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MP

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Posts posted by MP

  1. You can make a clock circuit or basically a pulse generator with a 555 timer so that it sends pulses to the step input of the chip. You can check this with the DIR in either position as this will determine the direction of the motor. This is actually a good pre-test to insure you are not shorting out your PC output board.
    The 100V capacitor will work perfect in the place of the one rated at less voltage.

    MP

  2. Hmmmm.....not really sure where this belongs. I have uploaded a voltage calculator for LM317. See the download area as soon as it is available.
    It is a nice calculator for figuring R1 and R2 for a particular output voltage when using the LM317. Makes less work. ;D

    MP

  3. The pdf file has some good information such as how to build the dummy load to test a power supply so that you know it is the supply and not a peripheral. Beyond that, I do not give TJ Beyers much credit (not exactly a friend of mine ;) ). $10 in parts plus a lot of your time when you can buy a new power supply for about the same as just the parts. For example, -->

    http://www.aaronix.com/catalog/default.php/cPath/131?reff=UL3KF1&pid=1965

    Has a 300 Watt ATX power supply for $12.99.

    And what do you have left when you fix your old one? Have you replaced ALL the bad parts or just the non functioning ones? Normal failure from a computer power supply is due to excess heat build up or power surges. This ruins some of the parts and weakens others. Sometimes you can chase problems for months to come. IMHO, I recommend to just replace it :-\.

    MP

  4. Billy, the design rules are really not that strict ;D. You have all the latitude you need as long as it does not fail the DRC check.
    In Eagle, I normally use the resistors from the "Discrete" library. The "Resistor" libraries are for special products such as SIL, DIL and Power resistor types.
    In the discrete library, I use the resus-5 package as the most common resistor. This is the standard ,5 spacing. There is also a reseu-5. This is the same resistor but with a different silk screen image.
    The reason I say the design rules are not that strict are this: Suppose you have a fairly standard or simple circut. You can run a trace or two under the resistor. Now suppose you have a really tight design. By using a reseu-7.5 or reseu-10, you can run 3 or 4 traces under the resistor. You will just have more lead exposed on the top of the board. If you have quite a bit of exposed resistor leads on the top because of this, do not forget to put a piece of very small heat shrink tubing on the leads to cover them before soldering to the board. You can also use insulation from wires that you have stripped.
    In the Eagle library, the capacitor packages follow the same rules. The number is the lead spacing. You can normally go through the discrete library and look at the different packages until you see the one you have. At one point, I asked the author of the program if there was a way to print out all of the library packages so that I could use it as a quick chart, but he e-mailed me back to say it could not be done without much work. Therefore, I have made a list of the packages that I keep on hand as a quick reference.

    MP

  5. I just noticed your post. I have not built this circuit, but it sounds like the message you are getting is related to the computer you are using. What operating system? Do you have administrative rights on the system? Perhaps you are asking the computer to act on an instruction that goes against a setting. Have you tried the circuit with a different computer to see if you get the same results?

    MP

  6. Actually, my data sheet lists 3.5 mA as minimum typical load current for the LM317. ;)
    In referencing a typical 2X16 display data sheet: It is true that the logic current on most LCD displays only draw 1 mA typical, but the lighting draws considerably more. This can be in the 100 mA to 200 mA range. Even higher on some of the STN LCD displays. You must have a contrast voltage which draw current and backlighted displays are even more current hungry. If this is a serial display, you are also powering a microprocessor chip. Ususally a PIC with a program in it to add the serial option. I certainly wish I could find a display with such low spec as 3.5mA or less. This would be my all time favorite for all of my future microprocessor projects. LCD displays are the one item that drains my battery powered circuits the worst. Unfortunately, everything I design with a microprocessor seems to have a display. I love them ;D.
    You will not have a problem with a LM317 for powering an LCD display. Also note, one never powers only a display. You will need other circuitry to send data to the LCD display. Typically, you will add the current draw of the microprocessor and any other peripherals in the circuit to the total draw. Microprocessor, Display, Contrast circuit, Analog to Digital Converters, switches, ram, or eprom. All will add to the current consumption. Try using a 9V battery to power a circuit with a display. It will not last for very long. You will find that you need to go to a battery type with a much better storage capability. This is due to the large current consumption of the display.
    The LM317 and LM337 are great for bench power supplies. Use the LM317 for the variable positive and the LM337 for the variable negative and you have a very nice variable bipolar bench supply. If you want to get less than the minimum 1.2 VDC on a variable adjustment, just add a couple of diodes on the output. This will bring it down to zero for the low end. Also note that this will bring down the high end by the same amount, so compensate accordingly on your calculations for the resistors.

    MP

  7. If this is refering to the following project:
    http://www.electronics-lab.com/projects/misc/007/index.html
    Then I do not think that you are going to be very successful with using a different type of switch in the same place. ;D The mercury switch is meant to be in your pocket and the movement of the switch activates the count. The closest option might be to use a switch such as Mixos has suggested and connect it to the shoe so that it triggers with each step. This is probably the simplest substitution.
    Another option might be a sound transducer, but it will require more circuitry to give you a trigger from the step.
    MP

  8. Billy, Mixos might be a better source for the Microchip devices (PIC). I have not used them for quite some time now. I primarily use the Atmel AVR series and ATMEGA series. In my case, I have a local distributor, which takes my sample order and ships them to me, usually 2 each.

    MP

  9. How this is possible:

    The IC companies want "you" the engineer to use their product in a design. If they give you a 25 cent part and you make a good design with it and it becomes a product, they will sell thousands of this part to the manufacturer of the product. This kind of makes you a part of their sales team in a way.
    I have gotten many microprocessor chips this way. It is better than purchasing several and then deciding which ones are best for your project. Also, many have a link to their newsletter and they will inform you if there is a new part. You can get a sample of it before it hits the market. Check the "Yes" box for the newsletter from these companies.

    MP

  10. Yes, I was refering to the Transformer as T1. It is possible I have seen this schematic somewhere else with the listing as T1 or I possibly gave it an automatic designation as it would have to be T1. I have not built this power supply but from what I read in the text of how it works, I think it is possible to make the changes in the parts I have indicated in the last post. Awaiting more comments to see if someone has any other ideas as well.
    Mixos: Since you were able to get 4 Amp out of this project, I am curious if you used a larger Transformer or adjusted the current limiting set point to achieve this. Or other method?

    MP

  11. Looking for a data sheet and/or application notes for the SK7804. It would seem that I had one at some time. I have a few of these chips in my bin with no information.
    Appreciate any leads, as I have googled myself ragged :P
    Thanks.

    MP

  12. Have you considered making the pulse tracer project and using this tool to inject a sound into the circuit? You could them probe it at the different stages and listen to see where you are losing the signal. These are just amplification stages with op amps, so the problem should surface quickly. If the signal tracer proves all is well, then you must have a bad mic.

    MP

  13. Rob, you want to figure wire thickness for the wattage needed. Then you convert the board copper to this dimension. I did have the information but I cannot find it. A google search for copper thickness and pcb might give you the result.
    Anyway, you have two choices for the thicker conductor needed. If you have the room on the board, you can make wider tracks or you can find thicker copper clad. The thicker copper clad takes more time to etch, so the etch resist has to be of good quality.
    In the past, I have also performed my own solder coating by wetting the copper with flux, then running a solder iron and a generous amount of solder along all the traces. If you get too much solder on the traces, drag a little solder wick across the traces with the solder iron on it to provide heat. Afterwards, cleaning up with denatured alcohol leaves a very nice looking board. This method works really good for surface mount boards.

    MP

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