Hi all,
Just got [this here handy RF Link transmitter/receiver pair from Sparkfun. Upon testing it out, I’m seeing a constant square wave (4ms pulse width) on the receiver’s data pin. All the time. The transmitter isn’t even plugged in. Any idea what’s going on? I don’t think there’s anything around causing interference. Anyone else have this problem?
Thanks in advance,
Randall](RF Link 2400bps Receiver - 315MHz - WRL-08948 - SparkFun Electronics)
I’m having similar problems. Anyone get these things to work correctly?
Oh thank you! I thought I was going insane - and it’s hard to go someplace you already are…
I get a ~6ms square wave with no transmitter on. With the transmitter on and sending data, I get some garbage from the receiver that looks nothing like serial data, basically just a pulse on the rising edge of the square wave.
P-P is about 2.6v on the data line (both ends of the system are powered by clean well-regulated 5v reading 5.0004 average under load) on the signal.
I spent a good three hours trying to make these things work. I have three sets of them, all three behave the same way.
I thought feeding the ttl-rs232 level lifter from Sparkfun was the problem (even though it works fine direct-connect to the device sending the signal), so I dug out a microcontroller and fed the {alleged} ttl into it directly and wrote some code to log the results. Nada.
I have to say at this point I suspect these devices just don’t work…
Grrr.
Have you directly emailed Sparkfun support? I recall seeing another recent thread reporting problems with this or the 432MHz set. Sparkfun may have received a defective lot and should be given an opportunity to investigate.
Hi Riden, thanks for your note!
Yes, I did, a little soon to have heard something back yet.
The upshot is that they’re being offered as a direct serial line replacement. The overwhelming consensus is that the minimum requirement is to send sync bytes, then check bytes. If one has to muck around with their already existing protocol, that doesn’t a “direct serial line replacement” make, imho. Unfortunately, adding another microcontroller into my application to handle waking up a receiver isn’t practical. The device is intended to be a black box with the serial ttl exposed…
[shrug] Live and learn. Enough time into those. I’m off to XBee - a transparent serial line replacement. 
[edit: fixed the spelling of your handle. Darned spell-checker doing the “right thing” wrongly - or is that the “wrong thing rightly” ? 
I agree that these units are NOT transparent and require either encoder/decoder chips or processors on both ends. Knowing that, it isn’t hard to get things working. I have several pairs in use around my home and lab.
On the topic of transparency, the BlueSMiRF modules are also supposed to be a serial cable drop-in replacement. They work better, but there is no way to signal via DTR or the other RS-232 control lines. I wanted to remotely bootload a robot and I had to hack my application code to look for a reboot sequence which would reboot the board. Had the DTR line been made available on the remote end, it would have been seamless.
The XBee modules do provide the functionality you desire including the extra RS-232 lines (including general I/O lines) making it very suitable for a lot of purposes. They do operate at 3v, so that must be kept in mind.