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Old 05-04-2013, 04:19 PM   #1
Registered: Jan 2010
Posts: 202

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I'm Just Glad It Worked -- Arduino Bluetooth Serial Connectors

I bought a few Arduino bluetooth serial connectors a few years ago, thinking they were a cool idea and could possibly help avoid having a slew of serial cables connected to the pile of various gear I have here.

I screwed around with them on a number of devices, but the one where I where I was connecting to a header on the board was a Belkin F5D8230-4 v1002 (scroll down, there's pictures and everything!) with the Broadcom processor was the main one I tested with. Serial worked with a cable -- why not try a BT adapter?

I like that particular platform as it has a regular miniPCI slot so you can put whatever you want in it. It's old, like 2003 old, but they work well if you're not looking for gigabit speeds on the switch in it and can live with 'G' wireless. Originally the Belkin was a pre-N AP, but I installed an Atheros card and some 9dB antennas on it so it's not exactly stock. It's running OpenWRT which I compile custom for whatever card I chose. I see a spontaneous reboot periodically, perhaps once every 60-80 days on average. Nothing to be concerned about. I recall an uptime of roughly a half year at one point.

I made a number of attempts to get the bluetooth adapters to work with that damn board though the 2 years since I bought them. They were marathon kinds of experiences, where I'd spend several hours and not come up with any sort of a reason why it wasn't working. I could connect properly with the adapters through bluetooth, but never saw a thing on minicom. I dunno, I probably tried five or six times, after buying a few more of the adapters thinking I'd damaged them or they were defective.

Today, I dug out a Ubiquiti NanoStation2 AP that I don't use (a _fantastic_ piece of gear), and noticed a serial port header on it. Figured 'what the hell', and after thinking about it last night, set out to create a connector for the board. I bought some 10 pin two row connectors a few years ago, along with the inserts and LOTS of other crap for the various projects I dig into. As long as it's not too far off the beaten track, I can probably fabricate a custom connector for what I need. I use what I think are called patch wires, so that if I were to come across a need for a different pinout, I can merely juggle the wires to the connector and I'm good.

Got up this morning and spent the better part of two hours making the cable. It's tedious. Stripping the wire is slow work, as is crimping the inserts on them. They're small, and I mean *really* small. Twenty years ago I could have seen these well enough, but even then, it would have been challenging. The spacing on the pins on the header is about .06". Now it's a matter of squinting though reading glasses and using a magnifying glass to confirm what I've done is what it should be.

I take my time, otherwise I end up throwing out inserts. Quality is better when I do as well.

Got the connector done, connected the Arduino BT adapter to the NanoStation2 and fired it up. Immediately I got a console after connecting to the BT adapter.

I was stunned. I couldn't believe that I'd been testing with the Belkin, which just was NOT going to work for whatever reason, for all that time. Had I tested with the NanoStation2 originally, I'd have been up and running in a few hours.

Eh, that's the way it goes. Live an learn. I'm glad to see that what I was originally doing was actually correct.

Something I'm trying to figure out now is if standard DB9 connectors you find on computers have a 5V pin. I just checked a USB-serial adapter I have with a voltmeter, and I'm not seeing one pin that is 5V. I can get 3.3V (which works with the Arduino BT adapters) or 5V off a header depending on the device, but the DB9 connectors don't seem to have it. Need to do more research.

I might see if I can get a few pictures of the connectors. Everyone knows what a standard 10-pin two row connector looks like, but when you see what the inserts look like that go in them, well, it's a wonder that I don't throw 80% of them out.

hah. I created a picture of the evil inserts, the connector and adapter I'm using. It's a cellphone picture, so the quality is crap -- but you can get an idea of just how small those inserts are. I used a paper plate for a background for contrast.

The inserts from hell.

Last edited by devwatchdog; 05-04-2013 at 05:16 PM. Reason: 'cause the voices told me to.
Old 05-05-2013, 12:58 PM   #2
Registered: Jan 2010
Posts: 202

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After searching a bit, I'm finding that there are a couple of choices on how to power a device from a DB9 connector, and probably more but these are what I found.

The first involves pulling a pin on the DB9 connector (pin 9 as I recall was mentioned), and connecting it to a 5V power source.

That would work, not really what I had in mind. I want something that will be portable across multiple devices, not just one. Plus, you're creating a time bomb out of a port where if you were to plug something else into it, you could potentially cause damage to either of the hosts involved. I'd forget, and eventually wreck something.

The second choice is using parasitic power drawn from the signal lines. I just ran a search on LQ, (which I should have done first!) and did not see where this particular issue has been mentioned previously. This has appeal as you're not doing anything except connecting a custom DB9 adapter to it. I have yet to find one that is available commercially, and it doesn't look like I will find one after a fairly extensive search. This is the technology used with a serial port mouse, so it's been around a while.

The Arduino BT serial adapter required 35mA for pairing, and 8mA after for operation. This appears to fall within what is available from a serial port parasitic power solution.
The adapter, however, will require power as well, and selecting components with low power requirements will be necessary.

I did, however, find a board.

That should get the job done. It appears that's as close as I'm going to get to a finished product. Very inexpensive, so I'm ordering several -- that allows for plenty of mistakes. heh. Haven't looked around there, hopefully they have everything needed to complete the board. The diagrams appear complete and their commentary seems to be useful. SMT isn't exactly my forte, but what the hell, when you have a pile of components and boards, eventually that blind squirrel theory comes into play.

I have to admit I do own a venerable old Tektronics o-scope (2246) and a trusty _old_ multimeter so I can probably figure out what is going on with that Belkin board that works with a serial cable but not the BT adapter. I recall it was providing 3.3 V, or thereabout, but perhaps the CTS/DTS isn't high enough. Dunno.

I'll look into some other solutions along the lines of the board. Might not need to go the route of SMT. I'm not adverse to an ugly looking solution. I can always pack it away in an enclosure.
Old 05-24-2013, 02:52 PM   #3
Registered: Jan 2010
Posts: 202

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I changed the kernel boot parameters prior to compiling OpenWRT for the Belkin and was able to get the Arduino serial-BT adapter to work.

I should have recognized the baud rate difference when connecting w/ the cable -- eh, water under the bridge now.

I still haven't ordered the parts to complete the boards I got for parasitic power from a DB9 connector. I've been doing a bit of research into working on SMT, and just want to do it right. I'll order the components before long. I'll probably be able to do a reasonably good job for, oh, something under $100 I imagine. I don't want to just cobble something together that works now, but once it takes a hit or two in my backpack stops working because the solder job I did was poor. Looking into SMT rework stations now.
Old 07-12-2014, 06:02 AM   #4
Registered: Jan 2010
Posts: 202

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I was wandering through LQ, and ran across this thread. Thought I'd update it with the lack of activity I've had on the parasitic power project.

I did order some boards I found. They can be found here:

Alas, the boards are bare as I haven't bothered to solder anything on them. I got them a little over a year ago and just haven't sat down and taken the time to work on the project. Moved to another state, got a time consuming job, and also have tons of other projects going on at any given time.

Need to get another O-scope, and some other various stuff, but I'm slowly replacing the gear I dumped when I moved.

I haven't dug into SMD previously, so this is a new endeavor. There is plenty of info on the dipmicro site on how to complete them.

Hmmnn...might be time to order up some parts to populate the boards.
Old 07-19-2014, 04:54 PM   #5
Registered: Jan 2010
Posts: 202

Original Poster
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Bought a X-Tronic Model #5040-XTS preheating/hot air rework station.

Bought the parts for populating the boards. Haven't worked on SMD before, but there are some excellent tutorials online.

Will follow up once I have made some progress.


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