SPP Bluetooth Module; Questions about default config - Page 1
Forum section: electronics / general

author: Isamun
author_rank: Regular Contributor
timestamp: January 04, 2014, 03:29:17 pm
content: Hi!Me and my dad are working on a project form the mid 90s. It uses a serial monitor to display a CLI-style menu system. We want to put one of those SPP (serial port bluetooth) modules in there to get wireless connectivity.The issue seems that, while the module remembers its baud rate and BT name, it seems to "forget" some of the other parameters which makes it inquireable and possibly more. In short it seems to require some lines of config after power up before we can pair with it.Anyone who has played with this before, did you find a way to store the full config so that you could use it without configuring it on every power cycle?The module in question is theGrove - Serial Bluetoothfrom Seeed. We are using the example code on an arduino for testing.Thanks!

author: mubes
author_rank: Regular Contributor
timestamp: January 05, 2014, 10:56:26 am
content: I've been burnt by this before because I was resetting the module immediately after changing parameters...so make sure you wait awhile if you're doing that so the nvram can be written.Also be aware that there's about a bajillion different versions of firmware knocking about for these modules, so it would be useful to know a bit more about which firmware version is in your module.Dave

author: Isamun
author_rank: Regular Contributor
timestamp: January 07, 2014, 08:52:41 pm
content: Thanks for the response.We gave up on the idea of using it stand-alone. It doesnt seem to become pairable without being configured at each power-up.This lead us to adding an arduino, a reed relay (for system reset), some control logic and the BT module. In this effort of trying to get things rolling the module stopped cooperating. Now we cant get any other signs of life out of it than a flashing LED (indicating power).The logical conclusion is that we somehow missconfigured the baud rate (since the module seems to remember that) and that now it doesnt understand anything we try to write on the serial line. We tried using 9600 and 38400 back and forward and could not get it to work.If there was some way to tell these modules to write something on the serial line i could scope it and figure out the baudrate. We have never gotten the module to speak back unless its connected to a master device.If we can reset the module back to some known default, then we could implement that into our code to make it behave the same way on each power up.In regards to the firmware;How do I go about finding the firmware on these modules?The documentation is rather horrible. From what I gather the module in question is BC417 based with some (dumbed down?) unknown firmware.Erik

author: Maxlor
author_rank: Frequent Contributor
timestamp: January 07, 2014, 09:28:03 pm
content: This might not be what you want to hear (buy new hardware!) but for this sort of application, the RN-42 works really well. It has this mode that's basically a drop-in replacement for serial cables. You can set it up using only jumpers. You can pair two modules, then remove the jumpers, and from then on they will auto-pair, all without needing any software configuration (until you reset them using another jumper.) The default baudrate is 115200, which in my experience has been fast enough to not require software reconfiguration. There is a 9600 Baud fallback jumper, but for other rates I think you need software configuration, which isn't persistent iirc.I've used the module for several projects, for example to achieve galvanic isolation in an ECG project. It works well within the constraints of bluetooth (pairing gets a bid dodgy once signal quality drops, i.e. with distance, and it takes longer to connect if both modules aren't powered at the same time, probably because they eventually enter power saving mode if no partner can be found within a minute or so.)In fact they're so useful that I built an adapter board that accepts both TTL and RS232 serial level I/O, as well as power from a standard lion battery, and keep them in my tools drawer just in case

author: zapta
author_rank: Super Contributor
timestamp: January 15, 2014, 11:54:46 pm
content: Quote from: Isamun on January 07, 2014, 08:52:41 pmCheck the datasheet, it may have a way to factory reset the non volatile memory.

author: mubes
author_rank: Regular Contributor
timestamp: January 16, 2014, 12:34:09 am
content: These things can be reprogrammed/defaulted via the spi pins on the base (shorter side) of the module. Google 'reprogram hc-05' for info...would provide links, but I'm on a poor ui, sorry.Some firmwares spit out some text when they wake up, so its worth checking if anything is coming out.Dave

author: Isamun
author_rank: Regular Contributor
timestamp: January 16, 2014, 01:47:32 am
content: Hi guys!Thank you for the responses! We have opted for some new hardware (RN-42) in hopes of eliminating the need for the MCU (arduino UNO). I found some info on hackaday about reprogramming the firmware of these modules, but I really dont feel like dicking around with that. Seems like a project of its own.My father went back to the owner of the lighting system to reinstall it. At some point we will finish this upgrade. But in any case I have to write an app that emulates a VT220 terminal over BT with some GUI for control of the system.I will ofcourse keep you all up to date on the our progress.

author: zapta
author_rank: Super Contributor
timestamp: January 16, 2014, 01:59:41 am
content: Quote from: Isamun on January 16, 2014, 01:47:32 amI am also in the market for a wireless replacement for a serial connection and from reading around the RN-42 is at the top of my list. Will probably order it tonight.Why do you need to write an app, doesn't the SPP looks on the computer as a virtual com port (I plan to use it with Max OSX). In this case, can't you use a standard terminal emulator?

author: Isamun
author_rank: Regular Contributor
timestamp: January 16, 2014, 02:03:04 am
content: The BT serial app we used for testing has some character issues. In any case we're only taking user inputs in the likes of 0-9. This makes the full keyboard both unsexy and pretty useless.PS: controlling device is a tablet.. Hoping for android or WIN8