Using piezoelectric to power a laser diode?

[bobrich@gmail.com]

Hi,

I'm a complete novice/noob to electronics.

I have a little project i'm working on, and would like to use a
piezoelectric power source to run a small visible laser diode for a
short duration (20-200ms). Does this seem feasible? The biggest
problem, from what i can tell, is the output voltage of the piezo is
likely to be much greater than the 2-3V i need to run the diode. The
other problem i'm having is actually finding suppliers of piezo devices
that would be suitable for this...all i can find are accelerometers and
strain gauges.

Any thoughts? The energy source will be a sharp blow from a small
spring-loaded lever.

Thanks!

 

[Phil Allison]

I'm a complete novice/noob to electronics.

I have a little project i'm working on, and would like to use a
piezoelectric power source to run a small visible laser diode for a
short duration (20-200ms). Does this seem feasible? The biggest
problem, from what i can tell, is the output voltage of the piezo is
likely to be much greater than the 2-3V i need to run the diode. The
other problem i'm having is actually finding suppliers of piezo devices
that would be suitable for this...all i can find are accelerometers and
strain gauges.

Any thoughts? The energy source will be a sharp blow from a small
spring-loaded lever.

** The laser diode is attached to a mouse trap - right ?

When the mouse sets it off - the mouse gets a blast of laser light in the
eye.

You will soon get yourself 3 blind mice.

Nice one - boob.




............ Phil

 

[Pooh Bear]

Hi,

I'm a complete novice/noob to electronics.

I have a little project i'm working on, and would like to use a
piezoelectric power source to run a small visible laser diode for a
short duration (20-200ms). Does this seem feasible? The biggest
problem, from what i can tell, is the output voltage of the piezo is
likely to be much greater than the 2-3V i need to run the diode. The
other problem i'm having is actually finding suppliers of piezo devices
that would be suitable for this...all i can find are accelerometers and
strain gauges.

Any thoughts? The energy source will be a sharp blow from a small
spring-loaded lever.

And for how long do you expect a sharp blow from a hammer to illuminate
this led ?

Graham

 

[John Fields]

Hi,

I'm a complete novice/noob to electronics.

I have a little project i'm working on, and would like to use a
piezoelectric power source to run a small visible laser diode for a
short duration (20-200ms). Does this seem feasible? The biggest
problem, from what i can tell, is the output voltage of the piezo is
likely to be much greater than the 2-3V i need to run the diode. The
other problem i'm having is actually finding suppliers of piezo devices
that would be suitable for this...all i can find are accelerometers and
strain gauges.

Any thoughts? The energy source will be a sharp blow from a small
spring-loaded lever.

---
That won't work.

Try this:

Vcc Vcc
| |
[10K] [100K] +-------+
| | |__ |
+------[0.1µF]--+------|--O|TR OUT|O---[R]--+
|- |A | | | |A
[PIEZO] [1N4148] +---|TH | [LASER]
|+ | | |_ | |
GND GND +--O|D | GND
| +-------+
[1.5µF] 555
|
GND

1.5µF will get you a 200ms pulse out of the laser and 0.15µF will
get you 20ms.

Or this:

+-----+
+------|~ +|----+-----+
| | | |+ |A
[PIEZO] | | [C] [LASER]
| | | | |
+------|~ -|----+-----+
+-----+
FWB

You'll have to determine the value of C experimentally. Start with
something like 10µF and work down until the laser flashes.

It worked for me with a plain old red LED and the piezo element from
a barbecue lighter, which you might be able to adapt for your use.

 

[John Fields]

Hi,

I'm a complete novice/noob to electronics.

I have a little project i'm working on, and would like to use a
piezoelectric power source to run a small visible laser diode for a
short duration (20-200ms). Does this seem feasible? The biggest
problem, from what i can tell, is the output voltage of the piezo is
likely to be much greater than the 2-3V i need to run the diode. The
other problem i'm having is actually finding suppliers of piezo devices
that would be suitable for this...all i can find are accelerometers and
strain gauges.

Any thoughts? The energy source will be a sharp blow from a small
spring-loaded lever.

---
That won't work.

Try this:

Vcc Vcc
| |
[10K] [100K] +-------+
| | |__ |
+------[0.1µF]--+------|--O|TR OUT|O---[R]--+
|- |A | | | |A
[PIEZO] [1N4148] +---|TH | [LASER]
|+ | | |_ | |
GND GND +--O|D | GND
| +-------+
[1.5µF] 555
|
GND

---
Oops...

The 1N4148 _cathode_ should be connectedto the 10k resistor:


Vcc Vcc
| |
[10K] [100K] +-------+
| | |__ |
+------[0.1µF]--+------|--O|TR OUT|O---[R]--+
|- |K | | | |A
[PIEZO] [1N4148] +---|TH | [LASER]
|+ | | |_ | |
GND GND +--O|D | GND
| +-------+
[1.5µF] 555
|
GND

 

[bobrich@gmail.com]

John,

All i can say is holy cow! I didn't expect schematics!!! I'll have to
give that a try!

The illumination just has to be long enough for the human eye to detect
it, which i'm assuming is going to be a function of brightness, but at
5mW i'm assuming 20-50ms is plenty..(my 200 upper end range is on the
long side)...lots of assuming though, eh?

I do like the mousetrap idea, though... If you can't smash em, blind
em.

Thanks again!!!!

 

[Walter Harley]

John,

All i can say is holy cow! I didn't expect schematics!!! I'll have to
give that a try!

The illumination just has to be long enough for the human eye to detect
it, which i'm assuming is going to be a function of brightness, but at
5mW i'm assuming 20-50ms is plenty..(my 200 upper end range is on the
long side)...lots of assuming though, eh?

You're aiming a 5mW laser at a human eye?

 

[Stef Mientki]

John,

All i can say is holy cow! I didn't expect schematics!!! I'll have to
give that a try!

The illumination just has to be long enough for the human eye to detect
it, which i'm assuming is going to be a function of brightness, but at
5mW i'm assuming 20-50ms is plenty..(my 200 upper end range is on the
long side)...lots of assuming though, eh?

You can easily see a 1 usec puls from a normal (high efficiency) white
LED, at 100 mA.
Stef

 

[bobrich@gmail.com]

You're aiming a 5mW laser at a human eye?

Nooooooooo. I thought i fixed that part of my post...sorry. I'm just
basically building a laser pointer for a little personal project. The
piezo power idea came from the desire to make it as compact as
possible, with the longest shelf life i can muster. In addition, the
chassis that this is mounted in will be moving kind of vigorously, so i
want to capture, in essence, a 'flash' that a person can see through
persistence of vision...rather than a continuous beam which would
rapidly become ambigous due to aforementioned motion.

The laser will, under almost any conceivable circumstance, be aimed at
a wall or 'calibrated' paper area so we can see how much the chassis
has deflected.

The application would be analagous to setting a similar device in the
head of a golf club. The laser is parallel with the club face, and
'flashes' upon impact with the ball. The position of the flash
relative to the alignment of the tee with the player will detect how
much slice or hook is in the swing.

Bad example, but it gives you an idea of what i'm trying to achieve.

You can easily see a 1 usec puls from a normal (high efficiency) white
LED, at 100 mA.
Stef

That's good info, thank you. I wasn't sure how much of a duration i
would need for it to be effective. I'm assuming the laser diode would
essentially have the same characteristics...the shorter the pulse, the
better.

John, if you're still hanging around...one quick question regarding the
schematics you wrote up. In the onces with Vcc, is that an external
power supply, and the piezo is just used to switch?



Thanks everyone for your replies!!!

 

[John Fields]

John, if you're still hanging around...one quick question regarding the
schematics you wrote up. In the onces with Vcc, is that an external
power supply, and the piezo is just used to switch?

---
Yes. Taking a look at it and adding the power and ground pins for
the chip _and_ fixing an error:

Vcc Vcc Vcc Vcc
| |K | |
[10K] [1N4148] [100K] +-------+
| | Rt| |__ |
+--[0.1µF]--+------+-------|---O|TR OUT|O---[R]--+
|- |K | | | |A
[PIEZO] [1N4148] +----|TH | [LASER]
|+ | | |_ | |
GND GND +---O|D | GND
Ct| +-------+
[1.5µF] | 555
| |
GND GND

Here's what happens:

When you whack the piezo a high voltage pulse will be generated
which would kill the chip, the 1N4148 diodes are in there to clamp
the positive peak of the piezo voltage to roughly Vcc + 0.7V and the
negative peak to about -0.7V.

The side (end?) of the piezo which generates the initial low-going
pulse (which is what the 555 wants to see) is connected to the 555's
TRIGGER- input, which will drive its output high for the time
determined by:


t = 1.5RtCt

In this case,

t = 1.5 * 0.1E-6R * 1.5E-6F = 0.225 seconds

which about what you asked for for long pulse. You can easily make
the pulse narrower by decreasing the capacitance of Ct or the
resistance of Rt, but I'd leave Rt alone and go for a smaller
capacitor.

One caveat about the input pulse is that it needs to be narrower
than the output pulse, (a 555 peculiarity) or the output pulse will
be as wide as the input pulse, which may be wider than you want. If
that happens, a possible solution would be to load down the piezo
with a resistor wired across it, or to diddle with the value of the
10k resistor and/or the value of the 0.1µF cap. Either way, the
value would have to be determined experimentally, and if that got to
be too tricky, then you could use a different one-shot and not have
to worry about it. Something like an HC123 or an HC4538 would work,
but you'd probably have to add a transistor to drive the laser
diode.

If you're looking for a nice, sharp, short pulse, then I recommend
that you _don't_ use the bridge-cap scheme since it'll smear the
pulse and you wont have nice edges.

 

[bobrich@gmail.com]

Thank you for the explanation! I'm learning stuff every day!

I guess the only issue is that i'm trying to use the output from the
piezo to directly power the laser, so i don't need an external power
source...kind of like the FBR + C(ap?) diagram you had at the bottom of
your previous email. I think i'm going to order up some parts for
both...if the cap+bridge is too sloppy, i'll go with the other. I'm
sure a few watch batteries would power the diode for years given the
usage i'm going for.

Thanks again for all of your help!!! I've been surfing forums for the
last few years, and forgot just how great USENET still is.

Take care!!

Bob