I received the new PIC micro-controllers so it is time to make the first part of the project, the smartcard reader. Unfortunately, due to lack of time, i only drilled the PCB... which took me some 5 minutes. Anyway, here is how the smartcard slot will be mounted on the PCB:
This is the PCB drilled.
The only through-hole component will be the smartcard slot
The slot has 4 pins. I drilled 4 holes on the PCB for these pins
The PCB is longer for the 4 additional mounting holes...
A closer look reveals the additional mounting holed on the PCB. These holes will be used to mount the slot AND the PCB. To fix the slot on the PCB, i will use a 3mm screw-nut...
Hands on the soldering iron
I used only SMD parts for this board, because on one side i will solder the card reader slot. I used also 2 screws to screw the slot onto the PCB. The hardest part was the 44-pins QFN package of the PIC. QFN packages have pins only underneath the package, so the only reasonable method to solder it in my house is with my hot air gun.
I will use these 2 screws for the smartcard slot
They fit perfect i the hole diameter...
...and the smartcard length
Soldering the PIC on the board was the hardest part. It is tiny (11x11mm)!
To program the PIC, i will be using my ICSP pogo-pin connector. But during prototyping, i will just solder 5 wires on the 5 pins. I will provide also power from the ICSP connectors, so i want it to be always connected. This is the PCB after having all the parts soldered:
Why, oh why do i always have to forget something?
...........
What is this resistor? When i first designed this circuit, i forgot to add the pull-up resistor for the I/O pin of the smartcard... Bummer....
This was one of the most well documented blog entries I have read in a long time. It was a pleasure to fill all the gaps I had about this topic. Well written an concise.
At 3 September 2012, 14:14:58 user pcb wrote: [reply @ pcb]
Thanks for share this pcb layout design work... its give me more better ideas for my future projects...
@Pat I see what you mean... I think i will make some tests :D
At 14 August 2012, 13:09:12 user Pat wrote: [reply @ Pat]
@Giorgos Lazaridis Yeah, like I said, it'll work... mostly. If you take a look at TPC 12 on the ADG714 datasheet, the frequency response at ~500 MHz is going to be around -8 dB. The maximum attenuation of a USB cable is basically the same as that ( http://www.usb.org/developers/presentations/pres0410/2-2_SSUSB_DevCon_PHY_Heck.pdf ) - so essentially, you've basically just put in a long USB cable.
So long as you're talking about devices that are attached with, say, like a 1' cable or something like that, you won't notice basically anything. It's all just a question of how much margin you have left.
@Pat this was one of my concerned, it works ok until now, and i have test usb devices like external HDD (which i copied some 300GB of data with no problem) and also my camcorder uses the USB for the video. Nevertheless, have order relays with 4p2t if the adg fails or have slow data transmission.
molis eida smartcard lock skeytika oti enas apo ellinas eixe kanei kati paromio me tilekartes kai tsoup na se pali :P ! ekseretiki douleia opws panta !
At 14 August 2012, 7:39:43 user Pat wrote: [reply @ Pat]
"I'm not sure if the ADG714 can be used for USB applications."
No, it can't. It's the bandwidth that matters, not the on-resistance. It has a bandwidth of 155 MHz, which is way below USB spec. This is because the ADG714's input/output capacitance isn't 6/4 pF: I'm not sure where you got that from (the digital input/output capacitance is 3/4 pF respectively). Its on capacitance is *22* pF. This is way, way too high: on a 50 ohm input that's a critical frequency of ~150 MHz.
Switches designed for USB (like the FSUSB46) have on capacitances more like 4 pF, leading to a bandwidth of well greater than 480 MHz.
This design will work... some of the time. Probably mainly with short USB cables and devices that are well within USB spec. Definitely with low-speed USB devices. But high-speed USB devices could easily struggle since you're probably tacking on at least ~6 dB of attenuation.
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