Trying to manipulate voltage

[michael91]

does anyone know of a transistor that will switch on and off in milliseconds that has up to three branches of operation,with max voltage of operation of about a volt? my goal is to add millivolts to a refference voltage being fed to a microproccessor.it must complete the cycle in milliseconds.thanks,michael

 

[duke37]

Please give a block diagram of what you want.
Transistors will switch in less than a millisecond so no problem there.
A transistor can only switch one signal so you will need three switches.
A silicon npn transistor will not be able to switch less than 0.2V so switching millivolts is not on. Mosfets can do better.
The cmos 4066 contains four switches which may do your job.
Could the microprocessor do the job with a suitable program?

 

[michael91]

i have to keep in mind you mayor may not understand what i am try to achieve.i am trying to add a device to a circuit that is ever changing in its voltage reference.i will attempt to draw a mental picture to give you the full scope dont worry as im sure you will see it....picture an ac signal and down the middle you have a straight line.that line is the desired value.(voltage)the top of the signal is one volt the bottom is 0.as the engine runs (each cylinder fires)the sensor retrieves a reading converts it to voltage and feeds that reading to the microprocessor.my goal is to manipulate that reading.0 to .5 v means deliver more fuel,.5 to 1v means less fuel.(to the computer)witch delivers the fuel accordingly.as i said the reading is ever changing.a simple resistor would bring down the value but that would be read as lean(more fuel needed) and i am attempting to reduce fuel consumption by making the microprocessor see less fuel needed with that small scope of voltage.5 to 1 volt.so in realitiy not add resistance but add millivolts to that circuit as easily and cost efective as possible

 

[BobK]

If I undertand you correctly, you want to take a signal that is an AC signal varying in amplitude from 0 to 1V and add some fraction of a volt to it so that a device monitoring it thinks it is above 0.5V when it is acually at a somewhat lower level.

Is that what you want?


Bob

 

[Resqueline]

In other words: you want to modify the (high impedance) varying (500mV) output from an exhaust oxygen sensor to fool the Engine Control Unit into delivering less fuel.

 

[michael91]

you dog you got me!yes yes yes! any ideas?

 

[michael91]

you are 100% correct! and quik i must say! have you worked on this or attemted any such thing and any ideas?

 

[duke37]

Plot a graph of output voltage required versus input voltage.

 

[BobK]

Hmm. Sounds like a good way to make an engine run badly. But if you really want to do this look up op amp summing circuit. Feed the signal into one input and a fixed voltage into the other.

Bob

 

[michael91]

thanx bob im on it!