Tech Forum

3-D printers (aka rapid prototyping machines) and laser cutters are very different animals. The laser cutter can be used to "machine" metals by laser ablation of the surfaces. A 3-D printer (such as MakerBot) uses a curable plastic powder or filament for producing layer upon layer renditions of whatever you draw on a Computer Aided Drawing (CAD) system.

Polyethylene Terephthalate (PET) filaments produce stronger products than the usual ABS plastic materials (A UT Austin student reportedly made a working pistol out of ABS but I am not sure I would want to trust my safety to the strength of plastic in this case).

The replicator (3-D printer) will run about $3,000. MakerBot also sells a digitizer for about $1,000 which allows you to reproduce an existing product by scanning it into the computer versus the laborious process of producing a 3-D CAD drawing. Using the Replicator and the Digitizer/CAD system together makes it possible to produce nearly anything you can imagine as long as it fits into the 3-D printer. I have seen a complete ball bearing set made as one piece (no assembly required) on a old 3-D printer which moved exactly like a metal bearing produced by sophisticated machining processes but the plastic did not have the strength to hold up in service. I can see using ceramic materials which can be fired to produce strength as a future wave in 3-D printing

Telescope position control is not for the faint at heart. First of all, the controller must be able to move the telescope in Azimuth (in a circle around the scope) and elevation (vertical angle from the horizon to the point above the scope - zenith) and convert these angles to the celestial equivalents of latitude and longitude called Declination and Right Ascension, respectively.

You must start with the telescope aligned with the Earth's axis of rotation which can be accomplished by sighting Polaris (the North Star). Then the telescope position controller must be able to track the object you are interested in by countering the Earth's rotational motion.

Before tackling building a positioning controller, (not an easy feat involving electronics, mechanical systems and programming) look at Celestron (www.celestron.com), Meade (www.meade.com) or Gemini (www.bisque.com/help/theskyv6/telescope/Gemini_by_Losmandy_Instruments.htm). Both companies make telescope positioners for a variety of telescope sizes and types.

Why would you use a big stepper to drive a telescope? Surely you are not considering a direct connection to the telescope's polar axis? That would produce a very jerky motion instead of the smooth motion needed for observation or photography. Therefore, you still need gears and you really need a high ratio worm gear or a series of compound gears to get a high reduction ratio. A relatively small stepper or DC motor will then work just fine.

Amateur telescope makers have used a wide variety of drive mechanisms. I have seen worm drives made by wrapping a threaded rod around a wood disk to form the "teeth". A screw with the same thread pitch can be used to drive it. If the scope is well balanced, little torque is needed to drive it. On the other hand, second hand worm wheels can often be found in places like ebay and other resellers.

Since a telescope moves at such a slow rate, some are driven by a cord or wire or strip of metal that is wrapped around a wheel instead of a gear. The cord/wire/strip is pulled by a nut that runs on a threaded rod that is turned by the motor. Since you can track from sunset to sunrise with only a half turn of the polar axis, you don't even need the full circle on that wheel. A fast mode or a nut that can be released would allow faster resetting for another observation.

Have you tried SAMS Photofact?: www.theschematicman.com - They probably had one for that radio, it's in the correct time frame. You'll need the make (RCA) and model number, perhaps even a version number on the circuit board. But, I don't know about radios, it did help when I was working on TVs.

Rider schematics were published up to 1954, too early to have included your radio which was probably made in the early 1960s. Howard W. Sams photofact service folders started in 1946 and may be still in production. I have an index which I believe I downloaded from www.servicesoftware.com in 2010. It lists 16,283 RCA schematics of radios, televisions, record players, and the like so if a schematic of your radio exists, it should be there. All you need is the model number to find it. I don't know the cost to download a schematic but it is not free.

You can also check  https://www.samswebsite.com/

Whether it's an old radio, TV, test instrument, audio gear — anything "antique", including older transistor radios, go to www.antiqueradios.com and check out their forum, especially under the section "transistor radios". This is the best source for help with antique electronics anywhere on the Internet.

All smartphones include a GPS and it would get the direction information from it, from the satellites. Try turning the GPS off to see what happens.

While I do not have an answer to your question about bringing a product to market, I know my self and others would be interested. If someone does give you the answers/help that you need would it be possible to keep a journal on the process and maybe submit an article to Nuts & Volts on how the process went for you. It may inspire others that have designs/prototypes to get theirs on the market.

Good luck in your endeavors.

In answer to your question — Yes you should learn about electronics fundamentals along with learning about microprocessors.

You need to have an understanding of the basics, however you do not need to get a degree in electrical engineering.

Your best bet is to check out your local library and see if they have any books dealing with electronics fundamentals. You may want to see if they have a copy of the ARRL Amateur Radio Handbook, they also have a book titled Understanding Basic Electronics which will help you get started. I don't know whether or not  you have your ham license but you may want to see if there is an amateur radio club in your area and get your self an "Elmer," which is ham radio talk for a mentor, as most hams that I know of are willing to pass on the knowledge they have acquired.

There are also several groups on Yahoo devoted to beginners which are worth joining.

Good luck in your endeavors.

Starting learning electronics with discrete components (resistors, capacitors, diodes, etc) or microcontrollers is a good question. Fortunately you can choose to start with either and be successful due to modern kits and the Internet. If you are "into" programming in C language, microcontrollers would be a good place to start.

To start in the microcontroller field, I would start with the BasicStamp. Parallax (www.parallax.com) has some good starter kits which supply the microcontroller, breadboard and other components to perform the experiments they have well documented in the enclosed manual. After gaining proficiency with the BasicStamp, you can move up to the Arduino (http://makerzone.mathworks.com/arduino) or Propeller (www.parallax.com). Nuts and Volts has projects every month on microcontroller type systems which can also be used to further your self-training.

If you don't feel comfortable with programming, learning the basics of electronics may be the place to start. Googling "electronics tutorials" will show you a number of FREE websites which offer electronics training for beginners. Also The Nuts and Volts Webstore sells books and kits to help you learn electronics.

Electronics is a neat field to study. It is not easy. It is not for everyone. But anyone who is looking for a challenge, electronics is the place to be. Whether you start with basic components or microcontrollers, you will eventually see the need to learn about the other field. Microcontrollers use basic electronic components to function as a system and often it is advantageous to replace a "kludge" of electronic components with a microcontroller app.

Some comments and concerns regarding your question. First, I am not clear if this is a repair or a retrofit. I would also presume this is a tube-type amplifier, since they were often built with point-to-point wiring and hum pick up was highly likely with so many signal wires running around the chassis.

Based on your comment of "adding a kit", I would presume that either this is a retrofit or the original noise filter cap was removed in the past. The fact that adding the new cap from line to ground reduced the 60 cycle hum (or 120, depending on the rectifier design), it seems that this might actually be a repair. Or, the filter caps themselves are old and leaky, so you are aiding them but not actually curing the problem. If the amp is old, it often needs to have the filter caps replaced and, sometimes, some interstage decoupling caps as well.

With that background, I caution that this involves principles of safety and if you are not experienced with working on mains circuits, this effort would be best left to a professional. Just because something works does not mean it is well-executed or robust. And since guitar amps get moved, jostled, banged around and often not treated caringly, there is a chance your soldered connections of this component could break loose without your knowledge and you could have a real shock hazard on your hands.

OK, assuming all that is well-appreciated, the type of cap you use is critical. This component is connecting one side of the AC mains to the accessible chassis. You cannot assume that a ground pin on a cord will save your life since you have no idea how well the ground-to-neutral impedance is controilled in the building's branch circuit you just plugged into. Hence, the cap itself must be suitably rated to be connected from line to ground. Therefore, this must be a Y2 type of cap.

If you have no idea what a Y2 cap is, then read this link first: www.justradios.com/safetytips.html. There are many good manufacturers of Y2 caps (Vishay, KEMET, Panasonic, etc.). Here is a good selection from Mouser:  www.mouser.com/new/Kemet-Electronics/KEMET_XY_Film_Caps.

Be sure that you do not rely on solder for mechanical support of live parts. Always wrap the cap leads snugly around the terminals it is connecting to and check to determine that it would tend to stay there if no solder was used. Solder is not meant for mechanical retention of massive parts. Once you feel it is well mounted, then use solder to make the electrical connection to the terminals.

Safe is a relative matter of degree. The safety ground wire in a standard three wire AC cord is there for a reason. However, the NEC does allow for devices that do not have that safety ground connection. Many electric and electronic devices are made without it.

The safety ground connection is there to insure that the fuse does blow or the circuit breaker does trip if a conductive outer case of the device becomes electrified. The current that flows from the hot wire to the safety ground blows the fuse or trips the breaker and then there is no danger of shock.

Devices that do not have that safety ground usually employ a double insulation method to prevent such a short to the outer case or to the user. Thus, if there is internal insulation AND the outer case is an insulating material like plastic, then TWO different insulators would have to fail for the user to get shocked.

Older devices, like early electric lamps, were made with metal outer cases and often the electric wires inside them were only a small fraction of an inch from that conductive case. Older electric cords were insulated with real rubber which deteriorated over time and became "frayed". The card board insulators in lamp sockets literally fell apart after some years of service, usually with over sized bulbs in the lamp (rated at 40 W so the user put a 60 or a 100 W for more light). Etc., etc., etc.

It is not possible to tell if a particular device, like your amplifier, is safe without examining it. If it was commercially manufactured in the US or imported properly, then chances are it is OK. Things like the UL (Underwriter's Laboratories) tag are supposed to tell the consumer that it has been inspected and found to comply with the code. If it is a kit or was made in someone's kitchen or garage, then it may or may not be OK.

Hum like this, is usually a result of what is called a "ground loop". Both the signal cable between the audio devices and the power cables to them are grounded and they form two different and distinct ground paths between them. If there is any 60 Hertz current flowing in either of them, then the circuit/signal ground planes in each of those devices will be at a different AC potential and the hum is introduced into the signal.

One way of eliminating this situation is to cut the safety ground on one or both of the devices. But this eliminates the safety feature of that connection. A better way to eliminate this situation is to use a balanced audio line between the devices and to connect (ground) the shield only at the source end of that line. In this way there is only one ground connection between them, via the AC power. Many times this is used in professional audio installations where long lines must be run. But this may not be possible on amateur equipment where single ended audio lines are often run.

Another solution is to use a differential input amplifier at the receiving end of the audio line. This can be accomplished with a transformer or with actual active circuitry. With a transformer, the center lead and the shield of the single ended cable are connected to the primary of the transformer so the shield is not connected to the chassis/signal ground of the amp.

Active circuitry with a balanced input is more complicated. I am designing such an amp at the present time to overcome a noise problem between my audio/visual equipment cabinet behind my chair and the computer on the desk in front of it. Due to the arrangement of the room, I had to run a 50 foot cable and it does pick up hum.

An audio transformer of sufficient low frequency response would cost a bundle. Since the audio is single ended (not balanced) this may be the only solution. I have searched and could not find a reasonably priced, differential input audio amp for this application. Professional ones seem to start in the hundreds and go up from there.

Another factor that helps to overcome noise and hum is the impedance of the audio line. Much amateur equipment uses a high line impedance which may be OK for a few feet, but longer, high impedance (10 KOhms) lines will pickup noise and hum from the environment. Professional audio uses lower impedance lines to overcome this.

The old standard was 600 Ohms but modern equipment often has extremely low output impedance (one Ohm or less) and a higher input impedance. This works in most situations. When long lines need lower termination impedance on the receiving end, a simple resistor can be connected across the line at that point.

As far as controlling the LED brightness, here are two possible solutions: one using PWM (pulse width modulation) and the other a variable DC power source. First, I'll describe the PWM circuit in Figure 1 which is controlled by a PICAXE 08M microprocessor. The output from a PWM generator is programmed to run continuously. The timing duration is controlled by the ADC reading on potentiometer R1. The LEDs are controlled by FETs Q1 and Q2. All parameters are set by the programming code.

main:low 1               ' LED set #2 off<br />      high 0              ' LED set #1 on<br />      readadc 4, b2       ' read voltage and set duration time, b2 varies from 4 to 28<br />      let b2 = b2/5 min 4 ' duration time = 500 * b2 * 2<br />      for w0 = 0 to 500   ' duty cycle scans from 0 to 100%<br />      pwmout 2,124,w0     ' frequency set at 8KHz, output leg#5<br />      pause b2            ' LEDs brighten during this for-next loop<br />      next w0<br />      for w0 = 500 to 0 step - 1  ' Leds dim during this for-next loop<br />      pwmout 2,124,w0<br />      pause b2<br />      next w0<br />     <br />      low 0                ' LED set #2 on<br />      high 1               ' LED set #1 off<br />      readadc 4, b2        ' read voltage and set duration time, b2 varies from 4 to 28<br />      let b2 = b2/5 min 4  ' duration time = 500 * b2 * 2<br />      for w0 = 0 to 500    ' duty cycle scans from 0 to 100%<br />      pwmout 2,124,w0      ' frequency set at 8KHz, output leg#5<br />      pause b2             ' LEDs brighten during this for-next loop<br />      next w0<br />      for w0 = 500 to 0 step - 1 ' Leds dim during this for-next loop<br />      pwmout 2,124,w0<br />      pause b2<br />      next w0<br />      goto main            ' repeat code
 

Figure 2 uses a combination triangle-square wave generator (U1) to control the variable DC voltage from Q3. R2 controls the duty cycle and R1 controls the minimum DC output from Q3. The setting of R1 will depend on the color and/or type of LEDs used. Basically, R1 is adjusted so the LEDs just shut off before the counter advances. The square wave output (pin7 of U1) is used to advance the 4017 (U2) which is configured as a count to two and recycle counter. The square wave output switches low at each minimum crossing of the triangle generator. This is used to control the "clock enable" (pin 13) on U2. The clock input is connected to Vcc so the counter will advance each time pin 13 goes low. One nice feature about this circuit is the 4017 allows for easy expansion (up to 10) if more LED strings are needed.
 

There were no details mentioned about the LED strings regarding how they are wired, the color, or voltage needed. In this case, I decided to show both circuits operated with the LEDs in parallel with individual current limiting resistors. The RL values shown are only guidelines as the specs on the LEDs and the brightness required by the user will vary. Both circuits require a regulated 5 VDC power source.

You could use a squirrel cage fan. It is a lot quieter for the same airflow.

Back in the day when there were ONLY tube amps, none of them used fans. Hot air rises and tubes make the air hot enough that convection cooling is all that is needed as long as you properly ventilate the box containing the amplifier. This means long slits, or a large amount of nice sized holes, in the bottom and the top of the box to let the air flow.

LiPo batteries which are probably what you are wishing to use do not like to be compressed, flexed, or prevented from expanding slightly during use. Encapsulating them in epoxy directly could do any and all to it, since the thermal expansion coefficient of the epoxy would differ than that of the battery.

There are other options, one of which is the inexpensive Lexan cases intended for protecting cellphones while camping sold at Walmart or other such stores. They have a silicone seal and clamping latch that protects the contents from moisture. If you needed to bring in signals or power, one could drill a hole, then feed the wire through and use RTV (silicone) to re-seal the hole. If you do this, route the wire from the bottom and drill a small drain hole that is at the lowest point. Air can pass through the cable itself, over time enough water vapor could collect in the case to become a problem under certain weather conditions.

Epoxy encapsulation is pretty drastic. Why not simply seal things in a plastic screw top container?! If the explosive nature of Li-ion cells is the concern, then you may be better off using the far more tolerant 3.2V rechargeable LiFePO4 (Lithium Iron Phosphate) version.

AA/AAA sized LiFePO4 cells sell for ~US$5 each, and are stated as good for 1000s of charge/discharge cycles too. See www.instructables.com/id/Single-AA-LiFePo4-cell-powered-project-in-a-parti/