Driving a Big Easy with a 555 Timer?

Community Projects
1

Hi All,

I have spent most of my morning attempting to put together a simple 555 timer and Big Easy driver. I have encountered a problem. The stepper motor clicks one time when the whole circuit is powered up, and then locks the motor shaft. The 555 is sending pulses as I have an LED blinking away happily at about one per second. The Big Easy LED is shining nice and bright. When I disconnect the 555 output and tap that output lead from the 555 to the input lead on the BED the motor does step. I also attempted to use 2 555’s to provide a distinct division between pulses and the results are the same. All I am trying to do is drive the stepper for a equatorial mount at a constant rpm for night sky photography, but obviously something is amiss. I would have thought simple pulses would suffice. I have used a 7805 on the 555 side and am powering the BED with a 12v wall wart of 1.5 Amp and its output is actually 11.6v DC. The motor is an Epson FM-257. Do I need a driver transistor on the 555 pulse, or a pulldown resistor on the 555 output? Thanks in advance for any advice.

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Without a circuit diagram it is impossible to guess what could be wrong.

You would be better off using a micro (e.g. $2 Arduino Pro Mini) than a 555, as it is much easier to time and control the pulses, and it takes far fewer discrete parts. http://www.ebay.com/itm/Pro-Mini-Enhanc … SwT6pV5YIu

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So a schematic is required for a 555 running in the astable multivibrator mode? Really? This is one of the most common, and most documented, schematics in the history of IC’s. All I am doing is sending the output from pin 3 of the 555, which is cycling at once per second, to the BED. This is a 5v pulse and is connected to the input of the BED, which is supposed to trigger the BED. After double checking all the solder points and other connections this morning there are no errors on that front (according to http://www.schmalzhaus.com/BigEasyDrive … rManal.pdf) . I get the same result when bypassing the 555 and manually supplying momentary triggers of 5v to the BED input. Any time the BED is powered up the motor locks even without a connection to input of any kind. I have attempted to power the BED directly from a 12v battery and get the same results. Any time the BED is powered up the motor locks and becomes quite hot in short order, but the BED does not. I just think I got a bad BED. I even used another identical motor with the same results.

On the Ardunio front I have no need or desire to learn coding specific to the platform. Seeing as the BED is supposed to work with any 5v pulse a 555 should do what I need it to do, and that is to turn the motor at a constant RPM. I already have a functional 555 circuit doing what it is supposed to do. I also have a dual 555 wherein I can control the frequency of pulses and duration of those pulses. I attempted to use it too and got the same results. I am seriously considering using a dc motor with both voltage and PWM along with gearing to get simple RPM control.

Not impressed nor happy.

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After doing some more research it appears I was mislead about the ability of the BED to be driven with a 555.

This web page makes it clear the BED is not designed to work in that configuration:

https://learn.sparkfun.com/tutorials/bi … ide/dicuss

Toni_K / about 5 months ago / 1

“That’s a great question! The inputs to the Big Easy Driver have to come from a microcontroller. We typically recommend using an Arduino Uno for beginners as there is a lot of example code for getting started. Any of the code in this tutorial is designed to work with an Uno.”

This email is in direct response to asking if the BED could be driven with a 555.

Greetings

On Mon, 9/12/16, AJ Neal <aj@zagrosrobotics.com> wrote:

Subject: re: Zagros Robotics, Inc. - Contact Us Form

To: theropod@xxxxxx.com

Date: Monday, September 12, 2016, 12:31 PM

"Yes, you should be able to whip something up using a 555 timer.

Best Regards,

AJ Neal"

So, it seems I was not told the truth, or there is one hell of a lot of misinformation out there. I have kept at attempting to make the BED work with a 555 and have only barely been able to get any of a number of bipolar steppers to work, and then far from smoothly. Some jerk one direction and then the other, while most just lock up and get very hot very fast. I would be willing to give my little BED away if anyone wants it. I don’t think I have damaged it in any way, and I have no use for it.

All I ever wanted was to turn a stepper at a constant rate to drive an equatorial mount to track the night sky. So, I am going to use a 555, a 4017, and a 2003 darlington array. Simple and easy. Or I could use cascading 555’s to drive mosfets. I’ve learned more about steppers in the past two months than I ever cared to know.

5

Good evening everyone,

As a followup to the barn door tracker project I just finished putting together the motor driver as it should have been from day one. A brand new Arduino Nano clone is driving a brand new easy driver board at 1/8th step mode with a 5 line sketch. I spuerglued a small aluminum finned heat sink directly on to the easy driver chip, built a coke box cardboard shroud for the 12v fan to direct max flow over the easy driver and Nano, and screwed the main perf board to the inside of an old iOmega Zip drive case, with Dermel alterations to allow for the fan to pull lots of air. This is driving a little 6v 1.8°bipolar stepper so smoothly! The easy driver chip isn’t even getting slightly warm, nor is the motor or Nano. Having not yet mounted the motor and gear drive to the tracker I have the motor turning at an experimental, but respectable, 15~ rpm. This is at least 5 times faster than my spur gears ratio and end use demand. I have also written and run the sketch to turn the motor incredibly slow. Under neither condition does the motor get warm even after the 10 minute test. The smoothness of this microstepping feature is amazing. There should be only the smallest vibration transferred to the camera mount. With spur gears I know of no way to completely eliminate vibrations from the system. Maybe it would be best to isolate the camera from the mount, which is in trun hard mounted to the tracking top plate, which is the driven part via a curved 1/4" x 20 tpi allthread. A matching nut is centered on a spur gear which is driven by a spur gear mounted on the motor and this pushes the top plate away. Perhaps before the weekend is out I can get the drive timed correctly and take a picture of my efforts to date. Unfortunately the prime months for sky watching have past this part of north America. I may “pot” the whole thing before finalization as the tracker is an outside effort. Here the dew can be quite heavy in the spring and summer, and can collect quickly after the sun sets.

RA

ETA: I am powering this directly from our off grid 12v~ battery bank, and driving both the Nano and easy driver on the back side of a diode and switch. The perf board also has a new 12v to USB outlet and charges my iPhone just fine. No, not included for any use with the Nano.

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Glad to see that you appreciated my suggestion!

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jremington:
Glad to see that you appreciated my suggestion!

Yes, I have seen the error of my ways. I did build a discreet component drive, and it works great, except that without a 10 turn pot the 555 just cannot time pulses accurate enough. I learn the hard way. I did post that I was “Stunned and Amazed” in another thread after I was given a Nano. It was driving a unipolar motor with it at full steps, which was accurate as hell, but shook the tracker. The easy driver was the key to both accuracy and smoothness. The first Big Easy Driver I tried, that I feel was bad from the beginning, gave me a sour impression. Luckily I have a friend that works in the automation industry and helped me understand the advantages of the microprocessor.

So, jremington, I do appreciate your input, and fully confirm you were right all along.

RS