This battery monitor circuit can be used to monitor the charge level of a battery in 3 different steps, indicated by 3 separate LEDs.
Just three LEDs are incorporated to provide an indication of the car (or boat) battery condition.
The LEDs light as follows: Preset P2 sets the voltage above which D3 goes out (13 V);
How the Circuit Works
P1 sets the point at which D4 lights (12 V); lastly, P1 sets the voltage above which D5 lights (14 V).
The calibration technique is, somewhat crucial, and will have to be repetitive many times considering that the numerous changes influence one another.
The image displays the author's prototype.
All components are fitted in a small plastic tube, with the LEDs at one end and a ' cigarette lighter' plug at the other.
This 3 step battery monitor circuit can then effortlessly be connected to the corresponding socket on the dashboard for a speedy check of battery situation.
If the proposed colours are used for the different LEDs, red will correspond to 'battery low'; yellow (with or without red) signifies ' battery normal'; and green will generally light once the battery is ' on charge'