DIY Video Probs

Submission by Frank Mc Alinden – Recently I purchased some Smartlinc video and led Probes . The reason for purchasing the probes was twofold. Firstly nearly every night I have to check my hv flags to ensure the tv,s dvd,s are set correct as my non ha compliant family tend to to turn kit on manually at times and therefore my flags status are incorrect so the probes should solve this problem.

Secondly I was asked initially by another HV/FirM User to build a port extender with stereo sockets on it for his video probes. The project has now taken a slightly different direction and a multizone probe controller is being developed to return the requested probe status to Homevision.

After receiving the probes I was anxious to try them out . I connected one to my bedroom dvd player and Probe Zone Monitor and tried it. When I turned my dvd player on the probe status led changed to red (ON)…turned it off and after about 5 to 10 seconds it turned green (OFF) .. After turning it on and off several times I decided to show the family my new toy and when I turned the dvd player off the probe status didn’t change. So tried another probe and the same thing ..always showed the ON status. Wasn’t game to try my last video probe in case I had a problem with my dvd player.

Decided to try and make a homebrew probe so contacted the” Master” (Keith D) and asked for some advice on which chip to try. The LM1881 video sync separator was suggested so ordered several from RS . when the chips arrived I quickly built the circuit as per the circuit on the suppliers website and tried it out. Had a look at all of the available signals out and decided I could use pin 3 vertical sync out as it was high when the tv/dvd was turned on (with a small negative pulse approx 100uS which could be filtered out if a problem im sure) and goes low when the tv dvd is turned off. I was quite surprised it worked first go so I built another two and tried them and they also worked. They change status a lot quicker than the smartlinc ones and the delay when turning off appears more to do with the kit rather than the probe.

Anyway so far they seem ok but require further testing which requires the probe hub to be finished to test properly. They only cost approx .00 (aussie) in parts so its worth having a go. If you do try building one please let us know how you get on.

Visit Franks Site

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