does the Tx module actively transmit (active RF) both 1 and 0? Or does it only transmit the 1’s, with RF silence indicating a 0?
The reason I ask is that I would like to use multiple transmitters with a single receiver. The datasheet doesn’t indicated any kind of “enable” (silence) pin or tri-state data input, so I’m wondering if I have to power down the Tx module to achieve RF silence between packets. The time to power up the device (10-20mS) may be too long for my intended use.
Of course, helpful suggestions & alternatives are always appreciated.
The data sheet says that it uses ASK (Amplitude Shift Keying) modulation. This is also know as OOK (On Off Keying). When the input is ‘0’ the carrier is 0%, when the input is ‘1’ the carrier is 100%.
So yes, basically it only transmits if the input is a ‘1’.
Waltr is correct, these only appear to transmit on data 1’s. A few other things you can look into for using multiple transmitters with a single receiver - you can encode your data with various hardware encoders/decoders. This would allow you to have a different hard set encode on each transmitter, and on the receiver you could use IO pins to set the decode bits to decode a particular transmitter. Or, you can do this via software, when sending data, send an ‘identification’ byte or two that your receiver will see, and can then determine which transmitter its talking to.
I’ve got a few sets of these modules, their definitely cheap and inexpensive, but they do work
krphop:
I’ve got a few sets of these modules, their definitely cheap and inexpensive, but they do work
Exactly what I need: inexpensive. I will need a half dozen of these for a robot localization project based on [[this article](http://www.eis.uva.es/~eduzal/015-m2vip_full_paper.pdf). I have read a number of white papers on localization via beacons, both active and passive. That particular article uses active, non-networked beacons that are cheap and easy to build; even easier than when the article was written.
Since you have some experience with these devices, would you say that OOK is like a “wired OR”, lending itself to I2C-style collision resolution? I don’t expect to need it. Just curious.](http://www.eis.uva.es/~eduzal/015-m2vip_full_paper.pdf)
most of these OOK 433 devices just transmit in the blind - no CSMA/CA as they have no receiver. In the US, the FCC regulations prohibit a high duty cycle - i.e., like no more than 0.1% or some such. This, plus randomized transmission intervals, plus unit ID and CRC, yield “good enough” for garage door openers, wireless thermometers, etc.
http://www.sparkfun.com/commerce/images … L_i_ma.jpg
http://www.sparkfun.com/commerce/images … L_i_ma.jpg