TM4C123G QEI and ADC

Arian Garcia

Other Parts Discussed in Thread: EK-TM4C123GXL

I want to input an analog value from a potentiometer joystick to then control the mouse through USB. My question is can I use QEI for to track the movement? If so, I will only have two inputs ranging from 0 to 4095, does QEI take two inputs for each axis?

over 9 years ago

0 Amit Ashara over 9 years ago

TI__Guru**** 244400 points

Hello Arian,

QEI takes in Quadrature inputs in the most basic mode or Steps+Dir signal in the other mode. Now how do you plan to get the inputs to the TM4C123?

Regards
Amit

0 Arian Garcia over 9 years ago in reply to Amit Ashara

Prodigy 150 points

Hello Amit,

I plan on getting the inputs from the signal pins of the potentiometers and wire those pins to ADC pins.

0 Robert Adsett over 9 years ago in reply to Arian Garcia

Guru 27665 points

Potentiometers and quadrature encoders are quite different things. It's certainly technically possible to have a joystick with either. However, IME inexpensive ones are likely either potentiometer or switch based and industrial joysticks either potentiometer or, increasingly, hall effect based.

Robert

0 Amit Ashara over 9 years ago in reply to Arian Garcia

TI__Guru**** 244400 points

Hello Arian,

But what is that you are getting on QEI pins?

Regards
Amit

0 Arian Garcia over 9 years ago in reply to Amit Ashara

Prodigy 150 points

I believe I am over thinking this. Seems like the "usb dev gamepad" will have the code I'm looking for to support analog inputs and move the mouse. Any idea where I can find this project? It does not seem to be in my usblib/device folder

0 Amit Ashara over 9 years ago in reply to Arian Garcia

TI__Guru**** 244400 points

Hello Arian,

It should be the folder in TivaWare installed on your PC.

D:\ti\TivaWare_C_Series-2.1.2.111\examples\boards\ek-tm4c123gxl

Regards
Amit

0 Arian Garcia over 9 years ago in reply to Amit Ashara

Prodigy 150 points

Amit,

Thank you, I had version 1.1 of TivaWare! So I am installing the current version.

0 Amit Ashara over 9 years ago in reply to Arian Garcia

TI__Guru**** 244400 points

Hello Arian

Do read the readme.txt to see how to test the application

Regards
Amit

0 Arian Garcia over 9 years ago in reply to Amit Ashara

Prodigy 150 points

Amit,

How can I use values that are being read from two ADC pins to move the mouse on screen?

Thanks

0 Amit Ashara over 9 years ago in reply to Arian Garcia

TI__Guru**** 244400 points

Hello Arian

The resdme.txt provides that information as well "These are not connected to any real input so the values simply read whatever is on the pins. To get valid values the pins should have voltage that range from VDDA(3V) to 0V. "

Regards
Amit

0 Arian Garcia over 9 years ago in reply to Amit Ashara

Prodigy 150 points

I have my joystick connected(the two potentiometer signals) to PE3 and PE2 and I have voltage going to the joystick but when I move the joystick nothing happens on screen.

0 Amit Ashara over 9 years ago in reply to Arian Garcia

TI__Guru**** 244400 points

Hello Arian,

Did you check the voltage on the PE3 and PE2 pins? How does it change with the movement of the joystick....

Regards
Amit

0 Arian Garcia over 9 years ago in reply to Amit Ashara

Prodigy 150 points

Amit,

Idle both are around 2.1V. For Pot2 when the joystick is moved left the voltage going to PE3 reads 30mV and moved right 3.3V. For Pot1 when the joystick is moved up the voltage going to PE2 reads 30mV and moved down 3.3V.

0 Amit Ashara over 9 years ago in reply to Arian Garcia

TI__Guru**** 244400 points

Hello Arian

The conversion use 0x7FF as the midpoint which is 1.65V (assuming 3.3V reference for ADC). You may need to adjust the 0x7FF to an appropriate code. Also there is a right shift operator of 4. Can you reduce it to 3..2..1 and check. I don;t have a Joystick on my setups so I can only make suggestion...

#define Convert8Bit(ui32Value) ((int8_t)((0x7ff - ui32Value) >> 4))

Regards
Amit

0 cb1 over 9 years ago in reply to Amit Ashara

Guru 47900 points

May I note that while the Joystick has introduced appropriate voltage levels to PE2 & PE3 - not one report has described the ADC's set-up and/or conversion results.

If the conversion is improper - or untriggered - even perfect hardware will fail.

KISS (always silent here) would see "dummy values" employed (temporarily) as replacement for "Live ADC measures." These dummy values should, "Move the Cursor" if the "Cursor Control Function" is proper & enabled. I don't believe this simple step has been test/verified! (due entirely to absence of KISS)

Once the Cursor Movement Function has been confirmed - the ADC operation can be examined - and once it's proper - those dummy values may be replaced.

As always - KISS directs the LARGE Process into constituent parts - which proves FAR QUICKER & EASIER to Test/Verify. Pity that "PC" or some other restriction eliminates KISS from most user consideration...

0 Arian Garcia over 9 years ago in reply to Amit Ashara

Prodigy 150 points

Amit,

I would like to add another button and remove the Z Axis. Do you have any idea where the pins are defined for the buttons?

0 cb1 over 9 years ago in reply to Arian Garcia

Guru 47900 points

May we note (and protest) that NOTHING is WORKING - and yet (now) there is the wish to ADD to the project! (i.e. 100% Anti-KISS!)

This train is careening (further) off-track - and one doubts that "over-thinking" is the culprit... (one {limited} battle - one {small} victory - at a time! "All at once" (seemingly) practiced now - is a sure "ticket to delay, frustration, uncertainty!")

0 Arian Garcia over 9 years ago in reply to cb1

Prodigy 150 points

Apologiez! I failed to note that I got my joystick and buttons working! I was able to add the extra button as well. Now I am looking into removing the Z axis.

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TM4C123G QEI and ADC