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Pololu Circuit Question

Posted by Deferr 
Pololu Circuit Question
April 30, 2010 09:46AM
I am getting ready to put Adrian's Pololu stepper driver circuit together and have run into a question. He mentions that if you are using 5v from the Arduino Mega, to leave out the 78L05.

Does this mean to leave out this section of the schematic entirely?

Re: Pololu Circuit Question
April 30, 2010 10:40AM
You have it right, other than usong the wrong symbol for ground. I have a set wired up like your modified schematic and it works perfect.
Re: Pololu Circuit Question
April 30, 2010 10:52AM
johnnyr Wrote:
> You have it right, other than usong the wrong
> symbol for ground. I have a set wired up like your
> modified schematic and it works perfect.

Great! I am thrilled to only have the wrong symbol for ground. I have just enough electronics knowledge to read a schematic and fumble through getting it together. I think I can handle this one (fingers crossed). Thanks for the help. If I run into issues do you mind me asking advice of you. It's nice to have a contact with roughly the same setup.
Re: Pololu Circuit Question
April 30, 2010 02:07PM
Not that it matters in this case but aren't the "in" and "out" pins are swapped on the 78L05?
Re: Pololu Circuit Question
April 30, 2010 04:34PM
smiling smiley Yes

The input on a LM7805 (or any other voltage regulator) is the high, unregulated voltage, and the out is the solid 5Volt good stuff.

I would also consider keeping the two capacitors there to minimize voltage spikes when the Polulu's switch on and off. Run and already regulated 5 volts from another card over ribbon cable leaves it very "soft" and unable to instantly supply large inrush currents, or absorb back EMF when motors are turned off. Keeping the 100uF electrolytic to handle big, long duration impulses and the 1uF ceramic to short out the high frequency spikes and noise may help make the board more reliable, fewer missed or extra steps.

EDIT: After looking closer at the whole circuit, I see that there are already 100uF electrolytic caps for each Polulu. And looking closely at the internal schematic for the Polulu's, they have their own internal 0.1uF surface mount capacitors, so no need for any extras beyond what is still in the schematic after the 7805 and attached parts are removed.


Edited 1 time(s). Last edit at 04/30/2010 04:44PM by rocket_scientist.
Re: Pololu Circuit Question
April 30, 2010 04:51PM
I am a little confused after looking even closer at the circuit. It looks like the only source of the 12 volts needed to drive the steppers and the extruder heater came from the connector that is now labeled 5V, Mega, Gnd. Should this still be:

pin 1 12Volts (in revised drawing labeled 5V)
pin 2 5V from ATMega (in revised drawing labeled gnd, should be mega)
pin 3 ground (in revised drawing labeled mega, should be gnd)


If so, you could do as little as not soldering in the 7805 to get exactly the desired effect, assuming that a pre-fabbed PCB board is being used.

Re: Pololu Circuit Question
April 30, 2010 06:34PM
Feel free to contact me directly, but if you have questions regarding these electronics it would be good to ask the questions in this thread so others may contribute and gain too smiling smiley I am following this thread.

degroof and rocket_scientist,
The schematic Deferr pasted came from [objects.reprap.org]
I concur about the LM7805. If it is backwards it needs to be changed there and in the svn. I would be happy to make the modifications in eagle and change the schematic on the page, but that will not help svn.

Re: Pololu Circuit Question
May 01, 2010 06:58PM
If you are going to be kind enough to redraw the schematic and switch the 7805 around, you probably should put pin numbers on it, too. 7805 Datasheet has the generic for all voltages.

Which capacitors and resistors would your recommend using for this?

Or do you need to get capacitors with the same voltage levels as you motors?
Re: Pololu Circuit Question
June 02, 2010 06:35PM
I've prompted Adrian to create us a BOM (Bill of Materials) for his circuit design as soon as he can.

Meanwhile: You want components rated at a somewhat higher voltage than you plan on using (as long as they physically fit the design, and are not too expensive!). So that means capacitors rated *over* 12V in this case. Something like Mouser Part 140-RGA101M1EBK0611P should be fine for the 100uF capacitors, for example.

Re: Pololu Circuit Question
August 02, 2010 09:01AM
Does this look about right?

C1, C2, C3, C4, C7: 100μF
C5, C6: 100nF
C9: 10μF
R1, R2, R3, R4: 100kΩ
R5: 1kΩ
40way 90degree header pin x2
4 Way 2.54mm PCB Mount Pin Header x9
3 Way 2.54mm PCB Mount Pin Header x4
2 Way 2.54mm PCB Mount Pin Header x1
3 way terminal block x1
LM78L05 3-Terminal Positive Regulator x1
40pin header socket x1

I linked to Altronics for some components as that's where I source my components from locally.

Would it be possible to create a stub on how to make an opto end stop from strip board as well and the parts required to do so?

Re: Pololu Circuit Question
August 10, 2010 12:44PM
In the last week or two Adrian has posted pcb designs to the wiki and sourceforge pages for Pololu designs. It looks like they are completed so I'm going to give them a try. The only problem I'm having is finding the MOSFETs: VNP14NV04-E.

I've tried multiple electronic suppliers in the US and all are out of this part. I'm looking for an alternative right now, but does anyone else have any suggestions?

Re: Pololu Circuit Question
August 10, 2010 01:36PM
Well, Mouser.com suggested 511-VNB35N07-E as similar to the VNP14NV04-E MOSFET shown in the Eagle files. It looks to be rated for higher Voltage and Amps. My knowledge is thin, so I'm unsure if this is completely fine, if it will work but I will have to make changes to other parts, or if it will not work at all.
Re: Pololu Circuit Question
August 10, 2010 02:06PM
Electrically it will work, but it is a D2PAK SMT package instead of a through hole TO220.

Re: Pololu Circuit Question
August 10, 2010 02:48PM

Are any of these suppliers useful? smiling bouncing smiley

-Sebastien, RepRap.org library gnome.

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything! grinning smiley
Re: Pololu Circuit Question
August 10, 2010 04:43PM
Nophead- Thanks, I forgot to check for the package number. Guess so much for that part...

Sebastien- All but one supplier is shipping out of the US or has minimum orders. It looks like Arrow ships small amounts from in the US but shows a 12 week lead time. I've e-mailed them to see if that lead time is for all orders or just for large orders. Hopefully the lead time is only for large quantities. I'm also going to keep looking for an alternate part while I'm waiting hear back from Arrow.

Again, if anyone has any other suggestions I would be more than thankful.
Re: Pololu Circuit Question
August 10, 2010 10:09PM
Sebastien- Arrow does ship small amounts so I will be able to order from them. Thank you for your help and pointing me to Octopart. That site is a great resource.
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