Trevor
Newbie level 5
Dear All
I want to build a fuel level gauge for a motorcycle using a 10-segment LED bar graph operating from a standard LM3914 driver.
The input signal to the driver IC is 0 - 5v so if I connect a bench power supply to it, and vary the voltage up and down from 0 to 5 volts, the bar graph lights and tracks the input signal voltage as it should. That's the simple bit.
The tank sender in almost all vehicles (I will have to buy or make a suitable one) is usually just a variable resistance which varies according to fuel level. It could also be made using a set of fixed resistors in 10 steps. One possibility is to have a set of reed switches operated by a float with a magnet that operates each switch in turn as the float goes up down. Each switch can be used to switch in a fixed resistor.
Now here's my question, can anyone give me a basic description of the electronics needed to interface a variable resistance (or set of fixed resistor steps) to the input of the LM3914? I tried just putting various resistors across the 5v signal but this didn't work. It obviously needs something more complicated.
I know the very easiest way is to simply have each reed switch in series with the DC supply to the LEDs but this means running 10 separate DC lines to the bar-graph and doesn't seem the proper way to do it.
Anyone out there an advise, I'd be very grateful.
Trevor
I want to build a fuel level gauge for a motorcycle using a 10-segment LED bar graph operating from a standard LM3914 driver.
The input signal to the driver IC is 0 - 5v so if I connect a bench power supply to it, and vary the voltage up and down from 0 to 5 volts, the bar graph lights and tracks the input signal voltage as it should. That's the simple bit.
The tank sender in almost all vehicles (I will have to buy or make a suitable one) is usually just a variable resistance which varies according to fuel level. It could also be made using a set of fixed resistors in 10 steps. One possibility is to have a set of reed switches operated by a float with a magnet that operates each switch in turn as the float goes up down. Each switch can be used to switch in a fixed resistor.
Now here's my question, can anyone give me a basic description of the electronics needed to interface a variable resistance (or set of fixed resistor steps) to the input of the LM3914? I tried just putting various resistors across the 5v signal but this didn't work. It obviously needs something more complicated.
I know the very easiest way is to simply have each reed switch in series with the DC supply to the LEDs but this means running 10 separate DC lines to the bar-graph and doesn't seem the proper way to do it.
Anyone out there an advise, I'd be very grateful.
Trevor