When you see a project with a digital display these days, you’ll be forgiven for assuming that there’s some kind of microcontroller behind the scenes. And while that’s often the easiest way to get a project from idea to completion, it’s rarely the most interesting way.
This digital pH meter is a great example of that “no-code” design philosophy. According to [chris], the main use for this meter will be to measure soil pH in his garden, and the reason for eschewing a microcontroller was more or less for the challenge. And quite a challenge it was. Understanding the concept of pH isn’t always easy, and many a budding chemist has fallen victim to its perils. Actually measuring pH isn’t much easier, with the need to account for a lot of variables while measuring small voltages. Adding to the challenge was the fact that pretty much every skill on display here — from using KiCad to SMD soldering — was the first time [chris] had tackled them.
To amplify the voltage from the off-the-shelf pH probe, [chris] chose an LMV358A, a high-impedance FET-input version of the venerable LM358 op-amp, so as not to load down the probe. A negative temperature coefficient (NTC) resistor in the feedback path provides temperature compensation. He also designed a split power supply to provide positive and negative rails from a single 9-volt battery. The 3.5-digit LCD display is driven by an ICL7106 integrated A/D converter and BCD driver chip. Everything went into a nice-looking plastic enclosure that’s very suitable for a portable instrument.
As of this writing, the Op-Amp Challenge has officially wrapped, and there’s a slew of last-minute entries we need to go through. Check out the competition and stay tuned to find out who the judges pick for op-amp design glory!
The black blobs on cheap PCBs haunt those of us with a habit of taking things apart when they fail. There’s no part number to look up, no pinout to probe, and if magic smoke is released from the epoxy-buried silicon, the entire PCB is toast. That’s why it matters that [Throbscottle] shared his journey of repairing a vintage multimeter whose epoxy-covered single-chip-multimeter ICL7106 heart developed an internal reference fault. When a multimeter’s internal voltage reference goes, the meter naturally becomes useless. Cheaper multimeters, we bin, but this one arguably was worth reviving.
[Throbscottle] doesn’t just show what he accomplished, he also demonstrates exactly how he went through the process, in a way that we can learn to repeat it if ever needed. Instructions on removing the epoxy coating, isolating IC pins from shorting to newly uncovered tracks, matching pinouts between the COB (Chip On Board, the epoxy-covered silicon) and the QFP packages, carefully attaching wires to the board from the QFP’s legs, then checking the connections – he went out of his way to make the trick of this repair accessible to us. The Instructables UI doesn’t make it obvious, but there’s a large number of high-quality pictures for each step, too.
The multimeter measures once again and is back in [Throbscottle]’s arsenal. He’s got a prolific history of sharing his methods with hackers – as far back as 2011, we’ve covered his guide on reverse-engineering PCBs, a skillset that no doubt made this repair possible. This hack, in turn proves to us that, even when facing the void of an epoxy blob, we have a shot at repairing the thing. If you wonder why these black blobs plague all the cheap devices, here’s an intro.
We thank [electronoob] for sharing this with us!
If we had to make a guess at the single piece of electronic bench equipment owned by the highest proportion of Hackaday readers, it would not be a budget oscilloscope from Rigol, nor would it be a popular portable soldering iron like the TS100. Instead we’re guessing that it’s a multimeter, and not even the most accomplished one.
The DT830 is a genericised Chinese-manufactured 3.5 digit digital multimeter that can be had for an astonishingly low price. Less than a decent hamburger gets you an instantly recognisable plastic case with a chunky rotary range selector switch, and maybe a socket for some kind of transistor or component tester. Make sure that there is a 9 volt battery installed, plug in the pair of test leads, and you’re in business for almost any day-to-day electrical or electronic measurement. They’ve been available in one form or another for decades and have been the subject of innumerable give-aways and loss-leader offers, so it’s a reasonsble guess that you’ll have one somewhere. I have three as far as I know, they make great on-the-go instruments and have proved themselves surprisingly reliable for what they are. Continue reading “In Praise Of The DT830, The Phenomenal Instrument You Probably Don’t Recognise For What It Is”