Newbie Question -- BS2 vs Propeller

L. Scott Hudson

Hello,

I'm sorry for the idiot question.· I'm a programmer not a roboticist, and I know absolutely nothing about robots or electronics, but I do plan on designing a robot, and then building multiples of that robot to distribute to a programming team (e.g. I have·very real·concerns regarding cost).

So here's my Q:· What's the diff between the $49 BS2 and the $12 Propeller?

TIA!

Scott

Mike Green

There are huge differences.

The BS2 is a long established microcontroller with hundreds and hundreds of pages of tutorials, manuals, magazine articles, educational kits, etc. It's programmed in Basic, has a lot of built-in statements for common I/O devices used in control applications. For $49, you get a complete module with a voltage regulator, EEPROM to store your program, resonator for the processor's clock, and a programming interface. You do need some interface components externally for the programming interface depending on whether you plan to use it with an RS232 serial port or a USB serial interface. The Parallax Basic manual shows some suggested schematics.

The Propeller is new. $12 isn't really comparable ... that's just the chip. A more reasonable comparison is the Protoboard for $25 which includes the voltage regulator, EEPROM for program/data storage, and the crystal for the system clock. You do need an external serial adapter for programming which can be shared (the PropPlug for $30). Other USB to 3.3V logic serial adapters can be used, but Parallax's devices are specifically designed for this use. You can also use an RS232 to 3.3V logic serial adapter.

The Propeller is a completely different kind of processor, there's much less educational material currently available. The programming language (Spin) is similar in some ways to C, but has some unique features and is much more sophisticated than Basic. The Propeller has much more memory than the Stamps, is much faster, and consists of 8 independent processors that share 32K of memory, each have their own 2K of local program/data storage and special purpose registers, and share all the I/O pins. Spin doesn't have the built-in I/O of Parallax Basic, but there's a library of I/O drivers (written in Spin and assembly language) and sample programs that can be incorporated into your own program that handle the same functions that the Stamp does ... and much more.

Typically, several Propeller processors are allocated to I/O functions and one or more processors handle the main processing tasks. One processor can generate video text, another can handle a high speed serial channel, another can control up to 32 servo motors, another might take turns doing ultrasonic distance ranging or IR distance detection or checking a compass or accelerometer, doing some basic initial processing on the data and leaving it for the main processor to do higher level analysis.

MinimumWage

Scott,

The $12 propeller is just the microcontroller. To fully use it you'd have to add an EEPROM, voltage regulator, crystal oscillator, etc. The BS2 has all these components integrated into a single 24-pin dip package for ease-of-use. A more fair comparison would be the cost of a BS2 to a breadboard-ready Propeller package like the Propstick or Spin Stamp.

Note also that they are different microcontrollers, with different capabilities and programming environments. You might want to download some of the (free!) Parallax product manuals and read up on the capabilities of each one.

For your robot project have you taken a look at the BOE-Bot?

Regards,

Mike

Mike Green

For an example of what can be done with the Propeller, download BoeBotBasic from the Propeller Object Exchange (obex.parallax.com/objects/category/2/) and look at the documentation. This is a simple Basic interpreter written in Spin that runs on a Propeller Protoboard and has some specific statements to handle the BoeBot servos, a PING ultrasonic distance sensor, an IR distance sensor, an HB-55 compass, an XBee wireless serial link, and a PC-compatible SD card for program and data storage.

L. Scott Hudson

Ok thanks for all the info... What if I plan on doing as much processing as possible in a DOT NET service on the PC, and hypothetically only need a controller to receive sensor inputs and to direct the servos... and also to interface with the PC.· Which solution would you recommend?

Scott

Mike Green

I would go with the Propeller given that you're a programmer already. In order to overlap the sensor reading, communications, and servo control, you have to so some very careful programming with the Stamp. In addition, the Stamp can miss some data from the PC if it's doing something other than a SERIN statement when the data is sent (there's no buffering in the Stamp). The Propeller doesn't have this limitation.

L. Scott Hudson

Ok. I'm not there yet but it's nice to know that I can get the results I need with MSRS and for possibly less cost as well. I thought I did my research on the BS2, which I still like a lot, but that was more or less in comparison with other robot parts manufacturers... not as thorough when comparing Parallax products to each other.

Thanks!

Scott

parts-man73

This is sounding curiously similar to the "Would this system work" thread

Curious_Roboticist said...
The Boe-bot (somehow, I have not decided yet) receives a command to go to the kitchen. The bot then sends a request to the computer for the best route to the kitchen based on the robots sensor input probably using GA(genetic Algorithms). (I think that is possible) The robot then follows that path until the sensors detect an obstacle in the way. The bot sends a request back to the computer for a new instruction set. Computer sends new instructions. This continues until the robot has reached the kitchen.

Is this the same project that you 2 are working on? Probably would make more headway if you pursue 1 thread or the other.

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Brian

uController.com - home of SpinStudio

L. Scott Hudson

Haha no but his does sound a lot like mine...