Tech Forum

This problem is easily solved with a "spring timer."

This is a spring driven 120 VAC switch available at Home Depot, Lowe's, or an electrical supply house. Often used to turn lights out in store rooms or laundry rooms automatically when not needed, it is a spring driven electric switch that fits inside a standard electrical box and is available in various maximum times such as one hour or 15 minutes.

To operate, one twists a knob to the amount of time needed, the load comes on, then goes off when the time runs out.

I suspect that the speaker cone is warped and sticking. It doesn't produce much sound until the power is enough to break it loose, then it sounds OK.

The circuit probably employed a tapped potentiometer (volume control).  After the wiper passed a certain point on the control -- usually the center point on the range -- circuitry connected to the tap became the dominant factor in determining frequency response.

Older amplifiers had a "Loudness" control for the volume control. You may see a "Loudness" switch on some receivers or amps. The loudness control is a pot with a tap to which a resistor/capacitor combination was attached to boost bass at low volume levels to compensate for the human ear's lack of sensitivity.

It would appear that this phono did not have a loudness control, rather a simple three terminal pot.

The "thin" sound being described is not due to a circuit, but due to the fact that our ears hear lower and higher frequency sounds less well at lower volumes. A search of the net on "Fletcher Munson" will show the typical contours.

That said, the question becomes: How do we compensate for it? In audiophile equipment a tapped volume control and a loudness compensation circuit (or digital equivalent) are the preferred method. However, it is easy to retrofit existing equipment to provide very good compensation.

The image attached is a model of a volume control circuit with loudness compensation. Consider the volume control to be an attenuator as a signal source to the next stage, and the low pass filter to be a second signal source.

In practical application, a 100K volume control is typical. At higher frequencies the Cfilter is essentially a short circuit so we need to be mindful of the lower impedance load on the previous stage. In practicality, I find that an Rfilter of 12 to 18K, and Cfilter of .056µF to .082µF work well. Rsum may be from 39K to 120K.

In my 70's Technics reciever, I use values of Rfilter = 12K, Cfilter = .056µf and Rsum = 120K. This results in excellent tonal balance at virtually all volume levels. If I want a warmer tone reminiscent of vintage Grundig tube radios, I either reduce the Rsum or pick a corner frequency that provides more lower midrange boost at lower volumes.

Scale values appropriately based on the volume control resistance value. Starting off with trimpots for the Rsum and Rfilter is recommended to get to the tone effect (or percieved flatness across volume levels) to that desired.

If I understand you, this may be because of the hearing response to various frequencies at different loudnesses. See Fletcher Munson curves on Wikipedia. Essentially the ear hears the middle frequencies on the audible range better than the highs and lows at low volumes. At higher volumes hearing response gets flatter and flatter.

Older sound systems did not have a way of compensating for this except manually with base and treble controls. Some modern ones may, but I don't see how because the sound pressure level is so dependent on loudspeaker efficiencies which now can range from a fraction of 1% for compact speakers to 20% or so for a full-sized corner Klipsh.
 

Thus, systems in which the amp is sold separately from the speaker cannot know where the sound power level will be. The old system you speak of had a specific built-in speaker and thus would not have suffered that problem. Therefore the thinness of the sound you heard at low volumes could well have been pure Fletcher Munson effect.
 

It should be noted, as it is on Wikipedia, that those curves have been refined some in later years but the phenomenon still exists pretty much as described by Fletcher and Munson. I do not see why a solid-state amp would not exhibit the same phenomenon.

It depends a lot on what you want to spend. If you do a search on "hour meter" you will find lots of suitable products. In general, hour meters are not resettable.

www.ingramproducts.com/Hour_Meters_Counters-Rectangular_Hour_Meter_12_to_48VDC.html is an hour meter that's non-resettable, cheap and easy to install. The datasheet says it will operate on AC power and there are only two connections. You could just connect between C and Y in your furnace if you want to monitor cooling. C and G if you want to monitor the fan and C and W if you want to monitor heat. There will be 24 VAC present between these terminals in the modes above. Between C and R there is 24 V all the time. You would also have to decide if you wanted to ignore the time the fan was on by itself. That would require creating an OR condition between the C and Y and C and W contacts using two relays by putting the Normally open contacts in parallel.

www.kep.com/catalog/ii/pages/products/HB26-hour-run-meter.html is an Electro-mechanical timer that also meets the specs with reset.

Some furnaces such as some Carrier models don't use the traditional terminals and the motors may be 3 phase internally and would be harder to interface. A heat pump would be slightly different. Some furnaces have humidifier or 120 VAC electronic air cleaner voltages available.

Some timers come with non-replaceable batteries with a 5+ year life. A "contact closure" is a common way to cause timing. A "contact closure" is easy to get. Just connect a 24 VAC relay across the terminals above. Some of the smaller rectangular meters would have a "standard" cut-out.

www.laurels.com/magna_clock.htm would meet your spec, but it has way too many features. With electronics, the case, power supply and "real estate" (the size of the PCB) make up most of the cost so, obviously, a thow-away, battery powered meter with no reset is the simplest.

The key here is knowing what to search for, "hour meter" and some interfacing possibilities and it looks like 120 VAC and 24 VAC are options for power and timing and a contact closure is an option for timing with one or two additional relays.

DC meters might work on low voltage AC too. Check the datasheet.

In answer to your question, the easiest way is to go with a digital display hour meter. The Eaton E5-224-C0450 fits your needs exactly. It can be powered by the 24 VAC normally found on furnaces, will display the time and is resettable. The time range is 0.1sec to 100000hr which should take care of your needs for a couple of years.

The advantages of going this route are you do not need to build a circuit, you can mount the unit where you like,  and the wiring from the furnace to the meter can be done with normal thermostat wiring.

I would wire the meter up to the coil of the fan relay so that when power is applied to the coil, the timer will use that as it's input.

Newark Electronics (www.newark.com) has them available for $50.44, their catalog number is 73R4520. You can see the catalog page at this site, www.newark.com/catalog_129/index.html?page=1904.

I hope that this information helps you out.

I've built up a MicroChip PicChip PIC18F23K22 for this purpose. The PicChip directly interfaces to a 2 line 16 character LCD display.

It shows running time in 99999 hours, 59 minutes, 59 seconds format.

The PicChip simply counts cycles on the 24 VAC thermostat. Circuitry is simple, 5 volt regulator, a transistor, a few resistors and not much of anything else.

In case of power failure, the PicChip writes the current hours to EErom every hour.

The whole project was built on a Radio Shack 276-150 perf board.

The simplest way to determine cumulative furnace running time is to use an elapsed time meter. Two sources are:

Grainger p/n 6X143:
www.grainger.com/Grainger/wwg/search.shtml?searchQuery=6X143&op=search&Ntt=6X143&N=0&GlobalSearch=true&sst=subset

Digi-Key p/n CRA216-ND or CRA-217-ND:
www.digikey.com/product-detail/en/10075/CRA216-ND/1657654  or
www.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=Cramer+10083

Any of these will run you about $100. Installation is simple: The elapsed time meter operates from the regular 120VAC mains in your home, and runs whenever it is powered. Just connect it to the same switched circuit that powers the furnace blower motor. These meters are equipped with a mechanical reset button.

Remember to power down your furnace system before making connections to the blower circuit.

A Hobbs meter will do most of what you want to do, i.e., keep track of the total time. They are used on Piston aircraft to sum the total engine-on time for maintenance purposes. They cost from $16 up on-line. They are only as remote as the pair of wires running to them and often are not resettable. I have a new Cramer one which goes t 99999.9 hours, is 110 volts 60 Hz, not resettable, and never used. It is , thus now at zero. I am the time of life when I should be getting rid of my "stuff" so if wnat it and contact me at [email protected] I'll send it to you.

I think I found exactly what you need, see Multifunction Counter-Timer kit K8035. I found it at apogeekits.com, under timing kits and modules index on the left side of the web page.

Check out the Curtis Instruments hour meters that are available from Digikey. You need to select the proper operating voltage. They are available with a rest option.

How complex do you want it to be? A microP with a digital display and many hours work, or a home brew digital circuit (many many hours), or an old PC with a serial port and a couple hours for programing (just use the switch to ground the RTS pin and have a QBasic periodically check if RTS is high or low), or hack a $5 digital kitchen timer to do the job?

I would go with $5 digital kitchen timer (or digital stopwatch). Rip the case open and explore how the Start/Stop button works. It may be pretty easy to interface that button with the switch that is operated when the motor is turned on.

Since you didn't mention precision, price and ease of construction must be more important to you. Therefore, I don't think that a laser-based system is necessary or appropriate.

For approximately a three foot cube working space, you could use a webcam parallel to one axis and another webcam perpendicular to that axis. Using an object of known size and location, you could calibrate that photogrammetry system in software.

If you feel you need a laser system, a lens in front of a Microsoft Kinect system could shrink it's working space, though that might not be necessary in your application. Both of these systems assume that there is an unobstructed view of the target (or targets), and that the object is reflective. Other approaches are necessary for transparent objects.

Can't help with most of your questions except for one "length of the laser to the object for a calculated Y coordinate" is a pretty tricky thing to do, even with a computer, at such short distances. The speed of light is about 300 million meters per second (roughly 1 billion feet/sec). If you are thinking of blinking the laser then measuring how long it takes the beam to bounce off an object ten feet away and return to a sensor then you'll need to measure time intervals of a fair bit less than 1 billionth of a second. 1 GHz is a billionth of a second.

To get an accuracy of say one foot out of ten you would need to measure time at 10GHz, to get 1" you would be up near 100GHz. That is possible but not for cheap. Even a $1000 O’scope wouldn't be able to measure a time interval that short. I believe vision systems like what you want (e.g., XBox Kinect) use multiple lasers and a video system. With two laser beams you get two dots, if the two beams are parallel the distance between the dots is proportional to the distance from the laser to the object. A PC does the distance calculation based on the video image.

I think your best bet would be to start with an XBox Kinect system and mount the transmitter/receiver on a rotating platform. The Kinect will do 3 dimensions all by itself. The rotating platform will let you look in all directions. I believe there are software platforms for communicating with a Kinect system.

Of course you can replace the bad components, but how do you know the module is bad? Perhaps the motor is bad.

A motor starter usually involves a large capacitor, but I guess an inductor could be used. I suspect that the fan has to be kick started because the compressor will overheat and shut down if the fan is not running.

If the 'device' has 2 wires going to it and three wires out to the motor then it is likely a motor starter. They can be a thermal device with a relay and that is most common.

Many compressors use them and they do fail. Most any A/C parts counter clerk should be able to match it to a direct or universal replacement for about $20.

A schematic along with the pot resistance would have been helpful, but here are some things to try.

The problem is too much voltage across the pot. The large voltage change at the wiper as you turn the shaft a few degrees makes it hard to fine-tune. If the pot is not connected to a low impedance source such as a power supply or battery, put a resistor across the end terminals to reduce the voltage across it. Try a resistor about 20% of the pot resistance.

This will help you fine-tune, but now the voltage range at the wiper may not be right for your circuit. In that case, or if the pot is fed from a low impedance source, connect resistors from each end terminal to the wiper instead of putting a resistor across it. Keep the sum of the resistors about 20% of the pot resistance, and try various combinations of resistor values until you get the required range.

I would expect that removing the photo diode would keep the alarm from activating, but it's impossible to guess the internal circuit configuration. Try temporarily shorting the diode with a clip lead. If that doesn't awaken the birdie at night, remove the diode.

Might not work by removing the photodiode.

What might help is to check the voltage drop over the photodiode with the lights on, and replace it with a resistor to give the same voltage drop across it.

Using a 100k potentiometer, turn it on the max resistance (100k) and slowly decrease the resistance until the same voltage is read as the original voltage drop across the photodiode. Measure the resistance – and replace with a fixed resistor of the appropriate value.

from: www.reliance.com/mtr/mtrthrmn.htm  Basic Motor Theory

Interpoles
Interpoles are similar to the main field poles and located on the yoke between the main field poles. They have windings in series with the armature winding. Interpoles have the function of reducing the armature reaction effect in the commutating zone. They eliminate the need to shift the brush assembly.