Jaycar QM1538 DMM cable

The Jaycar and equivalents DMM measures Frequency to 10MHz, Capacitance, True RMS volts, Temperature and micro-amps as well as all the normal things. But if the data logging cable is lost there is no information on wiring.


Discontinued, but other similar meters are still sold such as Voltcraft VC840 and a UT60E

  • DC Voltage to 1000V
  • AC Voltage to 750V RMS or 1000V peak (40-400Hz),
  • Resistance to 40M ohm,
  • Capacitance to 100uF,
  • Frequency from 10Hz to 10MHz and Duty Cycle from 0.1% to 99.9% (10KHz max).
  • Thermocouple temperature measurement from -40 to +1000°C

It's actually just an IR photodiode and resistor on the 3.5mm jack socket. The "earth" connection is Data out and the the tip is the power (from DTS). This is driven by an IR LED on the main PCB so there is very good galvanic isolation.


If the jack plug has a metal body it should be insulated with PVC or amalgamating tape. I used some screened twisted pair:

Black to DB-9 female plug pin 2, to shell/barrel/ sleeve of plug (data)

Red to DB-9 female plug pin 4, to tip of plug (power via DTR)

Screen cut back and insulated at 3.5mm jack end and only connected at DB-9 female end pin 5

Contact me if you need logging software.

Some 3rd party PC software for this and other meters. http://www.mtoussaint.de/qtdmm_multimeter.html<  (for OS X and Linux written using QT, In theory possible to port to windows too).

Also http://www.tonybarry.net/tonybarry/...< Jaycar QM1538 multimeter interface in RealBasic