If you want an Open RFID Tag, you can build it yourself.
All the parts are easily found in any electronic store. You can even substitute the parts for similar others. For example, all the resistors and capacitors values (except the tunning capacitor, that needs be calculated) are approximations. You can use any transistor or Schottky diode. You can even use another microcontroller. The firmware should run with minimum modifications on most of the PIC 12F and 16F microcontrollers.
Check the schematic and firmware section. There you have all you need to start and if you have any question, you can use the forum.
If you are a too lazy to make a PCB, you can buy a DIY kit in the shop. Each kit contains a professional manufactured PCB of the Open RFID Tag LITE version 0.3 and all the parts needed.
The KIT comes unsoldered. You will need some soldering skills to ensamble the SMD parts. The hardest component to solder is the SO8 (SOIC8) package of the microcontroller.
Remember that you will need a PIC programmer. The lateral connector of the PCB has the same pinout than the PICKIT2, but any other PIC programmer can be used.
Some firmwares have a RS232 "bootloader" to change some parameters, but you need to program the microcontroller first.
This is the part list included in the DIY kit. It may be useful if you decide to buy the parts by yourself instead of acquiring a DIY KIT.
R1, R2: 470 ohms. 1206 SMD package.
R3, R4: 1K. 1206 SMD package.
R5, R6: 10K. 1206 SMD package.
R7: 100 ohms. 1026 SMD package.
C1: 8.2nF 50V X7R ceramic capacitor. 1206 SMD package.
C2: 220uF 16V electrolytic capacitor. 6.3mm SMD case.
C3: 22uF 6.3V tantalum capacitor. "A" SMD case.
C4: 100nF 50V X7R ceramic capacitor. 1206 SMD package.
C5, C6: 22nF 50V X7R ceramic capacitor. 1206 SMD package.
D1: 5.1V Zenner diode, 0.5W. SOD-80C case.
D2, D3: BAT721S dual Schottky diode. SOT23 package.
LED1: Yellow LED. 1206 SMD package.
LED2: Green LED. 1206 SMD package.
S1, S2: Tactile SPNO Switch, TYCO, SMD package.
Q1: BC846. SOT23 package.
IC1: PIC12F683. SOIC8 package.
- SV1: 6 pin header.
The BAT721S Schottky diode can be hard to find. If you can't find it, you can use one of the next diodes (ordered by the Vf - lower is better):
- BAT721S - Vf=250mV @ 10mA
- BAT754S - Vf=340mV @ 10mA
- BAT54S - Vf=400mV @ 10mA
- BAT40-04 - Vf=450mV @ 10mA
C2 and C3 are polarized capacitors and the polarization should be respected.
In C2, an electrolytic capacitor, the black band indicates the negative terminal. However, in C3 (tantalum capacitor) the black/brown band indicates the positive terminal.
HOW TO ADD R/W SUPPORT TO THE ACTUAL 0.3 PCB
If you don't want to wait for the 0.4 version of the Open RFID tag, which will support R/W tags and some other interesting features, you can modify the actual 0.3 PCB in order to add these capabilities, but you should read first the design process of the modifications.
I tried to find the best way to modify the PCB without damaging it permanently (cutting a trace). After some time figuring it, I could accomplish the modifications but leaving aside one of the LEDs.
- 1 nF ceramic capacitor. 1206 SMD package.
- 10 nF ceramic capacitor. 1206 SMD package.
- 1.8 nF ceramic capacitor. Axial package.
- 33 Kohms resistor. 1206 SMD package.
- 1N4148 signal diode
THIS IS THE HOW-TO:
Desolder R2 and LED2
Solder the 1nF capacitor in the R2 footprint and the 10nF in LED2
Solder the 33K resistor OVER the 10nF capacitor (stack them!)
Note that I am using a 100K instead of a 33K.
Solder the cathode of the 1N4148 to 33K resistor (look the photo to know in which terminal)
The anode should go to the via at the right of C1 capacitor
Use a thermoretractile or an adhesive film to isolate the diode terminal.
Solder the 1.8 nF capacitor according to the image
You are ready to go!