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MP
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Posts posted by MP
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No it doesn't!
If you change the frequency of a square-wave that feeds a DC motor, the motor receives an average of half the supply voltage at every frequency until the frequency becomes so high that the inductance of the motor reduces its average current and slows it down.
With a 50% duty-cycle, the motor receives full voltage for half the time and no voltage for the other half of the time. The motor's speed doesn't change when the frequency is changed.
Oh, yes it does.....I think you have once again become argumentive on a device you have never used....Your statements would be true if you were feeding the signal directly to a motor. I think both of you have missed this detail. We are discussing the input of the L298. Not a motor.
In our discussion, we are feeding a clock signal directly to a L298, which runs on TTL clock signals. We are not feeding a direct voltage to a motor. If you are going to use PWM, you would have no need for the L298. It is all in the data sheet. There is no mention in the data sheet about changing amplitudes of signals or PWM. I have designed a good share of automated equipment with the L298. I'm not guessing, here....oops!, I mean this is not "Theory" ;D
MP
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Faizanbrohi: We are discussing how to get good results with photo etch. Not glossy paper. There is another thread about using your method. You should post in that thread. By the way, I totally disagree with your comment. There are many tight designs where glossy paper just pushes out crap. Works well for the hobbyist, but more professional artwork requires a more professional method.
Mik3ca: Sounds like you are on the right track. You have brought the exposure time down from one hour to 20 minutes. Your developer ratio might not be the problem. The black light might have been over exposing your artwork. You might want to try another board with a 10 minute exposure time as well. My exposure fixture has four of the black light tubes like what you have. This is only so that I can expose a 12" x 12" board with no problem. At the height that I mentioned above in a previous post, I never go more than 3 minutes. Just for your own knowledge, you might want to see how short of an exposure time you can get.
MP
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Excellent!
Thanks for posting.
MP -
No, You don't even need to change the width of the pulse to change speed. No, I am not talking about anything that has to do with "Pulse WIDTH Modulation", including any of the projects. I am talking about basic TTL clock signals that have been around for years. Simple. Change the clock speed and you change the speed of the motor. The signal is a 50% duty cycle and the pulse width is never intentionally modified. PWM or 'Pulse Width Modulation' works on the principle of changing the ON time vs OFF time of the individual pulse. This is not needed. A simple clock pulse stream of 50% duty cycle will vary the speed of this chip easily when you change the speed of the clock. When you change the speed of the clock, this is not PWM. Thus, PWM does not even come into play. I hope this explains it in a way that you now understand.
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You don't even need PWM for speed control since the input is looking for a TTL signal. You only need to change the speed of the pulse stream.
MP -
The L293 or L298 do not need PWM control. They are made for use with standard TTL signals. If you had looked at the first paragraph of the data sheet, you would have known this. Read the data sheet.
MP -
You would have to experiment around to see what the maximum exposure time would be. The light you are using is not very efficient. Do you have a place in your area that sells party supplies or lights for black light posters? There are many places where these are available. They really cut down the time for exposure. You can also get them in the round bulb type if you do not want to change your setup. When I built my system, I performed the test that I mentioned in the last thread. I killed a couple of boards but found my perfect height and exposure time.
The problem with slow exposure is that the light will find any small imperfections after time. The faster you can expose the artwork, the better.
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wow, 1 hour is a long exposure time. I usually never expose for more than 3 minutes. Perhaps this is why you are getting different results. I use a light table that has 4 of the fluorescent "black lights" in it positioned approximately 120 mm above the glass. You do not need dark black transparencies. On lighter work, you can use less exposure time. This is where the spacing becomes critical. You cannot get real tight artwork with transparencies that are not dark. Try the black light method and make some time tests on the same board using a black piece of cardboard to cover the board. Expose a small area for 1 minute, then expose same area plus another section for 1 minute, then uncover another area and expose again for 1 minute, etc. This will give you 1 minute, 2 minute, 3 minute, etc. exposures. Then when you develop the board, you can find your best exposure time. You might want to switch to a better photo resist and developer.
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gogo,
Look at a computer motherboard. All traces and pads are gold plated.
MP -
Happy birthday, Mike!
Tip a few ouzo's! ;D
MP -
I have never heard of anyone plating "after" solder mask. I cannot think of a good reason to do that. At best, your plating is a cosmetic in this case.
MP -
MOVED FROM MICROCONTROLLER FORUM
Lakhan,
You seem to have a problem with finding the proper forum. Please post your conversations in the correct forums.
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To All:
The project schematic is back in it's original form and is correct. Anyone making this circuit should have no problems with it's design.
Thanks Kyr, for joining the discussion and adding the additional comments about your project.
MP -
try here:
http://www.alltronics.com/cgi-bin/category.cgi
MP -
Your spacing is 10 mil. You should be fine.
MP -
The diode was not originally backwards. I should have looked closer after you the two of you told me it was wrong. Datasheet shows that it was in the correct placement.
This is why I strongly press on members that we do not make changes unless you are actively bench testing a project. This is the mess that results from it.
I think the original author might have re-submitted the schematic since I inquired about it to him.
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I use 3M transparencies. Hope you get it sorted out. I usually have no problems with traces down to 7 mil.
I hate the press and peel stuff. I ask too much from it and end up with too much touch-up afterwards.
MP -
You are on the right track kachew. All relays list a relay coil resistance. Just use ohm's law. You should come up with the same values as the manufacturer through calculation.
MP -
No problem! 8)
Hope you will share a picture of your finished product with the group when you are done.
Good luck!
MP -
The cathode side of D1 is connected to +5V through L2 as it should be or is this already modified?
I haven't looked at the schematic for the problem yet. No it has not been changed from the original. I have only asked the original author to get involved.
MP
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Good. I have notified Kyriakos to correct his schematic and re-post.
Sarma, thanks for the correction. Since I was not following this thread, I read your post as variable cap and not varicap.
If this schematic does not get corrected in the next month or so, please remind me and we will correct it without the original author's intervention.
MP -
I have made thousands of boards using transparencies from an inkjet printer. How old is the printer? The old inkjets did not have very good resolution. You can get a new high resolution inkjet for US$50 if you shop around.
I use darkest color and highest resolution. I also select transparency from the menu. I have never had to print twice.
One thing you might try is to go to the adjustment screen for your printer and fool it into thinking you are not seeing the test spots dark enough. This will cause the printer to go darker. It will be useless for printing on paper, but it will be good for your board transparencies.
MP -
please post a link to the project.
MP -
sarma,
variable caps are not directional like an electrolytic.It does not matter which direction you connect.
However, I do not see one in the project. Are you discussing the project in our project section here?:
http://www.electronics-lab.com/projects/rf/020/index.html
MP
Argumentive members
in Moderator's board
Posted
I get tired of the few argumentive members who want to go on and on with arguments about what someone has posted. In fact, at a point, I am fuming!
It would not be so bad if they posted a simple, "Here is how I understand it..." and then leave it alone. This would allow everyone a chance to share their knowledge. I have had members send me PMs about this and today I see this in a thread as well. Some members are afraid to post because even though they have years of knowledge of certain things, they do not have all of the theory books to backup what they would like to share. I think this is crap!
MP