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Thread: More thoughts on scoring transponders

  1. #21
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    Re: More thoughts on scoring transponders

    Was thinking more along the lines of always re-flashing the transponders before each match, and then re-numbering them for the match (could even just auto-assign it from the last octal of IP address). Or maybe have one or more of the ATtiny85 of the target panels or fire control modules record the last transponder ID with the transponder grabbing that for itself during first boot after re-flash.

    Flashing the little board I'm working on requires pressing a button or pulling the SDA line low during reset, so to have the bot's other controller re-flash the transponder via FTDI header after the official check/flash would require manually pressing the button or surreptitiously connecting a customized I2C device, an output pin, or a MOSFET to the SDA line. Even then, the other controller would have to somehow grab all the data received from the server during transponder connection and match setup (ID number, IP address, random 32-bit 'security' number, etc.) that are stored only on the server and target transponder.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

  2. #22
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    Re: More thoughts on scoring transponders

    Even better. Nice.

  3. #23
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    Re: More thoughts on scoring transponders

    I should be receiving three ESP8266-02 modules mid-to-late next week, so will finally get to confirm the footprint and then order the DXL WiFi transponder PCBs from OSHPark. Since custom enclosures can be a bit expensive, the current version should be able to be mounted inside a Hammond 1551P enclosure (comes in a version with mounting flanges, too) requiring a few small modifications to provide protected access to: RESET and BOOT buttons; one DXL, one 5V FTDI (GND, open-drain CTS/!TXEN!/!GPIO15! output, +5V, RXD, TXD, RESET), and two 5V I2C headers (GND, +5V, SCL/GPIO2, SDA/GPIO0); 5V power LED; and SCL/SDA activity LEDs (may not populate LEDs; just stick with pull-up resistors). Also, not sure if going to pass the antenna cable through the side of the enclosure for mounting the bulkhead RP-SMA connector elsewhere on the bot or just mount the bulkhead RP-SMA connector in the side of the enclosure. Should be more than enough room in the enclosure for the OKI-78SR-5 mounted on the bottom of the PCB with the ESP8266-02. It is the LXDC2UR33 and OKI-78SR-5 that annoy me a bit in adding ~$8 to the cost (small, efficient, expensive switching regulators vs big, crappy, cheap linear regulators), which bumps it up to ~$28 (less if use seeed for PCBs) per transponder when fully populated and enclosed (assuming $8.99 for ESP8266-02 module with antenna cable and antenna).


    Click image for larger version. 

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    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

  4. #24

    Re: More thoughts on scoring transponders

    That's a pretty cute enclosure! 40x40x20 isn't very large.

    However, I think most bots already have some kind of shell or "interior" where the electronics can go, so I'm not sure that box is needed -- that would reduce cost a bit.

  5. #25
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    Re: More thoughts on scoring transponders

    There are lots of exposed bits that really need to avoid touching anything else, and the enclosures are only $2.58 in singles (~$1.50 at 50+). The flanged version could even be zip-tied to the exterior of the bot as needed for a match; I found my spare 1551R from the lab camera enclosures, and being at least 2mm thick ABS does not have even a surface blemish after multiple point-blank rounds from a Crosman M74DP.

    Switching over to a single OKI-78SR-33 instead of both OKI-78SR-5 and smaller switching 3.3V regulator would save more on the cost, but cause issues with the illuminated target boards (3.3V not enough for two series LEDs). Could try squeezing a 3.3V linear regulator onto the board instead of the murata switching module; would drop cost, but increase heat by a lot.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

  6. #26

    Re: More thoughts on scoring transponders

    Could try squeezing a 3.3V linear regulator onto the board instead of the murata switching module; would drop cost, but increase heat by a lot.
    That's what I was thinking, too. If the 3.3V draws from the 5V out, you only drop 1.7V times 500 mA or so max, for less than a watt, so D-PAK / TO-220 would work. And that's still smaller than the Murata modules.
    Bonus: Rock solid 3.3V to feed the ESP8266 with no switching noise.

    If you're REALLY crazy, you'd use a two-winding inductor and regulate, say, the 3.3V using a switching controller and let the 5V be what it is relative to that.

  7. #27
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    Re: More thoughts on scoring transponders

    The LXDC2UR is the tiny 9-pad device above the 3-pins of the back-mounted horizontal OKI-78SR-5 and just below an 0805 capacitor. It is smaller than the pin pads of the D-Pak footprint in my library, and a fraction of the D-Pak plate/heatsink pad.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

  8. #28

    Re: More thoughts on scoring transponders

    LXDC2UR (Maximum Load Current: 600mA)
    I had not seen that before. I think I'm in love!

  9. #29
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    Re: More thoughts on scoring transponders

    Finally ordered the PCBs from OSHPark (3 for $9), but think I might finally have to order a stencil from pololu. Made several placement/spacing changes for easier assembly without high quality stencils and a pick-and-place machine (lots of labels), but still using 0402 (C1=0.1uF, R1=10kOhm, R2=330Ohm, ~3kOhm+LEDs) and 0805 (C2=10uF) passives. Because of the cost of regulators, only going to fully populate one of the boards after testing others as ESP8266-02 breakout boards through FTDI header with a 3.3V external supply (OKI-78SR-33) and 0805 shunt/inductor to bypass the LXDC2UR (shorts 3.3V of ESP8266-02 to normally 5V I2C/FTDI power buss). The dxl ttl protection can be either a tiny SOT-563 two-channel, low-pass filter with ESD protection or just a 0402/0603 TVS if I run into mounting/assembly issues.

    Minimal BOM
    (9) 10kOhm 0402 resistors
    (2) 330Ohm 0402 resistors
    (6) 0.1uF 0402 capacitors
    (3) 10uF 0805 capacitors
    (2) TE Connectivity 1825910 series pushbuttons
    (1) ESP8266-02 module
    (5) FDV301N N-channel MOSFETs
    (1) 6-pin (6x1) 0.1" SMD header (FTDI header)
    (1) 0402 LED for power indicator and current limiting 0402 resistor

    DXL parts
    (1) DFLR1800-7 reverse protection diode
    (1) SN74LVC1G126DCKR buffer (DXL full-to-half duplex IC; OE for TXD)
    (1) SN74LVC1G125DCKR buffer (DXL full-to-half duplex IC; !OE! for RXD)
    (1) NUF2230XV6T1G ESD/filter; or (1) 0402/0603 TVS + 0402 jumper/shunt
    (1) 3-pin Molex Spox 5267 connector (3-pin DXL header)
    (1) OKI-78SR-5 horizontal-mount 5V regulator
    (1) LXDC2UR33 SMD 3.3V regulator
    (1) 8-pin dual row (4x2) 0.1" SMD header (I2C header)
    (2) ~3kOhm 0402 resistors + (2) 0402 LEDs for SDA/SCL indicators; or (2) 4.7kOhm 0402 resistors with 0402 jumpers/shunts


    Now back to working on the software side...
    Attached Files Attached Files
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

  10. #30

    Re: More thoughts on scoring transponders

    DFLR1800-7 reverse protection diode
    If you're drawing a bunch of power through that, the 1.1V voltage drop will really hurt.
    If by "reverse protection" you really mean that, then I highly recommend a forward P-channel mosfet instead.

    For general protection, I've found that it's better to have a high-amperage PTC polyfuse (9A or so) and a reverse TVS with 16V stand-off.
    Any too-high current draw will make the polyfuse trip.
    And, reverse connection will cause the TVS to forward conduct, and make the polyfuse trip.
    Use 1 kW or higher rated to make sure it can stand the current while making it trip!
    (or use a higher-current rectifier diode in parallel with the TVS.)


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    Last edited by jwatte; 06-10-2015 at 01:16 PM.

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