Ne567

[marcbarker]

One more thing, RL circuit are used as an oscillator in a transmitter, and the same RL circuit can be used for tuning, right?
So does this mean that i can use a crystal oscillator for tuning?

Please define "RL circuit".

 

[trennonix]

Please define "RL circuit".

ah, ah sorry my bad, i meant LC (inductor and capacitor set in parallel)

How did you workout the baud rate that i get?
i was using a µC to generate those freq (i'm more of a software guy than hardware one),
would an NE555 timer suffice for the job or should i look for an alternative ?
(i hear ne555 are simple to implement)

 

[marcbarker]

How did you workout the baud rate that i get?

Educated guess-work based on nearly 30 years experience!

If you're using a uC, you don't need a 555.

Thinking about this, if you're a whiz software, you could just feed the 2-tone signal straight into the pin of another uC and detect* the tones there in software. You'd turn the recieved 2-tone signal into a square wave at logic levels, before feeding into uC.

*time each transition period. Average these periods as a rolling average. Decide if the average is currently at 700 or 1000 Hz. Call it a crude 'software PLL'

 

[Nigel Goodwin]

PCM

#4 mentioned ASK, but 567's don't respond to ASK. I used the term 'PCM' loosely to make a distinction. The nearest a 567 will do is 'half' of ASK, that is detect the presence of a single tone only, which one it is a predetermined choice of the two. To detect both tones would require two 567's, one for each tone. The response time delay of the 567 makes it a poor choice for receiving data (which I loosely called 'PCM').

There's a multitude of ways of doing ASK demod., but 567s I would consider a poor choice, unless the data rate was about low i.e. 5 bps.

A 567 was a 70's solution to a 70's problem - you only need one for ASK - and you only detect ONE of the tones, the output of the single 567 follows the original data supplied to the transmitter. And following the 70's theme, a simple 555 timer running as an astable was often used as the modulator, simply switched between two different frequencies.

Data rate was usually either 300 or 1200, depending on the tones chosen, in keeping with standard baud rates.

 

[trennonix]

1- what other options do i have for sending ones and zeros in a more modern, quicker and hopefully simpler way?
-I hope to send at least 24 bits in one sec (faster is better)
-I want to use the cheapest parts possible

2-a while back, i made a simple FM transmitter, one of those 2-transistor transmitters you find around the web,
can i simply replace the LC circuit with a crystal oscillator? (or other modifications are to be made)

3-"One more thing, LC circuit are used as an oscillator in a transmitter, and the same LC circuit can be used for tuning, right?
So does this mean that i can use a crystal oscillator for tuning? " no one has answered this question, Plz

 

[Nigel Goodwin]

Why don't you use a licence free radio module?, these are legal and simple to use.

You can use crystal control for both transmitter and receiver (many of the licence free modules do), some are AM, some are FM. some CW, some ASK and some FSK.

Only 24 bits in one second is incredibly slow (only 30 baud), most licence free modules are 1200 or 9600 baud.

 

[trennonix]

ready made modules are just too expensive (16$ for the couple!!!)
and let me get this straight, i can remove the cap and inductor from my receiver and put a 2-pin crystal in their place?

 

[Nigel Goodwin]

ready made modules are just too expensive (16$ for the couple!!!)

And how much are fines for illegal use of the radio spectrum?.

and let me get this straight, i can remove the cap and inductor from my receiver and put a 2-pin crystal in their place?

No, you have to redesign it completely, and make it into a real radio.

 

[trennonix]

we don't have rules for short range transmission
i just need to cover a house


as for a transmitter, can i do the preceding operation no problem or same story

 

[Nigel Goodwin]

we don't have rules for short range transmission
i just need to cover a house

So you're wiping out the local militaries radio comunications, and no one cares?. Sounds risky in that part of the world.

as for a transmitter, can i do the preceding operation no problem or same story

Same story.

 

[trennonix]

I'm not anywhere near a military base, but i think i should review some legal documents.

And wouldn't it be easy to mod an existing Tx and Rx to operate at 300Mhz?

i was thinking of running my device at 60Mhz right between RC toys and Radio

 

[Nigel Goodwin]

I'm not anywhere near a military base, but i think i should review some legal documents.

And wouldn't it be easy to mod an existing Tx and Rx to operate at 300Mhz?

Depends on how close to 300MHz they already are?, but why 300MHz?.

 

[marcbarker]

I don't mean to de-moralise you trennonix, but there is a far bit of knowledge required in RF design, this book link is an example. I suggest you download it and read a few pages a day. There's a chapter in there about Oscillators.
**broken link removed**

It came from **broken link removed**

 

[trennonix]

i thought that ready made modules were at that frequency, maybe 340MHz aren't they?

i was thinking of running my device at 60Mhz right between RC toys and Radio

 

[trennonix]

I don't mean to de-moralise you, but there is a far bit of knowledge required in RF design, this book link is an example. I suggest you download it and read a few pages a day. There's a chapter in there about Oscillators.
**broken link removed**

It came from **broken link removed**

I was more thinking of modifying an existing working Transmitter and receiver removed from an RC toy, but as we got more and more into the conversation, i started expanding my ideas
Would simply modifying inductors and capacitors in the oscillator have a tremendous effect on the working of any device (other than the frequency since this the whole point of modding the values)

 

[Nigel Goodwin]

i thought that ready made modules were at that frequency, maybe 340MHz aren't they?

Depends on the country, most are around 430MHz - but to be licence free they have to pass type approval tests.

i was thinking of running my device at 60Mhz right between RC toys and Radio

There aren't any blank spots in the spectrum anywhere, all are already allocated - what are you trying to do anyway?.

 

[Hero999]

27MHz is free in most countries and is easier to design for than UHF.

Sorry I haven't read the whole thread in it's entirety, what sort of datarate do you need?

If it's fairly low, I would be tempted to use PFM (Pulse Frequency Modulation) because it only requires a small amount of power and is trivial to both transmit and receive.

 

[marcbarker]

What about modifiying a pair of toy walkie-talkies? They have a range a little longer than shouting distance, can handle audio signals OK and run off square 9 V batteries. If there's anyone else on same frequency, you can easily bend the coils inside them a bit to find an 'empty channel'.

 

[trennonix]

marcbarker this what i'm trying to do but with an rc car radio
i looked at an rc car's radio and walkie-talkies, the car's radio is alot simpler to reproduce
bending coils isn't an option since i'm trying to make a commercial product, right now i'm still in very early prototyping stage so no need to worry about getting illegal half working radio into strangers houses

Hero999 i'm looking for something faster 30bps, 120bps would be ideal; i don't want use 27Mhz nor 49Mhz since most toys use this freq

 

[Nigel Goodwin]

If you're trying to make a commercial product, then you first need to find out 100% what the restrictions and possibilities are, plus what testing and approval you may have to pass - assuming it's for market only in your country, you only need to do this for your country.