Everything for Electronics

Unanswered Questions

Transformer Needed November 2011

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?

Richard Ashoff
via email

Building a “Recording”  Warning Sign November 2011

I'd like a circuit to power LEDs or an electro-luminescent display to be used as a "Recording" light in a small studio. Ideally, the sign would come on fully for several seconds at first, and then flash on and off slowly, ramping the voltage to the display or LEDs up and down, so as to create a soft blinking display.

Al Parry
Preston, MD

Loudspeaker/CB Combination November 2011

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.

Daryl McIntire
Seneca, SC

BASIC Stamp Help Needed November 2011

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?

Odessa, TX

Power Failure Circuit November 2011

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?

Philip Popiel
Thornton, PA

Power Conversion November 2011

I would like to make a special power supply/converter with a difference. It can be supplied from:

  • A nominal 12 VDC (nine to 15 actual) from a vehicle supply.
  • Or by a nominal 24/28 VDC supply (20 to 32) from a vehicle or aircraft supply.
  • Or, by international mains (90 to 250 VAC).
  • All three inputs need to be isolated and capable of being accidentally or deliberately connected at the same time.
  • Have all three inputs tolerant to transients, e.g., mains derived from generator.

The unit needs to have four outputs, all of which are DC and each of which is configurable internally by a trim pot to deliver four output voltages between 10 and 24 VDC (e.g., 12V, 15V, 18V, and 22V).

  • Output to be unaffected by change of input source.
  • Once set, each output voltage needs to maintain a tolerance of ±0.5 VDC, regardless of input changes.
  • Each output to be capable of delivering 120 watts.
  • Robust, portable unit.

I understand that these parameters are often mutually exclusive, but the following considerations are also desirable:

  • Low weight.
  • Small size.
  • Low heat dissipation.
  • Low noise.
  • Low interference.
  • High quality.

If the overall concept is too big, perhaps someone could direct me to previous power conversion solutions that may be married together to give a solution, and highlight the isolation issues that may apply regarding multiple input connections.

Kevin Dickinson
Mudgee, NSW Australia

Passive Mixer Problems November 2011

I've built this passive audio mixer that I really like. The only problem is that anything going through it sounds like it's in a stream of water. Lots of white noise.

After the mixer, it goes into the line level input of an old Teac audio cassette machine. Anything plugged into the cassette machine without going through the little mixer sounds great. The signal to noise is great. Very little white noise is present. What type of pre-amp do I need on each input to et the signal up high enough to override the white noise that my passive mixer generates?

Robert V.
via email

Frequency Changes In Cold Weather November 2011

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?

J. G. Jones
via email

Better Radio Communications November 2011

I’ve been a reader for some years, and electronics is my daily work. Now, I have to work with the Motorola PTP 600 radio. The system I am working now has three sets of PTP 600. They were set up the same way at three different locations to communicate to the main control hub. One of the stations has kept the connection pretty well since the first day, but the other two sometimes show slow or very slow data transmit. Looking at the status — as they are all set up with i_DFS — the link capacity sometimes drops to 20, the transmit in teens, and the vector error goes up positive. Please show me how I can get them to work  more stably. I am working in the war zone of Afghanistan!

via email

Single-Stroke AC Bell November 2011

We would like to operate a single-stroke AC bell that would ring once every time the phone rings in cadence. The telephone line power — 40 to 120 VAC at 15 to 60 Hz — should power the bell. We prefer no external power supply. A typical single-stroke bell has a coil voltage of 24 VAC drawing 0.5 amps.  Coil resistance is 10 ohms.

Michael Lenihan
Southampton, NY

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