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Old Jan 25, 2004, 02:51 PM
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Baltimore Bwi Rr Stn, Maryland, United States
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Quote:
Originally posted by KreAture
That was bare boards. No components.
Besides, I etch my own for $1 a board.
Do you do SMT parts, 2 layers, plated through holes, and solder plate? I f so you will get my next order.
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Old Jan 25, 2004, 03:01 PM
Impossible? Hah!
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Oslo Fornebu, Norway
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As I said. you can't "do" smt parts. There are PADS and they are wires... I do 2 layer, but have huge "issues" with vias.
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Old Jan 26, 2004, 12:57 AM
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Poke around a bit in the threads (try a search for etch or etching). I ran across one that gave the proceedure and the proper material to print on for the laser printer toner transfer method. Some people have had great success with this method, even on SM devices.

As for vias, as long as you can perfect your alignment method, use the smallest drill you can find and z-wire the pads. Of course, unless you are extremely good, you probably can't get vias beneath SMDs.

The absolute best way to work on SMDs is to use a long focal range stereoscope of around 7-10X and a higher quality temperature programmable soldering iron with interchangeable tips. (Spent a few years with my eyes glued to a scope building satellite boards.) I suppose you could substitute a higher quality video camera and monitor for the scope.

-John
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Old Jan 26, 2004, 01:47 AM
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Mr zagirules

You were asking who made the pcbs ...

My main job at work is the creation of PCBs. From simple single sided boards to big multilayer ones. I use PCB manufactures all over the world including those locally in my country. The pics here are boards created locally. My latest version comes in from the East (Tiawan) and is really nice.

----------------------

The TB6537

An interesting device. It was only a matter of time before ‘all in one chips’ became more useable. My only gripe about them is that they are not as flexible as to what I would want. And it still requires the overheard of a PWM generating circuit … be it a CPU or a 555 ic, FET drivers and all the associated power supply circuitry. It would appear to me that not much is being gained by the use of this chip .. other that not having to write code for it .. which is were all the flexibility lies.

Side note: The development of these controllers are not cheap. If you are doing it to make one or two for yourself, don’t bother. Rather just purchase them.

To make a decent controller to flog to your club member or buddies, then SMD is the way to go. If you have no experience in small SMD devices and thinking creating your own PCBs, better stop now. Do not pass Go .. do not collect 200. Save yourself the trouble. I have been in this business for the last 25 years, have made plenty of my own PCBs, but gave up on them for fine-pitched SMD devices. You need to be able to create 0,3mm through hole vias ect. If you can do this, I take back what I have just said. I do not want to sound negative, but this is the way things are.

Good luck
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Old Jan 26, 2004, 05:52 AM
Impossible? Hah!
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LOL. Man do you read wrong. I have tonns of SMD experience, I only make SMD boards and I use UV-transfer with Photoresist to transfer artwork to boards. I can do traces half a millimeter easily and with good repeatability.

I just say that doing Vias is very hard work and does not mirror the quality I want compared to the rest of the board. The fact that they are almost impossible to get good enough to place under a SMD is the reason why I try to avoid them.

Mr DIY: About the TB6537...
Do you realize the computing power needed in a PIC or AVR to sensor and commutate a regular 2-magnet brushless motor to run at 25,000 rpm ? You need to detect the half-way point on the driving voltages and change the output controll data 150,000 times pr minute or 2,500 times pr second. And you need to do this accurately without much jitter. (Jitter will make the automatic or adjustable lead-in angle adjustment useless.)

The TB6537 is not a processor based solution, it is a hardware based solution. It contains a digitally designed state machine that will do the job of both starting up the motor and then continue to commutate it. Since the design is not based on a CPU it will give much more reliable response-times and be a lot faster. This improves accuracy and makes for a very effichient, low development-time controller.

CD-ROM motors with the regular 3 sets of coils and 12 magnets make for a gearing of 4:1 thus needing a commutation rate 4 times higher to achieve same rpm. This is 10,000 commutations pr second, wich translates to 100us pr commutation. In this 100us time you need to read the current used, decide if it's too high, maby do PWM generation, detect if the time has come to commutate to next stage, find out what is the next stage and update the commutation-word on the outputs.
If we imagine we can boil it down we would still need:
2 : Read current, and decide if current is too high
3 : Check sensoring port, if time, gety new data, update outputs
2 : Go to top again and start over

In addition, the check would actually need to be performed a lot more often or else we would have a commutation accuracy of 15° and that is useless. We would not have any idea if we were doing anything between a 0 to a 15 degree lead in.

Luckally, the TB6537 doesn't work that way. Result is a very accurate lead-in where the point for next commutation is checked at the rate of the clock input. That is 10,000,000 times pr second or 600,000,000 times pr minute. At 25,000 rpm on a 12 magnet cdrom motor this would translate to a commutation accuracy of 0.015° or a check 1000 times pr commutation. The AVR running at same speed would have to use more than one instruction and thus (if 7-instructions are used) have a accuracy of 0.105° wich would be quite acceptable. It would simply take a lot of time to write good code.
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Old Jan 26, 2004, 07:18 AM
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Hi kreAture.

Not sure about what you are saying about reading wrong, Is it me or somebody else?

Quote:
Do you realize the computing power needed in a PIC or AVR to sensor and commutate a regular 2-magnet brushless motor to run at 25,000 rpm ? You need to detect the half-way point on the driving voltages and change the output controll data 150,000 times pr minute or 2,500 times pr second. And you need to do this accurately without much jitter. (Jitter will make the automatic or adjustable lead-in angle adjustment useless.)
I am not sure if you noted the pictures on page 4 of this thread, but I have built my own controller already and have observed what you have mentioned. The speed issues you pointed out were initially a problem, but quickly solved with the use of a high-speed logic device. It reduced the micro overhead to basically looking for when to commutate, what timing is being used and other background checking. All this inside 50us without problem. In fact the only timing problem I have is that of the on board Atmel Mega 8 ADC. It is slow, but we can make plans to get around that. Overall I am more than happy with the performance and the figures you mentioned above are actually well inside my unit’s capability. The 10 000 figure mentioned was the bare minimum I was designing for.

The Toshiba device mentioned is an interesting device and I would love to hear from somebody who builds something using it. For me, the 16KHz PWM frequency limit is too low. I have been using 24KHz + for my Mega 3 turn motor. But for CD-rom motors the 16K limit should not be a problem.

Other details mention in the Toshiba PDF is rather vague. It refers to positive detection being in synchronization with the PWM and then warns about the use of high-speed motors. (See page 7). My immediate impression is, this device may not be able to meet your specs described above. But then, I may well be wrong, but I suspect I am not. If somebody cares to decsribe more details of how this chip works, I am all ears ... or is that eyes

One more thing for now. My biggest headache in writing code, turned out to be the starting sequence. It’s the one area I must still modify to allow for the use of heavier props (mass wise). It is quite easy to design for a single type of load, but it’s a little more troublesome to cater for almost any load. If this device can do that without problem, I would be impressed.

So who is going to give it a go?
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Old Jan 26, 2004, 07:53 AM
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Oslo Fornebu, Norway
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Hehe, true. The starting sequence is a headache.

I asked Toshiba about the chip, that's why I know it uses almost unclocked logic for most of the work.

The PWM frequency seems to be reccommended however. I agree they only state a single frequency and find it odd.

A tip: If you drop the ADC completely and instead use a external or internal Opamp to detect the zero-crossing you can avoid the pesky ADC delays. Timing is easily done by using a prediction and adjusting the prediction before the next commutation if it doesn't match the later detected zero-crossing.
This is the method I will be using when making my first controller without the Toshiba chip.

As for flexibility and the use of a programmable logics chip. It appears this results in same situation as using the Toshiba chip. Only, instead of the formentioned flexibility, you sacrifice weight and board size. I hope I can get my controller woking well with cdrom motors without using the Toshiba chip or any other external logic chip, but I know the chances are probably slim. Or it will take a lot of work.
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Old Jan 26, 2004, 08:05 AM
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Yep .. I am indeed using op amps for my feedback as already explained in the description that went with pics a few pages back.

Quote:
As for flexibility and the use of a programmable logics chip. It appears this results in same situation as using the Toshiba chip.
.

Yes .. true, but far more flexable and adaptable.

Quote:
Only, instead of the formentioned flexibility, you sacrifice weight and board size.
Weight ... hmm maybe 1 or 2 grams.
Board size ... my new board uses a 44 pin device as opposed to the 100 pin device used on proto number 2. My new board is 26mm x 46mm and contain quite a lot more on it than proto 2. Its crammed.

Quote:
I hope I can get my controller woking well with cdrom motors without using the Toshiba chip or any other external logic chip, but I know the chances are probably slim. Or it will take a lot of work.
Its taken me a year of my spare time!!
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Old Jan 26, 2004, 09:26 AM
Impossible? Hah!
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Taken that long time ?
Hmm, I bet I have mnore free time than you

Anyway. It's more fun than the proverbial barrel of monkeys, so who cares it takes time ???
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Old Jan 26, 2004, 02:29 PM
broom driver
Barnsley, Gods own Yorkshire, Uk
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Sorry for the delay.

When I first saw this devices data sheet it had a aveox motor in the background


Quote:
Originally posted by KreAture
The 141 chip from ST needs a center-tap to work right.
not from the data sheets I have been reading

In the UK I have beeen told this device is about £4 I have yet to try and buy one

http://www.st.com/stonline/bin/sftab...able=a_214_109

THe problem with this chip is the amount of Bemf it can detect so you have to step the motor in open loop quite fast before you can detect the zero crossing point.
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Old Jan 26, 2004, 03:34 PM
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I can get samples of the 141 chip. I have already been offered them from a local distributor.

I'll give em a hoot and let em know I want some.
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Old Jan 26, 2004, 03:38 PM
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I just re-checked and now I've reconsidered. I don't want to test the 141 as it's a programmable chip. In fact, it's really a specially tailored DSP processor if one were to classify it. I'm sure it would be quite cool to use it, but for me it means hassle of maby needing a programmer for it and having to read up on the command-set it supports.

I'll see if I can find some other controller from Motorola or TI instead as I have contacts with them too.
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Old Jan 26, 2004, 11:55 PM
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Kreature
Quote:
Anyway. It's more fun than the proverbial barrel of monkeys, so who cares it takes time ???
.

Yes ... its for the enjoyment and CHALLENGE we get out of it. A lot of people can't understand that. Its such a nice feeling to be flying your own motor and controller.
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Old Jan 27, 2004, 12:51 AM
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DanC,

I did a fast check for low cost or free tools for the ST devices, but was unable to locate any specifically for the 141. There is a programmer or two that might work. I didn't find any development system, but I would hope they would have a downloadable one somewhere.

KreAture,

Motorola uses the MC68HC(7)05MC4. Look for the AN1627 application note. I believe the MC means 'motor control'. For some reason I passed this over, but I can't remember why - I think that particular microcontroller is a little rare. Also, if you are interested in writing 'C' instead of assembly (unlikely you will get the necessary speed) you can download a free version of CodeWarrior Lite for microcontrollers.
I looked at a lot of TI stuff - they have some BLDC motor control devices but most I found were sensored and the rest are DSP based. Lot of companies willing to license BLDC source IP at $1-10K. Check out the TMS320LF2401A. Snychronous 5 channel, 10 bit, 500ns A/D; 2 - 8 state sequencers; 3.3V; 40MIPS and all in a 7x7mm 32 pin QFP. That one just might be useful...

-John
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Old Jan 27, 2004, 01:10 AM
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JohnnyS ... yes those TI devices are nice and are very much DSP based. I found the app notes for these devices very useful for gaining knowledge. Having played with an Analog Devices DSP dev. Board, I found writing code for DSP chips a little more difficult. A steeper learning curve. I suspect however, the wish here, in this thread, is to create a controller that does not require software… and to be honest, I find it a tall order to get such a controller working well. For low current applications, it will probably work, but a software-less controller for various motors may prove a little more difficult. But time could change all that.
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