HT12 Encoder and decoder question

[Speedgnom]

Hello everyone.

I have a question about the HT12E and HT12D chips. I am trying to make a simple wireless remote controll car with those chips, but I have a question. Should I use an RF module for wireless communication so the digital signal can be processed or can I make my own transmitter and reciever? I know how to use the chips, but I don't know if I need special RF modules or can I use my own transmitter and reciever, since I don't know the exact way the HT12D reads the information from HT12E.

I also have another question. Is it possible to use only one output terminal of the chips for audio signals? Because the encoder chips has 4 terminals for input for calues 1s and 0s, and 4 output terminals for the decoder.
By that logic can I just connect a microphone with a transistor to one of the terminals of the encoder to get a value of 0 0 0 1 and transmit it to the decoder and have a speaker connected to the decoder on the pin that the value of 1 is assigned to?

Thanks in advance.

 

[Ogu Reginald]

I prefer to use the RF modules for the HT12E and HT12D chips.

 

[Speedgnom]

But it shouldn't be a problem if I use my own transmitter and reciever, right?

 

[Audioguru]

Why did you mention a microphone and a speaker?
A microphone will not press a pushbutton switch on the encoder and the decoder does not have a power audio amplifier.

If you set the encoder's oscillator to be an audio frequency then there will simply be a buzz if the decoder has an audio amplifier and speaker connected. I think each pressed pushbutton switch will sound the same.

 

[betwixt]

Agreed, those devices are not suitable for audio data linking. If you really want to link by audio, use DTMF instead but unless you are in a very quiet environment I wouldn't use audio at all.

Yes, use RF modules, they are difficult to make if you want them to be compliant with national/international regulations so I strongly recommend you buy ready made ones. You can get AM (OOK) or FM ones. FM tends to be a little more expensive but will give more reliable results.

Brian.

 

[Audioguru]

The old encoder and decoder ICs were made (are they still made?) for very cheap remote controlled toy cars. To be cheap, they do not use adjustable steering and power, instead they are "bang-bang" which is maximum left, straight or maximum right steering and maximum forward, stop or maximum reverse.
I am posting schematics of their radio parts. The transmitter uses only one transistor plus another as the AM modulator that is not shown. The receiver is a super-regen that uses only one transistor plus two more for the amplifier and motor driver.

 

[Speedgnom]

Thank you all for the replies. I guess RF modules will be best for my project.

I have a question on the side which is off-topic. Can anyone tell me a good way to make a kind of a walkie-talkie that encodes the output and then the other walkie-talkie has to decode it. Like a private channel, so no one else can listen to your conversation if they tune to the same frequensy. That is if it is legal to make such a device.

You have all been very helpful I really want to thank you all for your help.

 

[betwixt]

The legality of encrypted communication over a public channel will vary from one country to another, check with your national licensing authorities.

Because the range of transmittable audio frequencies is limited, you have to use a method of encoding that keeps the result within the audio pitch range. Some systems use 'chop and resequence' algorithms to rearrange the sound samples to make them unintelligible, you have to store them and put them back in the correct order to make it understandable again. Another popular system is spectral inversion, you swap high and low frequencies (a.k.a. Donald Duck mode) which you can re-reverse at the receiver to make it normal again. None of these methods is trivial, you need fairly advanced electronics to make them work.

Brian.

 

[Audioguru]

I made an encrypted encoder and decoder for a wireless telephone conferencing transmitter for a new bank's new head office. They had secrets.
I used a Motorola MC1496 balanced modulator/demodulator IC for the encoder and another for the decoder and made single sideband with suppressed 4kHz carrier.

High audio frequencies were received undecoded as low frequencies and low frequencies were received undecoded as high frequencies (as Brian said) so nothing was intelligible. The decoded signal sounded exactly like the original signal.

A ham radio user might recognize the encrypted sound and make his own decoder.