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HT12E HT12D working when wired directly but not through RF modules

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pkshima

Member
Hi,

I built the remote control given at the following link.

**broken link removed**

It didnt work. So to make sure the HT chips are not the problem I connected directly the data out pin (17) of HT12E to the data in ping (14) of HT12D using a wire. And it worked perfect.

I do know that the RF modules I have work because they work ok in other circuits. These are cheap Chineese thingies 433 Mhz.

Could someone please give me ideas on how to debug this issue. Unfortunately I dont have a scope :(

Many thanks,
Pradeep
 

Gayan Soyza

Active Member
I have noticed that HT12E & HT12D chips works with AC coupled RF modules.Cheap Chinese ones I use doesn't contain AC coupled.Their RX output will permanently high until TX sends low.

Nigel knows this incident very well.
 
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pkshima

Member
Thanks for replying.

any possible workarounds ?
 

pkshima

Member
Following Gayan's tip, I tried pull-down resistor on the data in of HT12D so that it returns to 0 when no transmission but to no avail :(

I am so frustrated. if these rf modules arent as easy to use as the internet claims, then what is the easiest way to do rf ?
 

pkshima

Member
Thanks for the reply Nigel !!
Unfortunately I do only a project or 2 in a year and therefore will not be able to justify the cost of a scope.

Anyways I played some more with circuit. I have 2 rf modules and it happens that using the TX of one pair with the RF of other works. Some combinations dont work at all while in some it works if I bring my screwdriver near the breadboard etc.

I thought the "works only when screwdriver near" happens only in self made RF circuits on breadboard.

The same RF modules work perfect in all combinations when used to try your RF tutorials.

Does this new info bring any ideas to you ?
 

peterbrown

New Member
Have you checked the resistor value between OSC1 and OSC2? This value should be matched with the receiver value. I canot remember the value, but you should find a match table on the datasheet or somewhere.
 

pkshima

Member
Ah found it !! It was a voltage issue.

The RF pair that was not working apparently needs exactly 6V to work. not a volt less not a volt more.
And I have been trying it at 5V, 9V and 12V.
I just powered it with LM317 and turned the pot till it worked.

Thanks for all the help guys.
 
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