Teardown Tuesday: Digital pH Meter

January 23, 2018 by Nick Davis

In this teardown, we open up a battery-operated digital pH meter, from HealthyWiser.

In this teardown, we open up a battery-operated digital pH meter from HealthyWiser.

This portable—pocket-sized, really—and battery-operated Digital pH Meter from HealthyWiser looks to be a rather simple and easy-to-use device based on its included operating instructions and the fact that it has only two buttons: one for ON/OFF functionality and the other for calibration purposes. HealthyWiser also provides the necessary pH powder packets—a total of six packets—which are used for calibrating the meter. The following figure shows everything included with this meter.


What's included with the meter: the meter itself, operating instructions, and calibration powder packets.

Taking a Closer Look at the Meter...

The meter's electronics are protected with a sturdy plastic enclosure while the pH sensing electrodes are safeguarded with a removable cap, as can be seen in the image below.


A removable cap protects the sensing electrodes.


The end opposite of the electrodes is an easily-removable battery case, and when the battery case is taken out we can peek down inside the enclosure to see the PCB (see the following image).


The PCB can be seen inside the enclosure.

Removing the PCB from the Enclosure

As can be seen in the above image, the enclosure looks to be an extruded (i.e., single-piece) enclosure as opposed to two or more plastic pieces welded together. If the enclosure is indeed an extruded part, this tells me that I should be able to simply pull out the PCB, saving me the time and effort of cutting it open.

So, using my handy needle-nose pliers, I clamped on to the PCB and slowly pulled until the PCB was free from the enclosure. Success! And because it was evident that the PCB had not been damaged during the removal process, I was not at all surprised to see the PCB power up after reconnecting the battery case (see the image below).


The PCB is still functional after pulling it out of the enclosure.

Scrutinizing the PCB

This PCB is a relatively simple and straightforward design, but, unfortunately, the brains of the meter are encased in epoxy, which keeps the "secret sauce" a secret. Well, we'll see if we can get past this epoxy... more on this later.


PCB Top Side

The figure below identifies the major components of this pH meter.


The components located on the PCB's top side.


As can be observed, this PCB design is rather simple. The only so-called major electrical component that can be identified via a part number is the Schottky diode; its part marking is 65B4. It's also worth mentioning that the PCB's copper trace finish looks to be of type ENIG (Electroless Nickel Immersion Gold), at least for the battery tabs.

The LCD's backlighting is accomplished using a single green LED, of which is located underneath the white paper-like material.


The LCD's backlighting is achieved using a single green LED.


The LCD's green backlighting (side view) is clearly seen in the dark.


PCB Bottom Side

The PCB's bottom side is extremely simple: it consists of a single unknown (i.e., no part markings) IC, the internal electrode's PCB connection, and two battery tabs.


The PCB's bottom side is very simple.

Attempting to Unlock the Epoxy

With the goal of identifying the IC that's encased in the black epoxy, I used the same approach from one of my previous teardowns when I penetrated an IP68-rated device, which was a solar-powered floating water fountain.

This approach included boiling the PCB in water. But after 15 minutes of the boiling treatment for the pH reader, the epoxy still prevented me from learning its secrets. Rats!

Not being ready to give up just yet, I decided to apply more heat using my heat gun. Success!... well, sort of.

While the high heat from the heat gun allowed me to slowly cut away the epoxy, I was unable, unfortunately, to distinguish between the epoxy and the IC's package, which resulted in me cutting away the IC's package along with the epoxy. Amazingly, however, I was able to salvage the guts of the IC. The image below shows the tiny IC that used to live in the IC package.

So even though I was successful in removing the epoxy, it still prevented me from learning the IC's part number and other pertinent information.


Removing the epoxy still prevented me from learning the details of the epoxy-encased IC.


This portable and battery-operated Digital pH Meter uses a rather simple PCB to perform its functions. And while the PCB's design uses only three ICs, the important IC—that is, the brains of the device—is well-protected in epoxy.


Next Teardown: Vehicle Code Reader and OBD-II Scanner

  • Gyurkan Mehmed January 24, 2018

    Do you think it will work if one solder external glass pH electrode terminals to the pads on the PCB?

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      Phil-S January 26, 2018
      Can't see why not. Just use high (very) impedance rules, keep the electrode coax failr short, centre conductor clear of the board and coax braid to ground. If the existing centre pin does connect straight to one of the "unknown" IC pins, then job done. Connections to high impedance op amps are often direct to the IC pin with the pin "floating above the board. You could try a mV source direct to the pad with the electrode lead detached and see what happens. pH 7 is 0-mV and pH 14 and 0 are approximately 60-mV per pH unit either side of 0-mV. The bipolar output of the electrode is offset at the op amp to give an approximate 0 to 840-mV output with a bit of gain as required
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    Phil-S January 26, 2018

    Being close to the electrode centre pin, I suspect that the unknown IC on the underside is going to be an op amp, probably a FET type. Your blob IC is going to take care of the fairly complex calibration, most likely an MCU of some sort or a custom chip

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