Digital Pregnancy Tests Use LEDs To Read Between The Lines

[Foone] saw a tweet a few weeks ago alleging that digital pregnancy tests are a rip-off. Regular, cheap tests have an absorbent strip running the length of the plastic, with one end exposed for collecting urine. A few excruciating minutes later, a little plastic window in the middle will show one line, two lines, or a plus or minus sign depending on the presence of human chorionic gonadotropin (HCG) in the urine.

As it turns out, at least two digital tests out there are the exact same thing, but with more steps. Instead of a window, they include circuitry that interprets the lines and publishes the result to a little screen in plain English. It can even tell you if you’re doing it wrong by flashing a little RTFM icon.

[Foone]’s teardown reveals a CR1616 coin cell, an 8-bit microcontroller, and a little phototransistor setup that shines LEDs on the strip and reads the incoming light. Unfortunately, the micro is the mask ROM version, so [Foone] can’t reprogram it to run Doom.

The original tweet’s author is probably not alone in assuming that digital tests are supposed to be more accurate somehow. We think the accuracy claim is more about removing the frazzled and/or incompetent human variable from the equation. If the test interprets the results for you, then there’s no mistaking the results, which is technically a higher degree of accuracy. But if you’re in doubt, you get a test from a doctor.

There’s been some discussion about the e-waste aspect of these all these tests — that it’s a shame to produce a microcontroller just to pee on it and throw it away. Sure, you could look at it that way, but unlike a lot of e-waste, these are tools. It’s unfortunate that this is the industry’s idea of higher accuracy, but what should we expect? It’s just testing for the presence of a hormone in urine. Interpreting the results is up to the viewer. We should probably be astounded that they got the cost down to two for $7.

Many people choose to wait a while to start spreading the news. With a Bluetooth-enabled pregnancy test, everyone can find out together.

Thanks for the tip, [Jay]!

27 thoughts on “Digital Pregnancy Tests Use LEDs To Read Between The Lines

  1. Too many digital gadgets are “Garbage In, Gospel Out”.

    You can take your BBT with a $10 thermometer (which lasts for years), and chart you temps to prove you’re pregnant (or not).

    1. Trending BBT over a period of time can give an indication of ovulation but that does not necesarily relate to proof of pregnancy. BBT can be influenced by many other factors.

      A hormone level test is somewhat reliable – though not infallible.

      the need for a micro and LCD to tell you what the lines already clearly do is just a marketing ploy- so while it s a tool the extra bits are just pure waste.

      1. Well, it seems it is not so easy… Here is an study to find if the strip and cassette formats are so precise, and the result is really surprising: “Volunteers disagreed with study co-ordinator reading of test results in 30 and 40% of cases for the cassette and strip test results, respectively, compared with < 3% when using midstream digital or easy-use visual tests."

        https://www.tandfonline.com/doi/abs/10.1517/17530059.2013.830103

  2. or make the pee strip replaceable so instead of throwing out the electronics after each test at least they stand a chance of being used a few times……but lets face it this is pure idiocy at play, it’s just not hard looking at the strip and discerning the absence or presence of the lines. Humans, get a grip and shun this stupidity.

    1. For those bashing the “unnecesary electronics” drum or “people are stupid if they can’t read a pregnancy test”. Research has shown that a traditional pregnancy test can be missinterpreted by 1 in 4 people. https://pubmed.ncbi.nlm.nih.gov/18457603/. So this is actually solving a real-world problem and it is not for you to call out people who need the extra clarity for what is a world altering propostion of having a child.

      While I agree on the electronic waste issue, the problem comes when people just do not believe the results and will buy another to make sure that it agrees with the first, I don’t think that can be solved easily.

      1. actually no, what makes you think that this electronic garbage…yep that’s right, it is one step away from garbage… is all that effective? Certainly reading your message implies that all of the sudden the problem of understanding is gone. Perhaps they just had poor eyesight or some other incapacitating condition. Aaand, the other unspoken implication is that they had no other way of solving this, something like ask their partner or friend neighbour etc so in addition of creating an ewaste catastrophe this product along with its other devices crap is just emeshing further isolation and breakdown of community. It is also costing more so there is that. Far from a sollution and yes crap sollutions should and must be as you say bashed because the planet has no mouth and no legal system to defend it. If you think this is such a problem then why not creat an smartphone app that once pointed on such a strip can in multitude of languages and voice included tell the person what that result means….. perhaps that could be a way forward for those that need the assistance. Then of course one could return to the pharmacy and I’m sure the staff could sort it out at no additional expense and finally a doctor because if it is indeed not looking right, chances are a doc visit is high on your agenda.

        1. Completely agree. And *maybe*, but the 1 in 4 stat sounds like BS, at least as stated. From the linked article abstract the issue sounds to be more with some tests not having good detection at low levels of hCG – something an electronic spin on using phototransistors isn’t all that likely to be better at – unless it is using a particularly good strip, and then you’re still just as well off with a good strip and no electronics. Get off my grass.

      2. > Research has shown that a traditional pregnancy test can be misinterpreted by 1 in 4 people.

        This can be solvable with better UI, not throwing more electronics at the problem. If the user is unsure about the results, I bet the pharmacy were the test was bought have someone that can interpret that.

  3. I played with a similar one a couple of years ago. It had an epoxy blob instead of Holtek chip, two LR44 batteries instead of CR2016, but it had an identical LCD. The interesting thing is that the display has additional segments for “1-2”, “2-3” and “3+”, so probably at some point someone envisioned telling how long into the pregnancy one is.

  4. I’m not much into this pregnancy thing, but it seems that “industry” has yet found a way to extract more money from the ignorant masses. Regular prices seem to be around 30ct for the normal version vs USD 4 for this.

    Getting a little PCB with uC and display is always interestig to hackers, but with masked ROM it suddenly looses most of it’s appeal. The LCD seems to have a few fixed segments instead of dot matrix, and that would be the last of it.

  5. Having a consistent threshold level for the line reading certainly should improve accuracy. After all, the lines are very analog in function and depending on HCG levels can be faint or bright, and probably also depend on the spectrum of light used to view them. Presumably the manufacturers have calibrated the threshold for best accuracy.

  6. I’ve played with a version of this that also indicated the amount of weeks of pregnancy which is probably harder to read from an analog stick (I think it relates to a crossover of two hormones; it had a feeding strip going to a kind of tablet with 4 LEDs shining on it): No IC, just an epoxy blob; Salvaged the battery, LEDs and display and connected the display with a couple of resistor dividers (0.7V AC from the top of my head) to an ESP8266 as a gimmick for brand-new “grandpa”.
    Yes, it’s e-waste, but it also interesting to see all the things you can automate (and the price of a tester is nothing compared to the price of raising a kid).

  7. Well, there are certainly more useless pregnancy tests out there. A friend sent me a picture where the instructions on the box and on a paper insert had opposite descriptions of what was a positive and what was a negative result.

    So the test fails to collapse the probability waveform and you end up with a Schrödinger’s baby I guess?

    Anyway I kept the photo and it’s now my standard image used when I need to discuss the importance of good documentation.

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