Matthew, you wrote:-
>I ran into a small problem with a circuit and was hoping for some help.  I
>have an output from another device of which runs 1.1 volts on to 0 volts
>off.  I tried to run this into a regular npn 2222a and it would not source
>enough current to drive the transistor to the on state.  So I went to an
>n-channel mpf102 fet and had better success but still I can not turn that
>thing on all the way.  So I started thinking about a 741 op amp and played
>with that with success.  This is the problem.  I don't have room for a -
>supply on this board.  Does anyone have a way that I can get this output up
>to a good ttl level with a meg ohm input resistance or so?
>Thank you for any and all help.
>Matthew Ormsby
>Matt@epfsc.com
>http://www.cyberport.com/~mormsby

I have recently had to do this - convert a small voltage (referenced to 0v)
slowly varying signal to CMOS logic levels - and I used a cheap LM393N
comparator chip wired as a Schmitt trigger referenced to a non-symetrical
voltage, after spending lots of time looking at expensive CMOS Op-Amps.
Rig it with a 1Mohm feedback resistor to the +ve terminal and a 68K input
resistor to the +ve terminal across which you apply your input voltage.
The -ve terminal is connected to the wiper of a 100K potentiometer which is
wired between the +ve (5v) and -ve (0v) supplies. Adjust the lower
transition point to about 0.2v by twiddling the pot and the upper transition
point should fall in to place at about 0.8v. If not, change the 68K resistor
to give you the differential you need.
The LM393N is a dual device (I guess it is available as a single 8 pin chip
device as well) and each amplifier only uses 500 micro amps supply current
at 5 volts.
Breadboard it to see if it suits you application.

All the best.

Dave.