voltage monitor

voltage monitor The 555 (or 7555) timer IC is a well- known device with a wide range of possible applications. Elektor has already provided many applications and here is yet another. The timer is configured as a mono- stable multivibrator and monitors a voltage level. This can be, for example, the +5 V supply voltage of a microprocessor system. The voltage to be monitored is applied to trigger input pin 2, via preset potentiometer P1. The timer is in the quiescent state when the input voltage. is higher than the trigger threshold set with Pl. Output pin 3 is then a logic 0. The green LED lights, indicating that everything is in order. If the input voltage drops below the set trigger threshold, the level at the output of the timer changes to a logic 1. LED D2 goes dark, but the red LED D3 lights. This means that the input voltage has dropped below the minimum permissible value. Brief voltage failures are "extended" by the 555 so that the red LED can clearly indicate them. In the ev...