Advertisement

Blog

Construction of an Emergency Transceiver

Art Kay from Texas Instruments has sent us this guest blog to post on April 1 for our engineering audience who may enjoy boating.

A few years ago, I took a short boat tour off the coast of Hawaii. As Murphy's Law would have it, our ship was hit by a major typhoon. It seemed like the typhoon lasted for an eternity and when it was over we found ourselves washed up on a deserted tropical island. Unfortunately, our GPS and ship-to-shore radio was destroyed during the typhoon. We had no means of communication to the outside world and we didn't even know where we were located. Somehow, we had to use the local materials to develop an emergency transceiver. I thought that I would document this design in case you ever find yourself in a similar predicament.

The receiver: As you review this reference design, please remember that we only had to work with the local plants and minerals from the tropical island. The objective of the receiver was to keep it simple and build a single diode AM receiver. Figure 1 shows the schematic for the receiver. Although the design seems relatively straight forward, the problem was that we did not have any wire, resistors, capacitors, diodes, or earphones. Fortunately, we were able to construct these circuit elements using local resources. This section will provide how-to guide for building these elements.

Figure 1:  Simple One Diode AM Receiver

Figure 1: Simple One Diode AM Receiver

Coconut shell diode: Probably the most challenging problem we had to overcome was to develop a semiconductor diode. As luck would have it, however, the coconut fruit is actually a pure semiconductor (see Figure 2). Furthermore, sea salt and lime make excellent P and N type doping impurities (see Figure 3). You might wonder why the simple coconut diode isn't used commercially. The answer is simply that coconut has a limited shelf life.

Figure 2: Excerpt from periodic table

Figure 2: Excerpt from periodic table

Figure 3: Coconut Shell Diode

Figure 3: Coconut Shell Diode

Clam shell capacitor: The clam shell capacitor is also worth noting because it makes an excellent natural capacitor. The top and bottom shells act as a parallel plate capacitor, and the capacitance can be easily adjusted by opening or closing the shell to varying degrees. Figure 4 shows the clam in two different positions and the associated capacitance. Please note that the voltage coefficient of a clam shell capacitor is extremely low which minimizes distortion. In fact, I think the clam shell capacitor should be used in commercial high fidelity audio applications.

Figure 4: Capacitance vs. Clam Opening

Figure 4: Capacitance vs. Clam Opening

All the rest of the components: The remaining components are common applications of tropical flora, and consequently, we will not focus on these. For further information, consult the Electrical Characteristics for Flora and Fauna in Tropical and Subtropical Regions [3].

The transmitter: Figure 5 illustrates the simple transmitter design that we used to call for help. This section of the reference design provides details on the components used in the transmitter.

Figure 5:  Schematic Diagram of Simple AM Transmitter

Figure 5: Schematic Diagram of Simple AM Transmitter

Gourd amplifier: It was of key importance that the transmitter had sufficient power to transmit long distances. The gourd from the talahoobaloo tree is an excellent natural amplifier. Typically, the voltage gain of this gourd is between 1,000 and 10,000. The power output is strictly dependant on the batteries connected, so we placed 100 limes in parallel.

Coconut microphone: Considering the principle of reciprocity, it can be shown that a coconut not only acts as an excellent earphone, but also can be used as a microphone. In fact, the coconut approximates an electret microphone and can be modeled as such.

Crystal oscillator: The crystal oscillator was fashioned out of a piece of quartz found in the islands cave. Unfortunately, one of the members of the castaway group was captured by some natives and boiled in a large caldron of water. Fortunately, the natives became distracted when the island's volcano erupted and he was able to escape with the needed crystal.

Final outcome: I am happy to say that the transceiver worked quite well and we were rescued a few months after the typhoon. We were all very happy about the rescue as we were getting sick of coconut cream pie, coconut on a stick, and fried coconut. Unfortunately, we were fined by the FCC for violating AM transmission power restriction. It seems that the lime batteries were even more powerful that we expected. Nevertheless, I hope you can make use of this design in the eventuality that you ever end up stranded on a deserted island. (See Figure 6 and Figure 7).

Figure 6:  Photograph of Transceiver with its Components Labeled

Figure 6: Photograph of Transceiver with its Components Labeled

Figure 7: Operation of the Transceiver

Figure 7: Operation of the Transceiver

References:

  1. Wenzel, Charles, “Crystal Radio Circuits,” Crystal Radio Circuits, TechLib.com, 1995
  2. Field, Simon Quellen, “Building a very simple AM Voice transmitter,” Building a very simple AM Voice transmitter
  3. Hinkley, Professor Roy, BA, BS, MA, PhD, Electrical Characteristics for Flora and Fauna in Tropical and Subtropical Regions, Island Press, New York, 1964

38 comments on “Construction of an Emergency Transceiver

  1. Art Kay
    April 2, 2014

    Hope everyone enjoyed our April Fool's Day fun. If you're interested in more from Art Kay and other precision design experts, be sure to subscribe to their blog at ti.com/TheHub.  

  2. Steve Taranovich
    April 2, 2014

    Hi Art,

    Thanks for the April Fool's Day humor—we appreciate a good laugh. We also appreciate your technical expertise

  3. etnapowers
    April 4, 2014

    Hi Steve, I agree with you, it's a blog with good technical contents presented in a very funny way. I wonder if the 100 pF and 1000 pF “shell” capacitors might really work well even in the presence of a pearl inside them.

  4. Tim W
    April 4, 2014

    Well done!  Anyone out ther remember EDN's “April Engineering Supplement”?

  5. etnapowers
    April 7, 2014

    @Tim, could you provide a link to the EDN's “April Engineering Supplement”?

  6. Tim W
    April 7, 2014

    It was a print supplement back in the 80's; pre-internet days.  It may be available in their archives?

  7. etnapowers
    April 7, 2014

    Is there any keyword to search in an internet archive backup?

  8. fasmicro
    April 7, 2014

    Hope everyone enjoyed our April Fool's Day fun. If you're interested in more from Art Kay and other precision design experts, be sure to subscribe to their blog at ti.com/TheHub.  

    Honestly, you got me on this. Nice try!!!

     

  9. fasmicro
    April 7, 2014

    It turns out that some of the April fool day electronics ideas could inspire non-April fool products. I mean there were many all over the map on April 1 and some looked real!

  10. etnapowers
    April 8, 2014

    @fasmicro, I subscribed the community Precision Hub, you're right there are many interesting blogs, concerning many issues that commonly an engineer faces at work. Thank you again.

  11. Sachin
    April 10, 2014

    @Art, you really had me going especially when you said you were making everything without actual wires and so I thought I could make one on my own if I ever got into a similar situation. But I had to stop reading when I spotted coconut in the periodic table; I still can stop laughing at this one. Thanks for the humor, you literally made my day!

  12. Sachin
    April 12, 2014

    Why are bringing up this idea here in the first place? It sounds pretty funny and creative but I think you are missing something or tying to make fool out of some individuals.  @steve.teranovich, I concur with you, this is in deed a Fools Day humor.

  13. SunitaT
    April 29, 2014

    The transmitter is a very good idea and initiative in that can be man made by an individual in the case of an emergency. The fact that the tools that one needs to make it are readily available is a plus and a win -win situation. Who would have thought coconuts could be use to make very good transmitters? Since the results came out well am sure everyone must be eagerly waiting to try it out. This is perfect especially in those places with no network receptions.

  14. goafrit2
    May 2, 2014

    >> I subscribed the community Precision Hub

    Any link? It is from UBM? Thanks

  15. goafrit2
    May 2, 2014

    >> But I had to stop reading when I spotted coconut in the periodic table; I still can stop laughing at this one. Thanks for the humor, you literally made my day!

    He has some talents. I had a student confidently named Hu as one element. The meaning? Human element. Why? Got it from an advert from Dow Chemicals

  16. goafrit2
    May 2, 2014

    >> Who would have thought coconuts could be use to make very good transmitters? Since the results came out well am sure everyone must be eagerly waiting to try it out.

    I have since moved to the Carribean where I have become a coconut merchant as it is now a raw material in the electronics industry. Watch out Bill Gates, I will add more figures than yours.

  17. etnapowers
    May 5, 2014

    Here a link. It's from Texas instruments website.

  18. goafrit2
    May 8, 2014

    >> Here a link. It's from Texas instruments website.

    Thank you very much. TI has always been an innovation powerhouse in our industry.

  19. etnapowers
    May 12, 2014

    You're welcome, the TI company is really a big player in the electronics fields. Many good engineers work there, and the company has a lot of patents , in their website I often found many interesting application notes.

  20. chirshadblog
    May 12, 2014

    @etnapowers: Well, brand name does matter a lot true but if you have the talent to fight or compete with the other resources. Most of the big names capitalize only from their brand name not with talent. 

  21. Victor Lorenzo
    May 12, 2014

    @etnapowers >> Many good engineers work there (…)

    I agree with you on that and I would extend it to some more companies. I've been in contact with very talented engineers from TI, Analog Devices, ST Microelectronics, Infineon, ams, and others.

    @chirshadblog >> Most of the big names capitalize only from their brand name not with talent .

    In some cases it is easy to find out where the lack of talent resides. In some other cases cost reduction has a very negative impact on talent and overall product quality.

  22. etnapowers
    May 13, 2014

    The brand name is deeply correlated to the talent of the founders of the name, ideally the human resources should select the personnel in order to mantain the importance of human capital and its know how.

  23. fasmicro
    June 2, 2014

    Many good engineers work there, and the company has a lot of patents , in their website I often found many interesting application notes

    TI and Analog Devices have certainly changed the industry. I think all of them indeed Linear Tech, Maxim, etc. The challenge which I find frustrating is that Wall Street does not value these companies very well.

  24. fasmicro
    June 2, 2014

    Well, brand name does matter a lot true but if you have the talent to fight or compete with the other resources. Most of the big names capitalize only from their brand name not with talent. 

    I am not sure about that. Apple will not buy your gyroscope because you are TI or STM if it does not work. I do not see how you think in a technical field people do not associate quality with purchase decision. What you can say is that we trust brands because they have a history and in hardware it matters. Why I cam open a new email account for a new email provider. If it works, fine. If not, I close it. That is not the same if I have to buy a gadget which if it does not work I have to throw away. Brands earn the respect but must still work to keep it

  25. fasmicro
    June 2, 2014

    In some cases it is easy to find out where the lack of talent resides. In some other cases cost reduction has a very negative impact on talent and overall product quality.

    Good point – I know some really good engineers end up in Wall Street because that is where the big money is. Also, the lure of software where you can make so much money is also taking some talents out of the electronics industry.

  26. fasmicro
    June 2, 2014

    The brand name is deeply correlated to the talent of the founders

    Largely in busines, talent is the business. If you cannot compete on talent, you have no business. The challenge for leaders is to find how to attract and keey top talents.

  27. etnapowers
    June 3, 2014

    The evaluation of Wall Street of the companies Linear Tech, Maxim, that you cited, will be better in the near future I guess, because  are doing very well in the hard and extremely competitive semiconductor market.

  28. etnapowers
    June 3, 2014

    Yes Victor, I fully agree with you, expecially for what you said about good engineers from TI, Infineon, that I have been lucky to know during some business trips.

  29. fasmicro
    June 4, 2014

    >> The evaluation of Wall Street of the companies Linear Tech, Maxim, that you cited, will be better in the near future I guess, because  are doing very well in the hard and extremely competitive semiconductor market

    One hopes so as the semiconductor market has not been getting good valuations while the web firms have despite the foundation upon which the web runs depending on the products of the semiconductor industry.

  30. fasmicro
    June 4, 2014

    While U.S. still commands so much knowledge base in the circut level, I am worried that in coming years, we will have challenges in the production side since most of the productions are outsourced to Asia where they develop capability and experience on the best practices.

  31. etnapowers
    June 6, 2014

    The big semiconductor companies have the strenght to survive to the instability of the market because they have a big range of products and I think that this is important as much as the evaluation at the present moment.

  32. goafrit2
    July 3, 2014

    >> The big semiconductor companies have the strenght to survive to the instability of the market because they have a big range of products

    Besides the diversified product offerings, hardware is not that easy to change.If you make a product today, say a phone, you invest in boards, etc. If you change one component, you need to redo everything. Unlike software which a night patch can fix things, hardware is not that easy. You are looking at 18 months to get back to business.

  33. goafrit2
    July 3, 2014

    >> The evaluation of Wall Street of the companies Linear Tech, Maxim, that you cited, will be better in the near future I guess, because  are doing very well in the hard and extremely competitive semiconductor market.

    You need to give a reason why. They have great quarterly earnings and yet nothing is working in the top evaluations. What will change that? I think our challenge is how they look at the growth trajectory of the analog industry.

  34. etnapowers
    July 7, 2014

    @goafrit2: that's a weakeness of hardware business and a strength of the software business. As the opposite, if a company builds a component that is innovative and impacts the market very strong, the return on investment will be immediately huge , for software it may take more time to have a similar return.

  35. goafrit2
    July 9, 2014

    >>  As the opposite, if a company builds a component that is innovative and impacts the market very strong, the return on investment will be immediately huge , for software it may take more time to have a similar return.

    That could be true especially in components. ADI has held the top position in converters becuase most of the original products relied on these components. Also, another point is that hardware barrier is higher because the person buying from you does not have the risk margin where it can try one API and if does not work, it will try another in the next hour. Hardware takes planning.

  36. etnapowers
    August 4, 2014

     “Hardware takes planning.” 

    @goafrit2: Agreed, high gain margin means higher risk , it's a unwritten law of the market.
  37. fasmicro
    September 10, 2014

    >> Agreed, high gain margin means higher risk , it's a unwritten law of the market.

    High profit margin to be more precise. That is what they mean by innovation. It is risky but the reward is always great.

  38. etnapowers
    September 11, 2014

    Innovation is the motor of business, it's really the key factor that represents the difference between a consolidated business having low profit margin and high volumes and a challenging business that  promises high volume and moreover an high profit, because the company which hits the market for first can hold the 100% of market share. The market leader can dictate the price and this is the reason for why the business based on innovation is very profitable.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.