I know enough about about microcontrollers to get myself into trouble, and almost nothing about analog circuits. I'm working on a project to read from 1 to 4 electronic gauges, but I need to be able to determine which of the gauges are attached to the system. These are battery powered gauges so none of the interface lines are active unless the gauge is transmitting data except for one. The gauges pulse the data request line about 10 times per second.
To ask the gauge to send data, you pull this line to ground and I'm assuming when it detects a missing pulse it starts to send data. What I'm looking for is some way to use this pulse train as a signal when a gauge is attached. What I'd like is a circuit that would source or sink 5V so I can tie it to one of my µP inputs that would signal when the pulse train was there and continue to signal for approximately a second after the pulse train was removed. I'm thinking of the latter condition as the upper bound of the button press time used to pull the line low to request the gauge to send data. I don't want the button press to be misinterpreted as the gauge being disconnected.
I've got an idea that a 555 timer as a pulse stretcher might work for this. Set the timer up for a 1-2 second pulse, and use the signal from the gauge to keep "refreshing" the timer. Any analog gurus out there want to help me with such a circuit?