Analog Sensors & Controllers: Should We Repair or Replace?

I like keeping good old stuff running as long as possible. One of my hobbies is to keep my 1988 Bronco II running; currently nearing the 400,000 mile mark. Over the years I have had to do some adjustments to the vehicle, especially since parts are getting harder to obtain. A few of these projects follow — all involving some type of electronic work. (And yes, there have been the mechanical fixes such as new heads on the engine at 310,000 miles and a couple of clutches.)

One of the recent items (which was not that fancy) was the rewiring of the dash panel. I got tired of having to replace a light bulb in the instrument cluster since it is a labor intensive task to pull the instrument panel to get to the light bulb. So, I decided to replace the light bulbs with LEDs. Fortunately, one can find an LED version of the main bulb type used in the dash lighting on eBay. And, since the entire dash wiring used a flex circuit that was getting a bit brittle after 20+ years, I decided to use as new set of connectors instead of the old ones so that the stress of removing the old connector from the flex circuit would keep the remaining copper traces in place.

Another project was a necessity as I ended up rewiring the headlight current path away from the steering column. In the original configuration, the headlight wiring ran through the steering column into the high-low beam switch. However, after years of operation I started to notice a warm plastic smell every time the headlights were on.

A bit of touching on the plastic that covered the steering column found the hot spot over the high-low beam switch module within. The solution was to wire up a solid-state relay box that used the existing switch and wire harness just to produce a control signal. Then pull power from the battery directly to drive the high and low beams. Figure 1 shows the details.

Figure 1

This simple circuit has been working for the last 13+ years.

This simple circuit has been working for the last 13+ years.

The last repair job ended up being a very simple fix that could have saved a lot of money. The 4×4 switching system decided to stop working one year. After some discussion with a shop and a diagnostic process, we found that the problem was in the transfer case where there was, as phrased, the “position sensor.”

This unit is considered non-serviceable and costs around $400 for the part. Now, as an engineer, I had to figure out how this “position sensor” functioned. After replacing the part and cleaning up the old one, I noticed some screws on the unit with special heads. Pulling out my security screw bit set and pulling the screws, I exposed the “position sensor” circuit.

To my surprise the circuit was essentially a circular board with circular traces and spring contacts to engage with the traces. The traces were dirty after the years of use. A bit of cleaning and the unit is as good as new — waiting to swap out the “new” unit when it decides to “fail.” If I had known how simplistic the “sensor position” circuit was, I could have saved some money.

Does anyone else have stories as to over-priced sensor circuits? How about some simple electronic repair on cars? Or am I the only electronics person who at times has greasy hands?

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24 comments on “Analog Sensors & Controllers: Should We Repair or Replace?

  1. David Maciel Silva
    January 3, 2014

    Hello Derek,

    Definitely you are not the one to carry out repairs, rs, the issue is the time to complete tasks in my point of view.

    I've done some repairs on my old vehicle, the power window system from time to time the steel cord that caused the glass to rise and closed almost burst, then had to disassemble the whole door of the vehicle and perform the replacement cord action.

    The latest repair was in a rice cooker my wife, who just do not care anymore, when you open the pot was discovered that a thermal fuse, replace it after the pan is new and I went back to eating rice (rsrsrsrs).

    And you readers have had trouble with simple correction in home appliances (whether or not that impacted on their food, I hope my wife not read it) rsrsr!

  2. Davidled
    January 3, 2014

    Cab inside Pot of rice cooker is too old and getting rust, which is harmful for body, as My wife said.

    When I try to replace this as ordering part which is a little bit expensive, she is so angry for fixing electronic device. I was told that buying it is cheaper than fixing or repairing it. She would like to get a new Rice Cooker.

  3. David Maciel Silva
    January 3, 2014

    In my specific case it was only the thermal fuse with a cost less than 1 dollar.

    I believe that compensates pack yes once the pot costs almost 120 dollares the best buy.;jsessionid=5E183E170CE959FDBA2E75FE3F468499.bbolsp-app02-140?id=1219066877486&skuId=1884156&st=rice%20cooker&cp=1&lp=3

  4. Netcrawl
    January 4, 2014

    Replacing an old parts with new one could be expensive, sometimes its much better to acquire new one than replace broken parts, ordering and finding spareparts is not an easy task. The problem is here what if that parts is not available in the market, or you need to go to other places just to acquire it. In my place we do have limited supply here, we need to go to big cities just to get it and it will cost you a lot.

    I think it depends on situations, if its small and still fixable, I'll fix it but if requires some major overhaul let's say you need to replace CRT for you're old stuff, I think buying new one could be a good idea. It could save you lot of money and time. 

  5. Netcrawl
    January 4, 2014

    @Maciel thanks for the share, buying or ordering online could be good but it depends on product availability and location, I'm still prefer the traditional one where I go to this hardware place and pick what I really need, you can even have soem quick chat with sales rep or technical guys.

  6. Victor Lorenzo
    January 5, 2014

    I know someone very skilled at repairing almost everything, my father. He has been repairing, reconstructing, and modifying ('hacking') from radios, tools, furnitures, recorders, to… even making his own trailer and modifying the carburator and the injection system, all the electric part and more from his 1952 Crestline Victoria Ford. Now he is too old and too ill to drive it so the painting and brakes are failing. I've tried to learn from him and I've known other very skilled guys, but he is still by far the best hacker I know.

  7. Victor Lorenzo
    January 5, 2014

    @Derek, “Or am I the only electronics person who at times has greasy hands? ” No, you're not alone in that small world.

    A couple of years ago one sales person and an applications engineer from a big components distributor came to visit me at my previous occupation. I called them for negociating some component prices. They didn't personaly know me in advance, only by phone, and from their faces it was clear to me they thought I was joking with them. I came directly to the reception from the production plant where I was fixing a bug in a machine I was designing, programming and constructing with a colleage at that time.

    One of them admitted later that they were more used to see design engineers and projects managers wearing business suits, not greasy hands and face.

  8. samicksha
    January 6, 2014

    @Derek, Car Meters seems good example when referring to Analog sensors, but Digital Sensor has taken over to analog at most of the places and one of the reasons i feel is data transmission which is not sensitive to cable length, cable resistance or impedance when accounting on Digital Sensors, Humidity and related corrosion are no longer an issue.

  9. Davidled
    January 6, 2014

    Today, digital sensor takes over analog sensor in most area. Some customer preferred analog fuel gauge instead of digital fuel gauge.  I think that analog fuel gauge using mechanical gauge inside fuel tank is more precisely than digital using A/D which providing the error of actual value.

  10. Netcrawl
    January 6, 2014

    @samicksha you're right there's an increasing requirements for a much higher level of accuracy and fast transmission, digital sensors are key in reducing fuel consumption, transmission application and safety.     

  11. Netcrawl
    January 6, 2014

    @Victor that was great! thanks for that, my uncle is a self-taught electronics and automotive specialist, he knows everything, the best things about my uncle is he doesn't have any formal education in electronics and automotive, he acquired his knowledge through reading technical books, spend his time cracking in his labs, trying to solve some problems. He also make his own stuff, modifying his own injection system and transmission systems. He has this passion for fixing and modifying stuffs.   

  12. D Feucht
    January 6, 2014

    One of the questions not asked very often during the engineering design process is when the end of life of a product under design will be reached. I too like to keep old equipment running for as long as possible, but I went too far with my 1988 Chrysler Caravan and sunk thousands of dollars into its repair at a time that was near the end of its life. The expenditure was not worth it.

    When the maintenance expense (also in time) of worn-out devices hits the steep knee of the curve, it is time to salvage it for what good parts remain. The knee can go by rather quickly at times, however! Discerning when a product has reached its economically viable end of life is another skill for us engineers to develop.

  13. samicksha
    January 7, 2014

    I agree with you completely Netcrawl, just add on, Digital sensors communicate directly with a microcontroller. However, analog sensors do provide analog outputs which one must firstly digitize (AtoD or comparators) it to sense the level. Besides, analog sensors are generally more accurate.

  14. etnapowers
    January 8, 2014

    @Victor: this kind of experience is really precious, and the ability to self repair the hardware is really important. This skill can help an engineer for example  during a mission at a customer facility: eventually some components of the application or testing board might fail or have malfunction, and the skill of making by himself the electronic repairs can help very much an engineer to solve many issues.

  15. Victor Lorenzo
    January 8, 2014

    @etnapowers, I agree with you, “the skill of making by himself the electronic repairs can help very much an engineer to solve many issues “. I feel myself very lucky since I've had the opportunity to learn from and work with several colleagues with that n'th sense required for knowing what's wrong, sometimes even only from a short problem description.


  16. RedDerek
    January 11, 2014

    I agree that Digital is taking over the Analog sensors. But still there is the coversion from analog to digital. For cars like mine, speed is not an issue in the case of the 4×4 sensor – it is either on or off. Distance was irrelevant. Problem is that the on/off condition was sensed as that “no mans zone”, that place between a TTL low and a TTL high. A bit of cleaning got things working nicely.

    It was just the cost I could have saved. I am a tinkerer and enjoy this type of messing around as a break in my usual constant design thought (weeknights and weekends, it never seems to stop! 😉 )

  17. RedDerek
    January 11, 2014

    @DFeucht – . I too like to keep old equipment running for as long as possible, but I went too far with my…

    Yes, there has to be a point where the cost of maintaining an old vehicle is just not worth the cost. Then again, if one had a Model-T, it could be worth the effort.

    I have not reached that point with this car. I gather about $500 / year in maintence cost is not a bad deal – that includes down to oil changes. Some years it is more, extra $10 in brake parts (I have that unconditional guarantee from PepBoys to replace my worn pads and shoes.) In the 25 years, it has been two sets of shocks (one free due to the warranty after 15 years), countless brake pads and shoes, two clutches, one set of heads, and a fuel pump and regulator. Not bad for these being the only major items. I'll keep the old beast running…

  18. anne121
    January 13, 2014

    I had to collect details on analog model and its uses in digital circuits. I liked making note of the use of digital sensors and their use in micro controllers. This article was very well written.

  19. yalanand
    January 31, 2014

    Replacing an old parts with new one could be expensive, sometimes its much better to acquire new one than replace broken parts, ordering and finding spareparts is not an easy task. 

    @Netcrawl, I totally agree with you. Its pretty hard to find the old parts online. Sometimes we are forced to buy the newer version of the old product becuase sometimes the old product are no longer available in the market.

  20. yalanand
    January 31, 2014

    Some customer preferred analog fuel gauge instead of digital fuel gauge.

    @DaeJ, Some customers prefer analog fuel gauge because they get ability to take a quick glance at the guage and comprehend what is happening. True A/D conversion introduces errors but still Digital gives more precise reading compared to Analog gauge.

  21. yalanand
    January 31, 2014

     there has to be a point where the cost of maintaining an old vehicle is just not worth the cost.

    @RedDerek, agreed. But some people find it very satisfying to maintain old vehicle in good condition. They dont worry about the cost factor but they are more worried about how to maintain the vehicle in good condition. I think non-availability of old vehicle component is major factor which increases the cost of maintainance.

  22. yalanand
    January 31, 2014

    Digital sensors communicate directly with a microcontroller.

    @samicksha, good point. The main advantage of Digital sensors is we can easily process the data gathered but in Analog sensors its very hard to process the data. That is the reason many people prefer Digital sensors because they can easily process the data.

  23. samicksha
    February 1, 2014

    Other than this analog sensors are subject to A/D conversion noise and errors, whereas this issue gets mitigated in Digital.

  24. etnapowers
    February 3, 2014

    Victor, you are right in considering yourself lucky, because the mentoring at work with colleagues expert in problem solving is really the faster way to become an engineer with great know how and problem solving skills. What you learn by a mentor on the job place you cannot learn from any manual.

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