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'[PIC] Seems like an easy way to add wireless to an'
What do you guys think?
> What do you guys think?
I just did a remote temperature sender with some 315MHz modules made
by Radiotronix (available cheap from Mouser). The range is decent,
even with a hand made antenna (I got at least 100 feet). I hooked the
modules pretty much straight to the EUSART. I did invert the TX and RX
line on both sides because serial lines are normally high and didn't
play well with the receiver's AC coupled output. I assume that would
be the case on that module too. A 2N3904 NPN or similar transistor
works fine as a NOT gate for this.
You have to deal with timing on both sides. I had to use crystals for
reliable communication. Especially in my case where the temperature
difference between the two units could be drastic. Following the
application notes from Radiotronix stresses that you need good bypass
caps and a really quiet power supply. Also, pay attention to the
impedance of your antennas.
> I just did a remote temperature sender with some 315MHz modules
> made by Radiotronix (available cheap from Mouser)
The Keymark 433/434MHz variety are available here (NZ) for a few
dollars. ISTR that 315MHz is generally the option in the US
> You have to deal with timing on both sides. I had to use crystals for
> reliable communication. Especially in my case where the temperature
> difference between the two units could be drastic
Some units I use with crystals, some with IntOsc. For IntOSc, Vcc and
temperature variations at either end mean Manchester coding rather than
plain serial is more reliable (IME). If the transmitter isn't on all the time
then you'll need a routine for receiver start-up. With no incoming signal
the receiver turns the AGC way up, looking for RF. The resulting output
is noise. The output of the receiver (Data) doesn't have much drive and
a noise filter might not work. Best way I've found is to send a balanced
(equal numbers of 0 and 1 bits) pre-amble. This stabilises the receiver
output fairly quickly and the receiving micro can then start to time bytes
so it can align itself to the transmitter micro
> Also, pay attention to the impedance of your antennas
18cm (about 1/8th wave) is good for 80-100m, 1/4 wave to perhaps
200m in favourable conditions. Either stiff laminated copper or aluminium
rod seem to work equally well, even with 3 x AA
M. Adam Davis
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