Keri Szafir's ThermoNIX Turns a Vintage Nixie Tube pH Meter into a Multi-Channel Lab Thermometer

Linking to external TI LM35 temperature sensors, this repurposed lab equipment provides a glowing readout of environment conditions.

Self-described "vintage electronics nerd" Keri Szafir has taken a classic Elwro 5170 pH meter, gently acquired from an abandoned chemical lab, and found a new use for it — turning it into the ThermoNIX multi-channel thermometer with Nixie tube display.

"A few years ago I salvaged two Elwro 5170 pH meters from an abandoned chemical lab," Szafir explains. "One of them gave its Meratronik V628 Nixie millivoltmeter (which I reduced to its display) to my Advanced Dial Home Device (ADHD) project, while also being a donor of a thick-film hybrid opamp, HLY7006R, which was required to fix a non-working V640 multimeter. The enclosure just sat there on my shelf until I got another V628."

Rather than have the enclosure just gather dust, Szafir decided to give it a new life as a lab thermometer — but one capable of connecting to a number of high-precision Texas Instruments LM35 temperature sensors, allowing it to measure the temperature at various points of the lab as well as outside.

Built around a salvaged Elwro 5170 pH meter, the ThermoNIX offers multi-channel temperature readings on a cheery Nixie tube display. (📹: Keri Szafir)

"The LM35 is an analog sensor which outputs DC voltage of 0+10mV/°C (there's also a LM34 which measures in °F)," Szafir explains. "So, 20°C will be output as 200mV. The LM35 can also measure negative temperatures if its output is pulled down to a negative voltage through a resistor, with 50µA flowing at 0°. If using -5V, 100k should be used."

The sensors connect to the old Elwro housing, into which a Meratronik V628 digital millivoltmeter has been installed — with an externally-accessible range switch and a calibration switch, alongside a rotary switch that allows the different sensors to be selected. The resulting measurement is then shown on the Elwro's original display: a pleasingly-vintage set of Nixie tubes.

More information on the build is available in Szafir's write-up.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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