• 0

DMM Shield multiplication factors


I have been playing with the Digilent DMM shield and trying to understand how the shield and the ic hy3131 work. My question is about the multiplication factors which are used for converting the adc value to real value.

For example, the multiplication factor in the library for 5V DC range is125e-1/1.8/8388608

If I'm correct, in 5V DC range the input signal is divided by 10 and fed into the adc whose reference voltage is 1.2V, so my question is why we multiply the value by 12.5? Shouldn't it be 12.0 instead because the reference voltage is 1.2V?


Edited by itlki
Link to post
Share on other sites

4 answers to this question

Recommended Posts

  • 0

Hi @itlki,

Welcome to the Digilent Forums!

We have reached out to an engineer more experienced with the DMM Shield.

While we are waiting for their input

Here is the DMM Shield's resource center.

Which library are you referring to?

Arduino DMM Shield Library User Guide

PIC32 DMM Shield Library User Guide

Zynq DMM Shield Library User Guide

Can you be more specific where in the library your concern is?

best regards,


Link to post
Share on other sites
  • 0

Thanks @jpeyron

I'm referring to the Arduino DMM Shield Library. In the library, there is a file called "dmm.cpp" which contains the configurations of the dmm IC (hy3131). Each configuration (called DMMCFG) has a field called multiplication factor. 

Link to post
Share on other sites
  • 0


As you noticed, this multiplication factor applies to the value acquired from AD converter. It encapsulates the converter gain, the converter maximum value (2 ^ 24) and a scale factor. This factor should be considered as a whole.

After applying this multiplication factor, the acquired values are corrected using the two calibration factors (additive and multiplicative).



Edited by Cristian.Fatu
Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now