Battery Monitor for Automotive or Marine Applications

The PM128E Backlit Digital Panel Meter from Circuit Specialists can be easily modified to produce a self-contained 2-wire panel meter capable of monitoring battery voltage in any application in which a battery’s voltage is within the range of 6-24 volts. The PM128E digital panel meter was chosen for its ease-of-use and -configuration as well as the backlight feature, which enables the user to read the panel meter at night. panel_meter-0


This digital panel meter is configured in a 5 volt powered common ground DC application with a 20 volt maximum reading, which we’ve accomplished by setting jumpers to DC and 20V and enabling the P2 decimal point. To make this unit self-powered, we have soldered in a 78L05 Voltage Regulator across the power connections and derived the input voltage from the IN terminals of the meter.


The meter and added circuitry were assembled in a PB-3P plastic project box to protect the circuitry and connections. The meter also could’ve been mounted directly in a vehicle or boat’s dashboard or control panel.


We are always looking for ways to use our own products around our facility here at Circuit Specialists, and this panel meter project quickly found a home on our trusty forklift.  The forklift’s battery is often low due to the heat in the warehouse (we are located in a desert, after all).  We attached the leads to the battery’s terminals, and just a simple lift of the “hood” shows the voltage of the battery.  We could have mounted it on the dash of the forklift, but having it under the hood gives the operator an incentive to check the battery’s water level more often, too.


George Leger has a Masters in Electrical Engineering from Stanford University, worked in private industry pioneering surface-mount technology and in government research labs for twenty years, published several papers on surface-mount technology, co-authored papers published in national symposiums on accelerator technology, was past president of SMTA and an adjunct professor at the community college level, holds a patent, and is a certified microchip design partner, serving as a consultant to many companies developing electronic circuits.

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