For a status monitor I'm designing, I'm using a TL431 to monitor the system's 5 volt supply for dips, as shown in the schematic. Monitoring the supply voltage isn't central to the task at hand but I'd like to know if there are dips. As is the norm with microcontroller projects, port pins are in short supply. What I would like to do is somehow "store" the fact that there has been a voltage dip until the micro can check the state of the port pin, and then use the same port pin to reset the flag. In other words, I would like to see the low level caused by a voltage sag when I get around to looking at it, then switch the pin to a high output momentarily to reset it. Any suggestions on how to do this simply?
I was going to use a dedicated voltage monitor chip for this task but the only chip I could find that allowed setting the trip level with resistors is only available in pain-in-the-butt SC-70 package (TI TPS3803). The TL-431 accomplishes the same thing in a more manageable SOT-23 package using the same number of external components. I originally used the PLVD module of the PIC 18Fk22 I'm using but the voltage range on the system being monitored is too tight for its specs.
Oh. By the way, there are two R2 resistors to allow adjusting the voltage setting with good resolution. The ElectroDroid app for Android calculates resistor values to achieve a specified ratio. Very handy.
I was going to use a dedicated voltage monitor chip for this task but the only chip I could find that allowed setting the trip level with resistors is only available in pain-in-the-butt SC-70 package (TI TPS3803). The TL-431 accomplishes the same thing in a more manageable SOT-23 package using the same number of external components. I originally used the PLVD module of the PIC 18Fk22 I'm using but the voltage range on the system being monitored is too tight for its specs.
Oh. By the way, there are two R2 resistors to allow adjusting the voltage setting with good resolution. The ElectroDroid app for Android calculates resistor values to achieve a specified ratio. Very handy.