Microstepper controller

[peu]

thanks for your replies, I hope in the future you post an hex with step/dir so I can control it using mach3 software. Thanks!!

[El_AMPo]

Working fine on the 16F628A

In my design I upgraded the power stage to an ULN2068 (1.5A max per output) and put an embedded FTDI usb to USART chip. All on a 100x50mm single sided PCB (I'll share the PCB as a sign of gratitude once I finish debugging it a little on the usb part).
Also i'm planning to put a safety stop serial command with another pic sniffing the serial commands, because if you make a mistake on the instruction it will execute completly before you regain control of the motor, and that on my aplication is critical.

I got a problem anyhow but i don't know if it's software related or from my "squeeze pcb components to the max to reduce pcb size" techniques.

Works fine on a half an full step mode, but on microstepping sometimes works and sometimes starts making a strange noise on the coils making them hum and jitter untill I reset the whole driver. It's probable that the pic or the gates gets a little dizzy from emi noise because all kinds of lab equipments are connected to the same line so i'm working on that.

One doubt i had is if driving the stepper motor by limiting to a fixed current won't reduce torque in half step modes? (2 coils at 50% current vs 1 coil at 100% current)
Then why is better to drive them this way?. I know constant curent means that is aproximately constant in torque independant of the coils activated, but wouldn't be better with full current on every coil at expense of more current?

[El_AMPo]

thanks for your replies, I hope in the future you post an hex with step/dir so I can control it using mach3 software. Thanks!!

You can build up an interpreter for the serial stream with another pic, no so pretty but is a simple and fast solution.

[Archangel]

Here is the device which brought me to PICs. I bought 3 kits from them, they work great and microstep.

http://www.piclist.com/techref/io/st...step/index.htm
http://www.piclist.com/techref/io/st...p/lini_use.htm
http://www.piclist.com/techref/io/st...570.4504050926
He was selling kits on the web site and eBay

[rmteo]

thanks for your replies, I hope in the future you post an hex with step/dir so I can control it using mach3 software. Thanks!!

Here's a single chip commercial grade solution A3984 - DMOS Microstepping Driver

The A3984 is a complete microstepping motor driver with built-in translator for easy operation. It is designed to operate bipolar stepper motors in full-, half-, quarter-, and sixteenth-step modes, with an output drive capacity of up to 35 V and ±2 A. The A3984 includes a fixed off-time current regulator which has the ability to operate in Slow or Mixed decay modes.
The translator is the key to the easy implementation of the A3984. Simply inputting one pulse on the STEP input drives the motor one microstep. There are no phase sequence tables, high frequency control lines, or complex interfaces to program. The A3984 interface is an ideal fit for applications where a complex microprocessor is unavailable or is overburdened.
The chopping control in the A3984 automatically selects the current decay mode (Slow or Mixed). When a signal occurs at the STEP input pin, the A3984 determines if that step results in a higher or lower current in each of the motor phases. If the change is to a higher current, then the decay mode is set to Slow decay. If the change is to a lower current, then the current decay is set to Mixed (set initially to a fast decay for a period amounting to 31.25% of the fixed off-time, then to a slow decay for the remainder of the off-time). This current decay control scheme results in reduced audible motor noise, increased step accuracy, and reduced power dissipation.
Internal synchronous rectification control circuitry is provided to improve power dissipation during PWM operation.
Internal circuit protection includes: thermal shutdown with hysteresis, undervoltage lockout (UVLO), and crossover-current protection. Special power-on sequencing is not required.

[El_AMPo]

Aratti,
i've found a glitch in the microstepping mode, maybe you can confirm if it's software related.

If you enummerate the coils from A to D, then when changing from coil D to A the transition it's not in microsteps but a full step. Maybe an end loop thing?

I've attached a video (check the green leds, the transition between the one down and the left one)



Happy holidays (the ones that have some)