Bare Bones Propeller
Humanoido
Posts: 5,770
Bare Bones Propeller
This updated Bare Bones Schematic is currently at version 1.4
and is subject to change without notice. It replaces versions 1.0,
1.1, 1.2, and 1.3. Use the blog's search feature to find any future
changes.
The suggestions from this thread, and some from another thread
are now incorporated into the circuit to maximize Propeller chip
performance, reliability, and facilitate ease of assembly for
beginners.
The circuit allows lower power operations, mainly 3-volts with
two (1.5 volts each) AA batteries, and experiments at lower
voltages. Bare Bones is a good reference circuit and starting
point for many projects.
By itself, Bare Bones is considered to be a simple machine
project with provided software on the schematic and the ability
to communicate with a serial terminal, providing virtual
representations.
The program runs in rcfast (~12 mHz) and at 1200 baud
to blink a serial terminal LED on and off.
This updated Bare Bones Schematic is currently at version 1.4
and is subject to change without notice. It replaces versions 1.0,
1.1, 1.2, and 1.3. Use the blog's search feature to find any future
changes.
The suggestions from this thread, and some from another thread
are now incorporated into the circuit to maximize Propeller chip
performance, reliability, and facilitate ease of assembly for
beginners.
The circuit allows lower power operations, mainly 3-volts with
two (1.5 volts each) AA batteries, and experiments at lower
voltages. Bare Bones is a good reference circuit and starting
point for many projects.
By itself, Bare Bones is considered to be a simple machine
project with provided software on the schematic and the ability
to communicate with a serial terminal, providing virtual
representations.
The program runs in rcfast (~12 mHz) and at 1200 baud
to blink a serial terminal LED on and off.
spin
477B
Comments
EDIT: Mike types faster than me.
Thanks Mike for this important reminder. The circuit will use a power supply with leads that end with .1uf decoupling capacitors. These will connect immediately near and closest to the Propeller chip pins, ground and +3V, on both sides of the DIP as the breadboard will allow.
You are making that assumption and NOT stating it in your design. Therefore, the circuit design is not following best practices and may not be reliable. Just add the two capacitors and the world is a better place and PLL's live to run another day!
The bypass caps are not missing because two are included across power supply leads, where it connects to the circuit (at VSS/VDD on both sides of the prop). I consider the filtering they do to be part of the power supply to provide a clean signal and source.
It looks like you type faster than me.
You're right! I made the assumption the power supply design would have the required filtering and forgot to mention it. The next drawing version will have a power supply note to avoid any confusion.
Just go with my soon to be released ~$10 Prop_Traverser
-Phil
If you knew this all along, you had every opportunity to let Parallax know this information (what you call poor design practice) so their material could be promptly updated. Perhaps you did inform Parallax and they did not want to change the schematic. One could say they were too busy, but this raises the question as to why they had time to issue two new updated manuals without the schematic change.
Not everyone has time to read posts on the Forum. Many people get information from the source - the updated Parallax PEK kit manual and the updated Parallax Propeller Manual, for proper propeller wiring information. It has no information about decoupling capacitors.
With the Bare Bones Prop, there are decoupling capacitors at the end of the power supply leads, by choice. The power supply is not on the schematic. An updated text about this config is added to the schematic page which I just uploaded to post #1. For clarity, the caps sit on both sides of the Propeller chip, on the breadboard pins closest to the prop's VSS & VDD lines, even though they are physically attached to the end feed lines of the power supply (and also the prop through the closest breadboard holes).
A few inches of wiring? Absolutely not. The distance from the power supply end connector with decoupling caps to the Props VDD & VSS pins is very close to 1/16th inch. This is the best we can do with a breadboard plug-in design even though there are other effectual considerations inherent in the breadboard pad.
It's news to me that the Propeller is now less robust as you say. Have you talked to Ken Gracey about this? Someone ran a hundred propeller chips for two years and they remained robust with no PLL failures whatsoever. "Large voltage spikes on the power or ground supplies or problems with ground loops" sound more like board problems.
Maybe some effects are less or absent when running RCSLOW or RCFAST at a lower frequency without a clock, as in this circuit. As I mentioned in another thread, I have props running years, without decoupling capacitors, that have never failed. I don't think my props are handpicked over others.
This over/under is an interesting question.
We have done DIP boards in the past, and placed quite a few parts in the DIP socket cavity.
The problem with this, becomes if you then want to stack it as plug-able, you ideally need fine male pins out the bottom.
Machine pins are costly, and fragile.
The picture in #8 nicely sidesteps that, by attaching on top of a DIP package, and you can plug the DIP-Prop into a std DIP socket, which can plug into any target (if you want an element of cheap damage protection).
PCB suggestions:
To make it stronger, I'd probably add connections down to P0, P1, and I'd bring the handshake lines to solder-pads.
- and you might be able to fit pads for a Si504 option- they come down to 2 x 2.5mm, and use a C1D interface to set Freq using a 4 byte real.
Do you really mean no caps whatsoever in the Vcc-Gnd, anywhere ? - or did you mean 'without local decoupling capacitors"
Over the years, it has been found that lack of proper decoupling capacitors lead the failure of the PLL circuit.
In your case, you may never see the failure because you are only relying on the RC clock circuit . The PLL might have been blow but you would never know it until you tried to run a standard 5Mhz crystal program.
Making a simple circuit look simpler by omitting parts is not helping anyone.
-Phil
If you plug in your power supply circuit (with the pair of 0.1uF caps on the leads as I presume you mean) and your power supply is powered on - presume by a 3V battery), it is possible to likely that the voltage spike at the prop pins could damage the props PLL or worse.
And, just a pair of 0.1uF is still IMHO not acceptable. You also need at least a 10uF cap there too, presuming you are not drawing considerable power from the supply. Overclocking shows up the problems of unsatisfactory power supplies because it exaggerates the problem.
But one thing at a time. I didn't mention filter caps here -- yet -- since I did not want to cause cognitive overload.
-Phil
One often sees minimal circuits like that that are intended to show a concept or a use case of a device, the clutter of "housekeeping" components being left out for clarity. It is often expected that a designer will be aware of these details and take care of them.
Yes, exactly. You just proved the complete reliability of this circuit, even without decoupling capacitors.
I agree. There is absolutely no fault of Parallax. The bare bones circuit is intended to show the concept without the clutter. It's a hobby project and others wishing to work with it may do so and can take care of any details they wish.
There is no such proof in there. Perhaps a Prop on a breadboard using it's RC clock works for years.
Fine but what if it's PLL has been blown by a dodgy power setup?
You would never know. Until one day you decide to add an XTAL or pull the Prop off the bread board for some other circuit.
A circuit that damages it's components is not good. Especially among hobbyists who tend to recycle components a lot.
Ah, so really, you are merely using the power supply capacitors, and the variable is then the lead length.
Every decoupling circuit has some inductance between the die, and the capacitors.
Another reason designers use local caps, is passing EMC - did you EMC test your 'no caps' design ?
Checked it for false resets on radiated energy ?
Yes the lead length from the power supply routes to the first master loader chip and I just ran it and it worked fine so there was no issue. As I recall, with more and more props added, it became a little noisy at around 50-60 props and the circs were redesigned into three partitions as explained in the Big Brain thread. I scoped it out at one point and settled on the acid test. In using breadboards there's a way to create grounding islands and I experimented with this, and will likely do more work in this area to improve circuits with large numbers of props. In the BSS, I built shielding, but this didn't seem necessary with the props. As you know I'm very interested in the signals created by the chip and at one time developed a kind of radiative non-invasive "brain wave" monitor for chip study. A lot of things change inside the chip depending on the program running and I'm interested in sensing these changes for knowledge of the chip without looking at the code.
Multiple people have pointed out an known issue and suggested the simple addition of two very inexpensive components to the basic circuit to help with the care and feeding of the PLL.
Like others have said, it's a known issue, so regardless of the initial Parallax documentation it should be properly documented going forward.
I don't understand the resistance in making the change.
You obviously have a passion for the Propeller and other Parallax products and you like documenting your projects and teaching others, so why risk setting them up for possible failure by not using the known best practices?
C.W.
Boys, boys!!
1. It's always bad practice to not use good engineering common sense, even if it works and you got away with it.
2. Engineering spec sheets rarely show everything. Their purpose is to show the important circuit concepts.
Get over it!!!
Duane J
Humanoido, add bypass caps to your schematic. It's the right thing to do. Claiming that they're hidden in the power supply doesn't make sense.
'Possibly so when your audience is engineers, who can fill in the gaps from experience. When your audience includes newcomers to the art, a somewhat higher standard is called for. When achieving even a modest standard is blocked by intransigence, yes, people will complain.
-Phil