Hello Guest it is January 20, 2020, 12:21:53 PM

Author Topic: SmoothStepper died  (Read 5588 times)

0 Members and 1 Guest are viewing this topic.

SmoothStepper died
« on: October 08, 2010, 12:30:35 PM »
Hey guys, I recently got my smoothstepper setup and I love this thing, it made my cnc machine so much better. I could now get faster rapids and it just seems to be smoother overall. However in the process of building an enclosure for all of my electronics I somehow killed my smoothstepper it seems, here's what happens.

I'm powering the SS with USB +5 and Mach 3 won't communicate with it, the red and blue lights stay lit. I get an error that a timeout has occurred and then after a few messages it tells me that there was an error communicating with the CryptoMemory. I've tried computers thinking it might be a driver issue but same result on all of them. I noticed something interesting though, after a couple minutes of being powered up a chip next to port2 gets warm. I check around the port for any debris that might be shorting it but there's nothing there.

The only thing I can think of that could have burnt out the board is that when I first had it wired up inside my cabinet I was supplying +5v from an external power supply, I measured its output at 5.26v, coming from an ATX computer power supply. And had it grounded to the chassis of the cabinet (the grounding jumper enabled).

Thing I can't figure out is that the input voltage was good, and I measured for any stray potential between the floating ground (coming from power supply) and the ground of the case and there wasn't any.

Thanks for any advice here, I'm just trying to figure out what NOT to do when I get the next SS.

Offline Jeff_Birt

*
  •  1,107 1,107
    • View Profile
    • Soigeneris
Re: SmoothStepper died
« Reply #1 on: October 08, 2010, 03:05:48 PM »
First thing to try is a new USB cable. Then look in Device Manger under the USB section and see if the SmoothStepper shows up. If it does not then something is likely wrong with the SS. Greg at Warp9 might be able to fix it for you.

When powering a SS with an external power supply you must move the ext power jumper which is located by the power connection terminals. Also, never hook DC Common to ground (the grounding jumper) unless you have a very specific reason for doing so. It is unclear if you used the power supply in your PC to power the SS or a different supply. If it was a different supply please note that PC supplies have a minimum load requirement before they will regulate properly (it is often 10% or more of their rated capacity.) While 5.2V would likely not damage the SS you could of had larger voltage spikes that could not be seen with a regular volt meter.
Happy machining , Jeff Birt
 
Re: SmoothStepper died
« Reply #2 on: October 08, 2010, 05:09:01 PM »
Well, that's the crazy part, the SS shows up in device manager and is detected by mach3, but then fails to communicate properly while at the same time getting warm at that one chip.

I'll check out the 5V output of my power supply with a scope to see if there's significant noise, or spikes.

Thanks
Re: SmoothStepper died
« Reply #3 on: October 08, 2010, 05:25:12 PM »
Glad the SS has made an improvement to your system.  Hopefully you'll be back in operation soon.  Sounds like there is a problem with one of the power supplies on the board, and it probably isn't 3.3V.  The FPGA (large chip in the middle) requires 1.2V, 2.5V, and 3.3V.  5V goes to all of the interface chips (like the ones near Port 2).  The USB chip is powered by 3.3V, so it is unlikely that 3.3V is in trouble.  It could be an unrelated problem that the chip near port 2 is bad, or it could be that the external 5V from the ATX power supply went over-voltage like Jeff mentioned.  They usually do require a minimum load to regulate.  On the board you will see "1.2V", "2.5V", and "3.3V" in the silkscreen.  You should be able to measure those voltages.  If none of them are above a certain threshold, then the FPGA will not allow itself to be configured.  When it is properly configured, the red LED will go out and the green one will light.  The fact that it can't communicate with the CryptoMemory is that the FPGA is not working.

Please let me know what you see when you measure those voltages.  Hopefully you will find something that is causing it.  If not I will exchange it for a new one.

Greg
Re: SmoothStepper died
« Reply #4 on: October 08, 2010, 06:06:36 PM »
Thanks Greg, I'll take a look later today when I get home from work. I did check some of those volts and they seemed a tiny big over what the silk screen said, like the 3.3 was at 3.5, and the 1.2 was at 1.4 or so. But I'll check them again and let you know here. I'll also try testing with a different DVM or my scope for more precision.

PS: What's the real point of powering the SS from the +5 header and not usb? Is it just for using smoothstepper to power break-out boards that require more than 500mA? Also, as a 2nd side note, under what circumstances would I want to ground it, I thought it was to eliminate ground loops (grounded all of my power supplies at the same point)
Re: SmoothStepper died
« Reply #5 on: October 08, 2010, 07:25:47 PM »
It sounds more like your meter is off.  It would be very unlikely to have multiple regulators read 0.2V high.  It will be interesting to see if you read a different set of voltages with a different meter.

I think you hit it on the head with the reason for the external 5V supply.  Although besides the higher current availability, some people have had better luck with a more stable SS system using the external 5V than the USB supply.  I think some USB ports do not output a very strong 5V, particularly laptops.  I also think it might have been more of a problem in the past though.  I personally haven't ever had a problem with the USB's 5V supply.

As for grounding, I think it is hard to define the center of the star in a star ground when using a USB device.  Should the PC be considered the center?  Or in this case the SmoothStepper?  I think that is why better USB cables help a lot because they have heavier gauge wires for power and ground.  Short cables help a lot too.  I think it is important to keep the ground of the SS and the ground of the PC at the same potential.  I would like to hear Jeff's opinion on this.  I consider him the noise and grounding expert!  I do believe it is important to keep the ground of the PC and the ground of the SmoothStepper tied together as tight as possible.  You don't want a ground loop that involves the cable.  If the PC's ground is different than the SS's, then a current will flow.  Jeff, any thoughts?

Thanks,

Greg

Offline Jeff_Birt

*
  •  1,107 1,107
    • View Profile
    • Soigeneris
Re: SmoothStepper died
« Reply #6 on: October 08, 2010, 07:39:59 PM »
Quote
PS: What's the real point of powering the SS from the +5 header and not usb? Is it just for using smoothstepper to power break-out boards that require more than 500mA? Also, as a 2nd side note, under what circumstances would I want to ground it, I thought it was to eliminate ground loops (grounded all of my power supplies at the same point)

The way the SmoothStepper is configured a USB port will only give it 100 ma of current. Some computers can have a tough time supplying the proper amount of current or voltage level to USB devices. This combined with some USB cables that have 28 AWG power leads can lead to problems. I built a custom controller for a company that used two USB devices so it had an internal hub. The current draw of all three devices was only about 250ma or so but it was enough to cause a significant voltage drop across a 6' USB cable that had 28 AWG power leads. A more stout cable solved the issue. As you mentioned another good cause for using an external power supply is when using BOBs that steal power from the SS.

As for your second question first let's clear up that DC Common, (i.e. negative, -), is not the same thing as Earth Ground. DC Common is the common return path for DC circuits. For example, your PC has a power supply that outputs +5V, +12V both of these voltage share the same DC Common (which is typically referred to as 'ground'). If you take a volt meter and measure from DC Common to the 5V output you get 5V, and from DC Common to the 12V output you would see 12V. It is the common current return path for each circuit.

Earth Ground is actually a connection to the Earth outside your home/shop. It's purpose is to increase safety and secondary provide a low impedance path to bleed of noise. It is NOT a current carrying path for your circuits. It is common practice to (earth)ground each sub assembly back to a common point and then to bond that point to your electrical systems (earth)ground. For example a DC power supply typically has an (earth)ground terminal that connects to its case. This (earth)ground connection helps to bleeds off electrical noise that might otherwise be radiated by the power supply but more importantly if insures that the case of the power supply will never go above ground potential and be a shock hazard. You do not want to go around connecting DC Commons to (earth)grounds unless you have a very compelling reason.

A ground loop is created when a voltage difference is created between two devices due to current flowing through a ground connection. For instance if you daisy chain an (earth)ground instead of star grounding it. Many power supplies will have the DC Common bonded to (earth)ground inside of them, if you create separate (earth)ground externally you could potentially create a ground loop by providing a path for DC current to flow through the (earth)ground.
Happy machining , Jeff Birt
 
Re: SmoothStepper died
« Reply #7 on: October 08, 2010, 08:40:20 PM »
Thanks for clearing that up Jeff.

So I took some measurements of the voltages:
1.2v -> 1.350
2.5v -> 2.653
3.3v -> 3.434

do these seem out of whack?

btw, I used an IR thermometer and the hottest chip is the the middle one of the row of 5.

Also tried a different USB cable, same result.
Re: SmoothStepper died
« Reply #8 on: October 08, 2010, 11:55:45 PM »
Jeff, Thanks for that excellent explanation.  I agree with everything except I'm not sure about the 100 mA limit.  I believe the USB port will typically put out more than that and the current limit doesn't go into effect until about 1 amp or so.  Under high load the voltage droops considerably like you mentioned.  All devices start out at 100 mA or less.  After configuration they can bump up to 500 mA if they are a high-power device.  I just experimented with the USB port on my development computer.  I placed a 6-ohm resistor from Port 3 pin 4 (5V) to ground.  I then plugged the USB cable into the board and measured a current of about 700 mA through the resistor.  I guess that would equate to a bus voltage of about 4.2V, though I didn't measure that.  The SmoothStepper was recognized by the OS without a problem.  I think the only reason for keeping track of the current is so that the OS can decide if a device will draw too much total power from all of the USB ports combined.  If a high-power device is plugged in, the OS would be able to deny it from bumping up to a higher current.  The concern is the risk of loading down the bus and having a bunch of USB devices drop out from the low voltage.  There is also a spec that limits a device to 10uF of capacitance for a similar reason.  Too much capacitance will suck a ton a current for a brief moment when the device is plugged in, which could reset other USB devices connected to the computer.  I made sure the SS conformed to that spec.  There is a 100uF cap on the board, but it is only on the external 5V input.  One other point is that a device doesn't even need to enumerate to draw power from a port.  You can draw more than 500 mA from a port and not even be a USB device.  Of course every USB host is different.  Some could have current limiting at various levels, but I think most have one level set a bit higher than 500 mA.  For what it is worth, I did a web search and found this interesting site that shows some data that a guy compiled on various devices and how the voltage drooped at low and high current levels.  I didn't study it much, but here it is:  http://www.girr.org/mac_stuff/usb_stuff.html

Maddios, Those voltages are very suspicious.  I am wondering if your voltmeter is that inaccurate or if you are measuring from a ground that is not the ground of the SS.  I am hoping that you are connecting to the ground of the computer or something like that.  If so, that would indicate that the ground of the SS and the ground of the PC are not at the same voltage.

It is interesting that you can see a temperature difference in that one chip.  I have a feeling that the board will need to be replaced, but I want to spend more time working through this so that if a new board is installed something bad won't happen to it because of some mis-wiring or something like that.

Thanks for taking the time to take those measurements.

Greg
Re: SmoothStepper died
« Reply #9 on: October 09, 2010, 12:35:35 AM »
Greg, I took the measurements from the little case around the USB plug.

As for my whole configuration, I figure there's really no need for me to externally power the SS, was just doing it because I thought I could, no need to really as I'm going to be plugging one port into the G540, and the other into an externally powered break-out board. So I don't see why I can't just leave it running off my USB connector.

If I decide to power it I'll order one of these: http://www.soigeneris.com/MeanWell_PS_05_Power_Supplies-details.aspx