View Full Version : Cannot get TV input to work

05-05-2008, 12:47 PM
···· Hello All,· I am having a real problem getting input to a TV from the Propeller. I am using the interface from Jeff Ledger's Propeller CookBook (3 resistors/4 pins) on pins p12, p13, and p14. I have an RCA out, and I·have tried rabit ears with wire antenna from the Prop,·splicing the RCA to Coax (the only input on rear of TV), direct center conductor---The best I have gotten·so far is·a·VERYYYY snowy/faint indication that there is a picture, VERY bad color , and the same·with a scrolling picture with the Demo.spin . You can see a definite and immediate caange in "picture" shortly after the Prop powers up, and upon·power off.
··I have run 6-7 other spin objects·,all with success (not video). I have not done anything to TV before, however I do have a fair knowledge of electronics, and have built 20+ sensor, motor driver, servo driver, temp reader, stepper control, ADC boards with success so far. I feel sure that I am not doing something right here, but·I am at a loss, after scanning the forums, Parallax site, third party sources, and Googled to·near death. I have used each and all the video objects in the exchange. I have tried all 125 channels on the TV--it does not seem to have a "video in", and only one Coax connection ar·rear---·probably 12-14 years old color.· Any help will be most appreciated in an area that I have little experiance with.

(In my profession,·there was·much of the time that I got information on a need to know enough to repair it basis, not a need to know it all. Much of the equipment decades older than I. Just enough to be able to find and implement a remedy·that is qiuck, cheap, and will last a hundred years. Makes for a "Swiss Cheese" database for me to work with---not an excuse, just that I can excell in some areas,and yet have to spend much research time on others.)···
·························· Thanks, JP··

05-05-2008, 06:57 PM
JP, the "Antenna In" connection won't work as this input expects modulated RF (picked up from an Aerial / Antenna). The Prop puts out composite video, which means you need to connect it to the "Video In" input on the TV. If your TV really doesn't have "Video In" a quick and easy way is to connect the prop's video output to the "video in" on a VCR, then connect the RF Out of the VCR to the TV's Antenna Input. Good luck it'll all be worth it!

05-05-2008, 07:14 PM
Yes, direct video in will be the way to go if you can.· But some older equipment may lack that ability.· In that case, perhaps either get the Propeller to produce modulated video (like on vhf channels), or use a video modulater box like used for the old Atari and Commodore machines... you should be able to pick one up off ebay or various surplus stores.

I'm a Prop noobie too, and I could swear I saw some reference to modulated video in some documentation, but damned if I can find it now.

I'm also not having much luck with the forum search...

I do see it mentioned in this Makezine blog about the Propeller:

There is even an extra option to modulate the direct video signal and create a short range broadcast signal (picked up on channels 2-16). This works from about 20' away without any extra antenna (just radiating off of the chip, sorry FCC). said...


edit -

Wonder if that came from this Hydra doc...


Post Edited (Agent420) : 5/5/2008 12:42:32 PM GMT

Mike Green
05-05-2008, 08:41 PM
There is an option to put out "broadcast" video which is modulated RF. You have to change some of the constants (tv_pins, tv_mode, tv_broadcast) fed to the video driver (see the comments at the end of the source for TV.spin. It works, but not well (the image is a bit staticy). It works better in black & white and if you change the crystal from 5MHz to a 6MHz crystal since that's a submultiple of the TV channel frequencies. It only works on the low VHF channels (2 - 55.25MHz, 3 - 61.25MHz, and maybe 4 - 67.25MHz). I never got the range (20'), but did manage to get a readable text screen one or two feet away from a short whip antenna.

05-06-2008, 06:40 AM
·· Much thanks to all, I will try another route with a TV that has "video in" and/or going through an old VHS that I have.· I·tried·using an old 75/300 ohm adaptor,and did get a slightly "better" unintelligible·picture ( although it may not be working itself). I am not yet comfortable with making much change in the .spin programming as of yet. Thanks again to all.I will post my results soon. Just from what little I can see now is exciting, the real picts have got to be a blast!

·· Thanks, JP

05-06-2008, 09:34 AM
·· I resumed my tests on a newer TV with Composite Video In and it works GREAT!!·· Tubular,· Agent420, and Mike Green, again thanks for helping me over the hump on this one. Usually once I can see "it" work and do some hands-on, then I can go on to more discovery. Seems like I mostly get hung-up on the simplest concepts. I got hung here by needing to output readings from an MCP3208 ADC and a 5 DOF gyro/accel, and got distracted by this--go figure.· Thanks again, and I will most probably be back with questions. (I don't post much, but I am a long time lurker:)

· Thanks, JP

05-06-2008, 05:35 PM
jpyle said...

I·tried·using an old 75/300 ohm adaptor,and did get a slightly "better" unintelligible·picture ( although it may not be working itself).

Fwiw, there's a difference between the adapter and the modulator...· With a simple·adapter, which is really just an impedance matching xformer, the tv is still expecting a modulated broadcast signal on a channel (not composite video).· Those old modulater boxes from Ataris and the like are powered, active units that modulate the video signal into a broadcast channel format that can then be inserted as you attempted.

Just a thought in case you create a project based on an older tv lacking video in.

Glad you got it working !· The video capabilities are certainly one of the most interesting aspects of this chip for me ;)

05-07-2008, 06:19 AM
··· Thanks, Agent420. After reading your post, and thinking about the old powered modulators (from a LONG time ago) I once knew that the impedence matchers and modulators were not the same thing. Still weak on Video, but I am getting there thanks to·you·and the good folks on the the forum.· I finished the stereo "card" and it works VERY well, much better than I expected. Now to resume my .spin studyies.

I have been·playing with·the Kalman filter, IMU, MCP3208 attempting a more agressive control for a balancer platform I ·built a year or so ago. Went from using a 5k pot with a lever "walking stick" for balance reference, to a gyro/accelerometer combo, but I have been struggling with the "tweaking", with limited success so far.

·· A very much appreciated Thanks again, JP

05-11-2008, 03:21 AM
To anyone interested, A powered modulator (E-Bay, $13.00) works excellent with the OLD tv that only has an "F" connector for input. Thanks, JP

05-12-2008, 05:13 PM
BG Micro's got them for $2, but you need your own power supply.


Data Sheet:


05-13-2008, 04:14 AM
Agent420, I THINK I could set that up-- I may order one just to try. I have a bushel basket full of "Wall Warts", and a couple dozen PC power supplys that have come in handy here and there. Thanks for the info---JP