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Cable TV Timer for Kids

Have you ever fought with your kids on their TV watching habits?  I've gotten tired of my daughter falling asleep with her TV on, and I wanted a way to shut it off remotely, outside of her room, on a schedule.  I didn't want anything like a timer to her TV set, as she could just unplug the timer.  So I wanted a Coax Timer.  I thought I'd just buy a Cable TV Timer and that would be that.

I looked all over the Internet, and asked around, and even though it's not that complicated, I couldn't find a Cable TV timer.   So I thought I'd just make one.  

Here's the sequence of my attempts, which should be titled "If at first you don't succeed, spend more money."

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Attempt #1:  Solenoid

 I figured that I had a Cable TV Switch:


and if I could just find a way to switch it, I'd be set.  So I got a solenoid from a used parts Internet site, and hooked it up like so (not shown is the power supply from an old printer that I rigged up to power it, as it needed 24-volt DC power.  This went to a normal christmas-light type timer to turn it on/off):


Then I tested it... it worked great at first, and I thought I had a solution.  Total approximate cost:  $2 for Switch, $5 for Solenoid, old Printer power supply, and $5 timer.     Yeah!

But while this worked initially, after a couple of minutes the solenoid got so hot I was worried about burning down the house!  That was when I learned that Intermittent duty solenoids get SUPER hot.   They aren't designed to have power on for more than a second or so, and if they do, it is like a toaster heating up the wire coil.  So I thought I'd buy a continuous duty solenoid.

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Attempt #2:  Continuous Duty Solenoid

I actually called and talked to a solenoid expert, and he said that if I wanted a continuous duty solenoid that moved the distance I needed, that it would cost me on the order of a hundred or so dollars!   What!?!?!  But I managed to find a A420-066947-00 solenoid on a surplus site (www.allelectronics.com) for cheap... around $8.  With shipping it came to about $14.    So I hooked this up with some JB-Weld to my previous switch like so:


This took some more work to set up, because moving a continuous duty solenoid a long distance is hard/expensive.  With the solenoid I had the action arm would only move less than a quarter of an inch.   So I bought some button switches (like 6 for $4) and soldered one to the inside of the box like so:


This solution also worked initially.  However, even with the Continuous Duty solenoid, it got so hot that it melted the JB-Weld holding the action arm to the switch!  

So solenoids were out... they just got too darn hot.   So I thought I'd use a relay instead.

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Attempt #3:   Relay:

So, I bought a DPDT Plug-in-Relay (part#275-0217) from Radio Shack, and soldered this to the board.   This relay was a bit expensive, around $9, but it worked on 120-volt AC power, negating my need for a DC-transformer, which was nice.  Here's a shot of that set up:


I soldered an old power cord to it (with the other end connected to a simple timer), and soldered the connections to the inside pins of the coax cable.  

When I tested this with an Ohm-meter, it worked great.  Timer went on, the switch connected the coax center leads,  when the timer went off, it disconnected them.  I thought I had a solution.

However, when I hooked it up to the actual TV Coax and a TV, the TV got a picture regardless of if the switch was on or off!    WTF?  My theory on the cause of this is that the cable TV signal is so strong that it jumped the air gap of about 1/16 an inch (shown in the picture above) between the relay soldering points.  

So, I thought I'd modify my solution and instead of switching just in to out, I'd switch from in to ground.

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Attempt #4:   Grounded relay

With the same set up as above, I soldered the unused (open) part of the coax switch center pin directly to the copper box.  This should give the Cable TV signal the same signals on both the center pin and the external wire mesh.  I tested this with a TV and the cable-TV jack coming from the wall (again, an Ohm-meter showed on/off like it worked), and the TV got a signal regardless of the relay function.

I also tried grounding it not to the box, but to a no-kidding ground---same problem.  The TV signal got through.  

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Attempt #5:  Cable TV Amp (Booster)

My next attempt was to use a Cable TV Booster.   These are designed to help boost your cable signal if you have a long run, or too many boxes connected, etc.   I didn't know if, when they didn't have power, they'd send the TV signal through or block it, but I thought I'd give it a try.  So I bought a Leviton 48210-VA from Home Depot for $40.  Here's a picture of that:


I hooked the power supply from the Amp to a timer, and gave this a try, connecting the coax "In" to the wall,  and the coax "Out" to the TV.  

While it degraded the signal, the TV picture STILL came through!  WTF?  I thought that MAYBE the TV is using the coax cable as an antenna, so I 'd try to hook it up the way I planned on using it (to my daughter's room) to see if the TV signal was attenuated through the house cable run.  

This WORKED!   Since my daughter has a cable-TV box in her room (Comcast makes you have one for even new TVs that can handle digital cable easily so they can make money), the cable TV box complains when it sees the interference on the line when the Amp doesn't have power.  So although her TV WOULD normally be able to display a few channels, the Comcast box blocks it all with a pop up stating that there is a problem with the signal and to contact them.  

So my solution for a Cable-TV Timer for my daughter's room is done!  I have an Amp connected to a christmas-light timer in the basement where the coax comes into the house, and when it has power she can watch TV just fine.  When the timer expires and the power to the Amp switches off, her Comcast box complains about the signal, blocking all viewing! 

  Total cost of this solution around $45.  I don't want to add up what I spent all together trying to get to work though!    

Finally, I should note that the relay attempts above (#s 3 and 4) may work like the Amp does, and that may be a cheaper solution.  However, I never did test them through the Comcast box, only directly between the TV and the wall.  But since I've already loaned that rig to a friend, and I've spent so much time/money on this project, I am sticking with the Amp solution and calling it quits.  

Comments

  1. great write up; can you rehost the images? It would be a great little weekend project. Thanks!

    ReplyDelete

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