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How Many Entertainment Appliances On ...   Knock Knock - Off Topic

Started Oct-22 by kizmet1; 1274 views.
Alfi (THIALFI)

From: Alfi (THIALFI) 

Oct-27

One for the TV, and one for Roku.

kizmet1 said:

Programming them is the problem if one doen't have a Smart tv. Most don't do much more than turn off and on and mute. I found out the hard way that I need an older control for one tv to go on. Then, once I get it turned on I can program a newer remote with.more functions.

About 25 years ago, on a Windows 95 machine, I built a TV remote code capture device, which could then be used to program a universal remote for whatever appliance you wanted to talk to with it. There are about 512 typical code combinations, which are pulsed infrared patterns at one of about 4 fairly common carrier frequencies in the ultrasonic range.

We used an overclocked sound card and an ancestor of Audacity that would permit a sample rate of about 96 khz, so that all the TV remote codes were below the Nyquist limit. We'd use a phototransistor and an operational amplifier to mimic a microphone, and just record the raw waveforms. Then plot them on the screen.

First step was to do the Fast Fourier transform on the waveform to come up with the carrier frequency for that TV remote. Then you would measure the time interval of the pulses and find the repetition interval of each code to figure out the start and stop durations and the actual bit rate.

Next was to just count pulses and spaces to write down the binary codes, which would be inserted between the preamble (start) and post-amble (stop).

I discovered that the codes inverted for each key press, so if a 3 was a 00010011 on the first keypress, pressing the 3 key again would output 11101100 for the second burst of data. The preamble was usually a 1111, and the post-amble was 0000, so there would be a long continuous waveform to get the attention of the device, then a minimum interval of 4 bits to tell it that particular code was finished.

Holding the key just repeats the same pattern over and over. Releasing the key and pressing it again would invert the data bits while preamble and postamble were the same. Pressing a different key would also invert the pattern alternatively, so in the event of noise, the processor could detect errors.

Repeating the pattern several times helped deal also with noise and errors.

Part of the codes I picked apart also had a 4 bit sequence at the end that was a checksum of the 1s and 0s, also as an error detection scheme.

So each code actually had 2 patterns - normal and inverted, and each key was chosen carefully to not be confused with any other, either the normal or the 1's complement version.

Once I figured that out, I could program a micro controller to decode the bit pattern and allow a remote control to act like a keypad for a industrial control in the oil field. You'd drive up, press the keys, and watch the display to change parameters from that air conditioned pickup truck when it was 118 degrees F at the oil well site.

We bought generic infrared tuned receivers for the carrier frequency of the remote transmitters, on 36 khz. The baud rate was about 9600 so there were roughly 4 carrier cycles per bit transition. It was amplitude keyed - that is, carrier was on for a "1" off for a "0".

Nowadays I'd directly sample the carrier waveform and write a small digital signal processing algorithm to detect the carrier then decode the individual bits, since cheap number crunching horsepower can be had able to do this for about 50 cents, and there is extensive open source code libraries one can use to quickly put something like that together, maybe even write a working program from scratch in a single evening with the proper know-how and development tools.

A learning module would decode the info from a dedicated remote, then mimic its output exactly for that VCR or TV or DVD player or animatronics spook house monster you built to make trick or treaters and their parents scream.

Showtalk
Staff

From: Showtalk 

Oct-29

If Kizmet can understand electronics, she can explain what you just said to me.

I forgot. Everyone doesn't tinker with things the way I do :)

kizmet1

From: kizmet1 

Oct-30

Can I send all my remotes to you and have you go to a Good Will and sync them with some older tv's?
New remotes are pre programmed to work on new Samsung now. Wonder if they are paying royalties to have that?
kizmet1

From: kizmet1 

Oct-30

He said (I think) a magic word as he waved a magic wand and synced everything.
Showtalk
Staff

From: Showtalk 

Oct-30

Ha, yes he did.

kizmet1

From: kizmet1 

Nov-22

The rest of the story:
I got a new tv. It is a Samsung. It comes without a manual. Assumes everyone has a smart phone and can download directions from one of the well known sites I have never been to. I got it going anyhow. Also assumes that owner has cable tv. I don't.
Nice to have a big picture but the volume is lousy. Now, I have to figure out if any of my old speakers can be used. I am using headphones on my old tv as I watch the new. The only good thing is that it doesn't weigh much.
Tried to get a 13 year old tv going but I can't since I had a power outage during the first GOP debate in 2016. Has something to do with being hooked up.to cable. A friend got a new tv and gave it to me.
Showtalk
Staff

From: Showtalk 

Nov-22

If you can make a TV work without cable or other access, you are more techie than you think you are.  

kizmet1

From: kizmet1 

Nov-22

I was thinking if returning it but didn't want to.go thru the hassel of packing it up.
I am very afraid of 1. being without a tv and 2. making a mistake. After the first few times of changing broken tubes on our first tv my mother let me do it as my hands were a lot smaller than hers. I made a few mistakes. One was on the tv when my uncle lived with my gm. He ended up having to call a pro as the family friend was in Montana.
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