Pregnancy tests used to be pretty simple sticks to pee on, but the move to digital versions has turned them into tiny computers, almost as powerful as the original IBM PC. Fascinated by the digital age of pregnancy tests, Twitter users Telephone and xtoff recently took apart examples from Walmart and Clearblue to show what’s really going on inside.
Each test, which costs less than $ 5, includes a processor, RAM, a coin cell battery, and a tiny LCD screen to display the result. The processor is an 8-bit Holtek microcontroller with 64 bytes of RAM, capable of running at 4 or 8 MHz depending on the battery configuration. It may sound very simple, but the chip is surprisingly complex.
“You might think it is very limited because it only has 64 bytes of RAM, but it actually uses a pipelined architecture to run at 1 instruction per cycle, which gives it pretty good performance for a 4 MHz processor.” explains Fung on the fun Twitter thread.
Fung suggests that the device “is probably faster at processing numbers and basic I / O than the CPU used in the original IBM PC.” The original IBM PC was based on the Intel 8088 microprocessor, an 8-bit chip running at 5 MHz. The difference is that this is a pregnancy test that you pee on and then throw away.
You might assume that adding an LCD screen and a processor to digitize this pregnancy test would improve the accuracy or modernize the test’s performance, but this is certainly not the case. This digital pregnancy test still includes a paper strip to measure the chemical reaction you create when you urinate on the strip.
The paper strip inside acts like a wick, so when wet, it activates the battery and turns on the device. The device then uses three LEDs and two photosensors to read the lines on the paper strip, which would normally provide the result of a pregnancy test. The processor, RAM, battery, and LCD literally exist to read the paper strip and improve the legibility of the test, displaying “pregnant” or “not pregnant” instead of the usual lines that can be difficult to read.
Unfortunately, the chip inside is not programmable, so people cannot Doom use these digital pregnancy tests. I would recommend reading full foone Twitter thread as this is an exciting analysis. While these digital pregnancy tests seem like an incredible waste of plastic and electronics, I’m just grateful that humanity has moved away from squirting frogs with urine to check pregnancy.
