# circuit help needed to change voltage

Thread Starter

#### minkey01

Joined Jul 23, 2014
185
Hi. Not sure what the official term is for this type of circuit, so I will just explain what needs to happen.

I would like to change a ±10V DC signal to a 0 to 5V DC signal.

The amps are small as it is just a control signal coming from this : http://www.expert-sleepers.co.uk/es3.html

And going into an Arduino thing pin.

Anyone have a circuit to give? Thanks!!

#### mcgyvr

Joined Oct 15, 2009
5,394
Thread Starter

#### minkey01

Joined Jul 23, 2014
185
Awesome! That page is exactly what I was looking for. Thank you.

Could someone check my math and circuit. I think it's right.

To shift my ±10V DC signal to a 0 to 5V DC signal, I have :

R1 = 25 kΩ
R2 = 25 kΩ
R3 = 12.5 kΩ

see attached pic.

Last question: That +5V in the circuit is from power, correct? My exact power supply is +5.25V. How would this change my math and resistor values? I still want to keep the final result of 0-5V control signal into the microcontroller.

Thank you!!

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#### MikeML

Joined Oct 2, 2009
5,444
You realize that this circuit is ratiometric with respect to the 5V rail. Any noise or variation on the 5V rail winds up in the AD input...

#### shteii01

Joined Feb 19, 2010
4,644
You realize that this circuit is ratiometric with respect to the 5V rail. Any noise or variation on the 5V rail winds up in the AD input...
Arduino boards usually have 5V output you can use to power devices. They could source the 5 volts for the circuit from Arduino board. I don't know off hand how stable it is, but I hope it is better than just noisy wall wart.

#### MikeML

Joined Oct 2, 2009
5,444
Arduino boards usually have 5V output you can use to power devices. They could source the 5 volts for the circuit from Arduino board. I don't know off hand how stable it is, but I hope it is better than just noisy wall wart.
The Arduino's onboard 5V regulator powers the Atmel and USB chips. They are running at 16Mhz, and the 5V rail has the typical digital hash on it. It is even worse if the Arduino is plugged into the USB spigot and there is no seconary wall-wart or input power to the onboard regulator.

I would not use the Arduino's 5V (without extensive filtering) as a reference voltage for anything that winds up back into the AD input...

#### shteii01

Joined Feb 19, 2010
4,644
The Arduino's onboard 5V regulator powers the Atmel and USB chips. They are running at 16Mhz, and the 5V rail has the typical digital hash on it. It is even worse if the Arduino is plugged into the USB spigot and there is no seconary wall-wart or input power to the onboard regulator.

I would not use the Arduino's 5V (without extensive filtering) as a reference voltage for anything that winds up back into the AD input...
So, external 5 volt precision regulator?

Thread Starter

#### minkey01

Joined Jul 23, 2014
185
Thank you guys for the suggestions. I am actually using one of these, which is an Arduino clone kind of thing :

Teensy 3.1

https://www.pjrc.com/teensy/teensy31.html

Those wouldn't have a stable V you were talking about do they?

#### MikeML

Joined Oct 2, 2009
5,444
My reading of the Teensy data is that it expects an input of 5.5V, and outputs a regulated voltage of 3.3V (not 5V)

The reference for the Atmel AD converter is a filtered version of the 3.3V. The REF is available as a pin, and could be used as a reference (provided that only a tiny current is drawn) for external circuitry...

The wall wart puts out 5.25V (less than the 5.5V that the Teensy expects)? Since it is a switcher, likely going to be noisy...

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Thread Starter

#### minkey01

Joined Jul 23, 2014
185
Teensy is powered by Vin (3.7V to 5.5V), so I'm ok with my 5.25V power. See this page with the Vin pin :

http://www.pjrc.com/teensy/pinout.html

I do believe you are correct with only outputting the regulated 3.3V. This won't work for my circuit? I would need some sort of external voltage regulator at 5v it seems?

Could anyone help me with a part number for the voltage regulator and how to wire it to my existing circuit in the posts a few above?

Thank you!

#### MikeML

Joined Oct 2, 2009
5,444
If the goal is to offset the -10V to +10V to the dynamic range of the AD input (0 to 3.3V), then the circuit you have posted will not work, and will have to be redesigned for the reference you actually have (3.3V)

Thread Starter

#### minkey01

Joined Jul 23, 2014
185
ahh, got it. i see what you are saying. thank you for the help!

#### shteii01

Joined Feb 19, 2010
4,644
ahh, got it. i see what you are saying. thank you for the help!
So Teensy is like Arduino Due and works with 3.3 volt analog and digital voltages?

#### MikeML

Joined Oct 2, 2009
5,444
Here is a level shifter that will work. How fast does the real input change from -10V to +10V? That effects C1....

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Thread Starter

#### minkey01

Joined Jul 23, 2014
185
yes 3.3v analog and digital on Teensy 3.1. except that it is also 5v tolerant on digital inputs.

Thread Starter

#### minkey01

Joined Jul 23, 2014
185
Mike - The signal is coming from a DAW (Digital Audio Workstation) into the ES-3. DAW are software programs that people use to edit music. So as fast as an audio waveform changes. Not sure if this answers your question. I don't know how to find out how fast. Is that enough info to figure out the cap spec? If not how could I find out the speed?

Thanks for that circuit! Totally awesome of you!!

#### shteii01

Joined Feb 19, 2010
4,644
Mike - The signal is coming from a DAW (Digital Audio Workstation) into the ES-3. DAW are software programs that people use to edit music. So as fast as an audio waveform changes. Not sure if this answers your question. I don't know how to find out how fast. Is that enough info to figure out the cap spec? If not how could I find out the speed?

Thanks for that circuit! Totally awesome of you!!
General rule of thumb is that audio is 2 Hz to 20 kHz. So if you dealing with analog audio, then you can safely assume that 20 kHz will be the highest frequency.

Thread Starter

#### minkey01

Joined Jul 23, 2014
185
ahhh right.. i remember this. unless you are a porpoise or something it can go higher.

#### shteii01

Joined Feb 19, 2010
4,644
ahhh right.. i remember this. unless you are a porpoise or something it can go higher.
Let me check my beak.