Circuit Boards

[daniel]

Hey, Guys, thanks for the tips, I will update you soon as to the progress.

Ron, That Texas Instrument paper is AWESOME! Thankyou for directing my attention towards it! I will let you guys know in a day or so whats up with the pcb.

On a side note, I went to the Orlando Maker Faire today! It was awesome! Very cool stuff to see! I think I need a tesla coil to complete my transition to the Darkside! Lot's of R2D2's running around.

[daniel]

Ok guys, I've progressed a little further. I believe I have eliminted most of the noise issues on the board. I did this by doing a few things...

(1) Added 1uf and 4.7uf caps to the exsisting .1uf caps on the PIC 18f4321 and the two TLC5940's(LED drivers).

(2) Added two resistors to the two unused PWM output pins on the LED driver chips.

(3) Found a unused floating pin on the Microcontroller that was outputing the system clock. Disabled it in the firmware.

(4) Added more ground paths.

Now, most of the weirdness and the "Kitchen Table effect" are gone, All of the randomness is gone. The only bug that remains is the glitch seen in the phase change routine. Now that the board does not seem to be glitching out from noise, I can focus on the firmware as the source of the problem.

Here is a little background on whats going on in the design.

(1) Every 4096 clock pulses the Microcontroller sends an array of valus over the SPI module to the LED drivers. The LED drivers take this array and set the values on the PWM pins accordingly.

(2) This array is sent over no matter if it has been updated from the previous transmission or not. For example, if you slide the red slider bar on the phone and the LED's go to red, and then you do nothing else, the values in the array are still repeatedly transmitted to the board every 4096 clock pulses and the LED's remain red.

(3) The glitch never happens when the LED's are set to one color, only when the phase change routine is occuring.

Between number (2) and (3) this makes be think that the bug is not in the transmission of the array, but in the way the array gets its values set for the phase change routine.

Anyway this is where I'm at now..... Thanks for the help guys!

[daniel]

I also want to implement some copper pours that are connected to ground, I figured out how to do it with eagle, but the DXF it exports is made up of too many overlapping polygons to be able to do anything with. Does anyone know how to get a better dxf export?

[khalid]

Nice board and programming ..i wonder why you chose to machine the PCB and why not etch it?
I do etch the boards and manually drill, initially i was slow but now as for as drilling is concerned i am faster than any CNC

[dana_swift]

My DXF's from Gerbers look just like the one you posted. I import the DXF into partworks, select all, and "weld". So far I have not had it fail to do any level of complexity.

Care to post the DXF?

Congrats on getting the noise problem under control!

D

[daniel]

Guy's, I am going nuts........ I cannot, get this thing to work smoothly, I am back to thinking it's electrical noise again....... Here's where I a at now,

(1) There was once major electrical noise all over the board causeing crazy problems, and the "kitchen table effect" as previously noted. These have been addressed with steps listed in a previous post and seem to be gone now. The only remaining glitch is in the phase change routine.

(2) I then turned to the firmware. First, I have turned off two of the colors in the phase change routine in order to observe just one. This is what I found (a) The LED's fade in and out nicely with the corresponding values in the array, until the LED's reach 0(Thes last 6 values in the array are 0's). (b) Sometimes, when they reach zero all is fine, and sometimes it glitches.

(3) I investegated the firmware further. I did these things,
(A) I checked the array and array index. 1024 elements in array, array index starts at 0 and goes to 1023. Rewrote them 3 different ways, all worked the same. Check!
(B) I took the function that turned on the LED's using the array values, and used the function manually with index's of the array(basically without the array index incrementing) and all worked fine. Check!
(C) I've basically did alot testing and or changes to the firmware and nothing changes. Same problem sometimes a glictch when LED'd go to zero.

Back to thinking it's noise, It's possible that when the chip gets to the end of that array, and starts to out put a some zeros(stay low) on that SPI out line, that it experinces some kind of spike. I will post a video soon.

I know this is a bit programmy for the forum, but since the board was made on th bot, I'll just go with it.

Khalid, I did it this way, because used tools I have and seemed easier to me then haveing to get extra stuff like toners, chemicals, and then learn how to transfer it all, and then after all that, I still want my bot to drill the holes, so I figured I would just engrave it as well.

[dana_swift]

When I was teaching electronics troubleshooting, I taught my students to always check the power supply first. If its not right, nothing will be right.

When circuits are squirrely, power is a very reasonable suspect. You need to use an OScope to look at the power, and the transients on the power. You may find the power supply is oscillating, I have had that happen before. Local decoupling is critical also. Power is the foundation of the electrical design.

At the start put your OScope reference (ground clip) at the ground reference point for the power supply voltage regulator. Be sure the power is within spec. (are you using 3.3? 5.0? 1.8?) If you are using a switching regulator be sure it is stable and always within the tolerance (usually +/- 10%) for digital circuits. If its a linear regulator its usually easier to make correct when you are new to designing power supplies.

Using the regulator ground reference point, how big are the transients on the ground traces measured at the CPU? How about the Vcc or Vdd traces?

Once the power is meeting spec, check the clock. Is it solid? That is the next thing the CPU requires to be absolutely solid. If you are using a oscillator IC be sure it is well decoupled. Extra "clocks" make CPUs wierd.

Then check the reset circuit and the power monitor if you are using one. Is it possible the CPU is getting reset after the power is up?

A scope is your friend, and its easy to learn to use. Start each of these tests with the triggering set to auto, then go to manual and adjust the trigger to grab transients at what appears to be "solid" voltages. There are ALWAYS transients, but the limits for the transients are the same as the limits for the average values specified for steady power. So if the CPU is looking for a nominal 3.3v with a tolerance of 10% the power limits are 2.97v and 3.63v. At no time can the average power and the transients add up to exceed the limits.

The 10% figure is fairly typical of what a CPU requires, some CPUs are based on CMOS logic which can be more tolerant of power supply "softness".

When you boil all this down, Pauls advice about adding lots of decoupling is what you end up doing. That keeps the power which is solid at the regulator, as solid as it can be at the load.

Hope that helps-

D

[daniel]

Thanks, Dana, I read, and reread your post as well as everyone else's. This is killing me, I've got 8 hours between yesterday and today alone and still no further. I would quit, but this is the stuff I want to be able to do. I made some changes on the board today, added some small caps and resistors to signal lines. No change, at this point I have no idea if it's firmware or hardware, it's gotta be firmware but I don't know.

I can power it two ways, but I get the same results both ways. One is with a wall wort, and the other is through usb via the pic kit 2. The usb probably has a clean supply. With that being the only glitch, I think it's firmware.

I am going to start a thread on sparkfun tonight, maybe someone there who has experince with this particular LED driver chip (TLC5940) will be willing to look at my code.

I thank you.

http://www.youtube.com/watch?v=oJJXiX5FIAM

[ssflyer]

Neither the wall wart nor the USB port will be clean at all - Easy way to isolate the issue to see if it is power supply related, batteries! Cleanest power there is.

[daniel]

Thanks for that tip Ron, I will implement that when I get home from work tonight so I can check the power supply off the list of potential culprits. I'm thinking it is in the firmware, Last night, I spent alot of time Adding Comments to my code. I am trying to make it read as easy and as quickly as possible before I ask anyone to look at the code. I have quite a bit more comment adding, before I comfortable asking someone to look at it, I don't want to waste anybodys time.

This is an important project for me, I want to pull all my skills together and use the bot to make a piece of interactive art work all the way down to the circuit boards. My goal is to control stepper motors and LEDs from my phone, tie it all together with a nice app, and make some instructables.