I have a 2.5V DC output signal ( its range is 0.5V to 4.5V), it needs to be scaled from 25% of supply to 75% of supply voltage. The supply voltage is a variable.Due to constraints i cannot use microprocessors or other fancy signal processing parts, need to stick with basic parts like opamps , resistors bridges ect. 0.5V output needs to be scaled to 25% of supply voltage and 4.5V output output needs to be scaled to 75% of supply voltage. Essentially the output needs to be ratiometric to supply voltage. Is there a way to do it with basic circuit like opamp etc?. If easier to explain please draw it if needed.Thank you.
Eng-Tips is the largest engineering community on the Internet
Intelligent Work Forums for Engineering Professionals
scaling and offsetting analog output 1
- Thread starter E2005
- Start date
MikeHalloran
Mechanical
What's the range of the variable supply voltage?
Mike Halloran
Pembroke Pines, FL, USA
Mike Halloran
Pembroke Pines, FL, USA
- Thread starter
- #3
The supply is +8V. I can scale output to this particular supply voltage with opam but the problem is user wants to be independent of the supply voltage. They want to choose a desired supply voltage and the out put sinal (0.5v to 4.5V) needs to scale to it in the following way - 25% of supply=0.5V and 75% of supply =4.5V. If the supply was fixed it would have been easier to choose particular scaling and offset values for an opamp circuit.
MikeHalloran
Mechanical
I understood that the 'user' wants to select an arbitrary supply voltage.
My question had to do with the range within which that voltage lies, because that affects what sort of circuit, and what sort of components, you need to specify.
Either you need to figure out the maximum voltage that the user is likely to request, or just take a WAG and make the range part of your contract, and maybe marked on your product.
I.e., things are different inside the black box if
Vssmax = +10V or 100V or 1000V or whatever.
You probably need to also specify Vssmin and/or provide reverse polarity protection.
Mike Halloran
Pembroke Pines, FL, USA
My question had to do with the range within which that voltage lies, because that affects what sort of circuit, and what sort of components, you need to specify.
Either you need to figure out the maximum voltage that the user is likely to request, or just take a WAG and make the range part of your contract, and maybe marked on your product.
I.e., things are different inside the black box if
Vssmax = +10V or 100V or 1000V or whatever.
You probably need to also specify Vssmin and/or provide reverse polarity protection.
Mike Halloran
Pembroke Pines, FL, USA
- Thread starter
- #5
OperaHouse
Electrical
Is this a onesie? This would be easy to do with a UNO which is cheap. I was posting the procedure but my finger hit something and deleted it all.
- Thread starter
- #7
- Thread starter
- #8
-
1
- #9
Thinking aloud, this sounds like an analogue multiplier job. Haven't quite figured the detail, but will sketch some ideas and maybe post them if no one beats me to it.
A bigger problem might be actually finding an analogue multiplier today! See if the old AD633 and AD532 are still available, maybe there are some newer alternatives at lower cost.
A bigger problem might be actually finding an analogue multiplier today! See if the old AD633 and AD532 are still available, maybe there are some newer alternatives at lower cost.
- Thread starter
- #10
ScottyUK , When i map 0.5 to 4.5V input range to current required output range which is 0-8V i get a transfer function Vo=sVin + b where Vo= desired output, Vin is the sensor signal (0.5 to 4.5V) and s and b are the span and offset. For s= 2 and b=-1. I get the desired output. If there was an analog way to implement this equation, that would solve the problem, am looking at your suggestion about AD633 and seeing if it can do this
Hi VE1BLL,
That's trivially simple if 'm' and 'b' are constants - in this case they're supply-dependent variables. That was the reason for using a multiplier. Of course I could be mis-interpreting the requirement completely and making this a whole lot more difficult than it needs to be!
That's trivially simple if 'm' and 'b' are constants - in this case they're supply-dependent variables. That was the reason for using a multiplier. Of course I could be mis-interpreting the requirement completely and making this a whole lot more difficult than it needs to be!
- Thread starter
- #13
VE1BLL and ScottyUK 'm' and 'b' are depedent on maximum supply voltage. My supply is chosen by user it can be between 5-20V. The only thing that does not change is the sensor output which is 0.5V to 4.5V. That needs to be mapped to 0.5V=25% of suppy and 4.5V=75% of supply. If supply was fixed , one can calculate slope m= Vout(max)-Vout(min)/(Vin(max)-Vin(min), if your supply changes then you have to change the gain resistors values of the opamp to map to new max supply voltage, thats the issue
OperaHouse
Electrical
Well, if it must be analog use a TL494 or similar. I saw a DC power meter in Electronic Design maybe 30 years ago I thought waqs pretty neat. I think I searched a couple years ago and found it. It used current to control the PWM 0-100%. The output was tied to a pullup to power being monitored. A RC filter averaged it out. A simple volts times amps. The Arduino design was based on this. No reason you can't pop the chip out and make hundreds. No pots and easier for those who don't know circuit design. Anyway. if this little board has to operate down to a 5V supply that certainly makes it a lot dicier.
Check and need to do some maths... or simpler,
Depending on the necessary bandwidth the approach that OperaHouse might work. Feed the signal in the PWM modulator with the low at 25% modulation and the high end at 75%. Buffer the output of the PWM to each supply rail, low pass and you have your output.
OperaHouse
Electrical
Everyone says...... I want it simple, just a board with 30 or so parts.
I've designed analog my whole career. I used to love the idea of tweaking pots. I've grown up. Life is easier with a with a $2 microcontroller and about six parts.
I've designed analog my whole career. I used to love the idea of tweaking pots. I've grown up. Life is easier with a with a $2 microcontroller and about six parts.
Another idea to throw into the mix: voltage to frequency conversion followed by frequency to voltage conversion. Similar to the PWM idea in practice I suppose, but one less parameter to deal with (only frequency, not duty). Maybe check out the LM231 datasheet for ideas. I haven't thought it through, but I figure you sensor input could drive a V-F converter directly, while the output would drive a NPN pulled up to your desired output voltage. Then you just need to do a F-V conversion, tune for offset, and presto!
- Status
Similar threads
- Locked
- Question
