I am looking for an AC/DC transformer with a variable voltage input of 47 VAC to 277 VAC, with a secondary output of 12 VDC.
Does anyone know where I can find one or have one made?
Please log in to post an answer.
I was wondering if it would be possible to cheaply build a system in which I speak into a CB type radio, and have the signal sent to a loudspeaker about 1,000 feet away or slightly more? The current system I have is a bullhorn, and I have to stand a good distance back from the crowd to accomplish my task. It kills my voice. I was thinking if I could buy a loudspeaker (what wattage?) and a set of CBs that I should be able to modify the other CB to feed into the amplified loudspeaker so I can simply talk into it.
Surely there is a commercial version, but I'd like to be able to do it on the cheap if possible.
Please log in to post an answer.
How can a long range wireless RS-232 link between two computers be built? I'd be very interested in how to get an effective range of 3-5 miles.
Please log in to post an answer.
I am a beginner using a Parallax BASIC Stamp kit #555-28158. How do I wire seven LEDs and program them to come on and off in certain orders or patterns? Is it possible with this kit?
Please log in to post an answer.
Our church has analog controlled dimmer modules. The controller has four scenes learned in some type of memory. After a power failure, the controller does not know the state it was in at the time of the failure. The default setting is that the controller selects scene 4 after the power is restored.
Since most of the time the power interruptions are at night when the church is not occupied, the system is wasting energy. For safety reasons, this was acceptable at one time, but the cost of energy is a concern. The four scenes and off modes are selected by a momentary contact closure. The manufacturer solution is to upgrade to digital control.
Is there a circuit design using a microcontroller that could capture the state the controller was in at the time of the power failure and restore the controller to the mode after power is available?
Please log in to post an answer.
I built the "Mail Delivered Detector" published in the June ‘06 issue of N&V (http://nutsvolts.texterity.com/nutsvolts/200606/#pg44) and was quite satisfied with the results. However, I found that the device stopped working in the cold weather. Adjusting the 25K pot on the receiver's 567 tone detector restored operation until the temperature changed and the device stopped working again.
As an example, I measured the frequency of the transmitter's 555 timer at 68 degrees F to be 320 Hz, and at 20 degrees F it was 280 Hz.
Can someone suggest any modification which will keep the 555 timer circuit in the transmitter on frequency as temperature varies between minus 10 degrees and 95 F, or a way to broaden the frequency range of the tone detector in the receiver?
Please log in to post an answer.
I’m just getting started with microcontroller cards. What is the difference between an AVR microcontroller card and a PIC microcontroller card? I am interested in purchasing a course kit that includes the books and the microcontroller card for the course.
Please log in to post an answer.
Conar Model 251 Oscilloscope
I need a schematic or manual for the Conar model 251 oscilloscope which Conar, I understand, was bought out by NRI/National Radio Institute/McGraw Hill. This is an old single channel 10 MHz analog scope. I need the manual to repair the scope. I already know the power supply works and the cathode ray tube works since I see a momentary dot when the scope is turned off. I am on limited income but will be willing to pay for a copy of the schematic or manual for this scope.
Please log in to post an answer.
Try this site for your Conar 251 info: www.industrycommunity.com/ee/ee-2-next3/messages/203.html
You might check out www.W7FG.com (Vintage Manuals).
Where can I get a schematic for the circuit board in my Stanley model 520 garage door opener? The circuit board has a burnt capacitor and I need to find the value to repair it.
Please log in to post an answer.
I have installed some 8' HO fluorescent lights, and now the FM radio has too much noise.
I put four snap-on RF chokes on the power cord at the radio. They did reduce some of the interference and I even plugged the line into a surge protector.
Is there anything I can do at the fixtures to knock out this RF problem?
Please log in to post an answer.
First, get a battery operated FM radio and test with that. If the noise is still present, it is coming over the air and the only way to stop it is to turn the lights off or replace them with something else that doesn't generate RF hash.
If the portable radio shows no sign of the noise then it can be licked by more filtering of the AC either coming out of the lights (the best place to put the filters) or at the radio.
I would start, as you did, with the radio side and try more and different kinds of RF noise filters. Once an acceptable solution is found, I'd do my best to find a way to add these solutions to each light socket to kill the stuff as close to the source as possible.
Digi-Key has all sorts of RF line-filters www.digikey.com/product-search/en/filters/line-filters/3408328?k=rf%20filters
Schurter Inc calls theirs EMI/RFI Line Filters www.schurterinc.com/content/view/full/25502/(language)/eng-GB
For more, do a search on-line for "rf ac line filters" or "RFI AC Line Filters"
MFJ might be another good source since Hams don't like EMI or RFI getting into their radios: MFJ-1164B AC Line Filter www.universal-radio.com/catalog/protect/4743.html
MFJ usually has a 100% satisfaction return/replacement guarantee for 1 year but I didn't see that mentioned for this product.
Your noise is probably radiated more than line coupled. Try putting the ferrite chokes on the power lines to the light.
Trapping at the receiver will not suppress the radiated interference! Surge arrestors are not designed to trap noise like this unless they include a noise filter, and then only trap line carried noise.
The first question that comes to mind is if Mr. Robin is 100% certain that the interference is on the power line side of things.
Generation of RF energy at 90 MHz these days is as easy as pie, and it's quite possible that part of (or most of) the problem is RF interference as opposed to noise on the power line.
Years ago, when I worked at installing 2-way radios in Police cars, there were numerous problems with a braking module on one particular type of automobile, causing enough radiated RF at about 155 MHz, so as to make the radio virtually unusable at low signal levels on a channel in that range. The modules had to be replaced.
My suggestion would be to use an FM radio powered from batteries to determine the source. If it is RF then the radio being powered by batteries will be just as affected as the one powered by the AC line.
The best answer in that case may be to try to increase the desired RF signal for the radio with an outside antenna. Replacing the lights or filtering the (probably) electronic ballasts may be quite expensive.
