I had been running a serial BT adapter for telemetry to my APM that I had from my Mulitwii days...I had a crash and killed it....bought another 4 pin HC-06 style serial BT module to replace it (exactly like all the other $5-$10 ebay modules)...but cant get Mavlink communications over it from the APM with my phone or tablet any more...
1. I changed the baud rate to 57600
2. I can type back and forth from my phone to PC with the BT module connected to the FTDI adapter I used to change the baud rate (also verified I could inquire the name, mode, etc. of the BT module using AT commands)...
3. When I try to use it on the APM, the tablet/phone pairs and connects, but no data apparently gets thru and I get Mavlink timeouts on the GCS on the tablet/phone.....I have double checked TX/RX....I use a Y cable to allow either the BT or a 915 Mhz radio on the copter...the copter radio works fine with the tablet with a USB radio but switching over to BT on the copter fails with Mavlink timeouts....again, I double checked that TX and RX wires are correct going to the BT module (I even switched them, not trusting my eyes/ohmmeter...no change)...
4. The module is rated for TTL inputs 3.3V to 6V..and it works fine connected to my 5V FTDI adapter on the PC
Anyone have any suggestions?....the module obviously works fine on the RF link side and the serial input side...but not with the APM...very strange
Replies
Bought another module... http://www.ebay.com/itm/290944831606?ssPageName=STRK:MEWNX:IT&_...
this one works fine....so beware of a look alike http://www.ebay.com/itm/281214488342?ssPageName=STRK:MEWNX:IT&_... it needs better logic levels even though it states it works with TLL levels (3.3V APM supplies compatible levels...ie 0.8V low and 2.4V high..) but apparently loads the APM too much to work...it does work with my FTDI adapter...
they are definitely different since the one that works has a very fast response to AT commands (must paste them into the terminal...typing is too slow)...vs the latter in which AT commands need a <newline> to terminate them...look the same, but arent
Update, just to check...I reprogrammed the BT module to 115K for MultiWii...hooked it up to an old MultiWii board...ran the Multiwii config tool from my phone...connected and transferred setting, acc data real time, etc....verifying that the BT module is fine...again, I ohmed out the y connector to be sure the data signals were the same for the radio as the BT module, so it should work when I replace the radio with it...doesnt, either with Andropilot or Droidplanner