impulse generator circuit design

[Robert Baer]

I don't think a 555 or PIC is going to do me any good.

What I want is to be able to take a relatively small constant current
(i.e., from a battery) and generate large amplitude/short duration
current pulses. That is to say I want to build up some energy for a
period of time, release it all in a burst, and repeat that process ad
infinitum.

The 555 does all of the timing you need, and the output can deliver
(current) pulses as you (not so accurately) describe; the current
available is specified on the data sheet; the output is a voltage and
can be converted to a (reasoable) current via a (erasonable value)
resistor in series to the unspecified load.
Instead of dealing withvague generalities concerning the requirement,
be eXplicit and state what you really need to drive (LED? inductor?
relay? spitzensparken?) as well as eXplicit parameters (2uSec pulse
every millisecond? 100nSec pulse at 300 per millisecond? fratzensprats
on the bumblelator?).

 

[Tom Bruhns]

I don't think a 555 or PIC is going to do me any good.

What I want is to be able to take a relatively small constant current
(i.e., from a battery) and generate large amplitude/short duration
current pulses. That is to say I want to build up some energy for a
period of time, release it all in a burst, and repeat that process ad
infinitum.

But as R. Baer wrote, inquiring minds would like to know...just what
sort of load are you wanting to put these pulses through, and what
amplitude current versus time are you wanting to achieve?

For example: you could want to pulse the current in an LED to a
hundred milliamps and a very few volts for a millisecond, or you could
want to pulse the current in an EG&G high speed flash lamp at ten amps
for a microsecond. Or you could want something completely different.
I believe you mentioned an inductive load in another posting. Note
that V = L di/dt: that is, if the inductance starts with zero current,
it may take some time to reach the peak current you want. Adding in
the inevitable resistance of the wire in the inductive coil just slows
things down further. This is the sort of thing that should be
designed, not just guessed at, to achieve early success.

Cheers,
Tom

 

[[email protected]]

But as R. Baer wrote, inquiring minds would like to know...just what
sort of load are you wanting to put these pulses through, and what
amplitude current versus time are you wanting to achieve?

I guess I would be good if I actually explained what I was trying to
do.

At the very basic level what I want is sort of compact electric motor
that gives me oscillatory linear motion and can run on a small bank of
batteries for about an hour. What I need is about 3mm of travel, a
frequency of that is tunable from about 50-200 Hz (just about any
waveform will do), and "decent" force. I can't tell you how much force
I need yet because I don't know for sure, but to give you a qualitative
description I would say that the force needs to be enough that you
couldn't stop the machine with your hand and maybe if you put a pin on
the end of the oscillating shaft then the force should probably be
enough to repeated puncture heavy card stock paper. I don't know if
that's a useful description or not. Sorry I don't have more specific
information, but I'm just starting this project and I'm trying to
assess my options before I go about trying to put anything together.


The simplest idea would just be to use a DC motor and convert the
rotary motion to linear motion with a cam or whatever. I still wanted
to look at other options, so I started to think about linear motors and
also just using an electromagnet to vibrate a spring loaded shaft (i.e.
by repeatedly pushing it away). I don't know anything about linear
motors and not a whole lot about electromagnets either, but given that
I want the battery pack to be both small (a 2 or 3 cubic inches max)
and last for a long time (and note be too expensive) I'm guessing I
wouldn't have a lot of current to work with. So anyways, I was trying
to think about ways to maximize the force I got out of that setup.

Quite possibly I don't know what the heck I am talking about. I'm just
brainstorming here. If you have any ideas I'd love to hear them, but
at this point I don't have anymore information to give you.

 

[Jan Panteltje]

On a sunny day (22 Nov 2006 17:55:00 -0800) it happened
[email protected] wrote in

I guess I would be good if I actually explained what I was trying to
do.

At the very basic level what I want is sort of compact electric motor
that gives me oscillatory linear motion and can run on a small bank of
batteries for about an hour. What I need is about 3mm of travel, a
frequency of that is tunable from about 50-200 Hz (just about any
waveform will do)

Stepper motor?
Get one from an old floppy drive perhaps.

 

[joseph2k]

On a sunny day (22 Nov 2006 17:55:00 -0800) it happened
[email protected] wrote in

Stepper motor?
Get one from an old floppy drive perhaps.

How about (fast) RC servos or an eccentric on an RC drive motor (with ESC,
either class)? Or maybe salvage something from an old teletype.

 

[Rich Grise]

How about (fast) RC servos or an eccentric on an RC drive motor (with ESC,
either class)? Or maybe salvage something from an old teletype.

Did any of you guys see what the OP said about force? At first, I was
thinking a big voice coil from a salvaged subwoofer, but he said it pushes
hard enough that you can't push it back with hand pressure, didn't he?

For that kind of force, I'd think I'd start looking at motor/cam
arrangements, or washing machine solenoids.

Thanks,
Rich

 

[Jan Panteltje]

Did any of you guys see what the OP said about force? At first, I was
thinking a big voice coil from a salvaged subwoofer, but he said it pushes
hard enough that you can't push it back with hand pressure, didn't he?

For that kind of force, I'd think I'd start looking at motor/cam
arrangements, or washing machine solenoids.

if you open the floppy drive you will see the head move from track to
track.
I uses a worm drive in my floppy, no way can you stop it.
So the mechanism is already there.
I estimate 80 tracks in about 3 cm, so 3 mm = 8 tracks = 8 step pulses.
The max speed is limited.... a different worm with a different stepper,
or even perhaps more power in the flop stepper could help.
Steppers are great, I have seen these move big camera setups in movie industry.
To a fraction of a millimeter