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.
"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 Hackaday.io write-up.