Crystal Radio Questions

Started by Joe in sci.electronics.basics8 years ago 10 replies

I'm winding a coil for a crystal radio. The original plan says to wind the antenna coil on top of the tuning coil, whereas another version...

I'm winding a coil for a crystal radio. The original plan says to wind the antenna coil on top of the tuning coil, whereas another version says to wind the antenna coil *adjacent* to the tuning coil, separated by about 1/4 inch. If I wind both versions of the antenna coil on the form, will one winding interfere with the other? That is, I would only hook up one antenna coil at a time, so ...


How to test the primary coil on a microwave oven transformer for a short.

Started by trg-s338 in sci.electronics.basics8 years ago 7 replies

I'm building a spot welder using a modified microwave oven transformer. The project calls for removing the secondary coil windings. In doing...

I'm building a spot welder using a modified microwave oven transformer. The project calls for removing the secondary coil windings. In doing so, I accidentally "bumped" the primary coil with a hammer resulting in 2 or 3 wires in the primary coil becoming slightly displaced by about 1/8 of an inch. I hope someone can tell me how to test the primary coil for a short circuit as a result of t...


How to optimize parameters for making a coil with high-Q?

Started by Arthur C. in sci.electronics.basics9 years ago 22 replies

I want to make a simple coil (inductor) with a Q value as high as possible. Now, I would like to know if there are simple guidelines on how to...

I want to make a simple coil (inductor) with a Q value as high as possible. Now, I would like to know if there are simple guidelines on how to choose the parameters to obtain this. Parameters are: - thickness of the wire - number of rounds - length of the coil - area of cross-section I understand that a realistic description of a coil involves (at least) a parallel parasitic capacitanc...


Basic auto ignition electric Q

Started by Paul Conners in sci.electronics.basics8 years ago 31 replies

Single coil, rotor & distributor cap system, 4 cylinder. Is the coil housing grounded? I always thought the coil housing was the return path...

Single coil, rotor & distributor cap system, 4 cylinder. Is the coil housing grounded? I always thought the coil housing was the return path for the secondary circuit / spark current. I know that the primary circuit doesn't use ground in the coil: it is grounded through the ignition points in the distributor (this is a 70's vintage car). Both the original and replacement coils do not...


Step Up Pre Coil/Transformer

Started by Bret Cahill in sci.electronics.basics6 years ago 3 replies

OK Honda no longer makes the original ignition coil that steps up the voltage by 3 -4 orders of magnitude. What's the easiest way to get a...

OK Honda no longer makes the original ignition coil that steps up the voltage by 3 -4 orders of magnitude. What's the easiest way to get a 40,000 volt spark out of a 12 volt ac system with a 100X step up coil? Bret Cahill


Designing The Perfect Coil?

Started by Ron Hubbard in sci.electronics.basics6 years ago 113 replies

I want to do an experiment in brainwave entrainment by making a 7 Hz sine wave oscillator out of an XR2206 frequency generator IC and a LM386...

I want to do an experiment in brainwave entrainment by making a 7 Hz sine wave oscillator out of an XR2206 frequency generator IC and a LM386 amplifier feeding a six inch diameter coil-- which should probably fit around my fat head. ;-) The LM386 has an 8 ohm output, so it shouldn't be hard to find a speaker, if I wanted to use one; but I don't know how to make a good 8 ohm coil to radia...


[Q] How to calculate influence of metal object on dc biased coil?

Started by Jason Wilder in sci.electronics.basics7 years ago 10 replies

I have a 100 mm ferrite rod on which I want to wind a coil using 0.3 mm diameter copper wire. The goal is to detect a car passing by at three...

I have a 100 mm ferrite rod on which I want to wind a coil using 0.3 mm diameter copper wire. The goal is to detect a car passing by at three meters. I plan to bias the coil with DC. How do I calculate the number of windings that I have to put on the rod so that I can reliably detect the car? This should be easy I suppose, but I can't find anything about it. Every book will tell you w...


sizing a freewheeling diode for a coil

Started by Matt in sci.electronics.basics10 years ago 38 replies

I am controlling the coil of a relay using a switching transistor. To protect the transistor I intend to use a freewheeling diode in parallel...

I am controlling the coil of a relay using a switching transistor. To protect the transistor I intend to use a freewheeling diode in parallel with the coil. I'm not sure of the issues in specifying the diode. My impulse is to simply use a 1N4007 http://www.fairchildsemi.com/pf/1N/1N4007.html (1000V peak repetitive reverse voltage, 1.0A average rectified forward current) because it is ...


Inductor calculation?

Started by Winston in sci.electronics.basics7 years ago 22 replies

I am trying to calculate the inductance of a multi-row, multi-layer air-core coil that has a square winding cross section, zero magnetic...

I am trying to calculate the inductance of a multi-row, multi-layer air-core coil that has a square winding cross section, zero magnetic coupling to any other object. Conceptually, it's a Brooks Coil, like you might use in a metal detector. Of the internet and hard copy resources I've used, no two equations produce nearly the same results. I've gotten everything from 219 mH on down...


Blown resistor in automotive latching relay

Started by AshMan40 in sci.electronics.basics11 years ago 14 replies

Hi all. This is my first post to this NG forum, so please be kind. I am trying to repair a 12v latching relay for my Volkswagen...

Hi all. This is my first post to this NG forum, so please be kind. I am trying to repair a 12v latching relay for my Volkswagen Beetle (~1975). It controls the dimming of the headlights (hi/lo). The trigger is a momentary ground signal (S) which actuates the coil. The arm that the coil pulls on has a plunger which toggles a rather complicated see-saw arm which moves a contact between po...


Motionless Induction

Started by RalfM in sci.electronics.basics8 years ago 7 replies

Hi, let's say there is a magnetic field of a _permanent magnet_, and a fixed/nonmovable induction coil is placed into field. Is it possible...

Hi, let's say there is a magnetic field of a _permanent magnet_, and a fixed/nonmovable induction coil is placed into field. Is it possible periodically to change (ie. "disturb") the intensity of the said magnetic field so that an induction happens without moving the coil and the magnet? Could an oszillator (or resonator?) or a similar electronic method help here to generate induction?


Need a quick inductive ignition tester

Started by Michael in sci.electronics.basics8 years ago 14 replies

To test a non-starting vehicle's distributor, I need an inductive ignition tester to see if the central high voltage wire is...

To test a non-starting vehicle's distributor, I need an inductive ignition tester to see if the central high voltage wire is getting juice. Can I whip one up with a simple coil of electromagnet wire (~50 turns), connect to a DMM and place the coil near the HV wire? Thanks, Michael


Simple Test for Coil On "Wasted Spark" 2 Cylinder Engine

Started by Bret Cahill in sci.electronics.basics5 years ago 21 replies

I suspected a CDI coil wouldn't put out enough voltage for the "energy transfer" -- the worst misnomer ever -- system and suggested shorting out...

I suspected a CDI coil wouldn't put out enough voltage for the "energy transfer" -- the worst misnomer ever -- system and suggested shorting out the spark plug electrode on one of the 2 cylinders by pounding the gap shut or stuffing it with a bit of foil. The theory was instead of jumping two gaps it would only need to jump one. The lower effective resistance would give a better spark on t...


Want to build a HEI ignition module similar to 70's style

Started by default in sci.electronics.basics9 years ago 15 replies

Does anyone have a schematic for a simple four pin HEI ignition module from 1970's+ ignition systems. They appear to contain an SCR and a pair...

Does anyone have a schematic for a simple four pin HEI ignition module from 1970's+ ignition systems. They appear to contain an SCR and a pair of diodes and resistors. Pickup Coil connects to two terminals and battery and induction coil primary the other two, mounting screw provides a ground connection. Original type mounted to the distributor plate on GM cars and others and was ~1/4 ro...


6#11oz, 20"

Started by Jim Thompson in sci.electronics.basics3 years ago 7 replies

6#11oz, 20", our first great-granddaughter... Olivia Lawless... Father: Chris Lawless Mother: Caitlin Coil Lawless, first daughter of our...

6#11oz, 20", our first great-granddaughter... Olivia Lawless... Father: Chris Lawless Mother: Caitlin Coil Lawless, first daughter of our oldest daughter Madeleine and James Coil (Yuma County Judge). ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | ...


Automotive relay question

Started by DaveC in sci.electronics.basics3 years ago 15 replies

I have a 12V SPST cube relay in my junque box. The diagram molded into the relay?s housing includes a component connected in parallel with the...

I have a 12V SPST cube relay in my junque box. The diagram molded into the relay?s housing includes a component connected in parallel with the coil which looks suspiciously like a resistor. It?s not a back-emf diode: I connected the relay coil using both polarities (using a current-limited power supply) and the same current draw is measured. What is the purpose of this resistor? ...


Automotive relay question

Started by DaveC in sci.electronics.basics3 years ago 2 replies

I have a 12V SPST cube relay in my junque box. The diagram molded into the relay?s housing includes a component connected in parallel with the...

I have a 12V SPST cube relay in my junque box. The diagram molded into the relay?s housing includes a component connected in parallel with the coil which looks suspiciously like a resistor. It?s not a back-emf diode: I connected the relay coil using both polarities (using a current-limited power supply) and the same current draw is measured. What is the purpose of this resistor? ...


MOSFET switching an inductive, high-frequency load

Started by Don Gilmore in sci.electronics.basics4 years ago 8 replies

Guys: I'm an ME working on a project where I must switch voltage to a small coil = on and off at a fairly high frequency (around 25 kHz) with...

Guys: I'm an ME working on a project where I must switch voltage to a small coil = on and off at a fairly high frequency (around 25 kHz) with a MOSFET transis= tor. The DC resistance of the coil is very low (about 1 ohm), but the impe= dance is much higher because of the frequency (about 100 ohms). I'm switch= ing 24 Vdc. Should I specify the max. pulsed current of the transistor based...


Creating sparks with a mosfet and ignition coil

Started by Anonymous in sci.electronics.basics3 years ago 29 replies

I would like to generate a series of ~1000 volt sparks continuously, for several hours, using a spare automotive ignition coil I have lying...

I would like to generate a series of ~1000 volt sparks continuously, for several hours, using a spare automotive ignition coil I have lying around. I found this 555 circuit online: http://www.sci-experiments.com/HighVoltagePulser/ My questions: (1) Is a 500-volt MOSFET really necessary? Would a 100-volt IRF530 work alright without frying? (2) Does the 0.1 uF, 250V capacitor take the ...


240V relay contact suppression

Started by MarkMc in sci.electronics.basics11 years ago 11 replies

Hi I'm using a relay with 240VAC coil and 240VAC contacts. From what I've been advised before with relays (not 240VAC), I understand it's a...

Hi I'm using a relay with 240VAC coil and 240VAC contacts. From what I've been advised before with relays (not 240VAC), I understand it's a good idea to protect the contacts with a capacitor and possibly a MOV like below; Is this required for AC and is it a good idea to have a MOV? Also, I assume I need do nothing on the coil side, seeing as it's AC? Normally, I'd expect a reverse bi...