audioguru

Badai, Tune the radio to a quiet spot between radio stations near the low end on the dial. When you move the radio near a motor, TV or monitor that is turned-on then the radio will make noise.

Uman, The 555 is designed to be powerful, with a 200mA output. But it uses quite a lot of power-supply current even when not driving anything, which causes a small battery to run down quickly. There is a CMOS version called the L555 or ICM7555 which uses hardly any supply-current. It has a powerful 100mA output. The 4060 has a CMOS oscillator and long divider. It uses hardly any supply-current and has only about a 10mA output. Because of its long divider it can use a small and stable cap in its oscillator and still give long times. The 2240 ate batteries.

Alex, Be wary of 900MHz since it might pickup interference from all your neighbours' cordless phones, unless they've gone to 2.4GHZ and beyond. I don't like lavalier mics because they make it sound like the user (or TV announcer/reporter) is talking through a heavy blanket (or actually a turtle-neck sweater). Have you ever heard an underwater throat mic? Vowels only, that they somehow say is speech. A lavalier is similar.

I got another Fatal Error about 1 minute ago. That makes them nearly 1 hour apart, during which time I did a lot of navigation.

Mixos, I got the same Fatal Error message about 1 minute ago. It seems to be much less frequent. I also got one "connection with server cannot be established" message about 1 hour ago. One error per hour isn't bad.

Electrodoc, What happened to the previous low-bass circuit? Now you want 100-250Hz high-bass? You're making a colour-organ! I can see midrange coming next, then........ It would be complicated to add low-pass and high-pass filters to that kit circuit, and calculating its existing response is difficult due to its feedback at each stage.

Alex, 1) Thanks for the great link about modifying radios. I like to modify and improve electronic items too. In your voice application, the music modifications won't apply. They talked about changing the de-emphasis capacitors: European radio stations use a different de-emphasis than North American stations (its a long story that I'll tell in another post). When you buy a radio then it won't sound right if it was made for the other market. But how can you tell? By listening to it. The high frequencies will sound too bright or dull if it is wrong. I'm still using a 14-year old SRF-29 at the beach, and I haven't even looked inside. 2) The Sony mic is only 1 1/2 inches long. Maybe they use a folded waveguide inside to make its acousical length longer. I dunno about it. Its mounting method would be a real convenience for you.

MP, A motor is not analog, keep it away from audio and video, or you'll have lots of "alternator whine". Noisy things should have their own ground buss. (Like a school bus?) Many analog/digital products have separate voltage supply busses in addition to the separate ground ones.

Alex, Due to quite long audio wavelengths, the longer a shotgun mic is, the better it is. I don't think that a 2 1/2 inch mic is any good. The Audio-Technica shotgun mics are 6 to 14 inches long. Good-luck with its mounting to your camera.

Stuee, You cannot simply apply power and audio to the device as the project's author implies. If you do, then the audio will cause the voltage of the resistor element to swing up and down, exceeding the absolute maximum negative voltage rating of the element (-0.5V), which will cause severe audio clipping and may damage the device. In the author's Note #4, he advises to use a +,- 5V supply to solve this problem, but that is also an error since it would exceed the absolute maximum supply voltage of 8V for the device. He also failed to mention attenuating the input so that it doesn't exceed its rating. That is why I mentioned biasing the pot and cap-coupling one end to ground when using a +8V supply, or using a +,- 4V supply. It is difficult to make a quiet +,- 4V supply from a car battery, but it is easy to make a +8V supply from an LM317, then bias and cap-couple the element. I must correct my statement about biasing and cap-coupling: 1) Bias the LOW end of the element to +4V, by using an equal-valued-resistors voltage divider of the supply voltage. Capacitive-couple the +4V to ground, so that audio is completely filtered out. 2) Attenuate the audio source so that it does not exceed 8V p-p. 3) Capacitive-couple the attenuated audio source to the HIGH end of the element. 4) Capacitive-couple the element's slider to your amp's input, or make certain that your amp has an input capacitor. If this element is the same value as the existing volume control, then when paralleled the combination will double the source's low cutoff frequency. How do you feel about the step sizes changing with volume setting, which makes the steps crammed together at the high end, and spread out at the low end? Some day, maybe someone will make an audio digital pot.

Kasamiko, I'm glad to hear that your circuit works well. It should be good for 180W with a 24V CT, 7.5A transformer and if all the transistors don't get hot. How did you heatsink them? One heatsink for all drivers and outputs? What size? That is good for you to use a "snubber" circuit across the output to eliminate interference.

Divide by 14??? OOOOOPS Sorry, I meant to take the output from the 14th stage, pin3. BTW, the number 2240 belonged to the XR2240, an obsolete chip that combined a 555 with a counter. EXAR are making much more sophisticated chips nowadays.

Alex, I did a quick search on Google and found a link that sells the quality ATR55 shotgun mic for only US$46. The link is here: http://www.atr55.com/ That is only the first link on Google. Also try a Froogle search. A local dealer probably won't come close. It certainly will pickup in the direction that the camera is pointing, but I haven't tried one with a loudmouth beside it. Will you try it?

Uman, I posted a link to the data-sheet, then later I posted a link to a whole 4060 timer circuit. If your computer can't open a PDF file, then download an Acrobat Reader from many manufacturers' sites. As I said earlier, the 4060 can be reset with a simple OR gate, made with diodes. One diode in series with the power-up-reset capacitor, and another diode between the reset pin and your (active-high) reset control. The posted project is for a 24 hour timer, using an unstable electolytic capacitor in its oscillator. To make it a 1 hour timer, I would use a much smaller value and stable capacitor then select appropriate divider pins for the set-up LEDs, with the output taken from the divide-by-14 pin.

Manny, It sounds like your idea will work. What a nice challenge.

Stuee, The DS1669 digital pot has memory built-in, so you can turn off its power and it will come back-on the same, but it updates its memory only if a change of 8 steps or more is made. The project that you referred has an error: the supply voltage is +,- 4V maximum, not +,- 5V. Your inputs may need attenuation so that they do not exceed 8V p-p. You need a -4V supply converter, unless the top end of the pot is biased at +4V and the bottom is capacitor-coupled to ground, using a +8V supply. The DS1669 data sheet is here: http://pdfserv.maxim-ic.com/en/ds/DS1669.pdf Have you considered the application of this linear-steps control for a logarithmic volume control? Therefore over this 64-step control, the top 10 steps will hardly make any difference in the volume, then turning it down further the steps will become broader and broader, until near the bottom they will be coarse. The difference in volume between maximum and half-way (32 steps) is noticeable but certainly not half-volume. If the volume is much too loud when you turn it on, then it takes a number of seconds to reduce it even on "fast" mode. That will seem like a long wait if it's blasting. But there is a way of "loading" the slider so that it is not that bad. How are you going to control the amps in unison? By using 4-pole buttons? How are you going to display the volume setting?

Alex, For long-range pickup that reduces background noise, consider a "shotgun" microphone. It is longer than a conventional mic and must be aimed at your subject, but may solve your problem very well. A not too expensive but high quality brand is Audio-Technica. They specialize in mics and wireless-mic systems. Their ATR55 shotgun mic is recommended, and even has a "normal" or "long-range" switch. The Audio-Technica web-site has a wealth of information for you and is here: http://www.audio-technica.com/index2.html Perhaps a local dealer will give you a tryout. If you use your camera's mic then it may pick-up zoom-motor sound and handling noises. With a short cord to a tripod-mounted shotgun mic, then maybe the wireless can be eliminated.

Most of my comments about cheap transmitters apply to all of the FM transmitters in our Projects Section. I will say no more.

Alex, If the receiver doesn't have a mic-level output, then it will need an attenuator, unless your camera has a line-level input. The Sony receiver is probably digital, so it will probably be very fussy about receiving a signal that must be EXACTLY on-frequency, like a radio station. That, and other reasons below, are why I recommend using a Sony-matching transmitter. Use a uni-directional cardioid microphone element to reduce background noise and echos. Cheap Transmitters: 1) Although a cheap electret mic element is quite good, it is usually omni-directional and picks-up background noise and echos. 2) An analog transmitter is difficult to tune to an exact frequency, such as 99.9MHz. It might actually be tuned to 99.85 or drift to there (that would be very low drift), then a digital receiver may mute. One moment it works, the next it doesn't. 3) The circuit may cause a tinny sound because it cuts low-frequencies so that customers don't complain about air-conditioning rumble pick-up. 4) The circuit probably does not have high-frequency pre-emphasis, as required for radio stations. So its received sound will be muffled. 5) The circuit probably has high distortion, which is masked by its narrow bandwidth. You get what you pay for.

Mixos, I got the same Fatal Error twice: 1) About 15 minutes ago, when I tried to log-in. 2) About 10 minutes ago, when I tried to reply.

In the interests of safety (exploding capacitors) and quality (previously posted), this dangerous and defective project should be removed from our site. Let us not have anyone injured. We already have a good re-engineered inverter (Low-cost, 500W).

It is no wonder that neither me nor my search could find it, "Tough Switch". What's tough about it? Where's the schematic?

Maybe it is programmed to give a different advertisement for each page, but sometimes the ad is the same on your next page which causes a conflict, "cannot redeclare".

That's the same occasional Fatal Error message that I get, ever since the Apache software upgrade.

Cdak, I am glad that you got your LM387 (obsolete) pre-amp working so well with an external 7th-order HPF used to reduce 50Hz hum pickup. Have you considered a simple notch-filter? Are you still using the 9th order LPF that you mentioned earlier? What frequency does the LPF cut-off at? Do you think that an available TL071 opamp will work as a preamp here?