audioguru

Gsmaster, Thanks, that's a good one that I haven't seen before.

Electrodoc, If the filtered circuit picks-up voices then obviously the 200Hz cutoff is much too high. For 100Hz, connect a 6.8nF (682) capacitor across RV1, and a 33nF (333) capacitor across R13. It is a very simple 2nd-order filter, so don't expect a miracle. Besides, if a voice occurs in a filter's passband then it will pass it. Of course, you can help matters if you move the microphone closer to the "beat" and farther away from the voices. I hope that your "beat" isn't coming from a cheap little radio. I also hope that your "beat" isn't from high-frequency bongo drums, wood-blocks or cymbals.

Badai, The Field Strength Meter is a simple untuned AM detector just like part of an AM radio. It is used to measure the radio-waves strength of a nearby radio transmitter. It might be sensitive enough to also detect nearby live mains wiring. What do you expect to measure from an appliance that is not turned on? It might have "risidual" electricity that is stored in a charged capacitor, but that voltage is a steady DC without any electromagnetic radiation (radio-waves). The power in an inductor is dissipated within milliseconds after turning off the power. Motors that produce spinning magnetic fields and maybe sparking, have stopped and therefore no longer produce radiation. You say that residual power remains in the appliance as long as the mains wire is not unplugged, which is true only if the appliance has continuous power, even when switched off, for a function requiring power like remote control or a clock. You also say that a handphone (cell or wireless?) causes interference to a nearby radio, of course it will because it is an operating radio transmitter. A field strength meter will measure its radio-waves strength. The radio-waves (interference) stop when the handphone is turned off. Good-luck with your detector of something that does not occur. As you can see from the links, perhaps you should change your objective to detecting active EMI.

The project is here: http://www.electronics-lab.com/projects/science/008/index.html JLB, I see your problem. I think that a capacitor is missing, either from the right-side probe to ground, or across the rheostat. Can you try it with about 1nF? Please let us know. The author's web-site URLs don't work to see if there is an update, so I e-mailed him with my query.

Jonathan, Even better, replace your 555 and gate drivers with a 4047 oscillator/divider/direct-and-inverted-outputs chip that directly drives the gates. Its digitally-divided outputs are exactly 50-50 symmetrical. An output of 300W from one pair of MOSFETs would be easy.

Kevin, A TV's Cathode Ray Tube (CRT) operates like a normal vacuum tube, except its "plate" is the screen (covered with phosphors). The screen is connected to the very high voltage which accellerates the electrons emitted by the heated cathode, which is near ground. The grid of the CRT (and normal vacuum tubes) modulates the current of the electron beam. The high voltage supply remains constant. Those "glass pressurized devices" are used for lighning arrestors. When the voltage at one end rises to its threshold, the gas inside ionizes and it conducts heavily, arresting the high voltage and its current to the other end, which is ground. A neon light bulb works on a similar principle. (Don't try plugging a neon light bulb without a current-limitting resistor into the mains, like I did when I was a kid!)

Kevin, Current is a FLOW of electrons. When a capacitor is charged, the current flow stops. The capacitor stores energy, which is its charged voltage and the potential, or ability, to deliver a current during discharge.

MP, Never mind the special LM387 "phonograph preamp", how about using a standard, available and low noise opamp? How do we get the project corrected?

MP, Digikey won't sell me an LM387 (quantity available = 0) and neither will Newark Inone. Why would anyone want to use it now, without any manufacturer second-sourcing it and with its non-standard pin-out? There is nothing special about it in this circuit, a standard low-noise opamp is fine instead. Cdak used it only because he had some. Answering your last post: 1) His external HP filter made a BIG difference because it attenuated hum pickup, as is shown in his graphs. 2) He didn't use a preamp? Of course he did, he used his LM387. I mentioned replacing the original circuit because it has errors (which are easily corrected) and therefore does not work. Nobody is correcting it.

Kasamiko, It can be controlled by a micro-controller chip.

Kasamiko, Please post a schematic of your monostable, maybe it is re-triggering (cutting power) when it should be driving the relay continuously. If you power the coil of the relay from a battery as a test then the relay contacts will be proven.

Mmphoneman, You are lucky that it has 2 channels and 1 that still works. Remove the fuses and power and measure for a much lower resistance on the bad channel, probably at the output transistors or power ICs. By comparing measurements of the good channel to the bad one, then you'll find the problem.

Stuee, Weren't you enquiring about digital pots for your car on the other post? The chip that you need is custom-manufactured for car audio systems, with scanning function-selectors, and either has audio digital pots and display circuitry built-in or it interfaces with those custom chips. Perhaps you could obtain them as a replacement part, but you probably won't receive any information about how to hook them up. It would be an immense task to re-engineer such a system using off-the-shelf electronic parts. May I suggest that you purchase a new "head-unit" with those functions built-in.

Alhilaly, As you can see the many replies about this project, the schematic and parts list have errors. Until the errors are corrected it is awkward to give you a detailed circuit description.

Mixos, That's a nice one. Also try rotating the SOIC by 90 degrees so that it can be an 8-pin DIP without any extra pin spacing.

Kasamiko, Doesn't your voltage monitoring prove that the relay is OK? Maybe the mains voltage is low before or after a power failure which causes a "freon" bubble with a delay.

Kasamiko, With 11V across the 47 ohm resistors, half the time, the power dissipated is only about 1.25W. Maybe they are small and normally reach a very, very high temperature at their maximum rating (5W) so therefore get hot at 1/4 of their rating. Try physically larger or higher power rating (10W) resistors. I looked for driver transistors having more gain (so that these resistors can have a much higher value and less power), without luck. You can't use darlington drivers without losing output voltage and increasing the heating of the output transistors. For the next circuit try a 4047 directly driving the gates of N-channel power MOSFETs with their sources grounded and the transformer's center-tap to +12V. 300W output should be easy by using one pair.

Kasamiko, 1) Maybe something is happening to the "freon" during the delay. The motor works hard, but normally, without a delay. But it runs smooth and quiet (and doesn't do its job) after the delay. Perhaps the "freon" developes a gas bubble because it warms-up during the delay, at a location where it should be liquid, so that the compressor doesn't have any liquid to pump. 2) Maybe condensation forms on the cooling coil during the delay, which quickly freezes when it starts running, blocking its air-flow. 3) Try a 10 or 15 minute delay.

MP, I was refering to Steven charging his capacitors with DC, just like recharging a battery. When you charge a capacitor, DC current flows into it. A charged capacitor has the current that has flowed into it "on-hold", waiting to be released (during discharge). Ante, I agree that a capacitor stores energy (which is also power) since the energy (power) that is stored is directly in relation to its voltage level and charging current (and capacitance value). Steven, Your capacitors retain a charge after a fat spark probably because the voltage decreases to a level that cannot keep the air ionized for that certain length of spark-gap. However, certain types of dielectrics also retain a charge after a complete discharge. These types cause audio and video distortion. Short circuit a charged electrolytic then measure its voltage rise when the short is removed. Do you see that your two paralleled 6KV capacitors do not have a combined voltage rating of 12KV?

Electrodoc, A very simple 200Hz low-pass filter can be added to the Velleman kit: 1) Add a 3.3nF capacitor across RV1. 2) Add an 18nF capacitor across R13. The LEDs will flash to the bass and beat of the music.

Kevin, Connect a resistor in series with a capacitor, so that the resistor can charge and discharge the capacitor. Connect a signal to the resistor. You now have a linear low-pass filter, with its output across the capacitor. It doesn't matter that the capacitor charging is exponential instead of linear, unless you need a linear triangle wave or sawtooth. If you feed the low-pass filter with a pure sine wave, then the output will be just as pure (very linear) as the input, except at high frequencies when its output level is reduced and is purer (less distortion and even more linear).

MP, Yes, a capacitor stores current, like a rechargeable battery. It also releases its stored current during discharge. The value of the capacitor determines how much current can be stored or released, per time. You might say that a capacitor stores electrons or holes, but I like to think of it as current.

Thanks, MP. Are you able to attach the schematic to the project? Maybe you could add a note about why the author neglected to tie-down (ground) the floating inputs of the unused gates. PS Maybe a warning not to use the circuit in winter if the humidity is low which causes a lot of static electricity. I recommend adding 1M resistors in series with the live contacts. Steven's spark generator could be used to test the effectiveness of adding these resistors.

Steven, Try feeding the generator to a step-up transformer, then rectify its output. When you parallel capacitors, the voltage rating remains the same, not doubled. But the current storage is doubled. If you put two equal-value capacitors in series, the voltage rating is doubled, but the current storage is halfed.

12412, There is no schematic. There is a photograph, a sketch showing the completed circuit board and external wiring, a PCB pattern and a parts-mounting diagram. If there was a schematic then I could see how it works and how it does it. I could also see whether the parts are matched to each other. Even if the title was correct so that I could find the project, I would not vote about it without seeing a schematic.