detecting a valid PAL / NTSC video signal - Page 1
Forum section: electronics / beginners

author: eevfan007
author_rank: Contributor
timestamp: August 08, 2015, 06:45:37 pm
content: I am making a very simple 2.4 ghz video receiver based on the rx2189 module.Details on this module can be found here:http://www.aliexpress.com/item/Boscam-2-4Ghz-8-Channels-Wireless-Audio-Video-receiver-Module-RX2189/2007399851.htmlI want to detect when a valid AV image is received from the receiver and then turn on a small LCD.I have looked for an IC that will be able to detect a valid PAL/NTSC image, but they are all too advanced.The ICes I've found are meant for advanced processingIs there a simple way to detect if there is a signal on the analog video out, from this module?Classic PAL/NTSC.I am currently doing an analog read with an arduino, and that works okey .. but I recon there is a more professional way to do this?

author: babysitter
author_rank: Frequent Contributor
timestamp: August 08, 2015, 06:59:32 pm
content: The LM1881 sync separator comes to mind, you might use your arduino to discriminate between regular sync pulses and noise.In the past there was a STV5370A OSD-chip, no longer in production. This was able to replace the noise-image with a internally generated chart. I used this at our amateur television repeater.

author: SeanB
author_rank: Super Contributor
timestamp: August 08, 2015, 07:20:16 pm
content: Just use a low pass filter to get the 50/60Hz frame rate and detect that with a retriggerable monostable, and a bandpass filter to detect the 15kHz line rate. AND them together and you have a basic detector that can turn the LCD on.If you are not too concerned simply detect the line and frame pulses using a comparator to only provide a pulse if the signal is over 500mV, which will work for most video with some brightness. Then use this to drive the LCD power. Will work provided the AGC does not make broadband noise if there is no signal.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 08, 2015, 07:31:35 pm
content: What does "turn on a small LCD" mean? Most modern LCD monitors automatically detect valid video input and blank the screen in the absence of a signal they can display.

author: German_EE
author_rank: Super Contributor
timestamp: August 08, 2015, 07:50:36 pm
content: Look for two things:1) A sync signal at a rate of 50/60 Hz between 0,3V and ground.2) The video signal between 0,3V and 1V, if there is a blank screen this will not be here but the sync will be.

author: Unknown
author_rank: Unknown
timestamp: August 09, 2015, 01:23:45 am
content: Quote from: babysitter on August 08, 2015, 06:59:32 pm^ This ^. It'll give you composite, H, & V sync & back porch / blanking, & you can either use the arduino or asimple tone decoderfor detection.(images are broken on that link - replace the "\" with "/" in the image urls)

author: dom0
author_rank: Super Contributor
timestamp: August 09, 2015, 07:33:19 am
content: I would've said "use a 1881 sync separator and a missing pulse detector", but using a tone decoder is a much nicer solution!

author: babysitter
author_rank: Frequent Contributor
timestamp: August 09, 2015, 10:51:34 am
content: Having experience with the 1881 really is helpful at the fast-pacing, innovative, high-paying world of analog video processing!Well, i might have exaggerated a bit.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 09, 2015, 11:54:08 am
content: Back in the day,we used LM567 tone decoder chips as line rate & field rate detectors at remote TV Transmitters.The ABC dropped the field group off the video feed & just ran line syncs to turn the Tx off at midnight or thereabouts.In the morning,they restored the field syncs,the 50Hz tone decoder locked on,& the Tx would switch back on.Line rate (15625Hz) was used as a video fail alarm.It is much easier to make the 15kHz one stable,as the C value for 50(or 60)Hz needs to be quite large-----if youdouse the field rate one,don't use tantalums or electrolytics,because they will drift.Earlier devices used proper sync separators,etc,but they weren't any more stable than LM567s & a lot bulkier.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 14, 2015, 07:59:42 am
content: Further to the above,there is no need for any other circuitry---the 567 will not respond to the higher frequency stuff in any case--if you have composite video,it will lock directly to field or line syncs,depending on what you choose.