PI CHIP

[Pete the Builder]

Hi Pete, i am in no hurry, so take your time. Priorites first and goodluck with your results. Any good news is better than bad.

Interesting board and great looking one at that.

Btw, fire away any questions you may have.

Cheers Sid

Sid, I haven't done diddly-squat. I'll send you a large stick so that you may beat me.

In my defense, I've had a bit of a change here, we (the royal 'we') decided it's time to move, so off we go! As I write this (8AM Monday morning) I've got to send a rocket up the agent's arse, get the Section 32 back from the solicitor, get the ******** who installed the security glass to come and finish the job before lunchtime, pat the bed, make the cat, etc, and it all has to be done with a broom up my bum so I can sweep the floor when I walk around. I can't wait until 9AM!

Great to see your very first board! Welcome to the club! Now the real heartache fun starts....

mschmahl also picked up a new bit of software and designed a PCB in another project; looks like people are really interested. It's really cool to see!

What happens now is that you get to enjoy the fun and happiness of PCB fabrication!

So what happens is that you check the board every which way from Sunday : you verify every single trace and every component, board size, hole count, everything. THen you get a quote from the fabrication place, and it's great. You're so confident that you order a solder mask option just so the board will look really spiffy. You send off the design. They send you back a reference number. Then :
1) You suddenly discover that the ****wad who made the MCU schematic library left out all the power and/or ground pins; and/or
2) You suddenly realise you've sent off the wrong version of the PCB, and the fab can't be stopped; and/or
3) You suddenly find out that the MCU manufacturer only makes a BGA version of your core component now.

Oh, the fun never stops.

Seriously, though, it's a great achievement to get anything out of an intimidating bit of software such as EDA. Kudos to both you and mschmahl...

Now, while I've done nothing on this design myself, I've been trying to work on the "you know what" (begins with Q and ends with sadness), and I've almost finished the coil board on the other UNIPI or UPIM. So basically, I've done everything except work on this project.

I apologise for my lack of focus.

To help manage my guilt, if there's anything I can do to help with any PCB questions or anything, fire away. I know far less than most people here, but I'm happy enough to answer, possibly correctly.

-PtB

[6666]

IBGold could I get them to please
thanks
6666

[sido]

Hi Sido I can supply you with Designspark schematic and PCB files for our 4011 UNI-PI board that Stefan did to save you the time.

Regards, Ian.

Hi Ian, that will be very much appreciated.

I will still continue to learn the program and may eventually be able to put some other experimental circuits in use.

Cheers Sid

[IBGold]

Hi Sido I can supply you with Designspark schematic and PCB files for our 4011 UNI-PI board that Stefan did to save you the time.

Regards, Ian.

[sido]

Hey all.

As you all know i have had no experience in using any E.D.S software before, so have downloaded Designspark and have been having a go at learning the software to produce the UNIPI Main controller board.

So far after loosing a few more hairs, hehehe, being frustrated, trying to work out what is what, measuring, placing, then removing and so on.........Below is the idea of what i was refering to PtB. Basically the rough idea of what it will look like after cleaning up tracks, removing all the vias (so to have a single sided board only) adding top layer links instead of vias where possible, adding a bottom layer groundplane where free copper is available etc etc....

Knowing me, I will probably scrap this one...re-read the Tutorials and start a fresh new PCB board layout.

I still have to learn on how to label connectors, components etc etc and add new components and footprints. So far so good apart from going bald.

Thanks Tinkerer and mschmahl for recomending this program.
BTW Moodz, with this program Designspark, you can import Eagle schematic's and pcb files.

P.S It is my first attempt everyone, so please go easy on me. Some component footprints are not right so have to create my own.

Sid

[sido]

Congratulations guys! A real community effort and moving ahead in giant paces.

Thanks for the great effort.

Tinkerer

Thanks Tinkerer for all your valued contributions.

If only i knew how to design PCB's, i would have already posted complete boards for all to make for experimenting much easier.

Never to old to learn, so digging in all my efforts to learn basic PCB designing which i should have done in Technical College many years ago....Actually, in Electronics classes we were being taught about Technologies that were 10+ years old while studying

Cheers Sid

[sido]

Best of luck and speedy recovery, Pete. I don't intend to imply that people are not familiar with the topic on this forum, though I did want to elaborate on EMC design when asked, and it's good to have information archived in threads. Maybe said several times, but EMC is an important topic for performance. Slow clocks still have fast transients, and even if there are no high speed transients generated by the circuit itself, there's a good chance something like cell phones will eventually introduce them into the device.

Here are some condensed documents on the topic:
http://www.atmel.com/Images/doc1619.pdf - Atmel's EMC primer for microcontroller designs, meat is hidden in chapters 3-4
http://www.analog.com/static/importe...als/MT-101.pdf - Analog Devices document looking closer at impedances and decoupling, and unintentional resonators formed from parts meant to filter such

...And a less condensed one:
http://www.mit.edu/~6.331/an47fa.pdf - Linear Technology's app note 47, a kalashnikov manual on high speed design, prototyping, oscilloscope measurements, and light hearted thinking. A long read but worth it IMRHO.

Hi ODM, thanks for the links provided. Have read the first two and a wealth of information. Have not got around reading the last link, but will do so.

Will also re-read them as it applies to this design structure and see your point in a low EMC designed PCB.

Cheers Sid

[Tinkerer]

Congratulations guys! A real community effort and moving ahead in giant paces.

Thanks for the great effort.

Tinkerer

[ODM]

Best of luck and speedy recovery, Pete. I don't intend to imply that people are not familiar with the topic on this forum, though I did want to elaborate on EMC design when asked, and it's good to have information archived in threads. Maybe said several times, but EMC is an important topic for performance. Slow clocks still have fast transients, and even if there are no high speed transients generated by the circuit itself, there's a good chance something like cell phones will eventually introduce them into the device.

Here are some condensed documents on the topic:
http://www.atmel.com/Images/doc1619.pdf - Atmel's EMC primer for microcontroller designs, meat is hidden in chapters 3-4
http://www.analog.com/static/importe...als/MT-101.pdf - Analog Devices document looking closer at impedances and decoupling, and unintentional resonators formed from parts meant to filter such

...And a less condensed one:
http://www.mit.edu/~6.331/an47fa.pdf - Linear Technology's app note 47, a kalashnikov manual on high speed design, prototyping, oscilloscope measurements, and light hearted thinking. A long read but worth it IMRHO.

[sido]

Hi Pete, i am in no hurry, so take your time. Priorites first and goodluck with your results. Any good news is better than bad.

Interesting board and great looking one at that.

Btw, fire away any questions you may have.

Cheers Sid

[Pete the Builder]

This is all really interesting info, and it's great to have it in one place, so other folks can learn from this discussion.

I'd like to just say, in the interests of not causing any confusion, all of the above is well and truly understood. I've attached an example of what I generally produce for clients. Hopefully, you can verify that in this case at least, I've followed the rules!

Just so I can add something useful, the rule of thumb is to add one monolithic 0.1uF cap every 3 digital packages. Also, power and ground traces should run in different directions, to minimise impulse coupling.

I'll have a think about the transistors, it's a complex issue with this design, and I need to understand exactly what signals and currents are going where. I do agree, it would be nice to screen stuff off, but this will only work if the power is properly routed and so on. I'll re-read the info above and if I need more details, I'll definitely ask!

It's good to know we've got good knowledge available from people here! Hopefully newcomers will benefit from all that's been mentioned so far here!

Cheers,
Pete
P.S. I'm off to see the specialist to try and get an 'all clear'... Fingers crossed... (I hate these visits, they waste so much design time - showering, driving, waiting, driving back, collapsing for a few hours to recover, then back to designing again! Wheee! )

[sido]

Understood, thankyou.

Its all a new learning curve for me and no better way to learn more from this Forum with detector design and peoples past experiences in common PCB design principles like yourself.

The more information posted, the more we can all learn.

Cheers Sid

[ODM]

Most microcontroller application notes have the same instructions for "hygiene", and for good reason. Crystal/cap traces should be as short as possible, and the route for vdd/gnd traces should go past capacitor terminals, individual caps for all vdd/gnd pairs. Pads for surface mounted filter caps are not that big to leave on the board as a precaution.

Series resistors serve a dual purpose. They are series termination for reflections which may grow to be issues with longer traces/wires, and they slow down the usually fast rise and fall times which contribute to radiated interference. The resistance value depends on what needs more attention - termination or rise times. They provide an added measure of protection against "workbench accidents" as well

Often series resistors can be unnecessary, and the need for them might only show up for longer traces on an otherwise clean design. But it's a consideration.

[sido]

Ideally you would treat the input side of a switching regulator with the same care as its output, even if buck regulators are less noisy in this regard than boost regulators. The current comes from somewhere too, emc design is basically about thinking of the current loops, and parasite capacitances. Long wires can make for large loop areas unless they're twisted. This is why it's important to have as solid "ground plane" as possible, if using one. Not cut underneath high transient current loops.

I don't think you need to consider the power supply wiring, just have a capacitor-choke-capacitor input filter. The choke can be just a lossy ferrite bead. Often just a simple ceramic capacitor at the power input pins will cut radiated disturbance by ten dB range. It would be preferable to use surface mount capacitors to have as short leads as possible - capacitor leg leads have inductance, and a ceramic capacitor has very low inductance compared to an aluminum electrolytic capacitor.

Series resistors, it's hard to give values - for wires it's usually higher resistances like 50..100 and for pcb traces lower, 10..50. Most of the time they're not necessary at all if the load (and its wiring!) is well behaved, more resistive than reactive, and they add unnecessary parts to a layout. But for long cables, and sensitive fast signals like clocks, it's a good idea to have them in place.

An oscilloscope is a good rough guide for showing where the issues are, if possible try to make in board measurements with as short ground wire as possible from the probe. The usual probe's long ground wire and gator clip can make well behaved things look dirty, and hide some higher frequency issues. One thing to try out is to just wave the scope probe tip at high gain above the circuit without touching leads, to see if there is radiated e field at some location.

When we look at frequencies in the Mhz range, we should consider the possibilities of isolating the source, (like the 10Mhz Cpu oscillator in this case).....and LCD module sync and vice versa when interconnecting with low frequency dependant circuitry.

In respect to the resistors mentioned, with I/O and (especially for low frequency circuitry) they can implement a inductive pickup and mess things up than not including them overall.

Experiment is the key with the lowest wire lead possible.

Surface mount concepts can achieve this, but beyond this simple PI controller in LF.

Cheers sid

[ODM]

Ideally you would treat the input side of a switching regulator with the same care as its output, even if buck regulators are less noisy in this regard than boost regulators. The current comes from somewhere too, emc design is basically about thinking of the current loops, and parasite capacitances. Long wires can make for large loop areas unless they're twisted. This is why it's important to have as solid "ground plane" as possible, if using one. Not cut underneath high transient current loops.

I don't think you need to consider the power supply wiring, just have a capacitor-choke-capacitor input filter. The choke can be just a lossy ferrite bead. Often just a simple ceramic capacitor at the power input pins will cut radiated disturbance by ten dB range. It would be preferable to use surface mount capacitors to have as short leads as possible - capacitor leg leads have inductance, and a ceramic capacitor has very low inductance compared to an aluminum electrolytic capacitor.

Series resistors, it's hard to give values - for wires it's usually higher resistances like 50..100 and for pcb traces lower, 10..50. Most of the time they're not necessary at all if the load (and its wiring!) is well behaved, more resistive than reactive, and they add unnecessary parts to a layout. But for long cables, and sensitive fast signals like clocks, it's a good idea to have them in place.

An oscilloscope is a good rough guide for showing where the issues are, if possible try to make in board measurements with as short ground wire as possible from the probe. The usual probe's long ground wire and gator clip can make well behaved things look dirty, and hide some higher frequency issues. One thing to try out is to just wave the scope probe tip at high gain above the circuit without touching leads, to see if there is radiated e field at some location.