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Posts posted by MP

  1. Gayan,
    These values should work fine. You can also use combinations of capacitors to equal a different value if you wanted.
    A lot will depend upon how smooth the DC is from your power supply. If you have problems, go to a larger value on the input of the 7805 to smooth out the signal better and a smaller value on the output if needed for better filtering of the higher frequencies.


  2. I assume you are discussing this project:
    In the instructions, it tells you that soldering the components together is critical. Also, note that since you are dealing with RF frequencies, you must shield your board so that stray signals do not interfere. There is a connection for antenna. This should be the only place that RF signals are introduced into the circuit. I highly recommend that you solder all components and house it in a metal box which is connected to your ground or commons on the circuit.


  3. Hi Gayan,
    It looks fine. That is exactly what I was describing. Actually, it looks like you saved a step by connecting the sensor to the floating "In Lo" so that inverting the signal was not required. Good work!
    In regards to the battery draw, there isn't much you can do about it. But I think you already know this draws a lot from a battery since you have already used this setup with another sensor. Will you eventually connect this to a power supply? If not, you might want to add some type of time-out circuit that turns off the displays after a pre-determined time. This is the source of your battery drain.
    Regarding the capacitors: Use tantalums for that size.
    Again, congratulations on your success.


  4. Gayan,
    I think you will have a problem with the decimal point since a display of 60.0 would normally be done on the 200V scale. If you float the input and make the reference voltage adjustable, you should be able to come up with a scale that allows you to go from 0 to 60 with your input voltage that is less than 2V...that is, if you invert the voltage first so that you are going in the correct direction when the temp sensor gets hotter. Let me know if this is not clear. I will expalin further about floating the voltage, etc.


  5. That shouldn't cause come of the segments to be brighter than the others. This could be due to the displays you are using or you might have damaged them. Some designs do not use the diodes to drop the voltage to the displays and some do. You might have a display that requires more current and the diodes might be dropping too much. Another thing to look for is the wiring to the segments. Each of the segments is lit from a pin on the 7107. You should check the wiring since this is a perfboard setup.
    If you use capacitors, 100n should be ok. If you go with bigger in the input of the regulator, it is ok as well. I recommend the use of capacitors simply because you are not only filtering the electronics from the supply when you use capacitors, but you are also filtering the supply from the electronics. This is a problem when using digital chips since they all incorporate some type of switching or clocking actions. This clocking action can move through the supply lines from component to component without the capacitors to smooth out the supply lines.


  6. Hi Gayan,
    I missed your question earlier about the meter displaying 30, etc. R4 should give you enough adjustment to trim the voltage scale, but not the actual range of the meter. If you are using the 2 volt scale, you are not going to display a 30. You will need to change the input scaling so that it is incorrect, then change the reference pot, R4, to match your temp sensor scaling. Look at the voltmeter in the projects section that has a selection switch for range on the input. Here is the link:
    This should give you the idea.
    I know all of the other posts are about voltmeters, but that's all this chip does. Your application is actually a voltmeter scaled out of adjustment. All of the design discussions are certainly valid. Good to hear you read up on these. I know there were quite a few pages.
    Caps will help keep the regulator from oscillating. I don't know how well regulated your supply is up to the 7805, but if the reading fluctuates too much, adding a cap on each side of the regulator will take care of this.


  7. You can invert the voltage with an inverting op-amp, ICL7660, or any other charge pump circuit.
    You will need to use positive and negative supplies on the 7107 to read the negative voltages. (Your attached schematic looks ok for this)
    In regards to the question about "Common", you can float this voltmeter. The input and the power supply do not have to be connected to common.

    Have you seen the thread in Projects Q/A about this chip and the two projects we have on this site that use this chip? You should go through those threads and look at the projects for additional information.


  8. T1 is in the "Transistor-fet" library.

    The resistors are listed by size. You probably already know they are in the "Discrete" library. A 7.5 should work ok for these.

    There is also an LED library with many different LEDs. You want to choose the one you will use.

    You can always print the board layout at correct size and see if the parts are what you want.
    If you do not have one of these libraries, you can download them from the EagleCad website.


  9. Ben,
    If you will grip the transistor leads with needle-nose pliers while soldering, the needle-nose pliers will act as a heat sink and keep the transistor from getting over heated.
    In regards to the circuit layout problem, are you sure the problem is capacitance? I don't know what your circuit looks like, but did you put it in a grounded metal box and try re-flowing the connections to insure you do not have a bad solder joint?


  10. aniruddha,
    If two, same-value, aluminum electrolytic capacitors are connected in series, back-to-back with the positive terminals or the negative terminals connected, the resulting single capacitor is a non-polar capacitor equal in capacitance to either of the original pair. The two capacitors rectify the applied voltage and act as if they had been bypassed by diodes. When voltage is applied, the correct-polarity capacitor gets the full voltage. On a capacitance meter with no bias voltage the two capacitors measure half capacitance as you would expect from capacitors in series. In non-polar aluminum electrolytic capacitors and motor-start aluminum electrolytic capacitors a second anode foil substitutes for the cathode foil to achieve a non-polar capacitor in a single case.

    Here is an article from University of Guelph on making your own high voltage capacitors:
    It has the formulas that you asked about.

    Here is a fun site that experiments with two sheets of insulated aluminum foil to make a capacitor that you can test in a digital clock circuit:

    Care to go a step further? Here is an article on building your own Air Variable Capacitor:

    Have fun experimenting!


  11. Sure, I agree this is a simple setup and that there are much more advanced circuits out there. OP stated that the author said it would work with a HDD motor and wanted to know if it was so. I am agreeing that there should be no problem in doing this. Author is clear on his site as to what motor this is for. Also, author has been using this design in his simple robot circuits for better than two years. Sounds to me like it is a bench tested design. Thus my statement, Why rumor that it will not work...  I see a lot of over-thinking functional designs on this site anymore..


  12. It is difficult to stepup voltage. Usually a power supply voltage is selected to be high enough for the application.

    Not really. There are several ways to achieve this. Basically, you just need to make a charge pump and proceed with the voltage requirements from there.

    If you use one of the voltage multiplier chips, you would use the 5 volt supply and configure it as a voltage tripler. For more current, the MAX660 is available. I don't know how much current your fan requires. I have seen some very low current fans.

    Combining the -5 and 12 volt buss is ok, but you cannot connect the common on the fan to the computer common. Other methods besides using a resistor divider or regulator is to use a resistor combined with a zener diode to give you the output voltage you want. LM317 will work well with either the -5 to +12 or the resistive divider, or the resistor and zener. Just remember the LM317 requires a few volts higher input than the maximum output voltage when making calculations for input voltage to the regulator.

    but then I would have ~15 volts going into my fan when the potentiometer is all the way on?

    No. Not if your are connecting this to the LM317. The output voltage of the regulator will be less than the input. You would just need to calculate the output voltage. For example, if you use 220 ohm for R1 in your LM317 circuit and a 2K pot in series with a 68 ohm resistor for R2 as indicated in the data sheet, this will give you approximately 12.02 volts maximum voltage and approximately 1.6 volts minimum voltage.


  13. After a little search I have found this small circuit that the author says it can drive a Hard Disk Drive Motor. Can anyone verify this please?
    The site is: http://grant.solarbotics.net/Circuits.htm

    The author has been using this circuit in excess of 2 years in robots he builds. I see no reason to rumor that it does not work.

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