Detect VGA signal

[JeffReckart]

Ok here is a wierd one! I just bought a new projector for our rear wall/ confidence monitor. and even though it is a low budget, it has an auto ON feature! It senses a Incoming VGA signal, and turns itself on!

Which gives me an idea! I can turn on the front projector with serial commands, and i also dabble with microcontrollers. the arduino in particular. the arduino has a serial port, to which i could configure to send the serial power on command to the front projector.

I'm thinking if i could get the arduino to detect a vga signal, then use that detection to trigger a serial command to turn on the projector. that way when i turn on the computer, the arduino will detect the vga sginal, and power my projector automaticily for me! Anybody have any idea how to detect a vga signal turning on?
JR

[daver2]

First thought that comes to mind is that a VGA signal has separate horizontal and vertical synchronising pulses. These pulses are not there if no VGA signal is present but should be there when the signal is present. Using the vertical (frame) synch pulse is the longer time period so should be the easiest to detect. As the signal is digital - you should be able to feed it directly into a digital input port of your microcontroller. Using an interrupt to detect either a high-going or low going edge (depending on the synch signal polarity) will ensure that you don't have to poll the signal and risk missing the pulses. An on-chip timer or counter should be reset to zero during the interrupt service routine - when you see the synchronising pulse. The timer/counter can then be free-running at some reasonable rate (say 10 or 100 milliseconds) and when the value exceeds that corresponding to a few seconds you have identified that the VGA synchronising pulse has been missing for that length of time and it is time to switch off your front projectors. You would limit the timer/counter to some high value (30,000 for a 16-bit counter/timer) to prevent it wrapping round to zero. When the synch pulse is detected - this would set the timer/counter to zero again.

Dave

[JeffReckart]

Ok, the VGA signals. Have any idea what level they are? AC or DC? 3.3volts, 5v 12v? My google skills are lacking this morning!

thanks!

JR

[hoosierdraft]

I'm finding .7V to 1.0V when I do a Google search.

[daver2]

My understanding is that HSYNC and VSYNC are TTL voltage levels (up to 5.0Volts ish) and the R, G and B signals are 0.7V peak to peak with 0.0V being black and 0.7V being fully saturated.

Dave