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Dec 05, 2016, 06:50 AM
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Mini-HowTo

PowerLab PL8 Bluetooth - FIXED


How neat would it be to have a bluetooth connection from a Mac/PC to a PowerLab PL8 in the next room I thought.

The Remote Control a Single PowerLab 8 spec made it look easy. Just need a diode in the Tx line. Not hard.



After minimal effort I had a bluetooth module set up at 19200 baud 8n1, announcing itself as "PowerLab PL8", with the CCS talking to it and I could see the "Ram" query being made as per the above document when connected to an FTDI serial interface.

So, excitedly I connected it to my PL8.



No LED on the bluetooth module. Only 2.9V on the 5V supply out of the PL8. With nothing connected it's ~5V, or about 4.3V with an FUIM3.

How ironic that a 1344W charger can't supply enough power on it's 5V output to power a bluetooth module.

So tempting to pull it apart and find out why...

Steve
Last edited by Steve Evans; Dec 12, 2016 at 02:08 PM.
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Dec 05, 2016, 07:36 AM
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Temptation got the better of me...

The three traces from the connector make there way along the edge of the board, 5V being the middle one.



The GND dives off towards the middle of the board, leaving signal and 5V to continue their journey round the edge. They pass some 40A fuses. I was shocked to see the solder from one terminal of the fuse overlaying the 5V trace. This is NOT what I expected of Revolectrix quality I must say.



The 5V trace is next to head inboard.



It surfaces on the topside through a via (in pad) to D14. R93 measured in circuit at 170R, so it looks like the 5V supply is fed via that and a diode to offer the LM78L05 voltage regulator some protection. Shorting out R93 would fix the problem.

The LM78L05 can supply 100mA and the module only consumes 30-40. Not sure what else that regulator is powering mind.

Tempted...

Steve

Last edited by Steve Evans; Dec 05, 2016 at 11:01 AM.
Dec 05, 2016, 11:56 AM
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Just tried supplying 5V directly to the BT module rather than from the PL8. No communication. I wonder if a Schottky diode is required. Such circuits normally don't need that, but perhaps worth a try.

Has anybody else interfaced to a PL8 using the guidance at http://www.revolectrix.com/support_docs/item_1374.pdf?

Steve
Dec 06, 2016, 10:16 AM
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After some perseverance it's working, sort of. The CCS hangs if there's an issue with the port, so the apparent total failure to communicate was actually a software issue. Now though the CCS is reporting CRC errors if I try to update the presets. I've tried adding another 10K pullup to improve the rising edge, but I suspect I need a schottky diode to improve the low voltage. I have some on order.

On the face of it, it's basically working, but needs to be more reliable.



Watch this space...

I ended up using a 1N5817 schottky diode which I measured at 200mV forward voltage, less than the smaller 1N5711 which I also purchased.

Steve
Last edited by Steve Evans; Dec 12, 2016 at 02:05 PM. Reason: Add diode selection.
Dec 12, 2016, 01:43 PM
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Some feedback from FMA was that they'd tried the same thing and got the same result. I'm pleased to say that apart from updating presets and presumably updating firmware, I can happily control the PL8 and graph progress from several meters away on my laptop in another room. So, I decided to tidy this up somewhat.

Given that there is not internal supply capable of providing the necessary supply for the BT module, I figured it was best to add my own. I took a Hobbywing 5V 3A BEC which is good for up to 26V input. I use these anywhere I need a clean 5V supply; I have one in my car powering my dash-cam for example. The BEC I received didn't have a capacitor sticking out; some seem to, some don't, but I removed the heat shrink, and the voltage selection link and soldered a bridge to permanently select 5V.



I then connected the input wires to either side of C2 which is where the input supply is switched to control the fans.



It was a convenient point as with a bit of double sided tape I was then able to neatly install the supply thus:



I then re-terminated the output lead (having removed the ferrite bead) to a Futaba female connector and soldered the white signal wire to the signal pin of J6, thus:



The connector was then attached using more double sided tape to the inside of the case thus:



This gives an internal control port, with better power, leaving the external port still usable. As the data signal is open collector you can have the bluetooth module connected internally and the FUIM-3 connected externally (for preset updates and firmware updates) at the same time with no issue.

I then shortened the cable I'd made above and fitted a Futaba connector at the end. I much prefer these to JR ones as they provide polarity protection. Revolectix missed a trick there when they could so easily have added the keyway in the PL8 case design and fitted a Futaba plug to the FUIM-3.



Lastly, before replacing the lid, I installed the bluetooth module.



Having the internal servo connector will make it easy to update to another module with longer range if I feel the need.

So, I now have a PL8 with bluetooth connectivity. Worked out rather well.

Steve
Dec 12, 2016, 01:52 PM
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Nice job! Thanks for sharing!
Dec 12, 2016, 01:59 PM
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I should add the caveat, proceed at your own risk... works for me, but I can't be responsible for the consequences of messing with PowerLab innards!


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