Servo - July 2009

Twin Tweaks ...

and does not use a common clock.

Synchronous communication is useful for high data rate applications — in the case of the device from Devantech, it is intended to connect to sensors that are frequently streaming data. Asynchronous communication has a lower data rate, but it is perfectly suited to the task for our robotics kits — infrequent bulk data transfers like downloading a program to a robot.

We had been foiled. Had we gotten the right part, we would have been able to easily implement the adapter and have the Viper running around on a new program. Of course, we can still program the Viper and all of our other robot kits with our trusty USB-to-serial adapter, but it’s still the principle of the thing that gnaws at us.

Wake Up Call

So, what is the deal, robot kit manufacturers? We’ve established

that with regard to capabilities, USB is the far better choice for the multitude of reasons mentioned above. Replacing serial connectors with USB connectors also does not seem to be a huge burden (assuming that you have the right parts). Is it cost? The FTDI chips are only $2-$5 a piece, and that is actually a bit of an overestimate. Assuming that the kit manufacturers build a lot in a single run, they’ll be needing a lot of these chips. Large quantities of these chips result in more favorable pricing, more in the $1-$3 range per piece.

There’s also the matter of those additional capacitors, but we’re sure that the addition to the cost would be very small, because these manufacturers are probably ordering loads of capacitors already. We do realize, however, that even this increase in cost of a few dollars per kit does cut into profit margins. Even so, we think the resulting price increase would still be less than the additional cost to

the consumer of buying a reliable serial-to-USB adapter (they usually run about $20).

The objection to this, of course, would be that when a user buys several robotics kits the money savings from serial ports will pay back the additional cost of the adapter. That may be true for serial (for lack of a better word) tinkerers like ourselves, but always needing the adapter whenever we want to program anything is still a hassle that we would rather not deal with.

So, this is our wake-up call — we’ve had it with serial connectors, and we want to see USB! SV

Recommended Websites

For more information, go to:

www.parallax.com www.ftdichip.com

www.junun.org www.acroname.com

5 reflectance sensors on underside

Item #975 $99.95

battery charger connector

piezo buzzer

4 AAA batteries (not included)

The Pololu 3pi robot is a high-performance, compact mobile platform featuring:

Two metal gearmotors

Five reflectance sensors

8× 2 character LCD

Three user pushbuttons

Buzzer and LEDs

All peripherals are connected to an ATmega328P microcontroller running at 20 MHz, with free C-programming push-on/push-off tools, libraries, and support for the Arduino environment. power button reset button