The Real Engineering

So obviously my trip here hasn’t been to be just a tourist, and there has been some transfer of engineering skills to me through my technical lessons in the afternoons.

Generally our technical lessons are structured as a one hour lecture followed by a 2-3 hour lab everyday. The lectures are mostly just a way of discussing as a class the different machines and problems we will discover in the developing world. Generally, because we can’t get into fixing manufacturing specific parts or reprogramming microprocessors, most of the refurbishing we do is done through training/retraining the staff and fixing power supplies.

It turns out that because the operating staff doesn’t necessarily need to be fluent in English, German, or whatever language the piece of equipment came in on, oftentimes the staff may be operating a piece of machinery incorrectly. Yikes. Imagine having someone place you on a respirator works, without being able to read any of the dials or manuals correctly. Actually, Larry (our instructor) says we will be extremely lucky if we can find a manual. “User Error” turns out to be the most frequent type of problem that prevents the utilization of a particular piece of equipment. I’ve heard stories of previous participants finding stockrooms, full of perfectly good equipment, collecting dust because no one knew how to work it.

But assuming someone does now how to operate it, the second most prevalent problem is with the power supply. The power supply is what turns the AC electricity (110V 60Hz in the US, 220 50Hz in Tanzania) into a smaller DC supply (anywhere from 1-12 V). The smart reader may have already predicted a problem; different power supplies in either country means different plugs, and things don’t always fit. So one of the first practical labs we had was to build a simple extension chord/plug converter. Turns out to be really simple; you just need the two different types of sockets, take a power chord, do some wiring, and it could be done in under 20 minutes. But we are still learning, so it took us like 5x as long. The biggest part was making it look pretty, Larry always wants all of the work we do to look good enough so that someone else would come along and think it was done by a professional.

Anywho, the most common technical problem we will probably have to deal with is the actual power supply within the machine. The function of the internal power regulator is to convert the AC to DC, and reduce/regulate the voltage. Theoretically a relatively simple circuit, but practically a place where a lot of components can easily break.

We built one today that converted a 29 V_rms input into a 39.9 V DC signal. Basically its just a diode bridge with a capacitor in parallel with the load resistor. If people recall their electronics classes, the diode bridge is shaped like a resistive wheatstone bridge, and you put the resistor or load in between the two parallel lines. What the diodes do is basically take the negative voltage parts of the input signal and make them positive. The capacitor then discharges in between positive peaks; in English, it smooths it out so that the the oscillating sine curve you see with the AC source ends up being a constant DC source that the medical equipment can actually use. Below is a diagram I whipped up in LTSpice last night, I tried uploading an actual picture of the finished product, but it was gonna take about 18 hours to upload. Deceptively simple looking.

Circuit we built in class

In other news, we had an invasion of grasshoppers into our home a few nights ago. Everywhere I looked, there would be like 3 grasshoppers on each wall. I woke up this morning and there were three hanging on my mosquito net. Haven’t found any good reason why they decided to do that….Also, our family watches this Spanish telenovella every other night called Maruchui, dubbed in English, and its hilarious/addicting. I think it may replace my 30 Rock addiction for the summer.

Finally, thanks to everyone for the birthday wishes. It made my day (despite the grasshopper invasion).



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2 responses to “The Real Engineering

  1. EWH Parent

    Thanks for creating this blog so we can hear about your experiences this summer. I am the mother of another student in your group.

  2. Sandeep Paruchuri

    Love it- the electronics (what you said made complete sense, even without the English translation) and I can totally relate to the false simplicity of the power conversion process. Having said that, I am going to give you hell for watching a telenova. Just fair warning.

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