0
\$\begingroup\$

Can someone help me with voltage scaling? I've seen some Logic Level Converters from SparkFun but time is matter so I cant wait to get those shipped. I found a topic here: Scaling DC Voltage [0V-6.5V] to [0V to 10V] and this scheme is fine for my project, but since i'm pretty fresh in components, i would like to ask what components would be ideal for this voltage scale. Thanks

EDIT: So my question is, which op-amp should i use to not exceed max output voltage of 5V, and which resistors in combination with that op-amp? My idea is to pick up signal from various sensor in car engine (MAP, MAF, cam positon, fuel system) and scale them down from 5v-0v to 3.3v-0v, process them in Raspberry Pi software i made, and send them processed back to ECU scaled from 3.3v-0v to 5v0v. In global, piggyback ecu with realtime tuning for pre 2000's diesel cars.

\$\endgroup\$
  • 1
    \$\begingroup\$ Please can you edit and expand your question (not in comments), adding (a) if this is a logic signal you're scaling (think so) or an analogue range, (b) what the input is driven by, (c) what the output must drive and with how much current. The more detail in your question, the better the quality of the answers you will attract. Thanks. \$\endgroup\$ – TonyM Jan 30 '18 at 13:55
  • 1
    \$\begingroup\$ Considering you can't wait for things to be shipped, I suggest you list your components and ask if any can be used. Nobody is going to take a wild guess at what you have. If you have nothing suitable then you'll have to wait to receive parts. It's very simple really. \$\endgroup\$ – Andy aka Jan 30 '18 at 13:56
  • 1
    \$\begingroup\$ "My idea is to pick up signal from various sensor in car engine" so there is the rub, each one of those may require different conditioning. Which ones are analog, which ones are basically switches.... etc etc. \$\endgroup\$ – Trevor_G Jan 30 '18 at 14:19
  • 1
    \$\begingroup\$ This really needs a block/circuit diagram for people here to stand a chance, Luka. Can you draw one (hand-drawn is fine but neatly please) and add that to your question. Types of sensors on the inputs, number and types of outputs. \$\endgroup\$ – TonyM Jan 30 '18 at 14:31
  • 2
    \$\begingroup\$ We still don't know what op-amps you have so if you want to use one of those you need to put some effort in. If you don't have any op-amps then you are going to have to get one shipped and this seems to defeat the object of ther first sentence in your question. \$\endgroup\$ – Andy aka Jan 30 '18 at 15:03
4
\$\begingroup\$

You can use any op. amp. you would like, search for GP one (general purpose). A simple LM358, OP07, OPA27, etc. LM358 are most common and used very often.

The schematics should be as shown below, with power supply of at least 6 volts DC to operational amplifier.

enter image description here

Then you have to set the Gain, which we mark with capital A. If you use a non-inverting operational amplifier (as in this schematic, you want the output voltage the same polarity as input voltage). Your gain must be the value, that when you will have 3.3V on the input, the output will have to be set to 5V. So let's say, that your gain will be calculated with equation Uout,max/Uin,max -> so 5V / 3.3V = 1.51515. Now, we have set your gain, but we still need to calculate the resistors. And because you have a noninverting operational amplifier, the gain cannot be less than 1, so from your gain (1.51515), we subtract 1 and we come to the number 0.51515. This number equals now:

0.51515 = R1/R2

To determine R1 and R2, we will stick to standard E24 or at least E12 resistor series, in range from 1k to 10k (could up to 1M, but sin this range it will be just fine) somewhere inbetween.

If we set R2 to the 10k, we see, that the resistor R1 should be 5150 ohm. But, because 5150 ohm isn't quite standard resistor, we will use a 5k and 150R resistors in series to get the values we would like. Ofcourse you can use the potentiometer (or trimmer in this case, more likely) and set it properly, but I think this is precise enough method too.

So the final schematic (as I was explaining) is here:

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.