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MP

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Posts posted by MP

  1. You will need some current limiting power resistors on the emitter side of the power transistors unless you are going to use MosFets. The reason this is done is because power transistors like the 2N3055 are not matched. Current will flow through them differently from one to the next. Because of this, when you parallel them together like this, you will have one that will be less resistive than the others and will take all of the current load and overheat itself. The power resistors are a safeguard. Something in the 0.1 to 0.22 ohm range with a fairly good watt rating will work.

    MP

  2. Here is a continue of the message that was started in the microprocessor area...

    For labeling, I have used a material in the past that was manufactured by 3M.
    This is a vinyl material. It is pretty thick, no worry about tearing or stretching it. You can also get it in a thin metal. I have used both. The material is coated with a light sensitive paint. I tried red and blue, but used the black mostly. You make the design layout in a cad program and print it to a transparency. You can use a black light or UV light to expose the label. All the parts of the label where the light hits is hardened. All of the areas where the light cannot touch is still soft. The next step is to wipe it with rubbing alcohol until the label shows all of your art or lettering. After that, you rinse in water and have a professional label. I have used the white vinyl with black paint which gives you a black label with white lettering and symbols, etc. and I have used the silver metal with black paint on it. This gives you a black metal label with silver lettering and artwork. You can reverse the artwork like a negative and switch which color is background and which is the lettering color.
    This material was widely used by graphic arts shops and was not easy to find. I still have a box for the 12" x 24" black on white vinyl. This is the size I purchased because I was using it on 19" rack mount panels. The box reads: 3M ID# 70-0061-5797-1. Also reads: Product # 8015.
    The distributor who I had been purchasing it from is no longer in business and I no longer have a source. :-\ Perhaps with others also searching, we can find a new source.
    Kepro circuits used to also carry a similar product, which is where I originally found out about this. I searched for the part numbers on their repackaged material and found the other source. Kepro sold the developer for a high price, but when I requested the MSDS sheet, I found out that the only ingredient in the developer also went by the name of "rubbing alcohol". So, all you need is the rubbing alcohol to develop this. No dangerous chemicals and no reactions. ;)

    Hope this is informative.

    MP
    :D

  3. Gustavo, if you scroll up to page 1 of this thread, Billy has posted some corrections to the circuit. I have also found a board layout file with schematic both in Eagle format on the Eagle site that uses these parts and is very similar. It was donated by a user. If you do not have the Eagle Layout program, you can get a free version from their website at the same time.
    http://www.cadsoftusa.com/freeware.htm

    Billy: did you find any other corrections needed after your previous post?

    MP

  4. It is highly unlikely that you will be able to do this. If it was sold as a toy, it will probably not use components that will allow you to tweak more sensitivity from the circuitry. You would literally be rebuilding the device. But that is only speculation on my part without being able to see the circuit. Perhaps you can map out the components from the circuit board. This is called reverse engineering. If you can do this, you would be able to know what you have to work with. Don't worry about component values at first, just draw how the components connect to each other.

    MP

  5. As Billy has stated, you will need resources for the software. It also depends upon the language you use. C does not do anything you do not tell it to do. Visual Basic sends an automatic line feed and new page unless you tell it not to. If you want to communicate to the outside world from Windows, you will normally need a DLL which will pass the information to the device. If you are using Win XP, you have more problems as you have to get past the built in security. I am assuming you want two way communication.

    A search on the web will give you the DLL and how to incorporate it into your code. Look for outport or inpout or combinations of these keywords as I have seen free versions of these on websites in the past.

    If this is for medical devices, how are you checking that the relay is closed or open or is not false triggering? Sometimes the parallel port data pins are energized when the computer is turned on. This could be a problem if you are not wanting to turn on a relay that is connected to the port during a reboot or when the computer comes back on from a power failure.

    Just some thoughts.

    MP

  6. Another way would be to take the power inverter diagram from the projects section of this site and modify it.
    I am referring to this project-->
    http://www.electronics-lab.com/projects/power/018/index.html

    Method 1:
    Instead of using a tansformer that steps the voltage up by 10, use one which will step it up by 3 or 4. This is accomplished by the number of windings on the primary vs the number of windings on the secondary. You do not have to modify a transformer, they come in different types. Once you have the correct voltage out (or close), rectify it for DC and regulate it or use a voltage divider to tweak it in to the exact voltage you want.

    Method 2:
    Another way to accomplish what you want with this circuit is to use a voltage divider on the 12VDC to make it only 4 volts. Since this is a 10 times step up circuit, you will have 40 volts AC.
    At the output of the transformer, you just run it through a diode to rectify it and add a large cap to smooth out the remaining AC.

    Method 3:
    Use the circuit "as is", run the output through the diode rectifier and add a cap for ripple rejection (DC voltage), then use a voltage divider or regulator circuit to trim it down to the voltage you desire. This could be done with zener diodes and resistors.

    If you need a bipolar supply, you can run the output of the transformer through a bridge and get -40 as well as the +40 volts.

    So you see, there are some choices. ;)

    MP

  7. gsmaster,
    Yes, I also have experience with the yellow stains. I have also had the occasion when the thermostat quit working in a heater and got the etchant too hot. Everything in the etch room that had metal exposed to the air became rusted.
    I hope you can find a way to post the ingredient that you use to the group. Please tell us more about it.

    Mixos: How does one start a new topic? Is there a button somewhere? I think there is a lot of information to share here.

    MP

  8. Not sure about the plexiglass. I made mine with thick pieces of glass and clear RTV. The materials were more readily available to me.
    Ammonium Persulfate turns blue as the copper is etched. The more copper etched, the bluer it gets, until you cannot see through it very well, either. I think it is easier to dispose of.
    The bad points: After it is mixed with water, it has a shelf life and if you get it too hot with the heater, it is ruined. This and more is probably in the data sheet. I used it for a while but went back to fecl3. I do not remember why. Perhaps you could post a comparison when you try it.

    MP

  9. I see nothing wrong with your board. And I have been making boards for quite a few years. Since your traces are thick, the edge is not a problem. In fact, the only place I have seen where this is critical is in microwave circuits where the trace thickness and length is calculated for precise ohm.

    If you decide you need thinner traces, you can make an etch tank that sits upright and put a fish tank heater in it to bring your temperature up. Also add a fish tank bubbler pump to your sdt up and some tubing to allow a wall of bubbles in your tank. These will allow better
    oxidation and cause the etch to go faster.

    MP

  10. Yes, this is a single op-amp filter with a gain stage ahead of it. So, if you are going to limit your design to only 2 op-amps, you have a choice. Do you want the more attenuation of signal outside of the frequency pass band or do you want more overall gain of your circuit? If you want both, you can just add another op-amp stage for gain. The more stages of frequency filtering you add, the more attentuation you will have of the frequencies you want to reject.
    Have Fun!
    MP

  11. Yeah, I am not familiar enough with either chip, but they are both audio amp chips. Sometimes one manufacturer makes the same as another and puts their prefix on the existing number. Was hoping that might be another source.
    You could probably do the same thing on the NEC website. Just find their contact link and ask them for the data sheet. I have had very good results from several manufacturer's websites in this regard, Sometimes it takes them a few days but you usually get an e-mail with a pdf file attached.

    MP

  12. Found it! The program is Quick Basic 4.5. Since it is not freeware, I will not post it. However, it is probably all over the net if you look. ;D
    With this, you can copy all of your Qbasic code and paste it into this program editor, then click the compile button and you have an EXE file. This saves you from having to go into the Qbasic code and click run from inside the editor window.

    MP

  13. Here is the best you will probably get with two op-amps. I have provided the formula in the drawing. You already have the cap values, you just have to figure the resistors from the frequency of cut-off.
    Just round the resistor calculated figures to a number that is an actual resistor value.
    The gain is 1.586 and has to stay there for the circuit to work properly.
    If you need help with this, let me know.
    MP

    ThirdOrderLowPass.pdf

  14. There is another form of basic that compiles your code to an exe file. It is much nicer than Qbasic because you just enter the name of the exe instead of going into the qbasic editor to run your program.
    In regards to the other: Using a 386 with only Dos loaded onto it is pretty rare for most of us who are reading these things from our tie to the internet. Most users are going to have a higher operating system. In such cases, the information in your tutorial is going to be invalid and cause lots of frustration. Therefore, I added the additional comments to your post. If you have a higher operating system (not dos only) your printer driver takes over the parallel port and you will have problems trying to communicate without fooling the port into thinking the printer is attached. Even when you use a Dos prompt in Windows, your printer drivers control the port.
    I actually wrote my stepper program in visual basic. There is a lot to be said of the user interface.

    I will look for the other quick basic and attach it to a post so you can compare.

    MP

  15. Actually, this needs a little more explanation if it is to work for someone stumbling across this for the first time.

    If you are controlling a stepper motor or anything else from the parallel port, you will need to fool the port into thinking it is connected to a printer. This is done by tying pin 10 (ACK) and pin 15 (ERROR) to a logic high with a pull-up resistor (4K7 works perfect). Pins 11 (BUSY) and 12 (PAPER_END) should be connected to ground. Pins 18 through 25 should also be connected to ground. I have never used opto-isolators on the data lines, but it is probably a good idea if you are not familiar with what you are doing or do not have limiting protection on your circuits.

    Now you can communicate through pins D0 through D7. These are pins 2 through 9. Pin 2 is D0, also known as the Least significant bit ot LSB. It represents either a 0 or 1.
    On a 4 wire stepper you will use 4 data lines per motor, for example, D0 through D3. Sending a 1 to the port brings D0 high, sending a 2 brings D1 high, etc.
    To make the motor turn, you send Binary numbers 0001, delay, 0010, delay, 0100, delay, 1000....(This was one step)... and repeat this for the total number of steps you need. Do not forget to add delays between these numbers or the motor will miss steps. The computer will send the bits to the port much faster than the motor can use them.
    You do not have to use binary numbers. You can send 1, delay, 2, delay, 4, delay, 8, delay.....etc. by using
    lprint chr$ (1);
    delay
    lprint chr$ (2);
    delay
    lprint chr$ (4);
    delay
    lprint chr$ (8);
    The semicolons tell basic to not add carriage returns or line feeds.
    How to generate a delay?

    delay:
    for x = 1 to 500 (or whatever you decide is a good delay time)
    next x
    return

    ...and please.....find something better than QBasic.. ::)

    MP

  16. What you are referring to is a MOD-60 or MODULO-60 counter. You can use a MOD-10 counter with one of the 74LS93s and a MOD-6 counter with the other to provide a MOD-60.

    Here are some links. Some are ppt, so the download will take a while. The time to wait is worth it, though. Great examples and illustrations and they have the circuit that you need.

    http://www.phx.devry.edu/fac/thomas/EET202/Cntrs.ppt
    http://tennis.ecs.umass.edu/ece221/lecturenotes/ece221-ch7-part1.ppt
    http://www.site.uottawa.ca/~rhabash/ELG3331LN08.pdf

    Good luck!
    MP

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