I've got four voltages:28 VDC, 24 VDC, +15 VDC, -15 VDC I want an LED to illuminate when all four voltages are "good". Can someone recommend come IC chips I could wire up to achieve this. I don't care what the tolerances for "good" are, 10%, 50%, whatever, anything reasonable is fine. I need to built a little 4" square circuit board or whatever size fits it. Thanks in advance for ideas!