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kendeb
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Current Amplifications

02/07/2008 8:04 AM

Does anyone make an amplifier that can take a variable current input and output an amplified current signal? I need to deal with a mA input that is below the sesning range of my cnnected device.

Any help would be apprciated
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leveles
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#1

Re: Current Amplifications

02/07/2008 11:26 AM

The principal answer is that a "transimpedance amplifier" can do that exactly. Look up Wikipedia about it, there is a lot to learn about, how it goes about generating a virtual ground at the input of the opamp. If you are not fussy, you can use any chip with a current mirror input (like LM2900 or 3900 a cheap older design). There your current "sees" only a diode. The output is a voltage in all cases, so you take a resistor and convert it into current, if you like.

But, That is just the beginnig. Any other circumstance unique to your situation can come back and bite you in the rear, if neglected.

Is the current about ground potential or not? Current sensing at voltage and feedback is a separate subject in power supplies.

What is the impedance of the current source?

Is the current bipolar or unipolar?

Do you need rectification at the end?

What are your bandwith / signal slope requirements?

How much and what kind of noise burden is on the signal?

You sure, you need current input on you sensing device (it is unusual)?

If I would be doing a simple setup (and if it is possible) I would prefer to convert the input current via a resistor into voltage, amplify suitably, convert it back into current via a resistor (if that is really needed).
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user-deleted-1105
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#2

Re: Current Amplifications

02/07/2008 1:42 PM

A couple of resistors and a transistor would do it nicely.... sensing resistor and emitter follower. Assuming you can live with the 0.7volt drop.

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Electroman
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#3
In reply to #2

Re: Current Amplifications

02/07/2008 2:12 PM

Hey Del.... I reckon I've at last found a use for my graphics tablet!!!

Seeing your sketch I reckon I could easily sketch that into 'Paint' or something and upload as a jpg file?? maybe?

John.

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user-deleted-1105
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#4
In reply to #3

Re: Current Amplifications

02/07/2008 3:04 PM

Yeh, I did it on my graphics tablet..really rough...didn't want to show off .

I'm assuming his current sig doesn't go negative or to zero...he prob wants something off the shelf..but I just love seeing what can be done with minimum components.

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Electroman
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#5
In reply to #4

Re: Current Amplifications

02/07/2008 3:44 PM

hEHEHEHEHEHE .... yep I've had mine for over 6 years now and it cost a fortune... a Wacom A5 size.... you can draw what you want and put it under a flap so you just follow the drawing.... well suppoedly... I always get lost....

Now where did I leave my Paint program..... can't find it in the menus.... Hmmmmm

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JohnDG
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#7
In reply to #4

Re: Current Amplifications

02/07/2008 7:55 PM

At last! I can now begin my collection of Unsigned Del Originals - I'll soon have the entire Art World by the short'n'curlies, clamouring at my door, begging for postcard-sized replicas.

(I'll cut you in, if you insist).

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user-deleted-1105
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#8
In reply to #7

Re: Current Amplifications

02/08/2008 3:10 AM

I had a little play with that freebie art software 'Gimp' (graphics Image Manipulation Pachage) even at low res (640x480) I managed this, as it gives you subtle variations of intensity. It also converst various graphics file types, so is V handy. I couldn't get to grips with 'layers' but it works well with the pressure sensitive pen.

This is the latest KrisDelTM virtual car... it's powered by a picture of a free energy PM motor. It has a picture of a stick of batteries in the boot as a backup, these are charged from a wind turbine which pops up when you hit cruising speed .

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JohnDG
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#9
In reply to #8

Re: Current Amplifications

02/08/2008 3:40 AM

ROFLMAO!

Impressive, tho'. Did the Gimp come with the pad?

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user-deleted-1105
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#10
In reply to #9

Re: Current Amplifications

02/08/2008 3:48 AM

No, but it's a freebie, I ran this thread asking for graphics software ideas... post #7 points to it.

Del

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kendeb
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#6
In reply to #2

Re: Current Amplifications

02/07/2008 4:07 PM

Thanks for the help I was able to find a device to do the job.
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MUKULMAHANT
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#11
In reply to #2

Re: Current Amplifications

02/08/2008 5:08 AM

<Assuming you can live with the 0.7volt drop.:>

If he has a " Current Source" (with implied high source impedance) then Del's 2 resistors are also redundant. 0.7V( maybe 0.6,0.55) forward drop is o.k

The amplified current flows from the battery thru' the customers' impedance+Collector.

Find out hfe first and zero shift will be needed.

I am now looking back to 1958. Should be OK even today .
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#12
In reply to #11

Re: Current Amplifications

02/08/2008 7:37 AM

I see you are reducing it to one component. I shall have to see if I can reduce that further

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vermin
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#13
In reply to #2

Re: Current Amplifications

02/10/2008 6:07 AM

Hey! It looks like you have th same box of crayons as mine!!! Wanna come over and color?

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user-deleted-1105
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#17
In reply to #13

Re: Current Amplifications

02/10/2008 4:01 PM

Yup, if we can have beer too.

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vermin
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#21
In reply to #17

Re: Current Amplifications

02/10/2008 11:58 PM

No problem! I was just soaking in the beer tub!

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JonRR
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#14

Re: Current Amplifications

02/10/2008 12:37 PM

Kendeb:

Easy answer -- Call AGM in Tuson Az. They can do 0-5,1-5,0-20,4-20,0-50,10-50 mA

input and 0-5,1-5A,and any of the above input values for out put off the shelf !

Boy do you guys like to avoid the question or what? Politicians or bloggers???

Jon
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JohnDG
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#15
In reply to #14

Re: Current Amplifications

02/10/2008 3:26 PM

JonRR, you said:

"Boy do you guys like to avoid the question or what? Politicians or bloggers???" (my emphasis).

To whom are you addressing this question?

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indel
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#16
In reply to #15

Re: Current Amplifications

02/10/2008 3:39 PM

Last time that I have witnessed a situation like that was with Robert De Niro asking:

Are you talking to ME?

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user-deleted-1105
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#18
In reply to #14

Re: Current Amplifications

02/10/2008 4:09 PM

Well if you want to be pedantic ...I don't think your answers addresses the question of the ..
SESNING range...
Politicians, bloggers and smartarses

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JonRR
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#19
In reply to #18

Re: Current Amplifications

02/10/2008 6:24 PM

Hey Del:

You just had to stay cnnected,am I sesning a need to inject something here?

At whom wast thou aiming ? the post asked a direct question for a manufacture of a device that........ for my part thank god for spell check!
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#20
In reply to #19

Re: Current Amplifications

02/10/2008 6:26 PM
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vermin
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#22
In reply to #18

Re: Current Amplifications

02/11/2008 12:12 AM

Main Entry: smart•ar•ses
Pronunciation: Get off your lazy ass, and look it up!
Function: noun

A debilitating disease characterized by the brain
losing adhesion with the inner lining of the
skull. The malady progresses as the brain is
squired by the top of the spinal column.
From there, the brain proceeds to slide down
the spine until it comes to rest and establishes
a new location in the pelvic region, somewhere
near the rectum and anus.

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Users who posted comments:

Electroman (2); indel (1); JohnDG (3); JonRR (2); kendeb (1); leveles (1); MUKULMAHANT (1); user-deleted-1105 (8); vermin (3)

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