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Posts posted by audioguru

  1. Rob,
    You have selected a challenging project, designing a power supply.
    Many details must be observed, and perhaps you have overlooked this one: The LM317 and its higher current cousins will current-limit when the input-output voltage exceeds 15V. This is for their Safe Operating Area in order to prevent secondary breakdown. With an input voltage of 35V then current-limiting will occur if the output voltage is 20V or less and at a 5V output it will give only a few hundred mA.
    A solution to this problem would be a paralleled booster transistor (PNP for low voltage drop) as shown on the spec sheets.

  2. Hotwaterwizard,
    The notch is very noticeable when you are fairly close to the loudspeaker. But if you are far away in a reverberant room, then reflections partially fill-in the notch, which sounds better.
    Thanks for your link about the crossover calculator. The car-stereo guys probably use high-order filters in order to keep their powerful BOOM from blowing-up their tweeters. But high-order filters are impractical because their parts must have non-standard values and very close tolerance.
    I notice that your link uses the Linkwitz-Riley (engineers at Hewlett-Packard) response instead of Butterworth in order to avoid the notch when even-ordered.

  3. D. Sandor,
    Thanks for correcting your schematic on the projects page, which is here:
    But you have also changed the transformer to 15V AC, which will give more than 19V DC. So now there will be more heating, but it has enough voltage to charge 8 batteries. 12V AC would halve been fine to charge 4 batteries, with less heating., or the original 9V AC with an LM317 current-regulator for even less heating.
    I can see your point about using a meter instead of having a battery-select switch or calibrated dial on a pot. It gives indication that charging is occuring! Most chargers use an LED.

  4. Hearse,
    The 4027 will not flip and flop without an oscillator. The oscillator determines the flash rate (number of flashes per second).
    Since you need an oscillator, you don't need a flip-flop circuit since the oscillator can drive one LED driver, and an inverted oscillator signal can drive the other LED driver. So the LEDs will alternate.
    A single 74C14 Hex Schmitt Trigger Inverter chip (or MC14584B), a capacitor and a resistor will do that. I am not going to design the circuit for you but I will give you some hints:
    1) The 1st Schmitt inverter, a capacitor and a resistor is the oscillator. A description of Schmitt triggers (the oscillator is figure 8) is here:
    2) The 2nd Schmitt inverter is the inverter. Connect its input to the output of the oscillator.
    3) The 3rd and 4th Schmitt inverters are paralleled on their inputs and are fed from the oscillator. Their outputs are also paralleled and drive the 1st LED (up to 10V supply without a resistor).
    4) The 5th and 6th Schmitt inverters are also paralleled on their inputs and are fed from the inverter. Their outputs are also paralleled and drive the other LED as above.
    With a 9V battery, the LEDs will alternate with about 18mA of current.

  5. Dsander,
    Thank-you for admitting that you missed drawing an important wire on your schematic. So then the 7805 will be a current regulator.
    I am glad that you realise that the supply voltage is too low for a 7805 current regulator to charge 4 batteries. If you use a 12V AC transformer then you will get about 15V DC supplying the regulators. The regulators will get mighty hot when supplying a low voltage (charging only 1 battery and/or supplying 800mA to a 2.9V camera), so when you update your project please mention heatsinks.
    By the way, with the batteries being fed a constant current then you don't need the pot nor the ammeter. The current will be the same for 1 battery as for 4. Just calculate the resistor and solder it in.

  6. Junk? No Way!
    I use the little 1/10W resistors that I can't buy anywhere, that come from fried telephones, answering machines and AM-FM clock radios that I salvage from the curb on each garbage-day following a lighning storm.
    But I hate surface-mount. When my arms became too short, I showed some surface-mount resistors to an optometrist and said that I need glasses so that I can read these, she said,"oh my god".

  7. Hotwaterwizard, you're right, the viruses stay away from me. I've never had one and don't run any anti-v software. But I do update and run a little virus-scanning program that I got from my ISP every month. Microsoft won't let me into their Update Center because my IE 4.01 browser is so old (it came with Win'98). If it ain't broke, don't fix it, right?
    My 1st add-on RAM chip (4MB) cost $200.00 and I gave it away a couple of years later when I replaced it with 32MB for $30.00. Since the 486 has a limit of only 64MB for RAM, I have a RamBooster program running in the background. It pops-up and does its thing for a couple of seconds whenever available RAM runs low (maybe every 1/2 hour).
    Defrag takes awhile but who cares when it's done in the middle of the night.

  8. Man! That translation gave me a hard time. The project is here:
    If wired as shown, then this project produces a notch filter at the crossover frequency. Due to phase shifts of 2nd order filters that are used, sounds at or near the frequency of the 3500Hz crossover from the woofer and tweeter cancel at your ears, if you are on axis and fairly close to the loudspeaker. The sound quality is not good.
    If the polarity of one speaker is reversed then the sound quality is much better, except then the frequencies at or near the crossover frequency are a little too loud.
    Many audio experts agree with this theory and one expert's explanation is here:
    To completely avoid these problems I always build two-way crossovers using 3rd order filters. The additional cost is only 1 capacitor since I use the woofer's voice-coil inductance instead of an additional inductor, and use a standard 3rd order filter calculation for the parts.

  9. Ante, thanks for your correction.
    Although the 7805 can be a current regulator, do you see that it can't be used here, since it would need at least 7V across it (plus the 6.3V or more for the batteries)?. The transformer voltage is too low for that. If the transformer voltage was increased then the heatsinks must be bigger.
    An LM317 will current regulate with only 3.2V across it.

    Since the PSU may be charging batteries and powering a camera at the same time, then the transformer must be rated for 1.5A.

  10. Hi Guys,

    I was wondering, how can this project charge four NI-MH batteries from only 5V in series with a diode, and how can a resistor in series with a voltage source supply "constant current"?

    The AA size NI-MH batteries that I have charging right now at 150mA, which is less than their recommended current of 210mA, measure 1.4V each, and they are not fully charged yet.

    So 4 X 1.4V = 5,6V plus 0.7V for the backwards-protection-diode = 6.3V or more to reach a full charge. Additional voltage must also be added for a voltage drop across the current limiting resistors. From a 7805 5V regulator?
    The voltage across the batteries increases while being charged, therefore the current will also vary when charged through a simple resistor.
    These problems are solved if the 7805 and its current-limiting resistors are replaced with another LM317 set as a current regulator:

    1) Connect a current-setting resistor between its output and its reference pins, and take the output current from the reference pin.
    2) Calculate the value of the current-setting-resistor: 1.25 divided by the desired current in amps (10 ohms gives 125mA). 1/2W is fine.

    Caution: A fully-charged battery that is still charging gets hot and may be damaged! Frequently check them, snce if you start charging batteries that are not completely discharged then you won't know how long to charge them for.

    Project link: http://www.electronics-lab.com/projects/power/035/index.html

  11. Thanks, MP:
    Those circuits WILL light 6 LEDs in a Knightrider fashion. They use diodes as OR-gates, so that 4017's outputs #1 to #6 light LEDs #1 to #6 in sequence, then output #7 lights LED #5, output #8 lights LED #4, etc. and back down to LED #1, then it starts over again.
    A brilliant use of diodes as gates. Don Lancaster (CMOS Cookbook) calls it "mickey-mouse logic", but it works well.

  12. Hi again,
    An analog circuit will make an LED Knightrider circuit:
    1) A classic 2-opamp ramp generator (1st stage is a comparator with hysteresis and the 2nd stage is an integrator and the stages connect together with feedback).
    2) The ramp generator feeds an LM3914 voltage-to-dot driver driving the LEDs in its dot mode.
    The lighted LED will appear to continue to go back and forth.

    Just more theory, guys.

  13. Hey guys!
    When I say USING it, I mean it!
    My 486 is used every day on the internet (cable) for surfing, e-mail, ordering parts and for word-processing invoices, etc. It is reliably running Windows 98, 1st Edition and very rarely crashes. It is all-in-one, like a Mac, so I can't even put a good video card in it (it has only 500kB of video RAM). Videos display at about 10 frames per second when small, and VERY jerky at full screen.

    What do you use your 286 for, and how often?

    Any other challengers?

  14. Hearse,
    Are you the same guy that was on another post-board requesting that the LEDs flash about 5 times on the left LED then 5 times on the right one, and back and forth like that? This circuit will do that with only 2 CMOS gate chips (4001B or 4011B, or 1 of each):
    1) A 2-gate Classic CMOS oscillator with a 10Hz output called FLASH.
    2) Another 2-gate Classic CMOS oscillator with a 1Hz output called ALTERNATE.
    3) 1 gate drives 1 LED, or parallel 2 gates to get more output power (up to 10V power supply does not need a current limiting resistor).
    One input of the gate goes to the FLASH output, and the other input goes to the ALTERNATE output.
    4) The other LED is driven by another gate or 2 gates in parallel. One input of the gate goes to the FLASH output, and the other input goes to the inverted ALTERNATE output.
    Note that the gate drivers must be the same type of gate.
    Connect the unused gate input of a 4001B oscillator to pin7, or the unused gate input of a 4011B oscillator to pin 14.
    A 4001B LED driver is active high with the anode of the LED connected to its output and the cathode to pin 7.
    A 4011B LED driver is active low with the cathode of the LED connected to its output and the anode to pin 14.
    I made a bunch of these flashers for my friends but with output transistors putting 80mA pulses into ultrabright blue or green LEDs.
    At night, they can be seen for miles, and work well as a flashlight. A bunch of them shining on the ceiling make cool patterns. The FLASHER oscillator has an additional resistor and diode so that it is ON only 1/4 of the time. I used a low-dropout regulator so that the flashes remain the same until the battery drops to 5V. With only 1 LED flashing 5 times, then a pause, then flashing again, then a pause again etc., a 9V alcaline battery lasts about 24 hours.
    I am sorry that I don't have schematic software to post these designs.

  15. Hi guys,
    The Chaser circuit will not make the LEDs go back and forth like YOURWINS cool animation of a Knightrider. Instead the LEDs will start with #1, then #2...... up to #10, but the next LED will be #1, then #2 etc. The reason is that the 4017 can only count up, not down. That is why the circuit is called a CHASER. If you put the LEDs in a circle then they will go around and around in ONE direction only.
    A Knightrider circuit will need the oscillator to be followed by an up/down counter, a flip-flop to change the direction, then a decoder.

    This is just theory, but it is true.

    Please post an animation of an LED chaser that is in a circle.

  16. Hi Ian, welcome to Electronics-Lab and to the hobby.
    1) Connect the positive terminal of a 3A DC ammeter to the positive output of the circuit.
    2) Connect the positive terminal of a 30V DC voltmeter to the negative terminal of the ammeter. This junction becomes the positive connection of the power supply to your load.
    3) Connect the negative terminal of the voltmeter to the negative output of the circuit. This junction is the negative connection of the power supply to your load.
    This way, the voltmeter shows the voltage across your load. The voltage will drop a little when the load current is increased due to the voltage-drop across the ammeter.
    In order to avoid the voltage-drop across the ammeter, a low-current ammeter in series with a resistor can be connected across R7 to indicate the output current. But the resistor must be correctly calculated to match the ratings of the low-current ammeter. Also its scale markings will require changing to "amps".

  17. Hi, MP, thanks for your anaysis of the original circuit and your comments on my recommended fixes. But I am sorry to have additional corrections for you:
    1) U2 can easily drive the 2.5K volume control. The 741 is spec'd with a minimum load of 2K. The 2.5K load on U2 will not affect its gain nor filtering function since it has an output impedance of 75 ohms divided by its feedback of about 30,000 (at 16Hz) = 2.5 milli-ohms. Therefore the effect of a 2.5K load on its output is very, very small. Since U2 can drive the volume control then U3 is not needed.
    2) What is the function of R9? Maybe it will limit the loading on U2 from the input of U4. But the input resistance of U4 is 2M ohms, and its input current is almost nothing (nano-amps)! Therefore since R9 does not limit anything, it can be replaced by wire.
    3) If the entire circuit was replaced by an LM386 (with its gain-adjust pins connected for a gain of 200) then it will be noisy, without having a sharp-cutoff low pass filter. The LED driver might also be missed but I doubt that it will work as intended (thump is red, thomp is green) since that would require DC coupling at the input. The LED probably just flickers with each heartbeat.
    4) With the original low-value for C2 then the output would sound like a "tic" instead of a "thump" or "thomp". Low frequency response is needed to reproduce a true replica of a heartbeat sound. Even a mechanical stethoscope makes a sound like "boom-boom, boom-boom" (have you tried one? I have). Look again at CDAK's professional-equipment's output which shows a very low-frequency "thump".
    I am not going to build a working circuit and apparently neither are you, so maybe the defective original one should be replaced in the Projects Section with CDAK's working one.

  18. I hope that this hasn't been posted before, the Search didn't work this time.
    The "date and time posted" shows as GMT timezone. Since I am in the Eastern North American timezone then it shows postings sometimes tomorrow and is very confusing.
    Does this board have a preference-entry for me to let it know my timezone like other boards have? If it has, then how do I get to it?
    If not, then maybe it should have.

  19. Hi Guys,
    Many people say that I should upgrade my computer. But even though it is nearly 10 years old, it does almost everything that I need. It has been downloading reliably for years from the internet at 350KB/s to 1MB/s (thats bytes, not bits like a 56Kb modem) on cable (they say it is impossible) while my son's 2.4GHz Pentium 4 gets 1.2MB/s on the same router. He downloads a file in 1 second and I have to wait for up to 3.4 seconds. For almost 10 years, it is still using its original bios/clock soldered-in coin battery.
    It's a Compaq 486DX-100MHz The processor is small and made like a Pentium and sits on a daughter board along with its 5V to 3.3V regulator. It is the last 486 processor that Intel made. The daughter board has the same size and pins as a regular old 486.
    Is anyone using an older one?

  20. Siddhu and Hotwaterwizard,
    I found (isn't Google great?) the link about "hypersonic sound" and their use an array of many ultrasonic transducers to create a plane (flat front not curved) wave that travels through the air without spreading-out. Another benefit of this system is that if you are in the beam then it demodulates when it hits you and the sound appears to come from INSIDE your head! But people who are nearby and not in the beam won't hear it.
    They think of using it for translation: one language is beamed to a person or group and another language is beamed to a nearby person or group etc. The link is here:

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