CCS/TMS320F28379D: Speed measurement of a DC motor using eQEP

nick reiss

Part Number: TMS320F28379D
Other Parts Discussed in Thread: C2000WARE

Tool/software: Code Composer Studio

Hello everyone, I'm using eQep module, from F28379D DSP card, to measure the speed of a DC motor.
For that I used the example provided in C2000ware.

I'm using an encoder HEDM-5600 encoder that has a resolution up to : 1024 counts per revolution .

the C2000ware example is using a resolution of 4000 counts per revolution.

So I went to "Example_posspeed.h" to change the initialization of resulotion but instead of 4000 they are initalizing eQep Encoder with a value of "16776" wich I don'ty know to what correspond.

hope someone can help.

here is the "Example_posspeed.h" code : Example_posspeed.h

over 6 years ago

0 Subrahmanya over 6 years ago

TI__Mastermind 24095 points

Hi,

In the same file there is a comment about this number

int mech_scaler; // Parameter: 0.9999/total count, total
// count = 4000 (Q26)

So, it seems to be the Q26 format representation of this number.
16776 / (2^26) = 0.00024998 is same as 1/4000 in Q26 format.

0 nick reiss over 6 years ago in reply to Subrahmanya

Intellectual 595 points

Thanks, I want to connect my Rotary Encoder to the eQEP pins, but the HEDM-5600 has a supply voltage of 5V. (and I think eQEP runs at 3V)

so do I need a voltage adapter between the Encoder and eQep ?

if so can you give me some example of circuit ?

0 nick reiss over 6 years ago in reply to nick reiss

Intellectual 595 points

here is the datasheet of the encoder : www.infineon.com/.../Infineon-Encoder_HEDS-5540-A14-AP-v01_00-EN.pdf

0 Subrahmanya over 6 years ago in reply to nick reiss

TI__Mastermind 24095 points

Yes - you'll need an interface circuit from 5v to 3.3v.
You can refer to any of the C2000 reference designs with QEP interface.
You could also look at QEP interface of launch pad -
www.ti.com/.../LAUNCHXL-F28379D

0 nick reiss over 6 years ago in reply to Subrahmanya

Intellectual 595 points

Hey I just looked at QEP interface for F28379D and i has 5V as supply voltage as you can see in the image.

so does that mean i don't need an interface between the two of them ?

0 Subrahmanya over 6 years ago in reply to nick reiss

TI__Mastermind 24095 points

Hi,
refer to level shift right next to this diagram "Figure 11. P10_EX-Header"

0 nick reiss over 6 years ago in reply to Subrahmanya

Intellectual 595 points

here is level shift, I'm not sure how to get the info from it.

0 nick reiss over 6 years ago in reply to nick reiss

Intellectual 595 points

Hey I'm still waiting for an answer if it's okay to connect my encoder with directly with the eQEP or i do need to use an interface between them.
hope someone can help me.

0 Subrahmanya over 6 years ago in reply to nick reiss

TI__Mastermind 24095 points

Hi, Since it's 5v signal you can not directly connect to the MCU input. You need to have the level shifter - you've already shown one above.

0 nick reiss over 6 years ago in reply to Subrahmanya

Intellectual 595 points

yeah but QEP is 5V too, right ?

0 Subrahmanya over 6 years ago in reply to nick reiss

TI__Mastermind 24095 points

Hi,
I'm not sure if i'm able to understand your question correctly - let me try again.
So, you've signal inputs from the encoder going to connector J15 shown above and further level shifted and fed to GPIO20, 21 etc. MCU inputs.
What goes to the MCU are level shifted 3.3v signals and NOT 5v signals.
Does that answer your question?

0 nick reiss over 6 years ago in reply to Subrahmanya

Intellectual 595 points

let me explain :

I have an encoder that has 5V supply voltage and i want to connect it to the eQEP module (connector J14).

AS shown in the image of the pin headers of eQEP it has also 5V voltage (not 3.3 V), so I think I don't need a level shifter (because the two of them have 5V as voltage) right ?
I'm not using any GPIOs

0 Subrahmanya over 6 years ago in reply to nick reiss

TI__Mastermind 24095 points

Hi,

From the header (J14) these 5v signals (EQEP1A/1B/1I) are further going into U2 (Level shifter you've shown above). Then the level shifted outputs indicated as GPIOxx are connected to the MCU. So, it's the 3.3v signal that goes to the eQEP module input of the MCU.
It'll be clear if you look at the complete signal path from header all the way to the MCU input.

0 nick reiss over 6 years ago in reply to Subrahmanya

Intellectual 595 points

here is what i'm trying to explain.

What I don't understand is that the two of them (encoder and J14) have 5V as supply voltage so why do I need a level shifter between them ?

0 Subrahmanya over 6 years ago in reply to nick reiss

TI__Mastermind 24095 points

Hi, You do not need level shifter between encoder and J14. You can directly connect encoder output to J14.

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CCS/TMS320F28379D: Speed measurement of a DC motor using eQEP