Electronics Meetup/Member Build-Openscan 1/18/2021 6pm

Hello all,
we will be meeting up Tuesday the 18th @ 6pm to continue work on the open source 3D scanner project.

We will get the pieces assembled and the device working and iron out the details of which software we will move forward with.

As always we will wrap up with any general electronics project questions.

I hope to have a zoom link as that worked well last time so check back here for that link as the time approaches

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Zoom Link!
https://us02web.zoom.us/j/85741081793?pwd=N3EwNjluV1RSOXU5Y1k0aDk5andhQT09

Folks,
I spent some time this morning looking at the Raspberry Pi and Arduino versions of the project.

Similarities

  • Both control the stepper motors and can send signals to trigger external cameras.
  • Both require building “Shield” boards to hold two A4988 stepper drivers and the external camera interfaces.

Differences

  • The Arduino version user interface is a small lcd panel and push buttons.
  • The Pi Version
    • provides a web interface (Wifi or Ethernet) for job configuration and control.
    • can directly control an 8MP PiCam V2 and store the accumulated images the Pi’s SD card.
    • Supports a ringlight board for the PiCam to provide uniform illumination

The Pi Version software has been tested on Pi4 and Pi3.

To me, the Pi Version looks like a more complete and extensible solution. However, I’m probably biased by having spent a lot of time developing Raspberry Pi systems.

Useful links

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If it doesn’t introduce specific issues outside of general project complexity, i don’t see a reason why we wouldn’t go with a Pi- It seems like a much easier thing to make modifications for should we feel that the first version could use some improvements-

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Camera Research Part 1:
Canon Rebel (T7) ~ 500-800 (depending on bundle!)
Rebel EOS T7 Kit, And it’s specs.

Would be good for streaming setup as well, which would put it at a premium but multi purpose. We would need to get a Zoom lens for it to mitigate perspective warp (true for all cameras). Canons have many great lens options.

For DSLRs, I don’t think it gets any cheaper (unless we purchase a camera with a locked lens, which I don’t recommend).

DSLRs seem to have an easy way to do shutter control:Here is an article about it - something called “gphoto2”- Here are the officially supported cameras

Something of note is that T7 is not on their official list, but T7i is… but the difference is around 400 dollars. I think It might be worth looking for a T6 (refurbished or otherwise): A refurbished with zoom lens goes for around $600..

Again, we could ask for this as an investment in both streaming and scanning. It’s also possible we look other places than Amazon.

Part two will be looking at Pi-Cameras.

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@RobinLloydMiller Thanks for digging into this! FWIW, the Pi Version is using gphoto for external control of DSLR cameras that support a USB interface. There’s also an opto-isolated trigger output for cameras that only support wired shutter control.

@Gary I looked more closely at the docs for Arduino and Pi versions to try to answer your question about “timed control”. I had the impression you were thinking about a completely open loop situation where someone would come in, set up their smartphone to capture images at some fixed interval and program the OpenScan to move to positions at fixed time intervals – the idea being that they would manually start them both at the same time and trust that they would stay in sync for the duration of the shoot. Is that right?

AFAICT, neither the Arduino nor the Pi supports that exactly. You can set a dwell time in either version to make the OpenScan hold still at a position for that duration but it doesn’t seem to include the time to move from one position to the next. I can see how that might get tricky unless the both axes move at the same angular rate and the programmed steps in each axis are equal.

Both versions do support triggering at each new position and holding still for a fixed dwell time.

Let me know if I’ve misunderstood what you were referring to.

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Mike,
Open loop was what I was thinking. The Arduino with the camera phone is setup to do exactly this.
They should have a very consistent step timing that can be accounted for with a photo taking app.

That said I am happy to embrace the goodness that is RaspPi

Robin,
I am not ready to shell out for a camera of that quality as much as that would be awesome. I will wait to see some of the other options you can turn up.

@Gary So it looks like we could support open loop in the Pi Version by choosing External mode and setting **Time Per Foto" to the desired interval and simply ignore the Release Time value, which, AFAICT, determines how long the shutter control output is active during the photo interval.

A little experimentation should tell us how much extra time, if any, needs to be added on the camera side to compensate for the time to move to the next position.

I’ve posted a query in the OpenScan repo’s issues pages to verify that this will work as expected.

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I found two ways to remotely/automatically ask a cell phone to take a picture. The open scan project uses a bluetooth button, available on amazon for c. $8. Other projects use the volume control found on earbuds to act as a shutter control. This second solution seems easier to me as it’s hardwired, and doesn’t require a battery. A link below provides the hardware specs for volume control, which could be easily triggered by an arduino, and I assume a Pi. The other link shows someone using the VisualSFM software. I’ve not played with Pis before but interested in learning.

https://source.android.com/devices/accessories/headset/plug-headset-spec

@PikePorter That’s a really interesting video tutorial. I had no idea open source scanning/meshing/rendering software had become so advanced.

The volume control hack sounds pretty straightforward. Seems more easily shared that the Bluetooth remote approach since that requires pairing and unpairing with each user’s phone.

Its definitely a lot for a personal thing, but perhaps Generator might? (On the basis of investing in a product photo camera, which i think has been a conversation floating around)

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