inverting signals
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Hi there.
I have a circuit that sends out a digital signal, and I need to
invert it. I need to turn the "on" state into the "off" and vice
versa. Is there such a thing as a normally off transistor or mosfet?
Sorry if this is a cryptic or dumb question.
Any advice gratefully accepted.
Mark Allen
I have a circuit that sends out a digital signal, and I need to
invert it. I need to turn the "on" state into the "off" and vice
versa. Is there such a thing as a normally off transistor or mosfet?
Sorry if this is a cryptic or dumb question.
Any advice gratefully accepted.
Mark Allen
Comments
There exist "depletion mode" instead of the normal "enhancement mode"
mosfets. You could also use a logic gate, and/or an op-amp connected in an
inverting fashion. Also, a BJT NPN transistor would also do the trick as
the collector is high when the base is low and vice-versa.
David Fixemer
Engineering Manager
Production Technology, L.L.C.
4701 Innovation Drive, Suite CB105
Lincoln, NE 68521
402-472-8239
> Hi there.
>
> I have a circuit that sends out a digital signal, and
I need to
> invert it. I need to turn the "on" state into the
"off" and vice
> versa. Is there such a thing as a normally off
transistor or mosfet?
>
> Sorry if this is a cryptic or dumb question.
>
> Any advice gratefully accepted.
>
> Mark Allen
>
Yes, there are such things. They are called inverters,
and usually come six to a package. Thus they are called
hex inverters.
Some examples are 7404 in the TTL series, or the 4049
in the CMOS series.
Bob
nienhuis@w...
signal because the MAX232 inverts it also. I had hooked up a 2N2222
transistor and an LED to monitor the data from the output of the radio
module, so I pulled moved my data line to the collector of the transistor
rather than the radio module. Viola -- inverted signal. You could also do
this with a gate, but since I already had this done, I used it.
Original Message
> I have a circuit that sends out a digital signal, and I need to
> invert it. I need to turn the "on" state into the "off" and vice
> versa. Is there such a thing as a normally off transistor or mosfet?
> Hi there.
>
> I have a circuit that sends out a digital signal, and I need to
> invert it. I need to turn the "on" state into the "off" and vice
> versa. Is there such a thing as a normally off transistor or mosfet?
>
> Sorry if this is a cryptic or dumb question.
>
> Any advice gratefully accepted.
>
> Mark Allen
A simple NPN transistor (or mosfet) provides inversion very
naturally. Hook the collector (or drain) to +V (5 volts or whatever)
via a resistor (try 2K or so), connect the emitter (or source) to
ground. Connect your signal to the base (or gate) via another
resistor (larger, maybe 10K or more). Take the output from the
collector (drain). When the input signal goes high, the output goes
low, and vice versa. The ground of this circuit and the one providing
the signal must be connected together. The specific values depend on
the transistor chosen, so you have to experiment a little to see what
works.
This is a simple inverter that costs maybe 20 cents. No ICs required
unless you want to do 8 of them at a time.
If you have a computer in the middle of this somewhere (Stamp or
otherwise), keep in mind that you can just do this in software - no
hardware is needed at all.