Many Faces of the Board Of Education

May 1, 2012
Technology Editor Bill Wong does a hands-on test of Parallax's Propeller Board of Education.

I have been playing with the Parallax Propeller (see Eight 32-Bit Cores Take Flight In Multiprocessor Microcontroller) since it came out. The Propeller has 32 Kbytes of shared RAM and 32 Kbytes of shared ROM. Each core has 2 Kbytes of RAM. It has a unique design that implement eight 32-bit cores that share a single 32-bit I/O port. Bit banging peripherals are the norm.

The Propeller Board of Education (Fig. 1) has the same form factor as Parallax's popular Board of Education (BOE) that runs a BASIC Stamp. The BOE can also sit atop Parallax's BOEBot robot.

Figure 1. The Propeller Board of Education has an 8-core 32-bit processor plus plenty of peripheral interfaces including a VGA port and a MicroSD port.

The Propeller is a more powerful chip and this new board surrounds it with plenty of peripherals. The USB port is for programming and debugging. There are half a dozen servo ports and a VGA display output. Program storage is provided by 64 Kbyte EEPROM that can be loaded into the Propeller's RAM when the system starts up. There is also a MicroSD socket. A number of I2C peripheral chips are on-board as well. These include a 10-bit ADC and a 10-bit DAC. There is also a Sigma-Delta ADC connected to an on-board Elecret microphone. A significant number of colored LEDs provide visual feedback.

Headers provide access to most I/O pins and there is a small breadboard used for experiments that can be done using the board. There is also an XBee header that can handle any of a number of XBee wireless modules. A serial interface to the XBee module provides easy access to a mesh network.

An on-board switching regulator can deliver up to 3A at 5V. This is key because the board is often used more motor control. The power switch even has a setting to enable the processor but disable the servos. That is handy for debugging a motorized robot.

I was hoping to write about my success in building a multichip system using one of the cores to implement a serial mesh network. As usual, I was distracted before I was able to finish it although there looks to be sufficient space and speed for one core to handle four bidirectional, serial packet interfaces. One challenge was a lack of macro support with the assembler. It would be less of an issue for a single port interface but it got a little tiresome having to replicate the code four times. I'll let you know if I ever finish it.

In the meantime, check out the Propeller Object Exchange for more soft peripheral objects and applications.

The other board that Parallax has delivered lately is one I have not had a chance to check out but one that has garnered a lot of interest. It is the Board of Education Arduino Shield (Fig. 2).

Figure 2. Board of Education Arduino Shield needs an Arduino board to be complete.

This board has the BOE form factor so it can be mounted on the BOEBot. It also has breadboard and servo headers. The Arduino board actually mounts under the shield. This means the standoffs for the BOEBot are a little higher than usual because there are two boards in the stack. Additional shields can be plugged on top of the Board of Education Arduino Shield.

The Propeller is actually a more powerful chip but it is not as easy to program as the typical Arduino board. On the other hand, Arduino is a very popular platform with lots of development tools and example programs. There is a host of training materials as well.

The primary reason for going with the BOE Arduino Shield is to gain access to the BEOBot robot. For that it is a great choice.

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