300MHz RF module

[audioguru]

You can't find the schematics and can't find the parts. Make something from a schematic and you can get the parts.

 

[bananasiong]

How about the transmitter? I have the schematic but don't have the parts. Can I replace those components?
I think the c9018 is KTC9018, if I want to replace with another transistor, which rating between them should be the same? Is it the frequency? What about the value of rfc?

Thanks

 

[audioguru]

If you change the transistor then the new one will have different capacitance and gain so the frequency and output level will be different. It looks like its frequency is not adjustable.
Try a different RFC, it will probably work.

 

[bananasiong]

Yes, the frequency of the transmitter is not adjustable, the adjustment is being done on the receiver. Must the value of the rfc for both transmitter and receiver be consistent? They are the same for the original circuit, if I change for the transmitter, then I need to change for the receiver as well right?

Maybe I should start replacing a part followed by another part.

Thanks

 

[audioguru]

The RFC doesn't affect the tuned frequency. Its inductive reactance is just a high impedance.

 

[bananasiong]

Hi,
The schematic of the transmitter comes with the transmitter, but I found that on the schematic, the oscillator is made by NAND gate, but it is a HEF4001BP, a NOR gate. If it is a NOR gate, then should I change to pull one pin down?

Can I use normal logic gate such as 74ls00 or 74ls02 to do oscillation? I've tried with the same circuit, cannot.

Thanks

 

[audioguru]

The output of a NAND gate goes high if an input goes low.
The output of a NOR gate goes low if an input goes high.

The modulating oscillator is for Cmos logic, not old TTL logic.

 

[bananasiong]

Then I have to trust the internet that HEF4001BP is a NOR gate but not a NAND gate. I have wasted another PCB which has already been drilled and ready to solder..

 

[audioguru]

A CD4011 or a HEF4011 is a Cmos quad NAND gate package. Its pins have the same layout as a 4001.

 

[bananasiong]

A CD4011 or a HEF4011 is a Cmos quad NAND gate package. Its pins have the same layout as a 4001.

Oh, then I can remain to use the design for NAND gate, thanks.

This is the receiver circuit that I've just done. The IC is LM567/NE567 phase lock loop.

This receiver circuit is designed for 12 volts, but I plan to use only 9 volts then I have to change to 9v relay. How about the zener diode?
From the schematic, I think when the signal is received, pin 8 of the phase lock loop gives a low, to turn the LED on and also the relay. If I don't want to use a relay, then I replace it with a resistor, and pin 8 to the microcontroller, can I?
I know the coil paralleled with the trimmer cap is to oscillate at 300MHz, but what's the purpose of the coil and the resistor at the antenna side? From the board, these coils are located near to each other.

Thanks

 

[ljcox]

This receiver circuit is designed for 12 volts, but I plan to use only 9 volts then I have to change to 9v relay. How about the zener diode?

If it is a 9V battery or a regulated supply, then you can remove the C945, the 510 Ohm and the Zener. I don't know if 9V relays are available. If you have to use say a 5V or 6V relay, then it is likely to need more current. So you should check the data sheet of the PLL to see if it can sink that current. You will also need a resistor in series with the relay coil in order to ensure that there is 5V across the coil (if it is a 5V relay). Don't forget to leave the diode across the coil.

From the schematic, I think when the signal is received, pin 8 of the phase lock loop gives a low, to turn the LED on and also the relay. If I don't want to use a relay, then I replace it with a resistor, and pin 8 to the microcontroller, can I?

Yes pin 8 goes low when a signal is received. If you want to connect it to a micropcontroller, you will have to insert a 10k resistor between pin 8 and the input to the micro. Leave the LED and its resistor to act as a pull up.

I know the coil paralleled with the trimmer cap is to oscillate at 300MHz, but what's the purpose of the coil and the resistor at the antenna side? From the board, these coils are located near to each other.

The coil on the antenna side is the primary of a transformer formed by the 2 coils. This is necessary to match the antenna impedance and the inout impedence of the receiver. I don't know why they have included the resistor.

 

[bananasiong]

If it is a 9V battery or a regulated supply, then you can remove the C945, the 510 Ohm and the Zener. I don't know if 9V relays are available. If you have to use say a 5V or 6V relay, then it is likely to need more current. So you should check the data sheet of the PLL to see if it can sink that current. You will also need a resistor in series with the relay coil in order to ensure that there is 5V across the coil (if it is a 5V relay). Don't forget to leave the diode across the coil.

Yes, a 9 volts relay is available here.

Yes pin 8 goes low when a signal is received. If you want to connect it to a micropcontroller, you will have to insert a 10k resistor between pin 8 and the input to the micro. Leave the LED and its resistor to act as a pull up.

Can I do this way: Use 9 volts for this receiver, 5 volts for the microcontroller, then pull up with a 10khm: resistor from the 5 volts supply and remove the led, 510hm:, relay, C945, then pin 8 straight away to the microcontroller, is this okay?

The coil on the antenna side is the primary of a transformer formed by the 2 coils. This is necessary to match the antenna impedance and the inout impedence of the receiver. I don't know why they have included the resistor.

I can't draw exactly the same as the layout, so it might not be working for mine

EDIT: BTW, which one is the decoupling capacitor? 47uF or 100uF? Or I have to include both of them?

Thanks

 

[ljcox]

Can I do this way: Use 9 volts for this receiver, 5 volts for the microcontroller, then pull up with a 10khm: resistor from the 5 volts supply and remove the led, 510hm:, relay, C945, then pin 8 straight away to the microcontroller, is this okay?

I suggest you post a circuit so we can see what you mean. The text is ambiguous and if you do it incorrectly, you may damage something.

EDIT: I have looked at the LM567 data sheet and the output is an open collector. Therefore, if I understand what you wrote, then you can do it. But I suggest that you still post a circuit so we can be sure.

EDIT: BTW, which one is the decoupling capacitor? 47uF or 100uF? Or I have to include both of them?

They are both decoupling caps. If you remove C945, you won't need both. I suggest you leave the 47 uF on the PCB

 

[bananasiong]

Hi,
I mean this. Is this the same as what you expected from my text?

Thanks

 

[ljcox]

Hi,
I mean this. Is this the same as what you expected from my text?

Thanks

Yes, that's what I thought you meant. It is correct as drawn.

 

[bananasiong]

Hi,
The coil on the PCB drawn by me is not as thick as the original one, its size is small just a little compared to the original one. Should I change the value of the capacitor a bit to match the frequency? Is center tap of the rfc to the on board coil critical? Should I change the place of center tapping to increase the sensitivity?

Thanks

 

[ljcox]

Hi,
The coil on the PCB drawn by me is not as thick as the original one, its size is small just a little compared to the original one. Should I change the value of the capacitor a bit to match the frequency? Is center tap of the rfc to the on board coil critical? Should I change the place of center tapping to increase the sensitivity?

Thanks

I'm not an RF expert.

If you increase the 5 pF it will decrease the frequency.

I can't see any tap on the RFC.

 

[audioguru]

I wonder how many pcb's need to be made to get the frequencies of the transmitter and the receiver the same.

 

[ikalogic]

for the data transfere, i suggest the serial UART included in many uControllers, for example ATMEL UART in MODE 2 can be used as 1 wire interface, where in your project, the one wire would be replaced by the RF communication

 

[Hero999]

I wonder how many pcb's need to be made to get the frequencies of the transmitter and the receiver the same.

It probably doesn't matter because the selectivity of the reciever is so poor.