Battery Voltage Indicator

About: My name is Ben Rawstron, I am a 16 year old junior attending our local Medomak Valley High School in Waldoboro Maine U.S. Since I was a young child, I have always been interested in electronic devices, auton...
A year ago, heavy rain and ice overnight caused Skimmer (my small motor boat) to capsize due to failure of the bilge pump battery. In order to prevent this disaster from re-occur I made this indicator to monitor the bilge pump battery voltage status. The LED light mounted on the dashboard is easily visible at night through our house windows.

Product Description:
Controlled by an ATTiny AVR, this programmable voltage indicator measures and reports the voltage with a series of flashes of an LED located on the dashboard when the bilge pump switch is in the automatic position. The light can be monitored through our house windows at night from well over 100ft. This battery voltage indicator is very versatile and can be used in variety of applications which require monitoring of a battery voltage level. For example, boats, ATVs, snowmobiles, vehicles, and solar projects which have batteries. In addition, this system delivers a constant 12 volts auxiliary at 1 amp despite the varying input voltage (DC 3-35V) which is ideal for small engines, solar and other fluctuating power sources. This means the voltage measurement is accurate to below 3 volts due to an additional 5V regulator which is the reference voltage and power source of the processor.

~ Small footprint; separate electronics means the single LED takes up a minimal amount of dashboard space
~ Electronics can be mounted away from the LED and the elements
~ LED automatically turns on at dusk
~ Works with both 12V and 24V systems
~ Can be programed to work on all voltages between 5 and 24V
~ Voltage status levels can be reprogrammed to a specific battery (AGM, Lead Acid, etc)
~ Bright and easily visible
~ Four battery status levels: Critical Low, Low (Needs charging), Good and Charging
~ Low power consumption
~ Runs on the battery it's measuring which means it does not require an additional power source
~ Smart power usage; automatically dims during the night and as the battery voltage drops to conserve even more power
~ As the battery status level becomes lower the LED is dimmed by PWM to conserve the already dwindling power.
~ Water resistant electronics case
~ Field adjustable dusk light setting means that the water resistant case does not need to be reopened
~ Adjust the dusk light setting by blinking a bright flash light in a certain sequence

Battery Legend:
The LED is steady when the battery is fully charged, blinks slowly (1s on 0.5s off) when it needs to be charged, and blinks rapidly when the battery is very low.


chip LED (optional)
MOSFET transistor for controlling the primary LED
5V regulator (LM7805)
12V fixed output regulator here
ATTiny 85 chip (See schematic for more details)
Chemicals for making PCB:
Ammonium Persulfate
Positive Developer
Acrylic Conformal Coating
Resistors (I used resistors that had a 1 to 4.7 ratio for measuring the battery voltage)

Electric soldering iron (fine point)
Multi meter
Wire cutter/stripper
Philips/flat screw driver
Dremel tool (drilling/cutting attachments)
Bread Board
Board developement (please see my other project on an autonomous robot for more information and view this website for examples)


Designing printed circuit board (PCB)
Testing the design on bread board
Making PCB
See Attached Eagle Schematic (Note: for some reason the labels have a tendency to lose their place after being save.)
Installing the battery voltage indicator

PCB fabrication:

The PCB was designed on the computer using the free version of Eagle. Explore the program and feel free to edit the circuit board design to fit your needs or improvements.
Attached is a schematic. Open it by saving it to your computer and opening it with Eagle.
Since the developing process takes place in a dark room, I can not take pictures of the process. Please refer to this page for making your own PCBs.

Use a fine tip soldering iron to solder the components onto the board. Be careful not to damage the components by overheating them with a soldering iron. Click on the pictures above to view the notes on the process.

I hope you enjoy my project and please view my other project on an Autonomous Solar Robot and why I have entered the Hurricane Laser Competition.

Ben Rawstron



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    3 Discussions


    5 years ago on Introduction

    what i want to know is the set up of your steering column could you take and post pictures of it, i am rebuilding a boat myself and that is exactly what i am looking for :D