Open Source Hardware versions of closed source hardware?
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Open Source Hardware versions of closed source hardware?

by jdoscher on Sun Dec 02, 2012 2:30 am

I shared my solar tracking robot (solarbot) on tonight's Show and Tell, and I need help from the forums. I have a couple closed-source components that work well for the robot, but their licensing is closed and they are not viable for integrating into a full-OSHW design because of this. I'm hoping forums members can share links or designs to similar or compatible components, allowing me to publish a full-OSHW hardware design. Adafruit parts are always welcome too :)

First is my power supply. Since the motor controller shield runs off 12VDC @2A, and the source of power is usually a battery or solar panel, input voltage may fluctuate between 12-24VDC. I am using this one currently:
http://www.mini-box.com/DCDC-USB-200
I am not using any of the advanced features, so I am hoping someone can refer me to an OSHW alternative.

The second item is the motor controller shield itself, which is an Arduino-compatible board, but is not OSHW.
http://www.pololu.com/catalog/product/2502
I am using this to control two 12VDC motors which draw about 2A max, but never at the same time. The circuit/app never ramps the motors up to full speed either, but I am leveraging the Pololu library to control & ramp up/down motor speed.

There are many motor control & power supply circuits out there- but I am not so great at finding ones that are equivalents to what I am using now. My hope is that I can build new circuits to replace these to not only lower the cost for someone else to build one of these, but create a project that is easy to license and generally unencumbered for OSHW. Thanks in advance,

Jay
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Re: Open Source Hardware versions of closed source hardware?

by westfw on Sun Dec 02, 2012 4:56 am

I guess that's a nice thought, but I think and open source hardware project doesn't NEED to use all open-source components (even "board-level" components.) If you clearly document the requirements of the non-open-source bits ("12V @ 2A" for the power supply, for example), and a source where you can buy them, then you've gone further than many OSHW projects.

Now, in your case, the power supply and motor driver are rather expensive, and overkill (according to what you say here), so it might be nice if you researched cheaper alternatives, but you don't HAVE to...
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Re: Open Source Hardware versions of closed source hardware?

by jdoscher on Mon Dec 03, 2012 2:49 am

Thanks for your reply, but I guess what I am saying is that I do feel I need to leverage open-source or freely available circuits here- not only because it allows me to license the entire project as OSHW, but also due to cost- I am taking on additional cost for a custom PCB already, and it makes far more sense to source board-level components and leverage other's work in these areas.

While I have already done significant research on these components- I ended up having to choose proprietary circuits due to compatibility or documentation/support.

I know the tone of forums can come off sounding harsh, but this isn't meant to sound that way- but I'm not looking for validation of my product choices, but hoping someone out there knows of tutorials, circuits, etc. that may be OSHW equivalents as my original post said.
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Re: Open Source Hardware versions of closed source hardware?

by westfw on Wed Dec 05, 2012 3:00 pm

Ah, if you are planning on including the power supply and motor driver as part of your "product", then of course you DO need OSHW versions. I had assumed you were just implementing the "middle" part, with instructions "connect a 12V 2A power supply, and an appropriate motor driver"...
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Re: Open Source Hardware versions of closed source hardware?

by adafruit_support_mike on Thu Dec 06, 2012 5:26 pm

From the description you gave, it sounds like the power supply unit you've described is serious overkill.. it's a boost-buck, capable of stepping high voltages down or low voltages up. If you only want to limit the voltage coming from a solar array, and only want a couple of amps, you'd probably do well with a switching regulator.

The Texas Instruments TL2575 ( http://www.ti.com/lit/ds/slvs638b/slvs638b.pdf ) puts all the control logic for a step-down regulator in a single package and costs a couple of bucks. The chip itself can regulate 1A of current, but it wouldn't be hard to bypass the internal transistor with an external one rated for higher current.

As for motor control, the Pololu board uses the ST Microelectronics VNH5019A, which costs about $7.50 at Mouser. The datasheet ( http://www.pololu.com/file/download/VNH ... e_id=0J504 ) tells you how to work with it and shows an example circuit on page 15 (Figure 5). Datasheet reference circuits are the polar opposite of closed hardware design. They're "please.. use this circuit (and buy our chip)" fare.
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