling reason is the size of the project box (actually just a spare
anti-static container from Maxim, which was smaller than any 'real'
project box I could find). Rotary switches aren't terribly common in
my area. I only found a couple locally, and neither was well suited to
the application.

Just on a lark, I did a google search on "DP3T slide switch" and got
a lot of hits - that could solve your space problem.
This was the first hit:
http://www.electronicsurplus.com/ccc2113-slide-switches.htm

Good Luck!
Rich

 

[ehsjr]

Rich,

Yes, you did answer my question, for which I am thankful (sorry if I
didn't acknowledge). I'll probably avoid the rotary switch and opt for
a dual micro switch...one to turn the light on (low), the other
on-off-on switch to control high/strobe/low modes. Perhaps the most
compelling reason is the size of the project box (actually just a spare
anti-static container from Maxim, which was smaller than any 'real'
project box I could find). Rotary switches aren't terribly common in
my area. I only found a couple locally, and neither was well suited to
the application.

BTW, the 3V LED I was using was indeed a Cateye LD1000. I was very
disappointed with the light output from this thing (especially at
$30+). Again, very bright from directly behind, but light output was
miserable once you move a few degrees either side (even with the
dedicated side-facing LEDs). I have a number of similar CatEye
products which seem to perform just as well, but only cost $8...so I'll
continue to use these as backup.

Referring to a post about reduced voltage levels, I hooked up a nearly
discharged battery, and only the central bank of LED's lit up in low
mode (while high mode managed to illuminate all of the LED's).

I have a prototype built, and will be field-testing shortly. Thanks
all!

Don't need a rotary switch - a double pole double throw
center off switch will do:

source ----------+-+---MOSFET---[LED]--- Gnd
| | |
o | o |
/ | \ |
555 pin 8 ---o | o---+
|
o-+ o
|
555 pin 3-----------+

Ed

 

[[email protected]]

Don't need a rotary switch - a double pole double throw
center off switch will do:

source ----------+-+---MOSFET---[LED]--- Gnd
| | |
o | o |
/ | \ |
555 pin 8 ---o | o---+
|
o-+ o
|
555 pin 3-----------+

Ed

Yup, I'm using a SPDT right now (on-off-on), which doesn't do
everything I want it to do(yet). Not sure about the ascii diagram, as
the characters aren't lines up correctly in my browser/usenet client
(google groups). Give me a couple of minutes to figure it out

Cheers,
Dave

 

[ehsjr]

Don't need a rotary switch - a double pole double throw
center off switch will do:

source ----------+-+---MOSFET---[LED]--- Gnd
| | |
o | o |
/ | \ |
555 pin 8 ---o | o---+
|
o-+ o
|
555 pin 3-----------+

Ed

Yup, I'm using a SPDT right now (on-off-on), which doesn't do
everything I want it to do(yet). Not sure about the ascii diagram, as
the characters aren't lines up correctly in my browser/usenet client
(google groups). Give me a couple of minutes to figure it out

Cheers,
Dave

One side of the DPDT connects the 555 to + (It's
the on/off for the 555). The other side connects the
mosfet gate to either V+ or to the 555 output pin, pin 3.
The focus was just showing the use of the switch -
it wasn't meant to be a detailed schematic. For example
not drawn, but assumed, is a resistance between pin 3
and the mosfet gate, say 330 ohm. And you can put a .05
across that reststor. The 555 ciruit is also assumed.

Ed