Stepper motor driver with pulse and direction interface

I am tinkering with a NEMA 23 stepper motor and a motor drive that has a pulse input, a direction input and an enable input. The motor is driving an indexing table with a 3M timing belt, with gears that give 8:1 reduction.
The drive can accept pulse frequency up to 200kHz. The motor is a common two winding bipolar with 1.8 degree step angle, and if not micro stepping I think that 1kHz frequency is fine. But I would like to take advantage of the micro stepping capability which means the pulse frequency must be much higher.
I expect that the mass that is mounted to the indexing table can be large, so to avoid problems with stalling, position errors etc I am trying to optimize the acceleration (ramp up and ramp down of the stepping frequency).
My question is what limitations I should expect from the changeInterval() function. I assume there is a 1ms resolution limit. is there a better way to control the pulse frequency accurately and with higher frequency than 1kHz?

Well, the average resolution of setInterval is actually very high (1 uS) but the speed of execution of JavaScript is really going to cause you problems - so while you could maybe get nearer 8kHz with a few lines of the inline assembler, other bits of JavaScript that run will get in the way of it.

It's a bit difficult really... You can get an accurate, very high pulse rate using the built-in timers and analogWrite, but crucially you won't be able to accurately count how many pulses have been sent out.

So if you really want the higher speeds with Espruino I guess you have three options - none of which is great:

• Use peek and poke to set up one of the hardware timers as a counter, then use that counter to count the number of pulses that have been sent with the analogWrite command.
  
• Some of the hardware timers have a register for 'repeat count'. I don't know if you could somehow set/query that with peek and poke in order to make sure that you sent out only the amount of pulses that you wanted.
  
• Modify Espruino's source so that you can use the software timer (in jstimer.c) to do what you want. It's what is used for digitalPulse/Waveform/etc and is capable of sending repeated pulses at relatively high (~50kHz?) rates. You'd have to add something such that it could keep track of how many pulses had been sent, and so that you could also change the interval between them.
  

Thanks. I will have to look into those options as time allows. This is not a high priority project right now. Perhaps I could generate the pulses with acceleration ramps in hardware and count the number of pulses to know the position.

Gordon,

Have you seen the new NXP dual-core mcu[1] which starts at $2(for 256K/108K flash/ram) ? it might be a good fit to enable Espruino with real-time :

1 core could run Espruino with all it's benefits especially with high ram. Another core run Arduino/Mbed,exactly for those real-time tasks. People who don't care to learn Arduino/Mbed, but want to add some real-time stuff can easily copy code from the net.

I believe there are even ports of the mbed to the lpc4500(a board called bambino-200) , which is another dual core chip from nxp, so it might make the job easier.

[1]http://www.eetimes.com/document.asp?doc_­id=1324539&

Hi Jack,

Looks interesting - however from my point of view, making people use two separate IDEs and languages goes against the idea of Espruino a bit - it should be nice and easy to use. The micro itself is capable of realtime without needing a separate processor - it's just how you expose it to the programmer.

I will probably add the ability to run (native) code in interrupts (and timers) soon, which should make life a lot easier. Things like counting pulses could be done in a few lines of assembler and then rolled up into a module so that the programmer using it didn't have to care about it.

I will probably add the ability to run (native) code in interrupts
(and timers) soon

That would be great this would allow me to add half duplex RS485 comms easily.