HT12A

[zachtheterrible]

I just got my HT12A and HT12Ds in the mail today and am trying to get the HT12A to work first because without an output signal from the encoder how can i get the decoder to work :lol: ?

Anyway I have the HT12A wired up exactly as in my crude drawing. I have my o-scope hooked up to the DOUT pin. Strangely enough, the only thing that hapens when I hit that momentary pushbutton switch is that the output latches and goes high.

What am I doing wrong??

 

[panic mode]

i think your chip doesn't oscillate. you wired it like HT12E instead of HT12A. so change the resistor from 47k to value shown, add crystal and two capacitors. that should do it...

 

[williB]

**broken link removed**
shame on you for making me look it up.. :lol:
it says that HT12A runs on 5 v not six..

 

[zachtheterrible]

i think your chip doesn't oscillate. you wired it like HT12E instead of HT12A. so change the resistor from 47k to value shown, add crystal and two capacitors. that should do it...

I thought that was just because it was being used as an IR transmitter. The crystal setting the precise frequency. Well that does clear things up a bit :lol:

shame on you for making me look it up..
it says that HT12A runs on 5 v not six..

Yeah, thats on my datasheet, i misread it somehow :roll:

ill let ya know how things go :lol:

 

[zachtheterrible]

Alrighty than. I tried a 3.5MHZ crystal, a 10M resistor, and two 150pf capacitors in the oscillator section. No results whatsoever.

What value of crystal would be preferrable? I get the feeling that 3.5MHZ is much too high. Unfortunately I don't have any lower value crystals.

Without the 10M resistor and 150pf caps, I can get a small 3.5MHZ sine wave out of the DOUT pin on the HT12A after closing D8.

I'm very quite lost here. Please help

 

[Nigel Goodwin]

Alrighty than. I tried a 3.5MHZ crystal, a 10M resistor, and two 150pf capacitors in the oscillator section. No results whatsoever.

What value of crystal would be preferrable? I get the feeling that 3.5MHZ is much too high. Unfortunately I don't have any lower value crystals.

Without the 10M resistor and 150pf caps, I can get a small 3.5MHZ sine wave out of the DOUT pin on the HT12A after closing D8.

I'm very quite lost here. Please help

3.5MHz is too high - IR remote controls commonly run from 455KHz crystals, this gives the required modulation frequency of 40KHz or so. Take an old IR remote to pieces and use the crystal out of that!, they are usually ceramic filters, and mostly rectangular, either yellow or blue.

 

[eblc1388]

3.5MHz is too high - IR remote controls commonly run from 455KHz crystals,

Spot on, Nigel.

Zachtheterrible, the datasheet did not mention other crystal frequencies that you can use so you are stuck with 455KHz as your only choice.

 

[zachtheterrible]

On the datasheet is says 455k(symbol for ohm), but ok, ill use a 455khz crystal, now to find a remote . . .

Ill let ya know how it went when i find a remote.

 

[zachtheterrible]

yay, i found a remote. The crystal is blue and says:

3 6 2
020-1

I can now get a nice looking square wave out of it, and it turns on and off when I open and close the button.

I tried using the HT12D as well. The oscillators are oscillating at very close to the same frequency as each other. I didn't bother to measure the frequency though. I changed the capacitors on the HT12A from 100pf to 150pf because I couldnt find any 100pf in my box of parts.

I cannot get the output of the HT12D to go high when I press close the input on the HT12A. Included is a schematic of exactly what my circuit looks like.

 

[Nigel Goodwin]

As a quick thought, you've left all the address lines floating, I don't know what effect that might have, but there's certainly a chance that this may result in them both being set to different addresses.

Also, is the input the same polarity as the output?, they are intended for IR remote control, and the remote receivers invert the data.

 

[eblc1388]

I tried using the HT12D as well. The oscillators are oscillating at very close to the same frequency as each other.

The data sheet of HT12D specifically mentioned that OSC freqiency of decoder should be 1/3 that of HT12A encoder. 8)

 

[zachtheterrible]

The data sheet of HT12D specifically mentioned that OSC freqiency of decoder should be 1/3 that of HT12A encoder.

oh dear, theres my problem :lol: . I skipped right over that. Sort of a funny place to put such an important thing.

As a quick thought, you've left all the address lines floating, I don't know what effect that might have, but there's certainly a chance that this may result in them both being set to different addresses.

I don't think so but ill make sure of that. The waveforms looked the same on my oscilloscope. Of course I couldn't compare them right next to each other because I only have one probe for now.

Also, is the input the same polarity as the output?, they are intended for IR remote control, and the remote receivers invert the data.

Yes, the input is negative, the output is positive.

 

[panic mode]

oh dear, theres my problem :lol: . I skipped right over that. Sort of a funny place to put such an important thing.

nah... you just know what to skip... :lol:

 

[zachtheterrible]

Made some changes. These are the frequencies that the chips are operating at:
HT12A- 434.7KHZ
HT12D- 144.9KHZ

434.7kHz/3= 144.7kHz. the HT12D is oscillating @ 1/3 of the HT12A.

I also connected A0 on both chips to ground like Nigle mentioned.

One thing that I noticed is that the output of the HT12A does not oscillate as fast as the actual oscillator (X1 and X2). I did not bother to measure the frequency. Am I supposed to make the oscillator frequency of the HT12D 1/3 of the output of the HT12A or the oscillator of the HT12A?

I am still not getting any kind of output from the HT12D. I think im doing everything right here.

 

[Nigel Goodwin]

One thing that I noticed is that the output of the HT12A does not oscillate as fast as the actual oscillator (X1 and X2). I did not bother to measure the frequency. Am I supposed to make the oscillator frequency of the HT12D 1/3 of the output of the HT12A or the oscillator of the HT12A?

I am still not getting any kind of output from the HT12D. I think im doing everything right here.

The output SHOULDN'T be at the same frequency as the oscillator, if it was it's broken :lol:

I thought we'd already decided that the input of the HT12D is inverted with respect to the HT12A? - so connecting them directly wouldn't work?.

Also, if it's IR, it's modulated on a 38/40KHz carrier - the receiver requires the data, NOT the carrier - an IR receiver IC strips the carrier off, and provides the correct polarity inverted data.

 

[audioguru]

Hi Zach,
Check the schematics from this remote control store:
https://www.rentron.com/remote_control/TWS-4-bit-pack.htm

 

[zachtheterrible]

I thought we'd already decided that the input of the HT12D is inverted with respect to the HT12A? - so connecting them directly wouldn't work?.

Also, if it's IR, it's modulated on a 38/40KHz carrier - the receiver requires the data, NOT the carrier - an IR receiver IC strips the carrier off, and provides the correct polarity inverted data.

I am now connecting them via a 433MHZ tx and rx so they are not connected directly now.
the 433MHZ RX does strip the data of it's carrier.

Those schematics don't really do me any good audio. Take a look at them yourself. They just tell what to solder the pins to basically.

The biggest question that I have now is this: Of WHAT does the HT12D oscillator frequency need to be 1/3 of? 1/3 of the HT12A output or oscillator frequency?

 

[zachtheterrible]

AWWW CRAP!! Now that i have a better understanding of these devices i read over the entire datasheets and finally have a much better understanding of them. Now I realize that the HT12A is meant for infrared and it doesn't seem like it works very well with the HT12D. The HT12E does not have that 38kHz carrier. I wish I had realized all of this before i went and bought them :evil:

I also thought that the HT12E only had one output, and that all of the rest of the pins were address only. Come to find out there are four data pins, just like the HT12A. Ah well, live and learn :roll: .

Im gonna go ahead and buy the HT12E.

 

[eblc1388]

Now I realize that the HT12A is meant for infrared and it doesn't seem like it works very well with the HT12D.

The datasheet specifically mentioned that HT12D works with HT12A.

Ah well, live and learn :roll: .

Yeah, learning is a continuing process. Blaming a datasheet won't get one very far.

Im gonna go ahead and buy the HT12E.

Only to learn again that it won't work with the HT12D. But don't let me stop you. Buy one and prove me wrong.

 

[zachtheterrible]

The HT12E will work with the HT12D. And yes, actually the HT12A will also work with the HT12D, i was wrong on that one.

Take a look at this .pdf. It shows the HT12E working with the HT12D.

Another reason I am going to use the HT12E is because it requires less components for its oscillator; one resistor. The HT12A uses a resistor, two capacitors, and a crystal.