This is a project that I have been working on for a while.
A friend of mine has a small farm on a hobby basis and raises sheep. By law every sheep in Norway is required to have an RFID tag in its ear. Though there are several RFID readers out there for reading this type of tags, they are quite expensive and not all that hackable. A reader like the HHR 3000 Pro would cost you about $900,- and to hook it up to an electronic weight would probably set you back another $3000. So for many hobbyist farmers this is not an option.
The base of the system is a FEZ Panda II running NETMF under C#. I could probably be made with something like an Arduino but as I needed to have several UART’s and a SD card to store data, it was much easier to go for the Panda. Also as the Panda has lots of IO pins, hooking up the HD44780 display is done directly with no serial interface and no use of the pins that would go to the Arduino style header. In fact all the pins for the Arduino shield interface are available with the exception of A0 that is used by the weight cell amplifier.
As this might be produced in small quantities I decided to go for a proper PCB. That means that reproducing the device is easy and it looks more professional.
The main box (IP65) holds the FEZ Panda II. On that the main board sits with its headers for the 2x16 LCD display and the weigh cell amplifier. It also have a small coin battery to keep the RTC running.
The RFID reader is mounted on a rod made of 16mm plastic pipe (used for electrical installations in Norway). There are several 3D printed parts on this rod and the handle has a small vibration motor mounted so the user will know when the tag is read. There is also a function on the rod for lamb fetal count, this is based on a PICAXE 18-M2.
The main board also has a Bluetooth interface so the data can be picked up by a PC, PDA or any other Bluetooth device.
One of the main uses for this device is when weighing the sheep. For this we got a 500kg weight cell of eBay and it’s hooked up to an onboard weight cell amplifier that feeds the A0 with data. The weight is constantly calculated and written to the SD card (and Bluetooth) once the RFID tag is read.
All in all a fun project and according to my friend “Weighing the heard is not work anymore. If one only could get the sheep on the weight platform faster”
With the load cell amplifier taken out. You can see the battery for the RTC
With the display taken out
The main board also have a Xbee footprint that can be used instead of the Bluetooth if so desired. The Bluetooth is soldered straight on to the pads SMD style.
There is also an option for a INA125 amplifier instead of the mounted one. A potential next version will probably have an integrated load cell amplifier.
The custom boards that I have had made for this project.
The rod also doubles as a handle for transportation.
As there has been some interest for this device I put a question out to GHI electronics about the availability of the Panda II. http://www.tinyclr.com/forum/topic?id=7826 and as the response was not a definitive yes I thought I might make my own custom board :-)
The FEZ Panda II sells for $39.95 but the only thing I really need is the microcontroller which cost $16.95. I still had to add my custom board on top of the Panda, so why not try to build a custom board around the USBizi100 Chipset that the Panda II is based on.
The USBizi100 is a 100pin QFP with a pitch of 0.5mm and by far the smallest thing that I have ever soldered. But with lot of flux it turned out very well. I haven't tested the complete system yet but everything seems to be working so fare.
This version has a single board holding the ARM3 microcontroller, Bluetooth, weight cell amplifier and jumpers to put the USB in host mode (for a USB memory stick).