Nuts & Volts - May 2007

◗ PARTS LIST

Item ◗ C1, C2 ◗ C3 ◗ C4 ◗ C5

Description
47 µF
0.1 µF
10 µF
330 µF

Source/Part No. 647-UVR1V470MDD 80-C315C104M5U 647-UVR1E100MDD 647-UVR1A331MED

◗ D1

◗ D2, D3

LED 1N4148

M859-LTL-4222N 512-1N4148

◗ J1

◗ J2

◗ J3

2.1 mm barrel DB9-F, R/A Pin socket

806-KLDX-0202-A 571-5747844-4 506-510-AG91D

◗ PB1

N.O. button

612-TL59F160Q

◗ Q1 ◗ Q2

2N3906 2N3904

610-2N3906 610-2N3904

◗ R1 1K ◗ R2, Rf 10K ◗ R3-R6 4.7K ◗ R7-R14 100Ω

299-1K-RC 299-10K-RC 299-4.7K-RC 299-100-RC

◗ RES

50 MHz

Parallax; 250-05060

◗ TB1-TB5 Two-pos term

571-2828362

◗ U1 ◗ U2

SX28AC/DP ULN2803

Parallax; SX28AC/DP 595-ULN2803AN

◗ VR1 ◗ X1-X9

LF50CP Pin header

511-LF50CP 517-6111TG

All parts are from Mouser unless noted otherwise.

download file on the Nuts & Volts website ( www.nutsvolts.com). It’s very simple: Once a serial port has been selected and opened, a timer is started that sends the packet every 20 milliseconds. Sending it more frequently makes no sense because the servo framing timer is 20 milliseconds. It won’t hurt, of course, and you can cause the control outputs to change at the packet transmission rate — so long as the transmission rate is just over 11 byte periods long.

I think that 20 milliseconds is probably a useful value for packet transmission timing considering the mechanical elements that are to be controlled with the board (servos take time to move). This will work with data rates down to 9600 baud (which you might want to use if the RS-232 cable is long). Do keep in mind that the little transistor level-shifter circuit is not true RS-232; the TX level out is only 5V. If you need a long transmission line, you can replace these components with a MAX232 or similar device. RA. 2 and

RA. 3 are available, so they could be used for hardware flow control on a derivative project, if required.

So, here’s an opportunity to save an old PC from the scrap heap. It doesn’t take a lot of resources to send serial data, so what I’m going to do is reformat an old laptop and devote it to animatronics control for Halloween and Christmas. For me, the next big question is the PC development language; I tend to default to VB because I have a lot of practice with it, but I would like to work with others who run different operating systems (Mac, Linux, etc.). So, I’m looking for a cross-platform development tool with which I can develop the same comfort as I

have with VB. Java seems to be the leading contender, but if you have another suggestion, I’m open to it.

Okay, that’s about it. Be sure to study the full listing and don’t be concerned if it doesn’t make sense right away. When it does, a big smile will cross your face and you’ll be off to other things. Not too long ago, I helped a customer in the Parallax SX forum to mix VPs for “background” serial I/O and Sony SIRCS decoding, and at the moment I’m working on a serial-controlled lamp dimmer. Once you’re used to mixing VPs, you’ll find that you can control virtually anything — virtually! Well, until next time, Happy Stamping! NV