While for some of us it’s a distant memory, every serious electronics hobbyist must at some point make the leap from working with through-hole components to Surface Mount Devices (SMD). At first glance, the diminutive components can be quite intimidating — how can you possibly work with parts that are literally smaller than a grain of rice? But of course, like anything else, with practice comes proficiency.
It’s at this silicon precipice that [Larry Bank] recently found himself. While better known on these pages for his software exploits, he recently decided to add SMD electronics to his repertoire by designing and assembling a pocket-sized CO2 monitor. While the monitor itself is a neat gadget that would be worthy of these pages on its own, what’s really compelling about this write-up is how it documents the journey from SMD skeptic to convert in a very personal way.
At first, [Larry] admits to being put off by projects using SMD parts, assuming (not unreasonably) that it would require a significant investment in time and money. But eventually he realized that he could start small and work his way up; for less than $100 USD he was able to pick up both a hot air rework station and a hotplate, which is more than enough to get started with a wide range of SMD components. He experimented with using solder stencils, but even there, ultimately found them to be an unnecessary expense for many projects.
While the bulk of the page details the process of assembling the board, [Larry] does provide some technical details on the device itself. It’s powered by the incredibly cheap CH32V003 microcontroller — they cost him less than twenty cents each for fifty of the things — paired with the ubiquitous 128×64 SSD1306 OLED, TP4057 charge controller, and a SCD40 CO2 sensor.
Whether you want to build your own portable CO2 sensor (which judging from the video below, is quite nice), or you’re just looking for some tips on how to leave those through-hole parts in the past, [Larry] has you covered. We’re particularly eager to see more of his work with the CH32V003, which is quickly becoming a must-have in the modern hardware hacker’s arsenal.
The pandemic brought with it a need to maintain adequate ventilation in enclosed spaces, and thus, there’s been considerable interest in inexpensive C02 monitors. Unfortunately, there are unscrupulous actors out there that have seen this as a chance to make a quick profit.
Recently [bigclivedotcom] got one such low-cost CO2 sensor on his bench for a teardown, and confirms that it’s a fake. But in doing so he reveals a fascinating story of design decisions good and bad, from something which could almost have been a useful product.
Behind the slick color display is a PCB with an unidentified microcontroller, power supply circuitry, a DHT11 environmental sensor, and a further small module which purports to be the CO2 sensor. He quickly demonstrates with a SodaStream that it doesn’t respond to CO2 at all, and through further tests is able to identify it as an alcohol sensor.
Beyond the alcohol sensor he analyses the PSU circuitry. It has a place for a battery protection chip but it’s not fitted, and an error in the regulator circuitry leads to a slow drain of the unprotected cell. Most oddly there’s an entire 5 volt switching regulator circuit that’s fitted but unused, being in place to support a missing infra-red module. Finally the screen is an application-specific LCD part.
It’s clear some effort went in to the design of this unit, and we can’t help wondering whether it could have started life as a design for a higher-spec genuine unit. But as [Clive] says, it’s a party detector, and of little more use than as a project case and battery.
While on the search for an alternative to directly buying the fairly expensive MH-Z19 CO2 sensor, [spezifisch] came across a ‘BreeRainz’ branded gadget (also found under other brands) that claimed to use an NDIR (Non-Dispersive Infrared) sensor for measuring CO2 levels, while costing only €25. This type of sensor allows for CO2 levels to be measured directly, rather than inferred, making them significantly more precise.
After cracking the gadget open (literally, due to the hidden screws), the CO2 sensor is clearly visible. While superficially identical to an MH-Z19, the NDIR sensor is actually called ‘HC8’, is produced by 广州海谷电子科技有限公司 (Guangzhou Haigu Electronic Technology Co., Ltd.). While being pin-compatible with the MH-Z19, its UART protocol is not the same. Fortunately there is a datasheet to help with implementing it, which is what [spezifisch] did.
This raises the question of whether harvesting NDIR CO2 sensors like this is worth it to save a few Euros. A quick look on German Amazon shows that the device in question currently costs €35, while a genuine MH-Z19 can be bought for €25 or less. There are also many MH-Z19 models (B, C and D), which cover an even wider price range. All of which points to finding an NDIR sensor-containing device can be interesting when it’s on sale, but if all you care about is the sensor itself, it’s probably best to just buy them directly.
One of the unexpected side effects of our this pandemic is a sudden growth in the global population of captive colonies of Lactobacillus bacteria and yeast. Also known as sourdough starters, they are usually found in jars with curious names written on top, living off a mixture of flour and water. They require close monitoring to keep them healthy and to determine when they are ready for baking. [Noah Feehan] has been working to instrument and automate the process for the past two years, and has created a high-tech jar to keep an eye on his sourdough starter.
For a sourdough starter to stay active, it must be kept within a certain temperature range, and performance is measured by how much the level inside the jar rises. Existing open source and commercial projects monitor these two parameters and transmit data out, but [Noah] wanted to include a few more features. The height of a sourdough starter rises due to the production of CO2, so he added an SCD-30 sensor module, which includes a temperature and humidity sensor. For level monitoring, an VL6180 time-of-flight sensor is mounted over a hole on top of the jar. [Noah] wanted to be able to see recent CO2 production and height stats right on the jar, a ESP32 module with onboard E-ink display was used. To draw air over the CO2 sensor at a constant rate, a small extraction fan was also added. Power is provided by a small LiPo battery. For long term logging, the data is sent over MQTT to a server running Mycodo environmental regulation software.
There are still several software improvements [Noah] would like to make, including battery life, user interface and alerts, but everything is open-source and available on GitHub, so feel free to jump in and build your own.
By now we’re all used to the requirements imposed by the pandemic, of social distancing and wearing masks indoors. But as [polyfloyd] and the rest of the board at Bitlair hackerspace in Amersfoort in the Netherlands were concerned, there are still risk factors to consider when inside a building. Without fresh air the concentration of virus-bearing droplets can increase, and the best way they could think of to monitor this was to install a set of CO2 sensors. To run them they didn’t need to buy any new hardware, instead they turned to a set of event badges, from 2017s SHA hacker camp.
This badge sported an ESP32 module with an e-ink screen, and of most interest for this project it still has a supported software platform and comes with a handy expansion connector on the rear. The commonly-available MH-Z19 infra-red CO2 sensor and BME280 humidity sensor fit on a PCB that follows the shape of the badge with a protrusion at the top on which they appear as an integrated unit. Processing those readings is a MicroPython badge app that issues warnings via MQTT and plots a CO2 graph on the screen. Everything is available, both the hardware in a GitHub repository and the software as a badge.team app.
We applaud anyone who makes use of an event badge for a project, and especially so for using one years after the event. The SHA badge and its descendants are uniquely suited to this through their well-supported platform, so if you have one in a drawer we’d urge you to pull it out and give it a try.