# [EVDL] Using a 4N25 to Isolate the input of the LM3914



## EVDL List (Jul 27, 2007)

I would think that if you found the flattest area of the curve, usually at
center voltages, and then limited the input voltage change to that area,
simple with resistors and then amplified the output up to where you need it
for the meter to read properly, you might get close to what you are looking
for.

Mark Grasser
Eliot, ME

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of [email protected]
Sent: Tuesday, May 27, 2008 1:13 PM
To: [email protected]
Subject: [EVDL] Using a 4N25 to Isolate the input of the LM3914

Does the fact that I will be using the LM3914 as an expanded scale
voltmeter, to measure 10 - 12 V make it possible to use the 4N25?

I seem to be able to get a 0.8Volt change in output of the 4N25 with a 2
volt change in input.? I believe I should be able to set the scale of the
LM3914 to respond to this.

Dave Delmam
electricDeLorean.com
evalbum.com/1482
_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev

_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

There are optos that are optimized for analog use, but with any opto you 
have to deal with degradation of the LED over time, temperature 
variations etc. I remember looking at one one time that had two 
detectors, one for signal and the other for compensation - but I don't 
recall the part #.

You might also look at :

http://www.allelectronics.com/make-a-store/item/VTL5C4/VACTROL-R-ANALOG-OPTOISOLATOR/1.html

Google the data sheet - looks pretty linear. Its a current to resistance 
device.

- SteveS




> Mark Grasser wrote:
> > I would think that if you found the flattest area of the curve, usually at
> > center voltages, and then limited the input voltage change to that area,
> > simple with resistors and then amplified the output up to where you need it
> ...


----------



## EVDL List (Jul 27, 2007)

> SteveS wrote:
> > There are optos that are optimized for analog use, but with any opto
> > you have to deal with degradation of the LED over time, temperature
> > variations etc. I remember looking at one one time that had two
> ...


----------



## EVDL List (Jul 27, 2007)

> [email protected] wrote:
> > Does the fact that I will be using the LM3914 as an expanded scale
> > voltmeter, to measure 10 - 12 V make it possible to use the 4N25?
> >
> ...


----------



## EVDL List (Jul 27, 2007)

You may want a series resistor for the opto LED. 


Cor van de Water
Systems Architect
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 542 5225 VoIP: +31 20 3987567 FWD# 25925
Fax: +1 408 731 3675 eFAX: +31-87-784-1130
Second Life: www.secondlife.com/?u=3b42cb3f4ae249319edb487991c30acb

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Lee Hart
Sent: Tuesday, May 27, 2008 7:04 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Using a 4N25 to Isolate the input of the LM3914



> SteveS wrote:
> > There are optos that are optimized for analog use, but with any opto
> > you have to deal with degradation of the LED over time, temperature
> > variations etc. I remember looking at one one time that had two
> ...


----------



## EVDL List (Jul 27, 2007)

> Cor van de Water wrote:
> > You may want a series resistor for the opto LED.
> > ______________________________
> > | | Q1 2N6027 |
> ...


----------

