My latest project is a better stepper motor driver for the desk clock. When I designed the clock, the resistor-based driver circuit was the quietest solution I could find. It was mostly silent, but over time the gears started to develop a slight rumbling sound. The motor itself seemed quiet, but the gears were starting to rattle. Another thing that really bothered me was the ridiculous cost to ship the tiny circuit board overseas. Shipping and customs costs were often 3X higher than the board itself.
I went searching for something better and believe I may have found a solution. The secret is to use a board called a CNC Shield V4 which is designed to allow an Arduino Nano to control three A4988 stepper motor drivers. The A4988 is replaced with a much better Trinamic TMC2208 driver. This reduces the noise and allows everything to run on 5V. A precision real time clock was added to serve as a reference timer.
Here is the bill of materials:
1) CNC Shield V4 – Amazon US$10.96 for 3 boards.
2) TMC2208 drivers – Amazon US$21.99 for 6 drivers.
3) Arduino Nano – Amazon US$16.99 for 3 modules.
4) DS3231 Real Time Clock – Amazon US$12.11 for 4 modules.
5) NEMA17 stepper motor – Amazon US$9.99 each.
The CNC Shield V4 was modified to fix a known bug and to wire the RTC into one of the unused driver ports.
Here is the circuit:
The TMC2208 was set to 16X microstepping mode. The algorithm adjusts the stepper motor delay to stay synchronized to the real time clock reference. The DS3231 is voltage and temperature compensated to stay accurate to around 1 minute per year. And the clock is significantly quieter.
One downside is that the CNC Shield V4 is huge compared to the custom driver that I was previously using. I am designing a new base to fit the larger circuit. It looks like it will fit. The ability to buy off-the-shelf components is a big advantage. It does not make sense to design a more compact custom circuit board.
Updates to the existing MyMiniFactory desk clock are coming soon. A larger version of the desk clock is also in progress. I designed it a while ago but did not release it because the gear noise was too high. That rattling noise is gone with this new driver circuit. And a wooden gear version of the clock is in progress.
Stay tuned for more information.
Steve
Steve,
I must congratulate you on your clock designs. They are very impresive and a joy to build.
I have built 3 of your clocks so far thus:-
1 - SP4 Large Easy Build
2 - SP8 Coup Perdu
3 - SP6 Silent Desk top (CNC Sheild V4 Rev 2.01).
The SP4 clock is accurate to within 1/2 minute a week.
The SP8 is accurate to about 1 minute per day. (still adjusting pendulum period).
The SP6 is running very quietly but is running slow at about minus 10 minutes per day.
I have tried different RTC modules but they give the same results.
Is there a way of adjusting the alogorithm for better accuracy or should I be looking elsewhere?
Regards,
Alan
Wow can't wait,
Steve: Thanks for the clock files my family and friends are impressed with the electric sp6 V4 clock so I know what I will be giving for Christmas this year.
We also went back to the sketch ver 1p05
Allen got the clock running checked all solder joints still had the problem compiled the sketch checked the tcm and 2208, replaced the 2208 finally found one he liked put it all back together been running 6 hours very accurate jumpers on hold and abort.
The silent clock with the V4 shield stopped running the stepper was vibrating took the clock apart and adjusted the 2208 a little it started running put it back together and it was running too fast replaced the 2208 and cannot get it to run right, I had a engineer that I hired from Texas Instruments when I owned Cavalier Motorsports had the same problem I did, he is going to work on it.
Silent clock with the V4, silent and accurate so far looking forward to printing something els.e
I have the SP6 clock with the CNC shield V4 where is what you are talking about.
I understand about holding the second hand I also notice that you need the have the jumpers in the right position. What position do you have the jumpers set on the clock you have running.
It is very quiet, from what I see so far I believe it is going to be a challenge to get the time set.
Don't know what Idid but it works stepper motor is going around
Steve: i built another board went thru adding the nano 2208 and rtc it counts will not run a stepper
I took the black and yellow V4 doing what I did with the red one and everything works I mean it kept printing I have two steppers and neither one works no vibrations or anything. I will start back on Monday.
I am going to build a new V4 and new 2208 and RTC I am going to take a few days off have some honey do to get done.
The nano is installed in the V4 it is writing,
the 2208 and the RTC have been removed removed jumpers no difference still writing added the 2208 still writing added the stepper motor still writing motor not rotating adjusted the Vref no difference in rotation added the RTC stopped writing removed it back to writing, at no time is there power going to the stepper.
This is what I see
When the Nano is removed from the V4 it works counting down but when I install it in the V4 it does not
the new zip code installed get two lines CNC Shield V4 clock movement - Rev 2.01, Waiting for the RTC nothing else no movement on the stepper.
When I download files from Youbionics and Backyard Brains I get the sketch as a ino. I do a lot in robotics
I cannot cut and paste the txt. I do ctrl c and nothing happens