Murphy's Maiden Journey of the Radio Shack Special...

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I would like to thank you murphy for taking on this fun project. It is always very interesting to see how other hobbyists go about in making this little marvel shine! My father always said... there are many ways to skin a cat...and you have just proved that. Keeping your story to myself would be an injustice to others who so willingly look for projects like this one on the world-wide web. So without further ado, here is Murphy's own words and pictures about his venture!

Constructing The Simple FM Regenerative Receiver From Circuit Diagrams and Information Published in P. Cambre's Website...

I have experimented with a number of RF devices which operate through the range of 80 to 110 MHz. Bugs and listening devices usually operate on this frequency range. For the amateur electronics constructor/hobbyist, the simplest and most basic circuits are the ones to go for [when you can find them - P. Cambre's FM receiver certainly fits this category].

Type 'electronics' or 'radio' into your search box and you will find as I have that the world wide web abounds in countless sites on the subject. Most, in my view, are unbelievably complex and poorly drafted. One would have to be very brave to take on some of these projects...which I am sure, would not work anyway. Many of the published projects that I have seen, make great use of special purpose IC chips, which invariably are unobtainable or very expensive in your part of the world. So projects designed mainly around descrete componentry [excepting of course the very useful operational amp buffer LM386 and similar] are my favourites.

In experimental circuits, such as I deal with, problems arise with obtaining a suitable circuit board. Building your own PCB is in my view not good economics. I have seen a fair bit of 'bread-boarding'...OK...if you are happy with that. I use a system I have developed myself which I have found 'simple & effective'. It is as follows...

Work out your circuit, placing components as you would on a chess board. With the main aim being to keep electrical point-to-point [path] distance as short as possible. Select a piece of stiff/firm cardboard. Cut square, size to suit circuit. Cut tin strips approximately 2.5mm's wide from shiny flat tin...crimp strips firmly to cardboard. We now have a firm board to which you can solder your components on to quite simply.

I have used this card system on many types of circuits successfully. Dealing with linear type circuits such as...multivibrators, transistor controlled switching devices and similar. With regard to RF circuits however, many other aspects have to be considered. RF circuits incorporating oscillator circuits, even though they are receivers, will emit radio energy. The inter-connecting circuitry between componentry is itself part of the electro-inductive circuit...thus effecting the operating frequency. I have dealt with this problem on my experimental circuits by building circuit stages on separate cards and connecting them with hook up wires. For example...a two stage transmitter consisting of an audio amplifier stage and oscillator stage. If these stages are situated too close together, the emissions will clash and the project will simply not work. So a little experimentation with the situating of boards will acheive better results. I used this method in constructing the FM receiver...that is... the RF signal receiver stage and the LM386 audio amplifier stage being separate. And it all worked out successfully.

From what I have learned from this experimental approach I can now go on to constructing a properly formulated version on a single card. My circuit schematics for the FM receiver and other projects may be view by anyone interested if they can download my material which is all CAD drafted using 'Turbocad 6' software. Or I can be reached by e-mail or even via Mr. P. Cambre on his website.

As of 2/21/03, Murphy continues to improve his unit. Here are a couple of pictures...along with a few words Murphy had to say about his latest design!

"The extra coil in the receiver is the antenna itself, which is mounted about an inch above the card...which incidently works very well! The only main difference is the amplified audio portion of the circuitry. I used an LM358 op amp instead of the LM386."

...Murphy continues to improve his design as time goes by. I will gladly keep everyone updated on his continuing venture!

This interesting little gadget shown below is an electronically commutated 12 volt DC Electric Motor...

The armature consists of six perminent cylinder-shaped magnets fixed to a disc and running in a small ball bearing. The activating coils are made from a 'beer can' cut spirally into a continuous strip 4mm's wide, wound around a small steel-core with a steel fixing screw through the center. Examples of the coils, fixed and unwound, are shown in the fireground of the picture. Current is supplied via two TIP 142 transistors which are switched ON/OFF by a magnet type switch activated by the rotating armature. Low current pulses are delivered to the bases of the TIP 142's in phase with rotation. When switched on, the current flow is virtually 'short-circuited', but as back currents generate and impedance kicks in, it runs quite comfortably at 2 amps at about 800 RPM and delivers reasonable torque.

Improvements could be made with a more efficient armature arrangement and better suited power transistors. The TIP 142's get very hot and tend to become unstable.

An interesting concept, indeed, building electromotive projects using up your old beer cans.