Proportional output circuit

[fluidcontrol]

I am working on a project of electronic interface circuit design. I describ it as following:
We can get a TTL level sensor output(0.5-4.5V), depends on the percentage of this output to 5V, we want to output a proportional output to battery voltage(chnage in vehicle application), such as 0.5V from sensor then 25%Vbatt+, 2.5V then 50%Vbatt+, 4.5V then 75%Vbatt+. As battery voltage chang, even if sesnor output doesn't change, the output voltage have to change to obtain the desired percentage.
I am beginner in electonic design, anybody could give me a suggestion or idea on how to do it?
Thanks

 

[IRstuff]

Is this a school project?

TTFN

 

[sreid]

For an analog circuit you need a multiplier. I would suggest an Analog Devices AD633.

http://www.analog.com/en/prod/0,,773_862_AD633,00.html

However, I would use a PIC processor, A/D the analog signals and scale/multiply in code.

 

[VEBill]

If you're trying to create an analog voltage signal that is proportional to the battery voltage, then use a voltage divider (two resistors).

The original posting is less than clear.

 

[nbucska]

If you want to translate a logic signal you may simply use
an open collector buffer (e.g. 7407) with a pull-up R

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[OperaHouse]

Agree with open collector, but would use something like an LM339 for the voltage sensing. That should get you started, I can think of three different ways to do this with this chip. When you get out in the real world, the problems will be harder.

 

[OperaHouse]

Just for fun, I worked out the circuit. Since you said this is a vehicle, I assume it runs from 12V. Regulator can be eliminated if you can source the 5V from the ECM. Specs as follows: 0V low level, 3 voltages based on three charge levels. Assume you mean % of battery charge not voltage. 25% of nominal battery voltage is only a litle over 3V. Minimal parts count would be: LM339, 7805, 2 caps and 10 resistors. 15 resistors would be better.

 

[fluidcontrol]

Thanks for all your suggestions.
Actually we are trying to make our own signal conditioning circuit to amplify the Joystick's analog output signal(hall effect sensor output0.5-4.5V) and control a propotional solenoid.
The propotional solenoid has three terminals, two of them are connected to vehicle battery+ and battery-, the third one is an analog signal used to determine how much the valve will be opened. The driver module integrated inside the valve will compare this analog signal with the vehicle battery voltage in another terminal, if it is equal to 50% vehicle battery voltage, then valve is in neutral, if it is equal to 25% battery voltage then valve fully open in one direction and if it is 75% battery voltage then valve fully open in another direction. So the above percetage(not the absolute voltage value) determine the valve openess.

So our signal conditioning circuit should implement following function:
Mapping TTL analog signal(0.5V~4.5V)from Joystick to another analog signal range(25%BatteryVoltge ~ 75%Battery Voltage) linearly, and then output this signal to proportional valve driver module.
That means if 0.5V from Joystick, the circuit outputs 25%BatteryVoltage and 4.5V relates a 75%BatteryVolatge.
Again to the same analog input value from joystick, if the vehicle battery voltage changed, the circuit's output voltage value varied too, but the ratio between circuit out and battery voltage should be approximately constant so long as the input isn't change.

Maybe this is very easy to some people, especially to Mr. IRStuff. I hope I didn't piss you off by posting so easy question.
Anyway I appeciate any help and will think about all your suggestions.






To Sreid:

 

[IRstuff]

The reason I questioned it was that making a measurement, that presumably had some degree of accuracy and then throwing it away making making dependent on the supply voltage seemed very odd.

TTFN

 

[OperaHouse]

You really threw me off when you said "TTL level sensor output(0.5-4.5V". This made it look like a liquid level sensor that was either on or off. The whole thing looked like a remote liquid level sensor and a battery monitor that used a single output line. Your last description is clearer.

I have a pretty simple solution. Use a switching regulator chip like the TL494. Tie the two outputs together with a pull up and average the output with a simple filter. A voltage fed to the control circuit will give a % duty cycle (5-95%) and the output will follow the 12V of the vehicle. This should be quite stable and cheap.

 

[OperaHouse]

And, you could use a less expensive dual coil servo instead of an expensive one with built in electronics. Reduce the switching frequency and you have dither at no extra cost for better valve operation.