Fried PropStick

TheGrue

Some how I think I fried my PropStick. I was building the attached Schematic for a Robot Remote Controller unit. I had wired up the XBee and Accelerometer on a breadboard for testing and all was well. I finished my board and tested each connection after I soldered it. I have not attached the switches or the LED's in the circuit. I just wired the resistors with jumper connectors for the front panel. The voltage regulator on the chip is putting out 4.5V without the USB attached and 5.5V with the USB adapter plugged into the PropStick. When it was on the breadboard it was a nice 3.3V

Can anyone see something in my schematic that might fry a PropStick? I would greatly appreciate a second pair of eyes.

Diagnostic Procedure followed:
After I could not get the PropStick to be recognized by the Propeller Tool for programming, I removed the Accelerometer, XBee and PropStick from my board. I tested all of the parts as follows> The accelerometer on a Demo Board = works fine. The XBee on the Parallax XBee USB adapter and was able to query the XBee with the X-CTU software and got a response from the XBee = works. Put PropStick back into a breadboard and applied a 6V battery to the VSS/GND and VIN making sure of the correct polarity of course. The Prop Tool could not find a Propeller. Tried several USB cables and ports, I even restarted my computer. I checked pin 32/VDD for the 3.3V output and saw the high voltages listed above.

Post Edited (TheGrue) : 4/5/2010 6:32:22 AM GMT

Sapieha

Hi TheGrue

First of al - On SCH --- You have reversed BAT Voltage

Regards


Ps. VIN-VCC is always +
GND always -

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Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
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Sapieha

Post Edited (Sapieha) : 4/5/2010 4:55:18 AM GMT

TheGrue

I did not catch that in the schematic but I know that I did not reverse the polarity on the board in real life.

Mike Green

Vdd (PropStick pin 32) must never be connected to more than 3.3V (with Vss at ground). Your PropStick will be fried with any Vdd > 4.7V ... Poof! With Vin connected, this should be the output of the built-in voltage regulator and should always be +3.3V when power is applied to Vin.

Vin (PropStick pin 12) is the input to the built-in 3.3V regulator and can be connected to any source of 5-9V.

Vss (PropStick pins 9, 10, and 29) is ground. All 3 Vss pins must be connected to ground.

Vss pin 29 doesn't seem to be connected on your schematic and needs to be.

One of the Vss pins on the xBee board isn't connected and probably needs to be.

Other than that, I don't see anything obviously wrong with your schematic.

You didn't include details on the USB adapter. I assume that you're using the built-in USB adapter on the PropStick.

Most likely you made some kind of error and your schematic doesn't reflect what's actually connected.

Post Edited (Mike Green) : 4/5/2010 5:21:04 AM GMT

TheGrue

Page 3 of the PropStick manual states that Pin 32 Vdd is the output of the on chip voltage regulator and provides up to 280 mA of 3.3 VDC. I was reading 4.5V and 5.5V coming out of that pin which to me says that the regulator fired and probably took the Prop with it.

Mike Green

That's possible, but the regulator is very robust. It's designed for automobile use (LM2937) and is rated for inputs up to 60V, is protected against reverse polarity inputs, and will shut itself down if it overheats or you draw too much current from it.

Consider calling Parallax Tech Support tomorrow. They may have you send the PropStick back for testing. They're pretty good about replacing things.

TheGrue

Aren't the VSS pins of the PropStick internally tied together as a common ground?

Mike Green

I would hope that all the Vss pins on the PropStick are internally tied together on the module itself, but they may not be.

TheGrue

Thanks Mike! You got it in one. I had a grounding problem. Once I checked all connections and made the VSS connect together it works.

Thanks again!

Timothy D. Swieter

TheGrue - so the VSS pins are not all tied together on the PropSTICK? Can you check the continuity of the pins to verify?

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" 16:9 LCD Composite video display, eProto for SunSPOT, PropNET, PolkaDOT-51
www.tdswieter.com

TheGrue

I checked the continuity of all the VSS pins and pin 10 had no connection to the other VSS pins. Once I connected pin 10 to 9 everything worked. Pin 9 and 29 already had an internal connection on the chip

WBA Consulting

I realize this thread is out of date and essentially closed, but I came across it while doing a search for the original "propstick" by Phil Pilgrim. The solution of connecting pin 10 to ground has me stumped. In the DipTrace layout for the Parallax PropstickUSB, pin 10 is not connected to anything at all, so I don't see how this could have fixed the problem. I am wondering of older revision PropstickUSBs had the BoEn pin connected to pin 10 and it needed to be tied to ground for this issue? If not, the solution here was probably just a loose wire that was bumped back into place while trying to check everything.

Humanoido

There is also continuity across both Vss pins on the Propeller dip so they're tied together internally as expected. A quick check on the PropStick should give the same results.

Microcontrolled

@WBA consulting: I've had the same problem before, and this solution worked for me. I didn't know that it wasn't connected.

WBA Consulting

Interesting. There must have been a rev change to the PCB as I suspected then because I have only used my Propsticks per the PEKit setup page and it doesn't have pin 10 connected to anything. I do have an older PropstickUSB somewhere, so I will have to look for it and see if it is different than my new ones.

Mike Green

You will find continuity between the several Vss pins on the Propeller and between the several Vdd pins. These are connected internally in the chip itself, but that doesn't mean that you can leave some of the Vss pins unconnected or some of the Vdd pins unconnected. The problem is that the connections in the chip are very small conductors, have some significant resistance, and can't handle much current. That's why all of them need to be connected externally together. The "dreaded" PLL failure problem occurs because there can be brief spikes in supply current demand that, if the current has to travel across the chip, can result in a voltage drop that can damage the system clock PLL multiplexer (the weakest link).