Arduino, Pca9685 and 16 fans 12v - art installation

Projects General Guidance
41

Sorry,

3-6 130 DC Toy Motor

42

  • Do you see any reason why you need all the motors to be on the same Arduino ?

  • Will you have a bank of 12v fans on one set of PCA9685s and a bank of 5v motors on a second set of PCA9685s ?

  • And yes the capacitors across the fans/motors have to be removed.
    The same IRLZ44N should work on those motors.

  • Don’t see any current ratings for the motors you linked. :face_with_raised_eyebrow:

43

  • I have similar looking 3-6 volt motors.
    Coil resistance is 10 ohms.

    • Lets say we have a 5V power supply.
      Start Current = 5V / 10R = 0.5A
      If we have 32 of these motors and they all turned on at a time:
      32 * .5A = 16 amp power supply would be needed.

  • Beware, if we connected four PCA9685s up to the i2c pins, all pullup resistors will be in parallel, i.e. 10k / 4 = 2.5k
    This might be too low a resistance to give good i2c waveform edges.
    You might have to remove the pullups from a couple of PCAs :thinking:

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44

Hello,

Sorry delay with replies, i've been busy whole week. I've seen your message ealier but i had to educate myself about what you mentioned.

Do you see any reason why you need all the motors to be on the same Arduino ?

I wanted to control everything through one code so there is not synchronization issue between triggering motors.

Will you have a bank of 12v fans on one set of PCA9685s and a bank of 5v motors on a second set of PCA9685s ?

This was my original plan. I have 6 PCA9685s in total but i wasn't sure how many i will be using.

Lets say we have a 5V power supply.
Start Current = 5V / 10R = 0.5A
If we have 32 of these motors and they all turned on at a time:
32 * .5A = 16 amp power supply would be needed.

I was planning to use this: 5V Power Supply

Beware, if we connected four PCA9685s up to the i2c pins, all pullup resistors will be in parallel, i.e. 10k / 4 = 2.5k
This might be too low a resistance to give good i2c waveform edges.
You might have to remove the pullups from a couple of PCAs

So should I remove the SMD 103 from every additional board when more than two are connected in series? Or just leave one with pullups?

45

This was my original plan. I have 6 PCA9685s in total but i wasn't sure how many i will be using.

I was planning to use this: 5V Power Supply

Does that mean you are using a 12V power supply for the fans and a 5V power supply for the toy motors ?
For a worst case situation where the motors are taking full current:
Let's assume yes, that would be 500mA for each 12V fan, and if the toy motors were say ~10 ohms that's 500mA each for the 5V toy motors.
Assume 32 fans (2 PCA9586) and 32 toy motors (2 more PCA9586).
Your 12V and 5V power supplies would need to be 16A each, maybe get a 20A each maximum.

With the above mentioned 32 Fans and 32 toy motors that is a lot of wiring !
For motors only, 64(motors) * 2(wires per) = 128 wires (think about their length too, the wiring has to be neat, and removable connectors will be a must).
Your wire management needs to be addressed and cleaned up.
Your protoboards need to be immaculate. :roll_eyes:
Suggest you practice soldering skills.

You have entered the point where the Arduino should probably be powered by the external 5V power supply, if this is an UNO, feed the 5V into the USB connector so there will be no chance of the UNO back feeding into your PC or laptop!

Also do not overlook the need for proper fusing as mentioned in previous posts.

So should I remove the SMD 103 from every additional board when more than two are connected in series? Or just leave one with pullups?

If you used four PCS9586s, this means 4 parallel 10k pullups on SDA and the same on SCL.
10k / 4 = 2.5k for SDA and 2.5k for SCL.
2.5k is okay but getting a bit low, suggest you keep it around 5k.
Therefore, if you did use 4 PCAs, you would need to remove the pullups on 2 of the PCA9586 boards.
Hence two PCAs would have pullups, 10k / 2 = 5k
:+1:

From the Nick Gammon web site.

4.7K reasonable waveform on SCL

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2.2k Still okay, on SCL

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46

  • Don't make the same mistake as many do.
    Wire up say 4 fans and 4 toy motors.
    Practice making the wire looms PCB mounting, protoboard soldering, and crimping connectors on cabling.

  • Write some code to operate the 8 motors to see if things are as you thought they would be.

  • Only when things are workable and working proceed with the other motor componentry.

47

Alright. I will probably be back with more questions and debugging soon... Thank you!

48
  • Mount your PCBs properly using M2 hardware.

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  • Look into using Brass Inserts if applicable.

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