topic Re: K82 FTM2 Quad decoder is inaccurate in Kinetis Microcontrollers

K82 FTM2 Quad decoder is inaccurate

JustSomeGuy — Tue, 29 Aug 2023 14:25:55 GMT

I'm working with a K82 MCU and a magnetic encoder attached to a motor. The encoder has 512 counts per rotation; with my targeted motor speed, the encoder output should be around 10KHz. I've configured FTM2 as a quad decoder. The clock is 60MHz and has a prescaler of 16. I am not using semi-hosting for debugging.

The quad decoder is not working properly - it might be losing counts, but that's hard to say because the bigger issue is that the direction is unreliable. When hand turning the motor, if I pause for a moment, then resume turning, there is a high probability that the direction will flip. I've been at this for a while; changing clock frequencies, adding filters, etc. to no avail. Scope captures of the encoder show a very clean signal. What could be causing this?

Re: K82 FTM2 Quad decoder is inaccurate

_Leo_ — Tue, 29 Aug 2023 18:22:14 GMT

Hi,

Thank you so much for your interest in our products and for using our community.

The frdmk82f_ftm_quad_decoder_peripheral SDK example use the FTM1, Does the same thing happen to you with the latter?

Have a nice day!

Re: K82 FTM2 Quad decoder is inaccurate

JustSomeGuy — Tue, 29 Aug 2023 18:38:50 GMT

Thanks for the reply. I'll have to dig up a freedom board and investigate. I'm currently working with custom hardware that has the encoder routed to PTB18 and PTB19, so FTM2 is all I have at my immediate disposal.

Re: K82 FTM2 Quad decoder is inaccurate

JustSomeGuy — Tue, 29 Aug 2023 19:32:14 GMT

It turns out that the problem was an assembly defect - one of the MCU pins was not soldered down to its pad. Firmware debugging is always an adventure.