View Full Version : Limiting voltage sent
07-29-2006, 02:24 AM
I have a basic stamp, a digital potentiometer, a 4.5v zener diode, and a regular potentiometer. I am looking to make a circuit that connects to a sensor but I want the voltage to be limited. For example my sensor sends out a signal 0v-5v and I want it to be limited between 4.5v and 4.2v depending on another sensor. I know a zener diode in line as a reverse bias will limit it to 4.5v but I am confused on how to get it down or up more and I do not want to interfere with anything below the voltage I clamp it at. If the sensor sends 1v I want that to stay 1v and if it goes to 2v then 2v but if it goes to say 4.6v I want it to only send 4.2 on the line. I wanted it to be digitally controlled but I have the regular potentiometer to use to watch the voltage before I write all the code and wire in the basic stamp and digital pot.
07-29-2006, 03:02 AM
If we're not limited in this analog contest, to the components that you have on hand, all you need is a 2-channel ADC (analog to digital converter) and you're all set. Let the Stamp make the decisions after that.
(Now I'll watch the analog gurus tear their hair out) http://forums.parallax.com/images/smilies/smile.gif
07-29-2006, 03:26 AM
Are there any examples of this in like the Basic Analog and Digital book or nuts and volts?
Edit: Also do you have any example chips to do something like this? As the voltage change is extremely quick, speed is a concern.
Post Edited (goldfingerfif) : 7/28/2006 7:44:04 PM GMT
07-29-2006, 04:26 AM
Ok after reading the BAAD I think you mean 2-channel as in 1 channel watches the voltage before the digital pot and then 1 after the digital pot and the Stamp will lower or raise the resistance accordingly. If this is what is meant the only concern to me is speed. The sensor that reads 0-5v is a car airflow sensor and well it will be used to lean the car out for increased horsepower so it will be hiding some of the air from the computer.
07-29-2006, 04:40 AM
Aha! Now we have the application. This is why it's better to lay your cards on the table at the onset.
There are high-speed ADC chips, but I can't honestly answer whether they will be ... fast enough or not. I'm just not that familiar with this type of automotive application - sorry.
08-02-2006, 03:07 AM
Is a resistor a good way to lower voltage? My current design is a stamp, digital pot, and a to d converter that raises resistance as voltage raises past the "clamp" mark and then lowers resistance if voltage drops.
08-03-2006, 12:46 PM
I don't think that you will increase hp by leaning the mixture. The best AFR for max power, max economy, and best air polution are 3 different settings. It would seam to me that if you use a stamp ot SX chip to read the voltage by A to D you could use the controler to output a voltage by D to A. I dont think that the sensors are going to react all that fast compared to the conversion time of the controllers. The SAE web site has a store where you can get books on engine design that would help on the AFR issue but they are very technical. Have you considered the O2 sensor as it has an effect on fuel flow.
One of my interests is automotive design and I have some books on engine design and simulation.