Connect to Ground Plane vs. Ground Bus for Propeller, etc???
ElectricAye
Posts: 4,561
Hi all,
I've only recently gained an appreciation for why power grounds should have a path separated from the signal paths. I think I get it, now, thanks to y'all. But what continues to puzzle me is why most chips have only a single ground pin. That would include the Propeller. Though the Propeller has two ground pins, Vss, I presume they are both connected to the same ground. But which ground should that be? Should it be considered a signal ground or a power ground? I guess my question is also a general one since most chips have only a single ground pin.
thanks,
Mark
I've only recently gained an appreciation for why power grounds should have a path separated from the signal paths. I think I get it, now, thanks to y'all. But what continues to puzzle me is why most chips have only a single ground pin. That would include the Propeller. Though the Propeller has two ground pins, Vss, I presume they are both connected to the same ground. But which ground should that be? Should it be considered a signal ground or a power ground? I guess my question is also a general one since most chips have only a single ground pin.
thanks,
Mark
Comments
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Toys are microcontroled.
Robots are microcontroled.
I am microcontrolled.
So would your standard PCB mounted voltage regulators dropping, say, 12 volts to 9 volts under 500 milliAmps be considered a digital device? I hope your answer is yes because that would make my PCB layout much easier. I would like to connect everything to a single ground plane.
thanks,
Mark
There are people here who can answer your question better than I can, but I think where you are mostly likely to get burned by this is when you design printed circuit boards (PCBs) using a ground plane, and you have a power ground return path running through/across the ground return path of a sensitive measuring circuit. The surges from the power ground path might affect the ground that is "seen" by your signal path and thus mess up the measuring device.
At least that's how I understand it.
switching regulators you have to be careful but you are probably using analog
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
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New ICON coming, gotta wait for the INK to heal, now we have colour!
an off-the-board table top power supply that gives me +5 volts, -12 volts, and + 12 volts with a ripple of 20mV peak to peak.
On the PCB, I'm using an LM1086 dropping +5 volts to +3.3 volts. And then two uA78L00 Series regulators dropping +12 down to +9 volts in two different PCB locations.
No servos, heating elements or inductive devices are involved. The PCB consists of 2 high speed comparators, 4 digital pots, one Real Time Clock, an SD card, a string of DS18B20 digital thermometers, a Propeller Chip, its companion EEPROM, one AND gate, and a heap of capacitors, resistors and 4 diodes. There are two headers that power some photomultiplier modules and a connector for VGA.
I don't think any of these components draw much current, certainly nothing like a servo or heating element. But the comparators and the AND gate will be switching quickly, so would there be any problem with those tied to the same ground plane as the voltage regulators? I've got capacitors galore attached to every chip.
thanks,
Mark
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
Thanks, mctrivia, you just made my day a happy one!
Have a great weekend!
Mark
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
This sort of thing confuses me enormously! I know it's preferable to have two separate power supplies - one for the logic and another for the servos - to stop brown-outs, but I always assumed the grounds should be common...
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Cheers,
Simon
www.norfolkhelicopterclub.com
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
Bottom line, try to keep your signal supplies seperate from your power supplies, Grounds included. I've learned all this the very long, hard, and painful way(literally - ouch!).
Phil,
thanks for your perspectives on this. It solves a mystery that's pestered me for years. I'm glad I finally asked about it.
Mark
I guess I'm still paranoid about ground-loops (coz I really don't understand them!) after seeing a clas-mate kill an expensive O-scope whilst I was in college!
I'm guessing that it's OK to have two completely separate supplies, so long as at least one of them is a battery? If they're both wall-warts, wouldn't that make a ground-loop possible?
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Cheers,
Simon
www.norfolkhelicopterclub.com
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P6955-ND
resister can be omitted if cap is not ridiculously big.
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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
Post Edited (mctrivia) : 4/25/2009 3:17:02 PM GMT
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Cheers,
Simon
www.norfolkhelicopterclub.com
You'll always have as many take-offs as landings, the trick is to be sure you can take-off again