Help Request: Simple Stepper Hardware with EMC's HAL

[kreutz]

Don't feel bad, we all learn from our mistakes...Keep on trying and, before you even noticed, you will be helping others.

[samco]

I would look at the links kreutz posted. Inexpensive to play with would be http://www.pminmo.com/ . I did this about 15 years ago.. started out with 4 transisters driving each of the phases of a unipolar motor. Then mosfets - then when I wasn't getting the speed I wanted.. current limit resister.. then found some chips that would do pwm.. Still only doing half stepping.

Finally we found some compumotor oem 650 micro stepping drives on ebay. All I can say is we never went back. Microstepping style drives are worth every penny.

Now if your doing it just to learn.. then have fun.

sam

[adamziegler]

Ah yes.. I probably should have said... this is primarily a learning exercise for myself. I will tinker around with this for a few months, and after I am satisfied that I can do something that works, I will probably spend some cash and get some real drivers.

What got me interested in playing around with this myself was the pulse generator in EMC's HAL. I started toying around and realized I was back to basics with my electronics abilities... figured I need a good refresher.

So.. that all said... how does this new layout look? Any advice on the diodes?

[samco]

I love emc2...

Large Brushed servo setup on the cheap (WIP)

I guess I should talk.. making my own cheap servo amp.

emc2 is a very powerful/flexible machine controller.

[kreutz]

All those mosfets come with a protection diode, so you can eliminate all the D1 diodes.

Use the IRL version of the Mosfets, they are "logic level mosfets" and you won't need to have two power supplies (+5, and +12) and a level translation to drive them, you will need only +5volt and logic gates. Use mosfets whose max Vds is rated for at least 20% more than twice your power supply's voltage.

Use a PCI or ISA (depending on your PC's age) Parallel port adapter card, so if something goes wrong, you won't trash your motherboard.

Good start.

[adamziegler]

Cool project samco... maybe I will tidy up my HAL file and post it here in case anyone else is interested. I know it was a bit of a learning curve for myself to get that file right.

Kreutz... thanks on the advice again... you are about 20 levels higher than me with experience, so it takes me a bit to grasp what you are telling me at times... but I am learning a lot in the process.

All those mosfets come with a protection diode, so you can eliminate all the D1 diodes.

Hmmm... I know this website isn't the "bible" of stepper driving but when I look at Fig 3.4 of http://www.cs.uiowa.edu/~jones/step/circuits.html I see diodes across the coil, and diodes across the switch. I eliminated the diodes across the switches in my circuit because of the mosfet protection diode (like what you mentioned). Are you also saying I do not need to diode across the coil? Any ideas why Jones has them them included?

Use a PCI or ISA (depending on your PC's age) Parallel port adapter card, so if something goes wrong, you won't trash your motherboard.

Ok I was planning on using some photocouplers... in particular the OCP-PCT4116/E (I have some tubes of them) found here: http://www.lumex.com/product.aspx?id=790 Is this photocoupler not enough?

Use the IRL version of the Mosfets, they are "logic level mosfets" and you won't need to have two power supplies (+5, and +12) and a level translation to drive them, you will need only +5volt and logic gates. Use mosfets whose max Vds is rated for at least 20% more than twice your power supply's voltage.

Ok... took me a bit to figure out what Logic Level meant. I think it just means they can be driven with lower voltage ... voltage levels common from a logic-level output (like a pic). Is that assessment accurate?

Lost me a bit on the two power supplies. Granted I haven't totally worked though this yet, but my plan was to power the output side optocoupler with the same 24V and common ground as used for the stepper. The input side will only get connected to the parallel port. Should that work?

Good start.

Thank you... that means a lot.

[kreutz]

Any ideas why Jones has them them included?

He uses the diodes because it is a general diagram with "generic" switches. Most of the other examples include bipolar transistors, when using bipolar transistors you will need those diodes as protection. mosfet transistors can handle the voltage surges if, as I told you before, you use Mosfets with rated max Vds >> 2 * Vcc

[kreutz]

Originally Posted by kreutz
Use the IRL version of the Mosfets, they are "logic level mosfets" and you won't need to have two power supplies (+5, and +12) and a level translation to drive them, you will need only +5volt and logic gates. Use mosfets whose max Vds is rated for at least 20% more than twice your power supply's voltage.

Quote:

Ok... took me a bit to figure out what Logic Level meant. I think it just means they can be driven with lower voltage ... voltage levels common from a logic-level output (like a pic). Is that assessment accurate?

Lost me a bit on the two power supplies. Granted I haven't totally worked though this yet, but my plan was to power the output side opto-coupler with the same 24V and common ground as used for the stepper. The input side will only get connected to the parallel port. Should that work?

The term "Logic level mosfets" refers to "Power mosfets" with lowered triggering threshold voltages intended to work driven by logic gates.

In practice the Vgs is driven up to 10 volts in order to get better switching times, but you can still drive them with 0 - 5 volt logic levels, generally by using "logic gates" in parallel, in order to handle the initial gate charge and discharge currents. Logic level from output pins from a PIC can't handle the required currents for IRL510.

Normal IRF type power mosfets require voltages from 12 to 16 volts in order to get the same results. Keep in mind that this is not a disadvantage of the latter, since higher voltage difference can move higher charge, in and out of the gate, faster... Hence the need for another power supply (one for the logic levels, another for the mosfet driver).

Using opto-couplers is another good alternative for PC protection.

[adamziegler]

I have adjusted the schematic a bit to attempt to use a transistorized current source. Any thoughts or suggestions on it? Will the zeners work for me as a voltage source, or do I need to just use a few diodes in series?

Again, I am using a ATX power supply, and half stepping them. (a ab b bc c.. etc) Thank you.

[adamziegler]

I re-arranged the design a bit to remove one set of transistors. I have ordered some parts, and plan to test when I get them in. Heres to hopping for no transistorized fireballs!

-Adam

[kreutz]

How did you calculate the current source?

[adamziegler]

I assumed voltage across the diodes ~0.6V across each diode (D2s). Transistors have about the same across the BE... but the TIP120 is a darlingtion, so the BE voltage is 2 x 0.6V. Out of the 3 diodes I am left with 0.6 V so I sized the resistor (R4 0.47ohm), to make sure the emitter could only drain ~1.5A (actually a bit less than that.)

It is my hope that the R3's will keep the TIP120 off when the opto isnt triggering them.

What do you think?