Hello board,
I recently bought the MO-RX3400 transmitter and receiver pair off of sparkfun. I got these working on a previous project using the Arduino board, but now I want to use the HC11 for a project.
Looking at the HC11 schematic it just seems I would use pins 21 (TX) for the data pin to the transmitter module? Or is there an easier way?
Also has anyone ever got this to work with the HC11, and could you provide a code snippet of the setup just the RF communications?
Thanks
HC11 as in MC68HC11, the old Motorola micro?
If so, yes, the HC11 UART can be connected just as you would have done with the Arduino. One thing to note though: The transmitter will be sending all the time when TX is at “idle line”. You might want to think about a means (e.g. three-state buffer such as 74LV125 or an NC7SZ125) to allow the TX pin from the micro to be disconnected to the transmitter when not actually transmitting. (I can’t recall if the HC11 UART can be disabled and the pin set to input which would produce the same result…) Use a 10K pull-down on the TX input to ensure it’s “off” when the UART TX pin is disconnected. This will help ensure that (a) you’re not hogging the band all the time and (b) that you improve battery life (if this is important…)
You’ll probably want to create a little protocol involving, say, break, pre- and post-amble characters, checksums, idle-line wakeup and the like to help align the transmitter to the receiver. I’ve got a project going with a Cypress PSoC and had to use a sequence after connecting the UART to the TX to allow the receiving station to adjust its gain and synchronize with the datastream from the transmitting station. This was needed because the receiver had numerous bit errors on the first few bits received soon after turn-on of the TX.
One more note: When your transmitter is off, the gain on the receiver goes to max (depending on the environment) and the RX pin of your HC11 UART will driven crazy by the output of the receiver. Make sure your structure your RX interrupt handler to deal well with a noisy input: No doubt you’ll get all sorts of framing and noise-flag errors.
You’ll need to experiment with the baud rate. I found ~1200 works reliably at 5V through a cinder block wall and 20-30 ft of separation.
Since you’ve already had this working with another platform you probably already know all this but I thought I’d throw it out there anyway…
Thanks a lot! yes the old Motorolla micro, I’m gonna work on this tonight and let you know what I come up with, I might need help haha