Multicard RFID spoofer

[jorenca]

Hi guys, first post here, I've been watching the blog (great stuff btw) for a while now and tought why not join the forum.

I'm relatively new to EE and I'd be happy to get some feedback about the design of this little thing.
It's a 125kHz RFID spoofer card. I tried to upgrade some (more basic) designs I've seen on the web so it would both support several card IDs (7 in this case) and not require a battery.

The only 2 controllers I had in my parts bin were ATmega8 and ATtiny85, and considering the low-power requirements, I picked the ATtiny.
I measured the max current induced in the card by the reader and got about 1.5mA
(which, according to the ATTiny85 datasheet is insufficient for powering the controler running at 8MHz - the only suitable internal osc? and I couldn't spare pins for external crystal osc, it seems to work OK however after a second of charging the electrolytic capacitor)

As I only had 3 spare pins for inputting the selected card ID, I  binary encoded (is this the correct term?) the 7 buttons using the diode madness (bottom part of the schematic).
Is there a better way to do this?
Can the components count be reduced? I tought about using the internal controller clamping diodes, but had limited success doing so.

Using the device is as follows:
* Place the card near the RFID reader and wait until it start beeping (with no pitch change)
* Press the button coresponding to the card ID you want to transmit
Video: https://youtu.be/QtRbtY0wWas

[cponcsak]

If you wanted to clean up your diodes, you could use a triple 4 input OR gate.


http://www.ti.com/lit/ds/symlink/74act11802.pdf