Originally Posted by bananasiong

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.

Originally Posted by bananasiong

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.

Originally Posted by bananasiong

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.

Originally Posted by ljcox

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

Originally Posted by bananasiong

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.

Originally Posted by bananasiong

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

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

Thanks

Originally Posted by bananasiong

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.

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

Originally Posted by 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

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.

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

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

Originally Posted by audioguru

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.

The selectivity of the receiver is too poor? Oh no, this is the only type of RF module available here.

EDIT: The rfc is not being center tapped, but it center taps the coil on the PCB.

Originally Posted by bananasiong

The selectivity of the receiver is too poor?

The crappy receiver has only a single tuned circuit. It has only a single transistor which might be in a lousy regen circuit. It is a very cheap circuit.

A real radio has many tuned circuits and transistors or an IC.

Who cares?

It's good enough for the job it was origionally designed for, to switch a relay on when it recieves a signal. Unfortunately it probably isn't good enough for what you want to do. Perhaps you should consider buying a module designed for data transmission.

I think this module can be modified for data transmission, but I've tried building a few PCB, they didn't work. I thought I can make it without any problem, because I don't want to use the RF module straight away.

This is the only RF module available here. I've found from Malaysia's website, there're good RF modules, work at 433 and 8xx MHz. Then I need to ask someone to order by credit card for me , and they are not cheap too.

Hi,
i found this, max7030, can I use this to transmit and receive digital signal? Is the value of the crystal oscilator critical? Or can I replace with some other value? How about the ceramic resonator? I thought the center pin connected to ground, then the rest can be connected either way, but there are 'in' and 'out' in the datasheet.
There is no trimmer capacitor, can this work well? I thought the stray capacitance on the PCB can affect the operating frequency?

http://datasheets.maxim-ic.com/en/ds/MAX7030.pdf

Thanks