Make a constant-current source of, say, 20mA. Using comparators set to different appropriate thresholds compare the voltage across the unknown resistance developed by the 20mA with those thresholds. Drive the LEDs with the comparator outputs. An LM324 has four opamps which could provide the current source and comparators.
I was looking to use a Bi-color LED for the indicator.
The lower range resistance input is 0 - 6 Ohms - this should turn the LED red.
The mid range resistance input is >6 to <9 Ohms - this should turn the LED green.
The upper range resistance input is >9 ohms should turn the LED red.
If you could advise me where i could get a schematic of this circuit that would be most helpful...
I was already considering the op amp circuit and glad you suggested what i was thinking. However, my electronic knowledge is only basic so i wil have to revert to some reference books for me to make a schematic of what you suggested!
Also, would it be possible to run your suggested circuit from 9V cells...?
I was looking to use a Bi-color LED for the indicator.
The lower range resistance input is 0 - 6 Ohms - this should turn the LED red.
The mid range resistance input is >6 to <9 Ohms - this should turn the LED green.
The upper range resistance input is >9 ohms should turn the LED red.
If you could advise me where i could get a schematic of this circuit that would be most helpful...
I have worked out a one-chip with two terminal bicolor LED solution. Look at the attached. Using a quad opamp, like a TLC2274. The simulation shows the current through the red and green leds (red trace and green trace) as a function of the unknown resistance at three different values of battery voltage (9,8, & 7V), showing that because the circuit is ratiometric, it is quite immune to variation of the battery voltage as it wears down...