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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 2010 Issue
We have four indoor/outdoor cats. My plan is to have each of them implanted with an RFID chip and to have a sensor over the cat door which will read them. The door is already wired to indicate "a cat has gone in" or "a cat has gone out." Now I want to know which cat, and also possibly have the cat door remain locked until a known cat approaches. I purchased an RFID reader module from Parallax and although this worked okay with the tags supplied, there was no response from the RFID chip borrowed from our friendly vet. Does anybody have a suggestion for (a) what type of RFID chip to use (there are more than one); and (b) where I can obtain a bare-bones scanner. I want to capture the tag ID using my own microprocessor when a cat is in range of the sensor.
#4103
Roger Hartop
Falls Church, VA
I would like to put together a flame sensor using flame rectification. I am familiar with how it works however, I need some ideas for the sensing electronics. The furnace I have uses a hot surface ignitor.
#4104
Pete Belliveau
Hopkinton, NH
I am building a Steampunk keyboard for my own use. I would like to have a small motor spin some gears each time a key is pressed on the computer keyboard. I have not been able to locate an encoder output or an activity monitor that will show key presses. I don't care which keys are being pressed, and the gears spinning are just for show. I would like a hardware solution over a software solution — but a complete *.exe program would be acceptable. (Maybe flashing the scroll lock LED when keyboard activity is being transmitted to the keyboard controller.) Monitoring the data stream for F0(Key up) occurrences would also work.
#4105
Dave Moore
Medina, NY
I'm trying to build a simple RF detector that flashes an LED when it detects a cell phone signal, as well as WiFi. I’m trying to keep it simple to keep costs down. I assume it would be easiest to use an amplifier, but I’m trying to get a PIC for the detection. The most trouble I am having is on the RF section. Finding the right antenna has been difficult. Ive tried using different wire lengths with some detector diodes, but have been having no luck.
#4106
Evan
Fredericksburg, VA
In some semi-automatic machines, there is a controller which controls the forward and reverse direction of the motor. The controller is driven by a small motor and gear arrangement with three options: light, normal, and heavy wash.
Please suggest a simple electronic replacement circuit for the same.
#4107
Ajay Kumar Verma
Patiala, Punjab
I have a transformer type AC/DC TIG welder I would like to add pulsing to the output. Does anybody out there have a circuit diagram so I could add
it on?
#4108
Dave Stypula
Johnstown, PA
Long ago, I was competent programming in Microsoft QBasic. Now most/all articles use either assembly or C. Do any of the popular microcontrollers program in some version of Basic? I am not into a "C" level of retraining at age 67. Suggestions... I’m looking for serious how-to articles — or worst case — books on using some microcontroller that includes interfaces to USB ports.
#4109
Bill
via email
How does an interpole winding work in a DC motor?
#41010
Michael Coy
Indianapolis, IA
May 2010 Issue
I want to send digital pictures and/or video remotely to a digital picture frame located at my Grandma’s house. The picture frame should have a wireless network ability so I can connect to it and update the video/picture content. What circuits or networking devices do this?
#5101
Michael Jimenez
Los Angeles, CA
I would like to make a simple/inexpensive anti-theft alarm — like you see in the doorways of shops. Some form of oscillator circuit that is interrupted (disturbed) by a small passive antenna-like circuit passing through the field would be good.
The active range should be about 1-1.5 meters.
#5102
Claes Kamborn
Stockholm, SWEDEN
I built a 3,000W, 220V, micro hydro machine and installed it for a family of five living near a stream. I need a load controller to offset the extra power whenever something is turned off. When the real load goes down, the frequency and voltage go up. The design should monitor the frequency (50 Hz) and dump some load to resistors whenever the frequency starts going up, and dump less of that load when the frequency goes down. If there is a better idea please let me know. Is PWM a good option?
#5103
Joseph K.
La Jolla, CA
It is my understanding that a standard automotive alternator produces three phase AC before the rectifier + (three diodes). If this is the case, what would the voltage and amperage output of each phase be, as well as across two phases (tapped directly off the windings)? I would base measurements preferably using a 130 amp AC Delco CS130 alternator, but any info will help. At this point, I don't need any regulation, as I'm just trying to find out average values. Also, what RPM would best suit the alternator for longevity, as well as best output (they don't put out full power until a set RPM minimum is reached)? Is there a set math formula to figure this out? At this time, I don't have access to the Internet.
#5104
Geoffrey Mayberry
June 2010 Issue
I am looking to buy or get enough tips to design and build a device to do service adjustments on old style floppy drives that are used in music keyboards. To run analysis and adjustment software, I have to remove the drive from the keyboard and connect it to a computer. But, the new computers don't have floppy connectors any more. The best device would have a floppy drive 34 pin connector on one end, a USB plug on the other, and some controller in the middle. The current USB external floppy drives are quite different from anything I could use for this project.
#6101
Timothy Edwards
San Diego, CA
I'm building an alt-az antenna rotor controller from scratch, but I'm having trouble with the circuit for controlling the AC motor in the Radio Shack rotator. I've tried using a TRIAC with little success. I believe they are my answer but I don't understand how to use them. What I need is a circuit that will accept one direction bit and one enable bit that will control a motor’s direction of spin. The original controller achieved this by feeding one or the other non-neutral leads of the motor with ~22V AC; the third lead is common neutral.
#6102
Matt Williamson
Houston, BC
My quartz cookoo clock has a photodiode to turn off the clock at night, but I want it to work at night. Can I just remove the photodiode?
#6103
Doug Cardona
Rincon, Puerto Rico
I want to set up a home driveway sensor similar to a traffic light actuator, by using a single wire loop in the pavement that senses vehicles by changing the frequency of an oscillator. I need to know how it works and how to build it.
#6104
W. Rogers
via email
I have a Hoover EmPower vacuum cleaner that causes the breakers in my home to trip almost every time I first power it on. After a few minutes of use, I can turn the machine off and back on with no problem. I am thinking that the initial inrush current is too much for the breakers (they are GFCI protected). Does anyone know of some sort of soft start circuit or any other trick that may help?
#6105
Jonah G.
Nashville, TN
I am buying my wife a car, but she will not get the garage. So, I agreed to buy her a remote start. I have looked around for one with a clock that will start the car every weekday. So far, no luck. I’m thinking one could program a PIC to start the car like at 8:30 am for 15 minutes, except Saturday and Sunday. Of course, with an override switch for vacations. Any ideas?
#6106
Michael McKenna
Milwaukee, W
I have puppets which I can control with a servo controller board attached to the serial port of the computer. I want to record the serial out to audio, burn a CD, and then play the audio from the CD and send the output to the servo controller board, as though it were coming from the serial port of the computer. Anyone have an idea or could help design a hardware solution to this need?
#6107
George Wood
Lakeside,CA
We develop products with PIC tech, but are unable to beat the noise. Can anybody suggest a solution?
#6108
Suresh Naidu
India
What is the least expensive system to use to program a PIC16F876A? I got one as a sample from Microchip; now I don't know what to use to talk to it.
#6109
Joseph Walker
Newville, AL
July 2010 Issue
I’m looking for a simple solution that measures the frequency of a pulse (.5 Vss). It does not need to measure higher than 1 kHz. Is there anything out there off-the-shelf or a kit; a small board with an LCD display?
#7101
Rolf Breuer
Cupertino, CA
I need a circuit that can be used to control a 12V fan in a truck and tune to the needed temp. I would like to be able to use a standard automotive temp probe into the cooling system. I would like to do this with a display if possible but it is not necessary. I will actually be building three and tuning each a little higher to turn on the cooling fans.
#7102
Dan
Scranton, PA
I am building a kinetic sculpture. I have a 5' wide plywood disk that weighs 50 pounds. I need to be able to spin the disk anywhere from between 60 to 500 RPM. Once the disk reaches a given RPM, I need the disk to maintain it precisely. Using just a normal AC motor doesn't work because the RPM seems to be constantly fluctuating. I am told that I need a .25 HP servo motor to achieve this. Any other ideas?
#7103
Leif
Los Angeles, CA
I am looking to do some development work of an injection pump in conjunction with a camshaft signal. I am looking to drive a coil with a
resistance of 1.6 ohms (at 20 C), and an inductance at 1 kHz of 1.72 mH. The signal needs to be a (frequency 4 kHz) PWM peak and hold type with two parts: a V_boost and a V_hold (or V_batt). V_boost needs to be adjustable between 30 and 70V, and the current adjustable from 4 to 12A; V_hold should be adjustable between 6 and 18V. A zener diode should be used to drain the current from the coil when the driver is deactivated; V_zener should be 28V. The signal out sequence will be based on feedback from a once-per-rev Hall-Effect sensor; conversion to TTL would be fine.
The camshaft may have 2, 3, or 4 lobes, and therefore needs 2, 3, or 4 PWM peak and hold outputs per rev; evenly spaced. The maximum speed of the cam is 8,000 RPM. The signal start (or delay) must be adjustable from 0 to 360 degrees. The spacing of the signals must be 180 degrees for a 2 lobe cam, 120 degrees for a 3 lobe, and 90 degrees for a 4 lobe. I have the new 16-bit microcontroller demo, but I am new to it and so ICs may be better, based on my experience level.
#7104
Matt McKean
Detroit, MI
1. I'm looking for a low cost ($1 - $2) optical sensor solution to detect the presence of an object in a bin. The size of a bin varies between 5 cm to 15 cm. Sensor and LED light source would therefore need to be that far apart.
2. Bins are grouped in a matrix of 8 by 20, and their status needs to be collected periodically. What kind of a circuit would be the easiest way to collect the status of all bins?
#7105
Rafael Skodlar
Milpitas, CA
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