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First, you won't find (as far as I can tell) any negative regulators that will take more than -40V input. Indeed, you will have trouble finding ANY regulator (positive or negative) that will take 36 to 75 VDC input.

So, since it appears that you have only +35 to +75 VDC available, I recommend something like the MIC28500 switching regulator (Digi-Key has them; http://search.digikey.com/us/en/products/MIC28500YJL%20TR/576-3969-2-ND/2764089 — note that these are surface-mount deals ... sorry!) to provide something in a voltage range that is easier for other regulators to handle (or you could just use two of those for the five and 6.5 volt outputs, and one for supplying the other regulators — note that one of these things can supply up to four amps!). So, I'd say:
• One MIC28500 for the +5V
• One MIC28500 for the +6.5V
• One MIC28500 supplying +12V (its max output) to the following:
Some sort of switching inverting regulators (like the LT3483 or similar) to convert the +12V to -6.5V, and -15V outputs.

Another switching regulator to boost the 12V to 15V, for example, something like the LM2574N.

If the MIC28500 chips are too expensive, you could just use one to supply +12V and choose other regulators from there (for example, an old run of the mill 7805 or 78L05 for the 5V).

I found all the above regulators by going to digikey.com and searching for 'voltage regulator IC.'

On the other hand, you could drop the voltage down to something easier for 'normal' voltage regulator ICs to handle using a resistor and a zener diode. So, you'd have a resistor of proper wattage and resistance in series with a 20V (for example) zener. Allowing for 2A of current (assuming we end up using inefficient linear regulators here, since the load is only 640 mA max) with an input voltage of 80V and an output of 20V, we need to drop 60V in that resistor at 2A, or 120 watts. Ouch! That's nuts! So, let's go back to the MIC28500 or similar.

Is there some way of getting a 'nicer' voltage input range beyond regulating it inside this power supply? That is, if you can manage to get the input voltage to a max of 30V, you greatly open up the possibilities for off-the-shelf voltage regulator ICs.

On the other hand, if you don't want to build it, I found that Acopian makes DC-DC supplies that could work — even if you just use one to convert that 36-75 range to something more friendly. The 48C5FT1000 supplies 5V and the 48C15FT400 supplies 15V, but they are pricy; about $188 each. TRC Electronics also makes such things, with various output voltages (trcelectronics.com).
 

Summary:
The options seem to me to be:
1 - Buy an off-the-shelf regulator(s), e.g., Acopian (expensive).
2 - Use some sort of down-regulator (Acopian, TRC, MIC28500, zener(!), etc.) to supply a lower voltage to the various end-user regulators, then have some number
(probably five; one for each voltage output) of regulators supplying each output voltage from the step-down intermediate supply. Use inverting switches for the negative; use whatever you feel comfortable with (LM7805, etc) for the + voltages (still somewhat expensive, and now you have to make it work).

There is a digital oscilloscope from Yokogawa that might fill your needs. The DL850 ScopeCorder will sample at 20 MHz with a 12 bit resolution. Since this is a modular instrument, you will need to select the components to fit your needs. See www.scopecorder.net.

I think a buried antenna will not radiate very much.

Considering the installation of a 'multi-station' intercom system wired throughout your premises can be somewhat of a task and perhaps a little more expensive than necessary as compared to the variety of 'wireless' intercom and phone systems already in use.


I opted to use a Uniden DECT 6.0 three-handset cordless phone system that offers excellent long-range wireless phone and 'conferencing' ability, selective between any/all three cordless handsets anywhere around my premises.


Although there are Uniden cordless phone units available with more handsets, this system can be purchased for a very reasonable price almost anywhere electronic equipment is sold. I carry one handset with me to any remote area, such as the garage, working in the yard, etc., and when my handset starts 'chirping' I can immediately identify [who] which handset is signaling me for conversation and, even if you don't connect to the phone line through the 'base set', this system can still be used as a long-range intercom system.

The intercom system desired is very similar to the headset intercoms used to communicate with camera operators and other studio personnel in every TV station and network for many years now. Although there are variations and expansions, the basis of these systems is a two-wire party line that carries both the conversation and the power (24 to 48 volts DC) to run the various stations so that no separate power connection is needed. They are probably similar to the two-station intercom circuits you have seen and many of these can be adopted for this use with the additional components shown in Figure 1. The basic idea is that each station must separate the audio and power components that are sent over the same two wires. Also, the audio must be blocked from entering the output terminals of the DC power supply because the filter capacitors in it will have a very low AC impedance and would short the audio to ground. There were also party line systems that used a four-wire connection to keep these two components separate, but I will ignore them here because a two-wire system was requested.

One wire is a signal and power ground, while the other carries both the audio and power. The basic audio circuit is simply an amplifier connected to the two-wire party line through a simple two-pole momentary switch which allows only one of these functions to occur at a time, thus preventing any feedback. I have shown a DPDT in the schematic to allow the speaker to be used as a microphone, but a separate mic could be used with a SPDT switch.

The coil labeled L1 is necessary to present a high impedance to audio frequencies on the party line which would be shorted by the filter capacitors in the power supply. It needs to have a fairly high inductance value in order to preserve the lower audio frequencies. You need whole Henries here, not milli or micro Henries. The formula for the impedance is 2*Pi*F*L and you want an inductive impedance value in thousands of ohms at about 100 Hz or lower. At 100 Hz for a 10 Henry (H) inductor: 2*3.141*100Hz*10H = 6283 ohms. This should work. It should be rated for the combined current of all the stations. The largest inductor I could find with a quick search is a 15 H coil but it was shown as "out of stock" with a delivery time of over 100 days. There are some being offered on eBay; search for "retard coil" and you will get what you need, but they are not cheap. There are high inductance chip-style inductors but I doubt they would work because they would not pass the DC current needed to operate all the stations.

In the stations, the capacitor labeled C1 blocks the DC voltage to the audio amplifier. It must have a voltage rating that is higher than the power supply output voltage and a low capacitive reactance in relation to the amplifier's input impedance. The formula for the capacitive reactance is 1/(2*3.141*F*C). If the amplifier you use has an input impedance of 10K ohms and you have 10 intercom stations, the combined parallel impedance on the party line will be 1,000 ohms; you will want a capacitive reactance of 100 ohms or less. Again, we calculate at the lowest desired frequency or about 100 Hz. A 15 µF capacitor will give us 106 ohms of capacitive reactance at 100 Hz and should work. I would probably step up to 25 µF or even 50 µf as the added cost will be tolerable and the low frequency performance will be improved.

Any of a number of solid-state or IC audio amplifier circuits could be used. Look for a high input impedance and a low output impedance suitable for driving your speaker. The gain needed will depend on the output level of the microphone or of the speaker when used as a mic and the desired line level on the party line. Since you want to use unshielded wire, I would suggest a line level of about +10 dBm or about three volts RMS in order to keep any noise to a minimum. Assuming the microphone level is -40 dBm, you would need a +50 dBm gain in the amplifier. I would go for one that provides +60 dBm to allow the volume controls room to work. The volume controls can be simple voltage division circuits with one side of the pot connected to the input signal, the other side to ground, and the output taken from the wiper; 10K or 50K audio taper pots should work with most types of amplifiers.

The figure below shows the DC power supply to have an output voltage that is significantly higher than the regulated voltages in the stations. This is because there are no filter capacitors on the party line. So, the regulator circuits in the stations must have sufficient voltage to stay in regulation, even during the loudest audio which will both add to and subtract from the average DC voltage provided by the power supply. So, with a three volt RMS audio level, half of the P-P value of the audio will be about 4.5 volts. This — on top of a supply voltage of 25 volts DC — will give a total voltage which will swing from 20.5 to 29.5 volts. If the regulator needs a three volt headroom to operate, this is subtracted from the minimum value of 20.5 to give a maximum regulated voltage of 17.5 volts. An 18 volt regulator would fall out of regulation on loud audio and cause distortion in the amplifier. Thus, there is a need for an unregulated voltage that is about 10 volts higher than the output of the regulators chosen.

Finally, a word about the type of wiring you wish to use. Telephone wires and Cat 5 network wires are relatively small gauge, so the power current will be somewhat limited. If you have multiple stations on a single run of such wire, the current needed for a single station will be multiplied by the number of stations on the run. This may cause problems with excessive voltage drops. Also, longer runs will add to this problem due to increased resistance in the wiring. The systems in TV stations I referred to earlier commonly only have to power headsets — not speakers — so less power is needed. I would suggest heavier gauge wiring; common lamp cord or even doorbell wire may work better. If you must use telephone or Cat 5 wiring, they commonly have four conductors and you should consider doubling up for both the ground and the signal/power conductors.

Think wireless!!! Go to gadgetshack.com and look at the Westinghouse two-channel basic home intercom system. For $59 per pair of units and a reputed "unlimited number" of units that can be used with full security, this is a lot cheaper and less of a "pain" than running cable. Running cable in an existing house is very difficult and installing cable in a new house is still expensive.

Start with a soldering kit (such as RadioShack's Cat. No. 64-2803), plus a couple of rolls of solder removal braid and a roll of rosin core solder (the RoHS stuff is "greener" but it's a pain even for seasoned veterans). If you plan to remove a lot of components from scrapped boards, a vacuum desoldering tool will keep your hair on your head.
 

I learned to solder at eight years old (52 years ago) with my grandfather's 250 watt soldering gun and a roll of solder that looked like it could be used to solder pipes, so the low wattage soldering irons used today are a snap. At 10 years old, my grandfather gave me a guitar amp. I learned not to troubleshoot the black tubes by touching them to see if they were warm (fried a finger tip in the process).
 

CAUTION: Wear safety goggles or glasses when soldering and don't even think about surface-mount devices yet.

Practice soldering by attaching two small wires together and then move up to a kit. Ramsey Electronics (www.ramseykits.com) has a lot of neat electronics kits for both beginners and old pros. Later, you will build some of your own designs or those from the authors of Nuts & Volts, and will need components; Jameco (www.jameco.com), Mouser (www.mouser.com), and Digi-Key (www.digikey.com) are good sources. Don't worry about microcontrollers now, but later you may try them and catch the programming bug.
 

Good luck, keep trying new things, and don't give up. Before you know it, you'll be an old pro too.

Old circuit boards are very useful for parts to build new projects. The motherboard caps are small with good capacity however you should check each capacitor for the correct value before using it!  A common failure mode for motherboards is/are the capacitors swelling and going bad or venting.

One can use capacitors for filtering a power supply, bypassing an IC, in timing circuits or isolating a higher voltage. You can also use a large value capacitor to clear the shorting whiskers in a Ni-Cad battery. MUCH better than shorting out your power supply!

Assuming you're not interested in a permanent monitoring solution, but wish only to take occasional measurements, a fast and inexpensive solution is to use a multimeter that has an RS232 interface and a temperature probe. One such instrument is the UT-61C available for $60 from www. multimeterwarehouse.com.  Attach the temperature probe to the cover of the baseboard heater (not the heater element itself), and record the temperature variations over time on your PC using the software included with the multimeter. When you're done, you have a multimeter (although not the highest quality) to use for other projects.

If you are interested in knowing how long the heaters were running for the least amount of time and money, I would suggest using a panel mounted hour meter. You can get the meters from Digi-Key, Allied Electronics, or any well stocked supplier. I would suggest getting a meter that responds to the 24 VDC relay coil voltage. The one advantage is that you can get a cumulative reading of the time the relay is energized without having to utilize a computer. While a computer program is nice, if you should take a power bump your computer may shut off and you lose the data you were trying to get. Since the meter is directly powered, if you lose power and then it is restored the meter will keep working.

If you are up to messing with a microcontroller, I have a solution based on using an Arduino and a Flash memory card to save the data. To better flesh out the project, I have created a web page with a description (I did bench test it) and schematics: https://sites.google.com/site/thermostattracker/home.

Basically, you use a small front end to transform the thermostat signal for the Arduino microcontroller input, run a program on the Arduino to collect the data, and store it on a Flash memory card that is plugged into a daughter card (referred to as a "shield") on the Arduino. Then, you can take the Flash memory card and plug it into a PC for post-collection data analysis (example, import to a spreadsheet). I'd estimate about $75 for the parts; almost all are available at a RadioShack. I also used the free Arduino simulator available at arduino.com.au to aid in the programming.

The easiest solution is to use a PC or laptop with an appropriate program such as: www.tucows.com/preview/240287  or  www.xmarks.com/site/www.world-voices.com/software/nchtone.html.  I found these by searching for "PC tone generator".

Transformer Calculations: www.electrical-design-tutor.com/transformercalculations.html

Transformer Winding: NOTE: There are many types of transformers and you didn't specify what it would be used for: RF-antenna/circuit impedance matching, AF impedance matching, AC Voltage Conversion

A good place to start: The Radio Amateur's Handbook, if you can get one.
Practical (power) Transformer Winding: http://ludens.cl/Electron/trafos/trafos.html

Get a copy of Coyne Television and Radio Handbook. Very good Practical transformer design, also wire and other charts. I see this book on the Internet book sellers.

Since you are asking about the primary turns, we assume that you need equation (2) shown in the Figure below, and you are experienced enough to already be familiar with equation (3), listed for reference. We also assume that you are interested in rewinding a power transformer (50/60 Hz) rather than an audio or radio frequency transformer. The main task is to get the minimum required number of primary turns without saturating the core, otherwise smoke. Everything else is just details.

An E-core transformer core is shown in the figure. It is constructed from a stack of alternating "E" and "I" shaped laminations of silicon steel. The "not shown" windings go around the center leg through the two windows. The key to the design is the cross-section area of the center leg through which the magnetic lines of flux pass. The Area (A_e) is the width of the center leg (w) times the height (h) of the stack. The A_e determines: 1) the power output capability (Wo); and 2) the number of primary turns (Np). It should be no surprise that a bigger core (A_e) supports more power (Wo). Bigger cores require fewer turns of larger wire than smaller cores.

Start out with either equation 1a or 1b. If you are starting with a known power output requirement (Wo), use 1a to determine the required center leg core area (A_e). Example: A 100 watt (Wo) transformer operated at 60 Hz requires A_e = sqrt(100)/5.58)*sqrt(60/60) = 1.77 sq in center leg core. You then need to select a stack of laminations for which w and h
multiply out to 1.79 sq in, or more.

More likely, you have a discarded transformer on hand that you want to rewind with custom windings. Equation (1b) tells us how much power (Wo) a center leg of a given area will support. Knowing the wattage allows us to select the proper wire sizes for both windings. Example: We have a 1.0 in stack of 1.0 in wide laminations = A_e = 1 sq in: Wo = (60/60)*(squared5.58 * 1.0) = (31 watts).

The minimum number of turns for the primary is given by equation 2 in terms of the primary voltage (Vp), frequency (f), center leg E-core area (Ae), and flux density of 80,000 lines per square inch. Example: Our 31 watt 1.0 square inch core is to be operated at 120 VAC, 60 Hz; Np = (120 * 10e8)/(4.44 * 60 * 1.0 * 80,000) = 563 turns.

If our 31W, 120V, 563 turn primary were to be accompanied by a 12V secondary, the voltage ratio is 1/10. The secondary turns Ns is proportional (equation 3). Ns = 56.3 turns. This is the open circuit voltage. Optionally, if we want the loaded voltage to be closer to 12V, add 5% more turns to the secondary (not shown in equation 3). Ns' = 1.05*Ns = 1.05*56.3 = 59 turns.

What size of wire should be used for our example 31W 120V : 12V transformer? Answer: Choose a wire gauge having approximately 1,000 circular mils of cross-section per ampere of current. See Reference [2] for a wire table. The 120V, 31W primary has I = P/V = 31/120 = 0.26 A current. Closest is AWG #26 wire with 254 cir mils cross-section for the primary. The secondary current is I = P/V = 31/12 = 2.58 A. Closest is AWG #16 with 2583 cir mils.

Note: The above formulas based on Reference [1] predict a full load temperature rise of 50 degrees C. If this is too hot for your application, decrease the flux density of 80,000 lines per square inch by 20%.

Practical considerations: In the olden days, it was possible to disassemble a transformer by removing the bolts compressing the lamination stack, then knocking out the laminations with a hammer and screwdriver. These days, disassembly may be impossible due to epoxy applied to the laminations. If possible, recover the insulating form on which the coil is wound from your scrapped transformer. This is a hard-to-make item. If you are modifying a not-burned-out transformer, only remove the secondary; re-using the primary.

Some small transformers — like the open frame RadioShack products — may have a large enough window space remaining to add windings atop the existing secondary. If you only need a few volts, or want to add a few volts to the existing secondary, the turns may be threaded through the windows without disassembly. Temporarily, tape sharp window edges to prevent scraping the wire while threading.
 

References:
[1] Reference Data for Radio Engineers, 4th ed, “Design of Power Transformers for Rectifiers,” pp 25, 1964, ITT.
[2] Lessons In Electric Circuits, Vol 5, Ch 3, Copper wire gauge table, www.ibiblio.org/kuphaldt/electricCircuits/Ref/REF_3.html.

Here are three video tutorials on building a transformer from an old microwave. They go into the design and windings design pretty well (alternative: just go to youtube.com and search on "mot salvage tutorial"):
 

www.youtube.com/watch?feature=player_embedded&v=KRoPHKpCYmg

www.youtube.com/watch?feature=player_embedded&v=YX3mYO-BIuQ

www.youtube.com/watch?feature=player_embedded&v=-NLy-LL_TGQ

The question about transformers does not admit to a simple answer. The primary and secondary windings are applied such that the ratio of the number of primary and secondary turns is identical to the ratio of the primary and secondary voltages. However, the above statement presumes an ideal transformer. It also presumes that the designer has already considered the frequency and waveform of the voltage applied to the primary winding, heating, and safety considerations, etc. This knowledge is required in order to permit the designer to select the proper type and physical size of the transformer core material, the bobbin construction, and other matters.

If your interest is constrained to power-frequency transformers — principally 50 Hz in your part of the world — I found an interesting treatise at http://ludens.cl/Electron/trafos/trafos.html. His complementary article at http://ludens.cl/Electron/Magnet.html discusses the underlying physical properties relative to transformer design.

Try:www.kadiak.org/tel/

Or just search the web using, "Telephone Technical Reference" to find a bunch more.

For a book on telephone electronics, see:
ISBN-10: 0750699442
ISBN-13: 978-0750699440
You can find them for about $10 new. There is even a Kindle edition, although it is close to $35.