Transferring data over induced coupling

[Bruce]

It took a bit of experimentation to get the 6+' distance. It's all about placement of the
small RFID LF antennas on the receiving unit. Once you get that dialed-in you get a
whopping range. The first pictures were the initial prototypes. These had around 3+'
range.

This picture is the final version that works at 6+' range. If you compare placement of the
small RFID antennas on this one to the one above you'll know how/where to put them for
excellent range. You can walk up to the initiator with the ID badge in your back pocket, and
it still gets solid comms.

The final ID board is about 1/3 the size of a credit card, and modified to fit into a keychain
type plastic enclosure.

SMD caps & resistors are all 0402 size. Boy were those fun to hand-solder on the last
prototype. Phew...

would I need to modulate the Debugout signal

I used a TC4422A high-speed MOSFET driver to drive the large LF antenna, and PWM to send
data like this;

ID_Init:   
    T1CON.0 = 0  ' Shut-down Timer1 during wake-up routine
    ' Wakeup sequence. 4mS ON, 500uS gap, 2mS ON, 2mS OFF. Then
    ' follow up with header & data.
    CCP1CON = 12   ' PWM ON
    PAUSEUS AGC_STABLE
    CCP1CON = 0    ' PWM OFF
    PAUSEUS GAP
    CCP1CON = 12
    PAUSEUS 2210   ' 2mS ON
    CCP1CON = 0
    PAUSEUS 2210   ' 2mS OFF
    ' Wakeup sequence complete
    
    CCP1CON = 12   ' Send header after initial wakeup
    PAUSE 1        ' 1mS high on receiver LFDATA pin
    CCP1CON = 0
    PAUSEUS 500    ' header complete
    
    ' Transponder should now be waiting for data payload
    FOR LOOPS = 0 TO 7 ' loop for all 8-bits
    CCP1CON = 12
    IF DAT.0[LOOPS] THEN
       PAUSEUS 500
    ELSE
       PAUSEUS 250
    ENDIF
    CCP1CON = 0
    PAUSEUS 500    ' this pause allows 500uS for ID badge to respond
    NEXT LOOPS     ' after challenge code is sent.
    CCP1CON = 0    ' turn off PWM
    ' Data payload complete
    PAUSE 5        ' Pause a bit so interrupt flag-bit can be set when ID badge responds
    TMR1L = 0
    TMR1H = 0      ' Clear Timer1 count before re-enabling
    T1CON.0 = 1    ' Re-enable Timer1 on exit
    RETURN
    
    ' Notes: After wakeup the receivers 16F639 AFE inactivity
    ' timer will expire after 16mS. Any gap in transmision that
    ' exceeds 16mS will require another wakeup sequence before data
    ' can be sent.

The receiving end just uses PULSIN to grab the inbound data.

[Byte_Butcher]

The final ID board is about 1/3 the size of a credit card, and modified to fit into a keychain
type plastic enclosure.

SMD caps & resistors are all 0402 size. Boy were those fun to hand-solder on the last
prototype. Phew...

Neat project! But 0402?
Do you have REALLY good eyesight or do you have really good lighting and magnification?
I'm pretty comfortable with 0603 but it's sure easy to lose those little suckers on the bench...

I'd love to see a thread with "Tips & Tricks" for dealing with SMD parts, along with suggestions and reviews of really handy tools, lighting, magnifying device, etc to make the job easier. More and more "neat new parts" are available as SMD only, and a lot of the "old familiar" through-hole parts are disappearing. SMD is a way of life now. I'd love to see a "SMD Help" category added to the forum...

steve

[Bruce]

But 0402?

Stuff just wouldn't fit otherwise, and we needed the free space for the 418MHz UHF & 125kHz RFID parts. There's a UHF antenna for the Linx RF transmitter on the back of the board just behind the Primeport logo.

These RF parts need x amount of clearance from board components, so we had to go with 0402 to squeeze everything into a keyfob enclosure on a board 1/3 the size of a credit card. The CR2032 battery holder & UHF antenna sucked-up 50% of the
board space.

The board photo looks big, but it's definitely not.

We do all SMD placement under a lab microscope, and beyond the initial prototype, we do all soldering with a RoHS comlpiant reflow oven, and lead-free solderpaste screened boards.

We use the Gold-Flow GF-B-HT reflow oven and a zoom stereo trinocular microscope mounted on a boom stand for SMD placement. Photos attached.

RF design is a whole new world, and if it's not spot-on, you ain't getting that FCC stamp of approval. So you allow for whatever clearance is needed for the RF stuff.

[Byte_Butcher]

These RF parts need x amount of clearance from board components, so we had to go with 0402 to squeeze everything into a keyfob enclosure on a board 1/3 the size of a credit card. The CR2032 battery holder & UHF antenna sucked-up 50% of the
board space.

The board photo looks big, but it's definitely not.

You don't need to sell me on the NEED for small precisely placed components! I understand why small SMD parts are desirable.

Now I'm interested in good tools and techniques to make SMD more accessible for us mere mortals.
I wanna know how us wannabees can do it most efficiently, without a HUGE expense.

We do all SMD placement under a lab microscope,

Excellent! Does your microscope have a model number? Are there things you particularly like or dislike about it? Is it... horribly expensive?
These are the kind of tools I seek, but it's nice to have good reviews from folks who actually USE them, rather than blindly whipping out the credit card.

I love SMD components! But they can definitely push the limits of my eyesight and dexterity, so I'm in search of good tools and techniques to make things easier.


steve

[mackrackit]

I do not do stuff as small as Bruce and I am not building for certification....

I have a set of loupe and one of those headband magnifyers like jewelers use.
I also, do not laugh, use one of these.
http://www.intel.com/support/intelplay/qx3/

pretty much everything I do is custom, so all I have to be able to do is a good prototype.

For reflow I use a toaster oven from walmart.

That is how this newbee does it....

[ardhuru]

Bruce, thank you so much for sharing the code. But the reason I'm hoping to use the hardware UART for data transfer is that the receiver would then be able to receive data in the background, making the the dot-pattern display servicing much easier.

Intend to try out that; will keep you guys posted on the results!

Anand

[Bruce]

Steve,

A couple pair of SMD tweezers, a toaster oven, and a pair of the headband magnifiers like
mackrackit uses is all you really need. The microscope I've had for about 10 years now, and
the nameplate was peeled off a long time ago, so I don't know the manufacturer, but it
was around $400.00 new.

You can probably get one on eBay for a fraction of that if you want one. Get one with the
ring light if you do. I love the one I have. Really comes in handy when you're working with
very small SMD parts. The batch reflow oven is awesome, but it's pricey at >$5K. If you
have deep pockets a reflow oven is the way to go, and there are some good ones a lot less
expensive than the one we have. You probably don't need the high-temp lead-free type.

Anand,

Couldn't you use IR? A surface mount IR module like in the photo would work if mounted
dead center on the board, and you can connect it to the UART.