1 Topic by C_D (edited by C_D 2016-01-27 22:14:31)

  • C_D
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Topic: Alternative Electronics for FreeLSS

For my own scanner I have made a different electronics board and since it could be used with any FreeLSS scanner I figured it might be useful to post about it here.

The board measures just 42x52mm, and mounts directly on the Raspberry Pi GPIO port. It has an on board buck converter module which powers the stepper driver (Pololu-style either A4988 or DRV8825) and also the Rasppberry Pi, so all you need is a single 12-24V plug pack.

To keep all the documentation in one place I have moved everything to here.

If anyone is interested in trying it out, i have a few spare boards available, just flick me a PM if you are interested.

https://drive.google.com/uc?export=download&id=0B8WCm2S2LKqadVFFbV9FU0tjM3c

https://drive.google.com/uc?export=download&id=0B8WCm2S2LKqaYjJudFNBY2hEWmc

https://drive.google.com/uc?export=download&id=0B8WCm2S2LKqaVXZlNEZEd1lYRkk

2 Reply by Viseng

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Re: Alternative Electronics for FreeLSS

The schematic indicates that the driver is connected to +5V, yet the Raspberry pi GPIO are 3.3V logic level outputs.  The datasheet for the driver confirms that the logic HIGH must be >0.7*5V  that is >3.5V.  The driver logic supply must either be connected to 3.3V or level translators used to make the interface compatible.  The former is acceptable since the A4988 is specified to work at 3.3V.  Failure to adopt either approach may result in erratic or non-operation, depending upon device and supply tolerances, temperature or amount of noise on supply.

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3 Reply by C_D (edited by C_D 2016-02-17 19:04:56)

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Re: Alternative Electronics for FreeLSS

Thanks for your reply, I responded on my Thingiverse page, but didn't see you had posted here too. You are correct, running with 5V supply does appear to be using the A4988 out of spec. Mine has worked fine, but it may not work for everyone. I would recommend reducing the supply voltage to 4.5V, this will keep the A4988 within spec (0.7*4.5=3.15) and the Raspberry Pi should be quite happy running on 4.5V supply, though it may cause issues with some Wifi dongles instead.

Will just have to wait and see if anyone experiences issues.

4 Reply by elmoret

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Re: Alternative Electronics for FreeLSS

The ATLAS 3D Scanner uses the DRV8834, which supports 3.3v logic levels.

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5 Reply by C_D

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Re: Alternative Electronics for FreeLSS

Ok, it looks like the DRV8825 and DRV8834 modules will accept 3.3V logic signals with a 5V supply so using one of those is definitely the best option on this board.