Servo 112004

Circle #97 on the Reader Service Card.

Chains, Cores, and Wallbanging

Left Right

Left Right

Figure 9. Harvey Wallbanger schematic.

the next.

Remove Nv (8, 12) and ground its input. Add the kill input diodes to the remaining Nvs. By repeatedly pressing the PIC switch, see how many processes you can squeeze into the Trichain.

Once you have the Trichain down, add Nv (8, 12) back into the mix. Remember to use both the Trigger (capacitor across the channel) and Kill (diode) connections. See how many processes you can get running in a Quadchain.

Did you catch the pattern? Cram in as many processes as you can and the pattern becomes 1010 or 0101. Two successive Nvs will not be active simultaneously. Thus, the maximum number of processes is the number of Nvs divided by two (n/2).

You can consider this the "saturation point" of the Net. When you hear a BEAMer complaining of a saturated Hexcore, you know that it has three processes running on alternating Nvs in a loop.It's now time to play around a bit. How about a BEAM stoplight? If you have three different colored LEDs, set up a traffic light pattern and play with the timing in a Trichain. Could be fun for a model railroad. Once you have that down, try the Tricore.

Step 2: Building With Cores

This project — Harvey Wallbanger — uses an unbalanced Bicore as its tiny brain — just barely enough intelligence to follow a wall! Time-Biasing inputs (refer back to Figure 1) are used to steer the bot and a single tactile sensor is used to locate the wall.

A Bicore is, obviously, the simplest Nv core possible: two Nv neurons in a loop.

Now, take a look at Figure 9 — the schematic for Harvey Wallbanger. The Bicore is shown at the bottom, with the remaining inverters ganged as motor drivers. In operation, each Nv is active for a period of time specified by C1 and its resistor(s). During this time, the process outputs to a motor, causing the bot to turn in a short arc. The bot will waggle left, then right, etc. If R2 and S1 were not present and the junction of R1 and R3 were connected to ground, the Bicore would be balanced and the bot would go fairly straight.

Because the resistances at each Nv are unequal (depending on the position of switch S1), one half of the Bicore will

You might look at this month's project and think, "Hey, I could do that with a 555 chip, or a PIC, or a handful of transistors, or whatever." True, all true -there are many ways to make astable (two state) oscillators. This series of articles is focusing strictly on the classic RC circuits used to make BEAM Nervous Nets. If you are more adept at one of the other circuits or ICs, then - by all means - make your own Wallbanger and let us know how it turns out.

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Circle #52 on the Reader Service Card.

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