OpenServo.com

jharvey · Posted: Mon Jun 15, 2009 12:27 am Post subject: open-regulator

So what do you do when you have a 12V supply and you need that 6V for the servo, well here's my solution. Low cost, fairly easy to build ect. I'm posting my files here

http://jaredharvey.com/openservo/open_regulator

My general intent is to run the I2C wires with a higher voltage on the VDC wires to decrease the current / awg size and RF. I see this used as an adapter / extender for the I2C wires that plug into the OSV3 and is located very close to the servo. Most signals simply pass through, and VDC is bumped down when you reach the servo.

I've done this layout with two separate regulators. I also put in some 0 ohm resistors that can be populated if one regulator will suffice. I've also allowed for an optional large input cap, you can simply hang something over the edge of the board next to the regulator. Any how lots of optional extras if desired.

Here's a link to a PDF that includes the schematic and the layout as it's drawn now. I'll update this PDF as time goes on, for now, here it is.

http://jaredharvey.com/openservo/open_regulator/open-regulator.pdf

Here's a link to the BOM

http://jaredharvey.com/openservo/open_regulator/power_reg.lst

The layout files are done with KICAD and I'm also posting a PDF copy so that you don't need anything special installed to review the files. The KICAD files should open just fine on windows or Linux platforms. I think KICAD might work with mac's but I haven't looked.

Please feel free to review and comment. Most of the values are just eye balled in there. There is a good chance this can be tuned quite a bit.

ginge · Posted: Mon Jun 15, 2009 7:15 am Post subject:

Looks good. One thing I would consider is upping that voltage to 7 or 7.5 volts. Although the OpenServo can run on 6v exactly, it isn't very tolerant to short drops in voltage and spikes in current.

This is because the LDO regulator onboard is rated for 0.7-0.9 nominal dropout on input, leaving very little room for the ripple effects.

It depends on how well those bulk caps will hold out.
_________________
http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/

jharvey · Posted: Mon Jun 15, 2009 10:19 am Post subject:

Already have some improvisations available for that. R4 and R6 make for an adjustable feature. The default is set to 6V, however if you break that bypass trace on R4 and install a couple resistors, you can pull that up to 7.5.

Hmmm, I should check that the R4 and R6 don't need to be very big. I've got them as 1/4 watt now, I'll have to make sure that will work.

jharvey · Posted: Mon Jun 15, 2009 3:59 pm Post subject:

I just updated the above to include the .com in the URL's. Oops.

I think the bulk caps should buffer fairly well. The use of the three should provide both a fair bit of storage, as well as caps that should dample the higher frequency spikes. Combined with the onboard decoupling caps on the OSV3, and it should be nice and solid. However, a real world test should answer any questions that might remain.

On think I'm tempted to think about, is the addition of a low voltage dector. Perhaps some kind of LED or such that would let you know that the output was lower than desired. However, I think I'm going to make it go before I think to hard about extras like that. Baby steps / get'er done.

I also just edited the top post to add a direct link to the BOM

jharvey · Posted: Sat Jul 25, 2009 1:17 pm Post subject:

I think I'm happy with my regulator design now. Except for a bad purchase on my part. Appears the front buffer cap I purchased is a couple times bigger than my board. Oops. I reposted my files here in a zip file.

http://jaredharvey.com/openservo/open_regulator

My basic theory for this layout is that the harness of wires that would normally go to the OSV3 would have this inserted into it just before the OSV3, with a connector on the end of the harness.

If you want to put on a connector and plug it in directly to the OSV3, such that the regulator is basically part of the harness end connector, you can go that route.

I put in multiple via's for input wires, that way you can daisy chain from one device to the next in a parallel power feed fashion.

Next step is to send it to batchpcb.com. I may etch one myself, however there are a fair number of vias. Drilling would be a bit of a pain, but doable.