• Fixing an old RC boat

    09/24/2019 at 22:01 0 comments

    Today I planned to mount an SQ12 camera on an old RC boat to make for some interesting footage.  I pulled out the old boat, put in the batteries for both the boat itself and the controller, turned it on . . .

    . . . and you guessed it nothing!  I had an almost identical extra boat and controller (the only difference was the frequency it operated on.) I put in batteries, got nothing.   I checked to make sure the batteries were good and they were.  

    I this point I feared the worse case scenario, the PCBs on both boats were ruined by the water.  Seeing that I was unable to turn them on, I decided to take them apart!  Sadly I had to damage the stickers to get to the screws to take the top off, but there was no other way.  I did have one screw well snap on me due to the fact the screws were torqued down so hard. Inside I found a a few styrofoam pieces and an internal box that likely housed the PCB and motors.

     I pressed on and opened the inner box.  Sure enough, it contained the PCB and motors.  I couldn't find any obvious signs of damage to the PCB.  Interesting to note is that some sort of grease was used to actually mitigate any water ingress, didn't expect to see any effort given as it was a cheapo product.  It would have been better if it used a greased o-ring but can you expect.  The grease was a bit cracked in areas, so I would need to fix that later before I closed everything back up.

    Seeing as everything looked fine in the PCB and motor box, I started thinking. Could it really something stupid simple as the power switch not working? I decided to short out the power switch leads.  It came to life!  I didn't open the other one and see if its power switch also failed (will likely do that in the future) but it's likely what happened to it as well.

    Upon reflection, the failure isn't too surprising.  The boat sits very low in the water and of course the points where the propeller shafts enter the boat means that water gets in the boat very easily, hence the sealed PCB and motor box and the styrofoam pieces.  The instructions mention every so often pulling the boat out of the water and holding it vertically with the bow pointed up to let the water drain out.  Just slightly above where the drain is located is the power switch, hence an easy point of failure.  

    My fix was to simply bypass the switch and solder the leads together.  I tried some contact cleaner on the switch, but that failed to work.

    Now came the resealing of the inner PCB and motor box.  The old cracked grease wasn't going to do.  I thought of what I could use that I had on hand and came up with petroleum jelly.  There are likely better options out there but as it's non-conductive and it was what I had on hand, it's what I used.  I used q tips to apply it (after removing the much of the old grease that could be easily removed.)

    After that I closed everything up. and made sure it still worked.  I then forgot about the styrofoam pieces and had to open it back up to put them back in.

    Anyways here's some footage I took. As light as the camera is, it weighed down the boat too much and had to put it at an odd angle to reduce the chances of the boat tipping over.

  • Attempting to get a PBX phone to power up without a PBX

    09/12/2019 at 15:21 0 comments

    Backstory: A relative's workplace has recently upgraded their phone system and I got handed an old Panasonic KX-T7636 desk phone that was going to be thrown out.

    The desk phone has a POTS jack in addition to the PBX line jack.  It didn't come with a wall wort so my suspicion was that it was powered from the PBX line.  I tried connecting it up to a phone jack and as I suspected, nothing.  

    I then decided to tear it down, find the voltage rail(s) and figure out what voltage(s) were needed,  and rig up something to feed  the voltage(s) into those rail(s).  After I cracked it open I studied the PCB carefully for hints.  I found something marked 3.3V on the silkscreen. I probed around a bit with my multimeter and it appeared to be the main and only voltage rail (with the exception of the circuitry for interfacing the PBX and POTS lines.) I also looked up the part numbers of the chips, and the one that I found a datasheet for, showed that it used 3.3V for the supply.

    I found an unpopulated SMD capacitor footprint that was connected to the rail and decided to use that as the point to feed the rail.  I macgyvered a power supply using an Ebay adjustable buck converter powered by a 13.8V linear power supply (can you tell that I need a proper bench power supply?) I soldered some speaker wire to the capacitor footprint leads.  Powered everything up. Still no external signs of life.  

    At this point I wondered if the phone was trying to communicate with a PBX before it would show anything externally.  Lacking an oscilloscope, I put my multimeter in AC mode and probed the PBX jack. I did get some AC voltages, so my guess appears to be right. The phone isn't going to play nice, until it can connect to the PBX.  I probed around a bit more I found that the lines that fed into the bridge rectifier that feeds the internal power supply only came from the PBX jack.

    At this point things have hit a wall. I could try to get more info on the PBX signaling and try to fudge it with a microcontroller, but perhaps that's going down quite a rabbit hole.  I'm not a phone system expert by any stretch of the imagination, just someone that was a bit curious.  Would love to hear from phone nerds if they happen to know anyway to hack it to make it operate as a normal POTS phone, but I imagine it would likely take more effort than it's worth.

  • A review of JLCPCB

    05/02/2019 at 13:45 0 comments

    Full disclosure: I was contacted by a JLCPCB rep offering to do a few boards for me in exchange for a review.  I should further note though that I have done business with them as a normal paying customer in the past.

    I used JLCPCB for my current board version for my Water Alert project. I also did a slightly updated board version of my Attiny Micro board, had them do a few additional boards for my Atmega328P Target, and for kicks some Sega Gensis/Megadrive cartridge PCBs from a design I found here.  

    The ordering process was easy.  I really like that they show you images of the uploaded gerber files and in this instance it pointed out an issue.  For my Atmega328P Target board, I noticed that a portion of the silkscreen was distorted.  Under KiCad everything looked fine. I looked up their instructions for exporting gerbers in KiCad and saw that the include extended attributes option was checked in their screenshots.  I went back in KiCad and did that and resubmitted them.  The silkscreen issue went away.   

    The PCBs arrived quickly via DHL for a total turnaround time of about a week (I normally use the least expensive shipping option that usually takes a few weeks, but since it was on them chose the fast option.) They arrived in vacuum sealed packaging (usually they arrive neatly stacked in the package, but it's not really a big deal.)

    Overall the PCBs came out quite good.  Alignment was good.  The edges of the boards were nicely routed. Silkscreen text is nice and sharp (with the exception of R4 and R5 labels on my Water Alert board, although to be fair the text is a bit small.)  Order numbers were printed on the boards.  One thing that I'm really impressed is that JLCPCB is able to get soldermask between the pads of fine-pitch surface mount component footprints as shown on the Sega Genesis/Megadrive cartridge PCB (note that although I didn't specify gold fingers on the edge connector, it should be specified if you're doing something more than testing/prototyping/just tinkering.)

    My recommendations to JLCPCB:

    Give us the option to change the PCB quantity before the order is submitted.  JLCPCB changed their default quantity from 10 to 5 and I didn't notice until I uploaded everything.  Since one the boards had to be manually approved it would have been a bit of a wait if I just deleted the order and started over again.

    Retain promotion offers when an order is cancelled. On a previous order, a free shipping promotion was offered.  There was an issue with a board I uploaded so the order was cancelled. When I re-uploaded with the issue corrected the free shipping promotion didn't re-appear.

    In summary, I'll give them a thumbs up. I'd also like to thank them for offering to spin a few PCB designs at no cost in exchange for a review.  I currently don't have a regular stream of income at this time so saving anywhere I can helps greatly!

    https://jlcpcb.com/