Receiver Frequency for RX-B

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kanni1303

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It's a super-regenerative receiver, L1 and C8 set the frequency. The antenna and nearby objects will cause frequency shift, it isn't a good design.

Beware of those capacitor values, they look very suspicious. I'm guessing the the third digit in pF capacitor values is the multiplier so for example 104pF is actually 100nF.

Brian.
 

It would be appropriate to link the full article, I think. https://www.circuitstoday.com/5-channel-radio-remote-control
The related transmitter uses a 27 MHz crystal.

A part specification like "5 mm ferrite core" isn't particularly specific, I fear. It also shines a light on the project quality.
 

And.... if I understand the transmitter schematic, it's using what I assume is a logic device either as a shunt to sink the oscillator signal or load it to the point it stops oscillating or bias the output stage. Not a good or reliable idea!

Brian.
 

I read the TX-B Rx-B datasheet there is another pin in TX, is transmit with carrier frequency. i think if so, we can use the pin instead of using the external modulator and transmit. But i am not clear in that how to set the transmission frequency.just the pins 12 and 11 acting as oscillator input. Pls tell me that i can try this, is it right one that will be feasible one. i just need to control a bot wireless. i tried for RF module but just for controlling why i should go for data transmission, my bot should be economically cheap so that it will add a point to me. The receiver is ordinary radio frequency receiver and demodulator, they used same transistor used in modulation, I fear to proceed with this Pls help me whether i can go with this... will it work correctly to control relay switch wireless...??? Thanks for ur reply...

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I guess the same... because 151,203 are not available, but 104,105 are available...


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"5mm ferrite core"
for that purpose only i asked which part is responsible for fixing the receiver frequency so that i can replace the inductor with help of the formula...
if so means i would be much easier to remodel the circuit by own... i know the Tx gives the output at frequency range of 0.5KHz - 1KHz which is modualted and transmitted by supporting circuit...


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Here I attached the Tx-2B Rx- 2B Data Sheet
 

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  • TX-RX-B.pdf
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The 'carrier' referred to in the data sheet is low frequency and used when IR LEDs are sending the data rather than RF so you can't use it for 27MHz. All you need is the 27MHz carrier to be keyed off/on by the digital signal at pin 8.

I think there is a mistake in the example schematic, either a choke or resistor should be in line with pin 8 of the TX IC. Pin 8 is a digital output so connecting it directly to the 27MHz RF does not make sense. I would try a resistor of around 4.7K although there would be a risk of the oscillator self-biasing the output transistor anyway.

In the RX, the core type in L1 is not important, only that it has an inductance of around 1.9uH so it resonates at the same 27MHz frequency as the transmitter.

Brian.
 

If so means... you are saying that the carrier circuit is not good, my try is can i use any other modulator like FM with this Tx and Rx...???


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see here also : 4 CHANNEL TRANSMITTER
 

I think you should research how the data is sent. The different commands (forward, backward...) are sent by switching the transmitter on and off in a special sequence. There is a different sequence for each command, this is what the receiver decodes so it knows what you want it to do. The oscillator between pins 11 & 12 decides how quickly each bit of the command is sent out and the bits come out on pin 8. The manufacturer refers to this as the 'carrier frequency'. There is another output on pin 7 which is the same on/off signal but chopped by a higher frequency and is only used when IR LEDs rather than RF is used.

The actual transmission is at the frequency decded by the quartz crystal and the receiver tunes to it with L1/C8. So when you press a button on the transmitter, a sequence of bursts of RF at 27MHz corresponding to the data for that command are transmitted.

You can use any transmitter as long as the receiver is capable of receiving it. The design in the data sheet doesn't look good to me because the transmitter uses a digital output pin connected directly to the RF signal which is bad practice and the receiver can easily be detuned by objects close to the antenna. It is designed for lowest cost rather than best performance and for a very small extra cost it can be made better.

Brian.
 

the technique is for each command duty cycle is different as you said transistor on/off like wise only, this technique is used by the transmitter... and i need only the control hence if there is any interference doesn't cause any data loss... no data i sent with this Tx... i just want to confirm that can i increase the frequency to GHz so that i can have less interference... and also if you can suggest me any other radio transmittter alone with this Tx-2B that i can control with the same 5 controls... and also thanks for your reply...


 

You can use any transmitter and matching receiver. I do not know which ones are available in your country. Perhaps someone more local can advise you.

Personally, I would use AM for this because you only have one data output to control the RF carrier. If you use FM, you still use the same data output to modulate the frequency but you also need a control to enable the RF carrier just before sending the data and to turn it off afterwards. You might be able to use the 'PC' signal for this but there are no specifications for it in the data sheet. Also, with FM it is usually necessary to add a 'preamble' data sequence before sending the command itself, this IC does not seem to have that capability.

If you use AM, there are many transmitters and receivers on the market that operate on 315MHz, 433.92MHz and 866MHz that should work OK.

Brian.
 
sorry for late reply...
here is the new one can i attach my TX/RX-2B to this one
**broken link removed**
**broken link removed**

 

The original design you showed has fixed transmit frequency!

Before going further, are you aware that you need a transmission license to use other frequencies?

Some commercial transmitter/receiver modules allow you to slightly tune them but only within a few 100Khz or so. If you want to make it completely tunable, you will have to tell us what frequencies you want to use because the design will be significantly different for each band. Be warned - tunable HF and above oscillators can be difficult to build and control, particularly in mobile applications.

Brian.
 

None of those are suitable.

Your transmission is a series of pulses at a fixed speed, decided by the resistor in the transmitter. When the TX2B output is high, you should be sending your transmitter carrier, when the TX2B output is low, the carrier should be switched off. You can think of it as being like a very fast Morse code with a different letter for each command. Your receiver has to respond by saying "I see a signal" or "No signal seen" to recover the original pattern as sent by the TX2B. In other words, it has a digital output which can only be '1' (signal present) or '0' (no signal). The designs you show are for analog transmission of voice or music where the output can be any level to reconstruct the original analog input at the transmitter.

Brian.
 

Okay i am going to try with HT12E and HT12D IC reference from : Circuits Today Module

with **broken link removed**
and **broken link removed**

but my query is if i switch ON two inputs will it give same output in the decoder...
that means can i switch on two devices at same time...

technically
can i send all the 16 possible inputs on the 4 controller input (AD 8-11)and receive the same 16 possible in the output decoder...
0000
0001
0010
......
1110
1111

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or can i use AM or FM for this encoder and decoder IC
 

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