[sdiy] Passive Window Comparator

[Michael Buchstaller]

Hello dear Electronics Gurus,

Not very synth-related, but DIY:
For a customer i need to make a cable/wiring tester. There comes a cable with 4 wires,
GND, +5V, +12V and +24V, and the device is supposed to show if the cable is connected
correctly. No Battery or power supply.
It shall show a (green) LED indicator for each of the 3 Voltages if it is OK (within +-2 Volts, say)
and an (red) indicator for overvoltage (e.g. +24V at the +5V pin).

How can i do this simply ?
I thought of using 3 diodes from the 3  power leads to a low-drop-regulator to make say +4V and
use an LM324 as a comparator; divide down the input voltages so they will not exceed the 4V.

But i think there should be a more simple solution ?
Maybe the OK led with the "normal" resistor, and the OV led in series with a Zener so it will only lit if
the voltage is too high ?

Any opinions ?


-Michael Buchstaller