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Topic: Arduino-controlled OOK modulation with quartz crystal (Read 1 time) previous topic - next topic

engineer.bg

Hi everyone,

I don't have an extensive background in RF and a couple of hours of googling didn't yield a clear answer, so I figured its best to ask. Most of the "cheap" RF projects use inexpensive RF transmitter/receiver pairs, which do e.g. OOK modulation on the carrier frequency like 315 MHz, and wire it up to some PWM pins on Arduino to receive/transmit data, e.g. using VirtualWire.

So far so good, but I was wondering if it can get even simpler/cheaper:
- PWM pin connected directly to a quartz crystal (any crystal freq will do)
- VirtualWire RX and TX pins set to the same PWM pin (ok, this is minimalistic approach, but should work)
- simple wire antenna connected to the crystal (with appropriate length)

Could this work? I've seen a similar approach to receive/transmit directly via RS232 from a PC...

Thanks in advance!

johnwasser

A crystal has to be part of a positive feedback loop in order to oscillate.
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engineer.bg

In order to have a stable oscillation for a "longer" period - for sure, but what about short bursts if e.g. excited at 9600 baud or higher?

johnwasser


In order to have a stable oscillation for a "longer" period - for sure, but what about short bursts if e.g. excited at 9600 baud or higher?


Couldn't hurt to try.  Good luck.
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engineer.bg

FYI, where the idea came from:
http://sci-toys.com/scitoys/scitoys/computers/radio/computer_controlled_transmitter.html

david17

What is the 3rd connection on the Xtal?
Is this the 1st April?
David.

johnwasser


What is the 3rd connection on the Xtal?


That's not a crystal.  That's an oscillator.  It take power and ground for input and the output is a square wave. There is probably a crystal inside, along with the positive feedback circuitry I mentioned earlier.
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david17

Just found this.
"It's a CMOS oscillator, and can handle about 10 volts
before it turns off and stops oscillating. The overvoltage
doesn't seem to do any damage, so there may be an overvoltage
protection in the circuit, by design or by accident. After
putting 12 volts in and getting no oscillation and no heating,
I went back to 9 and it worked fine again.

The spec sheet will tell you the limit is 5 volts. "
David

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