Which one- BS2 or prop

.:John:.

I am trying to build a robot that will transmit info continuously between a computer and Boe-bot. People have been telling me to use the prop. However, I do not see the point is buying a prop and proto board because all the stamp will do is receive ALL the directions and commands from the computer. The Stamp will just execute them. Why would I need a prop?

-CR

Mike Green

It's not that you "need" a prop. The Stamp has some limitations. In particular, it ignores serial input if it's doing something else like reading a sensor or outputting a servo control pulse. It's a single threaded processor. It does only one thing at a time and nothing is buffered. In addition, servos require a control pulse about every 20ms. Stamp programs that involve servos have to work in a 20ms cycle and squeeze in other functions during the spare 18ms or so of a cycle. There are ways to get around this, mostly by using external peripherals to do the time-sensitive work. You can get 3rd party serial buffers to eliminate the "dropped serial input" problem. You can get several types of external servo controllers that take care of the 20ms pulses.

The major advantage of a Prop in this setting is that it can do this stuff all by itself. It can devote a processor just to handle any number of servos. It can devote a processor to provide a full duplex serial channel with a large buffer should you need it.

.:John:.

thanks mike.

Question: How difficult would it be to modify my boebot to use a protoboard instead of a stamp?

D Faust

The holes of the protoboard line up with the boe holes, just unscrew one and put the other on.

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.:John:.

Does the prop work with all the same hardware as the stamp?

Mike Green

It can, but you can't just plug things in willynilly. The Prop is a 3.3V logic device while the Stamps are 5V logic devices. There's a whole long "sticky" thread at the top of the Propeller forum stuff that goes into detail about this issue. For most devices, all you need is a series resistor in the I/O lead from the Propeller. Often 1K will do. I have a Propeller Protoboard-based BoeBot with a PING, an IR detector and two IR emitters, the two wheel servos and the PING bracket servo, an HB-55 compass, an SD card, and an xBee wireless link to a Mac (or PC). I used an I2C I/O Expander for the HB-55 because I was running out of I/O pins if I wanted to keep some free for a VGA monitor and keyboard/mouse for use in debugging. There's also a TV output that I've tried with a short whip for reception on a small portable TV on channel 4 ... It sort of worked, but I wasn't impressed.