please help

A

admin2far

New Member

• Jun 26, 2007

• #1

Hi

I am looking for a component/sensor that will responed to changes
in small currents.
should be something that grow or shrink depend the current.
the problem size need to be no more then 1 sqr cm (width and length)
the best i can think of is Solenoid but they are big (and not good).
any idea?

Thank you

ronnie

 

Papabravo

Well-Known Member

Most Helpful Member

• Jun 26, 2007

• #2

How small a current are we talking? How small are the changes? I would never have thought of using a solenoid; do you know some new physics that I missed while getting my graduate degree? What's wrong with a resistor and an opamp?

 

B

Blatman Bond

New Member

• Jun 27, 2007

• #3

Please describe the signal being measured

AC or DC, etc. What you used for?

 

Last edited: Jun 27, 2007

A

admin2far

New Member

• Jun 27, 2007

• #4

using d.c.

simple circuit with LDR and this "sensor" that will "grow" or shrink depend the current.

thank you

ronnie

 

Last edited: Jun 27, 2007

Papabravo

Well-Known Member

Most Helpful Member

• Jun 28, 2007

• #5

I haven't the slightest idea what you are talking about. When you say "grow" and "shrink", do you mean the physical dimensions of the snesor will change. If that is what you meant then what evidence do you have for the existance of such a thing?

Also, I asked you for the magnitude of the currents, and the magnitude of the current changes. You flipped off a one sentence reply that meant nothing to me. Either answer the question or solve your own problems.

 

B

Blatman Bond

New Member

• Jun 28, 2007

• #6

I'm still don't understand what it's grow and shrink used for.
If you mean "grow" like any VU-meter (solenoid based), or any stronger solenoid, you can drive it with transistor or op-amp that represent the measured current.

 

B

Blatman Bond

New Member

• Jun 28, 2007

• #7

VU-meter need small current to move.

 

A

admin2far

New Member

• Jun 28, 2007

• #8

it's something for a blind person,I want him to feel (he can't see).
must be small size for portablility.

 

Leftyretro

New Member

• Jun 28, 2007

• #9

Well you application is not real clear but possibly Nitinol wire, sometime called 'memory wire' might be useful to you. This is a special alloy that changes it's length due to the heat generated by the current passing through it. I saw it used to drive chart pins across moving chart paper in process control equipment made by Foxboro co. It was very linear and would hold calibration well. The wire did have to be pretensioned to a certain value but did have decent force. You might be able to find some of this material used on E-bay but here is a vendor I found selling this material.




Lefty

 

H

Hank Fletcher

New Member

• Jun 28, 2007

• #10

Sounds like he's trying to make some sort of portable Braille display? Cool project, and I think he was right the first time - look for some very small solenoids. They shouldn't need much power as they wouldn't have to extend/retract far, so portability seems like it might be possible. I guess how many dots (characters? Sorry, I don't know much about Braille) would be a factor, so you might want to share that with us.

I know things like this exist, at least for English blind people. There was a woman I went to university with who carried around a machine that was the same kind of thing - an electronic notepad that she coud type and feel the playback of. Try to search for some videos on the 'net of something along those lines, and you can learn from what they did.

 

M

mneary

New Member

• Jun 28, 2007

• #11

You could also look into pager motors; some of them are just over 1 cm long. Remove the vibrator weight and replace it with something he can get more information from.

 

B

Blatman Bond

New Member

• Jun 29, 2007

• #12

Might be help.

Piezo crystal shrink and grow by electric field, but too short. Might be solenoid is your best option. What about small speaker. Just detach their cone (leave their spring) and drive it with voltage. Measure the current with resistor and buffer it with small amplifier to drive it.

 

A

admin2far

New Member

• Jun 29, 2007

• #13

Hi
First thank you all for the ideas,
i have pager motors and yes they are small but spin,changing spin to push pull
too complicate the project.
Nitinol wire sounds good but i know they are not cheap,
I check for very small solenoids they also not cheap.
maybe i create a very small electromagnet...

thank you