Using Picstep's PIC to microstep other driver chips.

[zoltan]

I begun to build it. I have a lot of TEA3718 from printers thrown to the recycling company. I build with two TEA3718 in parallel for 2A on phase. I have seen something similar with LMD18245 for 6A, but I have no LMD18245 to build with two in parallel on phase. I have problems with Eagle still learning, it is almost one year since learning and still know almost nothing.

[spalm]

I was playing around a while ago with resistor ladders and plunked out a spread sheet with a HEX (or R2R) type ladder and compared that to a 4 bit weighted resistor array. You probably really don’t need more accuracy, but this is a different way of looking at it. It takes fewer resistors (only 4) and can be made to arrive at more values. There are over 50 different values of voltage instead of the 16 with the standard HEX style.

Basically you have three outputs on a PIC. High, Low and Tristate. So instead of binary, you get trinary. Instead of 16, you get 81 (but a lot end up being duplicates). You put a resistor in series with the outputs and then tie all four together. Use 4 different values. Now you can go through all the combinations of pulling some high, some low and tristating others.

The spread sheet shows some output graphs. The 4 yellow resistor values can be changed and the results viewed on the right. Plunk the ones you like into the yellow column by the CALC chart to view the sine curve. There is also a curve for “perfect” and HEX. These are superimposed below the tables.

Of course you would have to change the tables in Alan’s code to match the values that you have selected, and then add a table of TRIS bits, but it seemed kind of fun to play with.

It is not too often that you come across a trinary application.

Steve

[pminmo]

I not speaking out of PIC experiencs, but if they are like other micros, I suspect you going to see enough variance in pin output characteristics to affect the accuracies your playing with.

[lucas]

I build with two TEA3718 in parallel for 2A on phase. I have seen something similar with LMD18245 for 6A,

Where did you see that, it has already been said here that it won't work and I don't see it working with those TEA's neither unless there's an undocumented trick somewhere.

@Spalm: I've been in electronics all my life and can't remember hearing anything on Trinary applications, the concept: yes, but never the term.
Your suggestion certainly has advantages but I don't know anything about PIC programming, so this is way over my head for the moment.

[pminmo]

Carefull.... its one thing to parallel drivers in the same package, but when you have a multifunction device such as the tea3718 it isn't a good design idea. Same with the LMD.

[zoltan]

Hi,

First of all I have seem on some industrial equipment made in Germany. The service technicians had a lot of LMD18245 as spare parts for those drivers and because they had no problems, never, gave me few LMDs for my picstep. The drivers were almost identical with those find here: http://www.sb-microstep.com/EnglishSite/English.htm only small differences on layout.

Zoltan

[pminmo]

I didn't say it couldn't be done, but look at the deadband time and the switching times on a LMD18245! From mfg lot to mfg lot they don't spec min's and max's just typical's.
Can it be done, sure, but it doesn't make sense to base a design on paralleling them unless you have a basket full of the LMD's and don't care if you smoke a percentage.

On the other hand a device like the L298 since it contains two drivers on the same die those can be paralleled. ST is ok with that, but they advise not paralleling two different L298's.

[beliefdrive]

Some china stepper use this solution for microstep driver

[Khalid]

Can we use SLA7026M with PICSTEP?

[pminmo]

Not without considerable work, the LMD has elements that would have to be done in external components.

[Khalid]

Thank you Phil.. I have some laying around so i asked..