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Following is a list of unanswered reader questions,
printed in the Tech Forum, from recent issues of Nuts & Volts Magazine.
Be sure to include the ID number printed at the end of the question when
offering a solution. Answers should be e-mailed to forum@nutsvolts.com
April 2009 Issue
I want to add a USB port to a CD boombox. How complicated of a process am I looking at?
#4094
Mark
Hawley, PA
May 2009 Issue
I have five table-top water fountains which I want to run constantly. They are designed to use two AA batteries for each fountain, which is impractical.
1. What plug-in DC power transformer (voltage and amps) can I substitute for the 10 batteries to power all five devices?
2. How should it be wired — in series or parallel?
#5093
Garry Smith
Indianapolis, IN
July 2009 Issue
Curb Sensor
I would like a circuit to build an electronic automobile curb sensor.
#7095
Lynn White
August 2009 Issue
The MOSFET leads in a TO-220 package to carry about 280 amps look small — about 1 sq mm cross section — though short length. What is the best way to connect the drain and source terminals/leads and what size heatsink is required to 250 watts for a 2,500 watt inverter?
#8091
Mohammed Ahmad
Mississauga, Ontario, Canada
What do they have that will tie HVAC controls on a computer for home and commercial applications?
#8094
Paul Finnigan
Arlington, VA
October 2009 Issue
I want to use the flip style package (like a "flip-style" cell phone) for an electronics project. It’s sometimes referred to as a book-style package solution, where there are electronic functions integrated on both sides of the hinge. I am having trouble identifying the best interconnect products to use for the hinged interface. Can I develop a prototype on a (reasonably) low budget?
#10093
William Quillen
Laurel, MD
I’m trying to raise the temperature of a tungsten heater from room temperature (25 C to 900 C) with a ramp of one hour. My filament is very small and hence has a small resistance — 0.08 ohm at 1,200 C. At room temperature, its resistence is 12-13 times smaller. Powering the filament is a huge 50 amp variable transformer. I am also using a temperature controller (Omega cni32). Most power supplies I have seen use a phase angle firing SCR with soft start and current limiting capabilities.
#10094
Hugo Leon
Champaign, IL
I want to monitor the temperature of my attic during the summer months.
Ideally, I'd also like to know how long the roof fan runs for, but it's hard wired and probably more difficult. I considered doing this by using a sensor to detect the sunlight. As the fan blades spin, the device would count the
turning of the fan blades. I'll settle for a simple temperature detector that can send the data to my PC and some program that will graph the temperature over time. The attic isn't used so a long averaging time constant isn't required because nobody is walking by disturbing the surrounding air. I considered a simple thermistor with a 5-10 second RC circuit going into a Linx device that will transmit the data back to the PC. I would also need some program that would receive, interpret, and graph the data.
#10095
Peter
Boston, MA
I have a RadioShack antenna rotor that I would like to have automatically controlled to the signal strength of the DTV station I have selected. Is there
a circuit I can attach to the antenna control knob that will adjust it to the DTV station that I am viewing?
#10096
John Szymanski
Mt. Airy, MD
Does anyone know of a supplier of re-buildable batteries or even parts suppliers for them? I need a small battery for experimental use. I must be able to change the plates as needed.
#10097
Harry Pedersen
Yelm, WA
November 2009 Issue
I’m looking for an FM circuit with these features:
Fixed digital 95.5 MHz
Mono
Earbud output
Battery powered
Small as possible
#11092
Don Bartelson
Merritt Island, FL
I need to locate a DC-to-DC step-up transformer that goes from 120 to around 330 volts. It is for a DC-to-DC converter that will drive a laser diode and can be low wattage.
#11095
Thomas Wagner
Coldwater, MI
I’m working on an electric go-kart and need help predicting the performance of a combined battery and super capacitor. I need a formula that would show the current output of a small battery and a large capacitor. I’d want two battery types (lead acid, LiFePo4, etc.), so the formula needs to have variables for different battery characteristics. The new supercaps are in the range of 35-100 Farads.
There is one manufacturer that makes a 50 AH lead acid combined in parallel with a large (maybe) 35 Farad capacitor.
Ultimately, I want to know what will happen if I put this in my kart and accelerate for six or even 10 seconds.
#11099
Cary Z
Indianapolis, IN
December 2009 Issue
I'd like to build a circuit for the purpose of summing four separate audio signals into one line level output. In no particular order, the inputs would need to accept: a stereo line level auto, and a stereo auto from the head phone jack of my mp3 player. Preferably the gain would be set so the volume wouldn't have to be turned up to be heard. Lastly, I would like two mics (optional use), each needing their own adjustment for gain and level control.
#12091
RCD
Arcadia, FL
I read the Oct 09 article on “The Green Standby” and was wondering if there is a circuit that would turn on or off all the cube powered equipment attached to my computer when it first gets turned on. Could this be accomplished by sensing a power level change when the start button is pressed or is there a better way?
#12092
Peter Lowe
I'm designing a dual 12V, 50-pound-thrust trolling motor assembly for a small boat. It will run from 24V to achieve brief bursts of relatively high speeds on an engine-restricted local lake. I’ll be using two independent PICAXE controllers for direction and speed control for each motor. I've already designed and tested the basic PICAXE controller circuits on small motors using a relay for directional control, and a PWM-driven bipolar on the ground side of the motor circuit for speed control. My questions are these: Should I use a semiconductor H-bridge or a relay to switch directions on the larger motors? I'm leaning heavily towards a relay for simplicity. Also, I need a part or circuit that can be driven with the PICAXE-level PWM signal and control the 12V motor (running from 24V) with an unknown surge current level (possibly over 100 amps per motor).
#12093
David T. Bupp
Carlisle, PA
I want to embed four different short voice phrases that I'll record beforehand and load on to a device that plays them from pushing one of four buttons out of an eight ohm speaker. Can’t seem to find a simple way to do that. Doesn’t have to be as crazy as an mp3 player with LCD screens and LEDS, but it has to sound better than just generated tone on a piezo. Wondering if anyone has a schematic or something on the code to point me in the right direction.
#12094
Greg Swizz
San Diego, CA
I would like to connect the line-out signal from my PC sound card to the handset jack of my office phone in order to record voice mail greetings that I have composed on a PC. Can a direct connection be made to the microphone terminals of the jack, or is an interface circuit required to match the signals?
#12095
John Reynolds
Rochester, NY
Recently, the OP-27 op-amp has come up in some suggested preamps for VLF reception. I can find no cross-reference to this particular device, but it seems to have the same footprint as the old 741 and the newer CA3140. I would like to use this as a preamplifier for a low impedance untuned loop antenna for VLF. Since it will operate at low impedance in and out, does this come into the category of a "transconductance" amp as opposed to a voltage amplifier?
#12096
John Seeley
Palm Bay, FL
It seems that the LiPo battery is all the rage these days but — outside of voltage and maybe current hour ratings — there are a number of other trailing numbers and letters in the specs that are unknown to the average person. I've even heard of some exploding. Can someone enlighten us a bit?
#12097
Charlie Moher
London, Canada
I have a machine that calls for a 3.15A 125V slow blow fuse. Will a 3.15A 250V slow blow fuse be wrong? I can't find a 125V SB fuse. Do they still make them?
#12098
Deb
Orlando, FL
January 2010 Issue
I have CD and DVD players which, when playing certain discs, will stutter, skip, cut in and out, and sometimes abort the playing altogether. It only does it on some discs, and at the same place on these discs. However, these same discs will work on other players just fine. On at least one player, the problem got progressively worse, and had trouble with discs it played without errors in the past. Is there a way to repair this? Cleaning the lens and disc sometimes helps, but not always. I am playing only commercially made CDs and DVDs, not home burned ones.
#1101
Michael Kiley
Crestwood, IL
I am working on a project to provide 100 inexpensive, disposable electronic devices for a church. Each device requires a cheap, low-distortion, parts-stingy sine wave generator, easily tunable using only one pot from 1 kHz to 1 MHz, preferably using one common and cheap IC like an op-amp or a few transistors. To be compact, the parts count should be under about a dozen. I have plenty of XR8038 and XR2206 function generator ICs, but they are far too costly for this project. My experiments have produced only square waves or triangular waves, but meet all my other criteria. What is the best sine wave design?
#1102
John Williams
Can anyone help me find the datasheet for the following component: RA2892 from Raytheon? Also what is an equivalent (cross reference) that I can use?
#1103
Mohamed Fathi
Egypt
I have a problem with my speakers humming on my desktop PC. I think this may be wall wart related but not 100% sure. Is there a way to fix this problem or do I need to buy a new set of speakers?
#1104
John Sparozich
Philadelphia, PA
I recently replaced the trans in my Ford van. Somewhere between 00 and 02 model years, Ford changed the speed sensor output to the PCM, but I have an analog gear driven sensor. The newer sensor is digital (variable reluctance). I need to change the signal back to analog so the speedometer, ABS, and cruise will work. Is there a device to do it, or is it even possible?
#1105
Chris Camp
Dalton, GA
I've had electronic engineering schooling back in the 80's and have tinkered a little since then. I've never had a computer until now and would like to know some free or reasonable circuit design/test software download sites to tinker with.
#1106
Jeffrey Howard
Alexandria, IN
February 2010 Issue
I want to create a motion sensing electronic flow faucet. The solenoid valve is normally closed with an operating voltage of 24V. I'm new to this hobby, so I'm not sure where to start as far as the circuit design goes. I thought of purchasing an electronic light switch and modifying it to trip the solenoid valve, but the switches are expensive.
#2101
TJ Treinen
Oklahoma City, OK
Where can I find or make a simple spot welder suitable for rebuilding battery packs?
#2102
John
I want to monitor the open or close status of 20 or more doors in a building. Are there devices made that would send a location address and magnetic door switch status via Cat 5 cable about 200’ back to a central panel? I would like these devices to share a common pair and be powered from the central panel too. The panel would light up an LED.
#2103
Mike Carland
Valencia, CA
I would like a diagram for a three-phase AC motor control that I can build myself. I can find all kinds for DC, but not AC. Could someone point me in the right direction?
#2104
Sebastian Jaime
Miami, FL
WB4WLZR
I am working on a project to enhance my Lincoln 225 amp 220 volt AC welder. I wish to find a circuit that can change the 60 Hz AC to a variable higher frequency. Welding aluminum with a tungsten torch (TIG) requires a variable frequency higher than the 60 Hz to make the best weld due to the nature of aluminum oxide and alloy. It is suggested in my reading that
commercial TIG welder circuits change the sine wave to a square wave.
My welder has lugs on the transformer to switch to in order to select the range of amperage for welding steel. I will continue to set a range for the metal thickness of aluminum. My concept is to add an auxiliary box to house the power supply for the electronics, the cooling fan, and either the cable to a foot switch or rheostat mounted to the torch head or surface mounting. A selector switch will turn the TIG feature on or off to continue to use the original welding feature or to TIG weld.
I have found circuits where the frequency can be varied, but at low voltage and amperage — nothing in the ranges I need. The components would be smoked immediately when switched on, or an arc was struck. One article on converting an AC to DC MIG welder suggested the diodes in the rectifier have a peak invert voltage of 1,000 volts for the momentary time when striking the arc, and be able to handle the amperage of the original welder — 225 amps. Although I am not going to convert my welder to DC, the information of peak voltage and amperage for any suggested circuit design may be helpful.
#2105
John Johnson
St. Clair Shores, MI
I am looking for a circuit for testing the load of rechargeable batteries used in radios, cordless tools, etc. It must be switchable to allow testing of various voltages between 2V and 36V.
#2106
Travis Branch
Winston Salem, NC
I have a Victoreen 592b Geiger type device. It requires nine batteries; six of them are the 22.5V photo style battery, the other three are unknown. There is no part number or voltage listed, but the location for them makes them as 1-1/8" diameter and a little over 1/2" high. I have searched the web and the Victoreen site but cannot find anything about any kind of battery fitting this description or any information about this device. Can anyone help with the information so I can use my old friend?
#2107
Norm Doty
Hollywood, FL
March 2010 Issue
I have a Casio portable color LCD TV (handheld) that has been made obsolete by the new digital signals. I would like to use the display in an upcoming project. Can anyone direct me to where I could find information on driving color displays with a microprocessor?
#3101
TJ Treinen
Oklahoma City,OK
I have experience programming, soldering small projects, and wiring. I've built my own computer from parts. I have a stack of records from the ‘50s, ‘60s, and ‘70s, and two record players (never tossed the old electronics). I saw a device in a store that would record your records to USB. Can't I build my own? Any suggestions?
#3102
Sunny Russell
Kenosha, WI
I have been experimenting with a 10,000 watt AC alternator. This is the kind that is usually called a generator that outputs 110/220 VAC for use as a backup power source. Although I have had a good deal of experience with electricity and electronics, I have yet to find a good explanation of how this type of alternator actually works. Every source I can find on alternators deals with automotive alternators which I assume are similar. I have an application where I am using the variable speed from the gas engine that turns the alternator to create a variable AC voltage output. I know an alternator of this type has no permanent magnet so it needs to get up to some RPM before it generates ANY voltage at all. On mine, this kicks in somewhere between 35 and 50 volts AC. Can someone explain how this type of AC power alternator actually works and do you think it is possible to excite the fields externally so the output voltage kicks in more consistently at low RPM?
#3103
Greg McMurry
Pacific Palisades, CA
How does one find the wattage of a 24 VDC motor that has no name plate? I want to purchase a speed control for my electric bike, but they all want to know the wattage of the motor.
#3104
Frank Whelan
Lompoc, CA
What is the difference between an ordinary light dimmer and a ceiling fan speed controller? They look the same except one is twice the price.
#3105
Terry Stine
Peoria, AZ
How can I use a PIC controller to generate the required voltage in a DC/DC converter with an LCD display or USB communication with a laptop?
#3106
Cornelius
I'm looking for an anemometer circuit using the cooling effect on transistors. I found some on the Internet but they typically only measure low (<2 mph) wind speeds. A circuit with an analog output I can interface to a microcontroller would be great as I plan to add other sensors. Mechanical anemometers need to be calibrated which I'd like to avoid (and I’d rather build a circuit anyway). I need an anemometer to measure "normal" wind speeds (up to maybe 50 mph). I'd like to install a wind mill next year to assist in powering my house but I want to log the wind speeds and frequency to determine if it's worthwhile installing the windmill.
#3107
Dave Berkebile
Wilton, NH
I want to build a stereo headphone control box for a home recording studio monitoring setup. It can be passive or active, but if it is active, it must have high quality circuitry, as should all the other components. It needs to have left and right channel volume controls, plus a low-noise switch (leaf switch?) to reverse the left and right channels so that I can quickly change the signals between left and right channels without removing the headphones. Can anyone offer a schematic and parts list?
#3108
Starliner
Preston, MD
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