Advice on Teensy board choice

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WizardOfYendor

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Hi,

I am hobbyist/amateur/tinker and I have a volunteer project I am working on to replace a very old telescope stepper motor drive control system. I try not to go too deep into the details but things I need in this controller are:

About 15 digital input/output pins.
Crystal oscillator for the clock. Precision is important.
Ideally 2 timers that call ISR's. I can get away with one if need be.


There are a variety of microcontrollers out there, wonder if there is a teensy board that will fit the bill.... any recommendations?
 
In theory, any of the ARM Teensys should be able to do this. But perhaps, it depends on the quality of the internal timer support.

At an initial glance:
  • Teensy LC: 26 digital pins, all 26 pins are available via through hole soldering, 10 of the pins can be PWM pins, 7 hardware timers;
  • Teensy 3.2: 34 digital pins, 23 pins are available via through hole soldering, 11 pins are available via solder pads underneath the Teensy, 12 of the pins can be PWM pins, 8 hardware timers;
  • Teensy 3.5: 54 digital pins, 40 pins are available via through hole soldering, 14 pins are available via solder pads underneath the Teensy, 20 of the pins can be PWM pins, 14 hardware timers;
  • Teensy 3.6: 54 digital pins, 40 pins are available via through hole soldering, 14 pins are available via solder pads underneath the Teensy, 22 of the pins can be PWM pins, 14 hardware timers;
  • Teensy 4.0: 40 digital pins, 23 pins are available via through hole soldering, 17 pins are available via solder pads underneath the Teensy, 31 of the pins can be PWM pins, various timers.

According to the 1062 data sheet, the Teensy 4.0's timers are:
  • General Purpose Timer (GPT): A 32-bit up-counter with 12-bit pre-scaler
  • Periodic Interrupt Timer (PIT): A 32-bit counter timer that features programmable count modulus, clock division features etc.
  • Quad Timer (TMR): It provides four timer channels with variety of controls for individual and multi-channel features
  • Quadrature Encoder/Decoder (ENC): It provides interfacing capability to position/speed sensors
  • Enhanced FlexPWM: It contains PWM submodules each of which is set up to control a single half bridge power stage
  • Watchdog Timer (WDOG1,2): The WDOG1 and WDOG2 protect against system failures by providing a method by which to escape from unexpected events or programming errors
  • Watchdog timer (RTWDOG/WDOG3): It is a high reliability independent timer that is available for system use
  • External Watchdog Monitor (EWM): It is designed to monitor external circuits, as well as the MCU software flow

Now, some of the timer support may not be available on the Teensy 4.0, since not all pins are broken out. Somebody who is more familiar with the internals would have to comment about which timers you can actually get to.
 
Thanks for the detailed response!

I'm digging around trying to find specs of the board but do you know if the clock is using a quartz crystal or ceramic resonator for the oscillator? Precision is important given the application (which is, in effect, a giant clock :) ).

Also trying the operating temp range. I'm presuming it's -10C to 85C.
 
Well, Paul S. is the only one who can say with authority exactly what components are used, and what the tradeoffs were.

You might be able deduce what external chips are used from the schematic of the various Teensies (https://www.pjrc.com/teensy/schematic.html) or by doing visual inspection of the board.

The other way if are skilled at the low level electronics, PCB design, and tiny soldering, is to build your own Teensy. At the moment, Paul has not released the chip to allow building your own custom Teensy 4.0. But the chip is available to build your own Teensy 3.2, 3.5, or 3.6: https://www.pjrc.com/store/ic_mkl02.html

If you haven't seen it yet, the datasheets for the various boards are at: https://www.pjrc.com/teensy/datasheets.html.
 
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