RFID scanner device critique - Page 1
Forum section: electronics / projects

author: delmadord
author_rank: Regular Contributor
timestamp: April 28, 2014, 08:17:56 am
content: Greetings,this is device I am working on right now for my bachelor thesis and I would appreciate some notes from you.Thanks for any feedback!

author: Dago
author_rank: Frequent Contributor
timestamp: April 28, 2014, 10:21:11 am
content: The first thing I noticed is that you do not have a real ground plane. You really should have a proper continuous ground plane in a device like this.You also do not seem to have almost any decoupling caps. Basically every microchip supply pin should have at LEAST one capacitor (I usually use 100n caps for this, but the value depends on the chip and the frequency etc.).

author: delmadord
author_rank: Regular Contributor
timestamp: April 28, 2014, 11:13:53 am
content: Thanks Dago for your answer,Both your points seems perfectly valid to me.The reason, I do not have more decoupling is, that ATmega has one cap, in arduino pro mini is has only one too and it works. THe FT321X has decoupling caps according to datasheet. Other did not have any decoupling shown in DS.Moreover, there is no real high current (less than 100mA) or high frequency stuff going on, I believe. Since the board will be made DIY, there is not much I can do about size of the components/vias, so I am not sure, how to get more space for decoupling caps and to proper ground plane on the bottom. Will this be a big concern?

author: miceuz
author_rank: Frequent Contributor
timestamp: April 28, 2014, 11:58:20 am
content: Quote from: delmadord on April 28, 2014, 11:13:53 amIf you are already comfortable with etching single-sided boards, I'd suggest doing a double-sided one it's just a little bit more complicated - you have to drill the holes and align the layers before ironing toner, make via rings a bit bigger to allow for bigger tolerance margin. On another hand - since it's a final project that you will be showing to people, did you consider ordering boards from one of abundant cheap pcb fabs? It shouldn't be too expensive even for slovakian level of living. Make a proper double sided board, add decoupling, try to disturb the second layer as little as possible so it acts as a proper ground, connect all the top copper to ground too and you should be golden. Note, that you can always hack a fab made pcb if you make some mistakes, look at Dave's teardowns - even the most reputable manufacturers have bodges in their multi$ devices.

author: lapm
author_rank: Frequent Contributor
timestamp: April 28, 2014, 12:53:34 pm
content: Quote from: delmadord on April 28, 2014, 11:13:53 amThose microcontroller proto boards are designed down to price, not reliability. So they put in absolute minimum of components to make them work under most common situations... RFID reader is not one of those cases...

author: Teledog
author_rank: Regular Contributor
timestamp: April 30, 2014, 04:59:55 am
content: Excuse my naivety, but worked on a few RFID readers in the past.The interrogation inductors{which I don't see here} typically have a fairly high voltage on them.Blown a few chips testing them..Just sayin'...

author: delmadord
author_rank: Regular Contributor
timestamp: May 06, 2014, 05:21:19 pm
content: Quote from: Teledog on April 30, 2014, 04:59:55 amIt uses a cheap ebaysolution, it will plug. But thanks for interesting note, I did not know that.