Hello gang,

I'm new to microcontrollers and new to electronic circuit design. I've
read up on how a transistor works and I think I get the theory but they
don't function as expected when tested.

I have a PIC that outputs to an LCD which works great.  I also need to
share 4/8 of the LCD data lines as an input to another microcontroller.
I need a method of keeping data not destined for the 2nd microcontroller
away from it while addressing the LCD.  I thought I could put some
2n2222's in line with my 4 shared data lines.  When I need send data to
the other microcontroller, I would bring the base of on my 4 transistors
high, send the data, and bring it back low. 

When testing my transistors with 5v applied to the base, I get the same
voltage from the collector and emitter. The collector and emitter are
not tied in with anything so I would expected nothing from the collector
or the emitter.   

I also applied 5v to the collector and an LED w/resistor to the emitter.
When I apply 5v to the base the LED turns on, if remove 5v from the
collector, the LED stays on because of the 5v applied to the base 

Should it work this way ?

Sorry for the long post, thanks.

Best Regards,
Steve Maroney

Business Computer Support, LLC
Mobile Phone:504-914-4704
Office Phone: 504-904-0266
Fax: 866-871-7797



-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
Of Terry Harris
Sent: Monday, June 22, 2009 6:32 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Resistance calculator

On Mon, 22 Jun 2009 22:23:58 +1200, Russell McMahon wrote:

>Target R = (Target x existing) / (Target - existing)
>
>        RB = (RA x RC) / (RC - RA)
>
>This simple formula is immensely useful when prototyping
>
>eg 87k is required.
>Assume only E12 values at 1% are available.
>
>RA = 100K
>RC=  87K
>
>RB = (100 x 87) / (100 - 87) = 8700/13 = 669k
>680k will probably suffice.

But how or why did you choose 100k for RA? 

It happens to be right for 87k and E12s but isn't for say 83k and E12s
or
87k and E24s.

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