# Making a voltage divider

This isn't specifically for an Arduino but figured it was close enough for people to be able to help. I have an analog I/O that puts out 5V but the analog input can only take 3.3V. The I/O device is a volume sensor with three wires. Positive and negative for power and then the output wire. Since this isn't an Arduino, I can't use a variable divider as I don't have anything that can read that voltage. I just need something simple that takes the 5V down to 3.3V through that single wire.

If it is a digital signal a level translator would be great, I do not like dividers for digital, a voltage divider should work in either case. Use the calculator at this link, it works great: Voltage Divider Calculator A 1K to 5V and a 2K to ground will be close. You can play with the calculator and determine what you want to do depending on what resistors you have.

The volume sensor output is analog.

I guess my issue is, I'm not really sure how to wire it all up. I'm not familiar with this type of stuff. I have a prebuilt transmitter that reads that volume sensor. I didn't build any of it myself. The transmitter has the one input wire. The volume sensor has three (positive, negative and output). How would I wire that up with the voltage divider?

Do not expect to resolve this in a few days. Watch a few videos on basic electronics and the Arduino. At that point you will have an idea of additional videos to watch. The other option is to hire somebody to do the project for you. If you look for a volume sensor I got "About 380,000,000 results (0.77 seconds) ". I do not have the time to look at them all especially when you could provide links to the technical information on the hardware parts.

Sorry, I should have posted that

Here are the specs. This is all the website has.

Specifications:
Pressure:
– Model PSF-20-5: 0 – 20 in. H2O / 0-50 mbar
– Model PSF-20-10: 0 – 40 in. H2O / 0-100 mbar
Output: 0 – 5 VDC (analog)
Maximum pressure: 200% full scale
Accuracy: +/- 0.5% full scale
Power: 12 – 30 VDC
Mount: 1.5″ Tri-Clamp (1.984 in. / 50.4 mm)
Media temperature: -40 – 255°F / -40 – 125 °C
Stability: <0.2% FS / year
Protection: IP65
Construction: 304 SS
Height: 4 1/4 in. / 105 mm

There is an amplifier inside, so I suppose the output impedance is low, certainly lower than 1k. So if you use R1=10k and R2=15k for the voltage divider, it should be alright.

To reduce a 5V analog signal to 3.3V, use a divider ratio of 3.3/5 = 0.66, keeping the lower member of the divider less than about 10K for an Arduino ADC input. It doesn't have to be exact as you can calibrate the output later.

2.2K and 3.3K works (ratio = 0.6, which gives a bit of safety margin).

Yeah that's it. I thought I copied it in my reply but it didn't come over

Is that a Dutch expression ?

jremington's 2.2k and 3.3k is okay, a lower impedance means less noise.
My 10k and 15k is also okay, I don't know how strong the output voltage is.

If you want exactly 3.3V output instead of 3V, then you can tune it by adding a resistor parallel with R1.

No, just meant the copy and paste didn't seem to work.

So I think I understand using the two resistors and watched a video on how to connect it all on a breadboard but what I'm confused about it I only have one wire. Everything I see is using positive and ground/negative. This is just the signal wire. I don't need to drop the volts to that actual sensor.

The 0...5V output is the voltage between the GND wire and the output signal wire. There are two wires. You have to connect the GND to the Arduino GND, which means that the GND of power for the sensor will be connected to the Arduino GND and to a computer if a USB cable is connected.

I don't know which wire is which:

Power the sensor: 12...30V to power input and GND.
Signal output: signal wire and GND.

Oh I think I got it. So the sensor/device wire and the ground would be connected to the voltage divider, with the sensor wire going to the input and the ground going to ground in the system (which for this build is a block terminal with a lot of other grounds going to it). Then obviously the positive of the volume sensor goes to the power terminal.

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