In my previous post. I show you how I got the basic LPC1114FN28 working on breadboard and my first version of the circuit board made.
I originally called the project ARMbeduino after following the Arduino philosophy, where the codes are written on the computer and then download into the chips’ flash memory via a serial link. After several revision changes, I decided to rename it ARMbed-1114FN28. The reason is that my version of the board does not support plug-in shields like the Arduino, but rather, it was designed to be plugged into another board, very much like the mbed platforms.
So after about a month, my 2nd revision of the circuit boards arrive. I regret choosing the blue colour coating instead of red like my previous version. Selecting different colour finishing doesn’t cost anything, so I thought I’ll give it a try. Next time I’ll go back to red. When I reflow this board in my reflow oven, the silk screen came out a bit scorched! The controller in my reflow oven is a bad design and I haven’t got round replacing it with a better one.
I tried to make the size of the board similar to the size of a mbed LPC11U24 platform. Since I got rid of the bootload button in my design, I can shrink the size down further and move the SWD socket to the back of the LPC1114FN28 chip. Here, you can see the comparison of the size between the new and old boards.
So here is the populated ARMbed-1114FN28 board. I moved the USB socket to the bottom to make room for the 3.3V LDO regulator. My original design used the SMD electrolytic capacitors, but they are too big and getting in the way, so I replaced them with tantalum and ceramic types instead.
Compare with the mbed LPC11U24, the board is slightly larger as you can see from the picture below.
Now I’ve modified the blinky program so that you can see the different when the new blinky program gets downloaded to the ARMbed. Take note of the steady green LED when the device is put in bootloading mode and the red/yellow LEDs blink rapidly during program download and verify.
As you can see, my ARMbed goes into bootloading mode initiated by FlashMagic and after the new program is downloaded, the device will reboot to run the new code.
One annoying part that I need to do before every program download is to remember to checked the “Keep RTS asserted while COM port open” option in the Advanced options, otherwise when download finishes, my ARMbed won’t auto-reboot! I need to hit the reset button. This option seems to reset itself after every download. I haven’t figured out how to make it set permanently.
So here it is, my journey into the world of ARM processors. With this ARMbed-1114FN28 board, I plug the device into a breadboard and build circuits around it. I can concentrate on the circuit without worrying about the working of the micro-controller part. One advantage of my ARMbed board over the mbed LPC11U24 is that I can also remove the programmed LPC1114FN28 chip and plug it into the final circuit, effectively, the board becomes a simple programmer for the LPC1114FN28 device. Of course, if you need extra RAM and more features, you’ll have to seek alternatives like the mbed LPC11U24.