While some of the following have been embellished for entertainment value, most are real questions that I have received.
Question: What does 'STMD' mean?
Answer: It is an acronym for STepper Motor Driver. I couldn't invent a cool-sounding name if my life depended on it.
Question: Can you help me modify the design to run a motor at 5 amps per phase?
Answer: No. Go buy a Geckodrive.
Question: Is it possible to parallel the LMD18245T for increased current capacity?
Answer: No. Go buy a Geckodrive.
Question: I just got done building my board and programming my microcontroller. The documents say the 'alive' LED should be on for 1/2 a second and then off for 1/2 a second. Mine is on and off for more like 4 seconds. Why?
Answer: Since you programmed your microcontroller
yourself, you need to verify your fuse settings. In particular, make
sure the CLKDIV8 fuse is unprogrammed (logical 1). This is not the
default setting of a new Mega48. In the default setting (programmed,
logical 0) your microcontroller is only running at 1/8th of the
Question: What happened? Now my 'alive' LED has stopped flashing and is illuminated all the time!
Answer: The microcontroller firmware has detected a fault.
This could be a watchdog timeout, etc. The appropriate fault code has
been logged in EEPROM and you can read it out with an AVR programmer.
Cycling the power should clear the fault and allow for normal
operation. The fault code will still be retained in EEPROM.
Question: Hmmm... now my 'alive' LED is flashing very quickly. What is wrong?
Answer: Check the voltage being supplied to the board; it
should be greater than +8 Vdc at all time. If you are using a 'weak'
supply it is possible for the voltage to sag as the microcontroller
turns the LED on. This sag resets the microcontroller and the LED turns
off as the output pin is tri-stated. When the LED turns off, the
voltage rises and the microcontroller begins to run again. And so the
vicious cycle continues...
Question: In your parts list, R20 is missing. In the assembly instructions it is listed as being optional. What is the purpose of this 5 kohm potentiometer?
Answer: R20 is a 'feature' that I never implemented. It has no functionality and should be ignored.
Question: I just looked at some pictures of assembled boards on your website and I noticed that you used some test points. I do not see these test points in the parts list?
Answer: Some early boards I built used test points so I
could clip oscilloscope probes to them during debug. The points add
about $2-3 per board, so I haven't been including them in the parts
list. In fact, with a multimeter, it is easier to do spot checks
without the test points installed because the empty hole prevents the
probe lead from slipping away as easily. If you want some test points,
check out Digikey #5005K-ND. This is a red test point but other colors
Question: The STMD requires step & direction signals to operate. I want the motor to rotate as soon as it is powered up. Is this possible?
Answer: Yes. Turn on the 'Test Mode' DIP switch. Now when
power is applied the motor will rotate based on the direction signal.
The enable signal is still required, so you must wire it high if you
aren't using it.
Question: OK, that worked, but how can I adjust the speed?
Answer: There is a spot on the board for a potentiometer
(R20) that could be used as a user-adjustable speed control, but the
open-source firmware will need to be modified to take advantage of
this. Either do it yourself or ask me for a quote.
Question: I hooked up a motor that internally had a shorted winding. Now my board won't work. How can I tell if the LMD18245 drivers chips are damaged?
Answer: I have been able to detect most damaged LMD18245's with an ohmmeter.
Question: I need the board to walk, talk, and quack like a duck? Is this possible?
Answer: Sure, just ask me for a quote. Seriously, the
microcontroller's program memory is only 40% utilized, so many custom
features and functions can be added.
Question: Is it possible to modify the design to have 'step clockwise' and 'step counter-clockwise' signals instead of 'step' and 'direction' signals?Answer: Yes. I have developed special firmware that does this. Note that the 'test' mode of operation will only allow the motor to rotate in a single direction as the 'direction' input is now another step signal.
Question: Do you have a single board that can control 3 or 4 stepper motors?
Answer: No, I prefer a more modular design. Otherwise, if
the magical smoke gets let out of one driver channel and that channel
is not repairable (burnt traces, etc.) you may have to trash the working
driver channels as well. Modularity is much better from a replacement
Question: Nice product. Do you have any servo motor drives?
Last Updated: Dec. 28th, 2007
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