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Herbert 1701 Species D Generations 1 & 2

The previous Herbert robotic life-forms all had a single logic circuit and while some made use of different components, the results were the same from a logic point of view. If the robot has enough power then do something. Not a very exciting logic circuit, but something necessary for all life, even artificial life. We can continue to use this simple logic design in one form or another, even with very advanced life-forms. Slightly modified it can become: If you are hungry then eat. For now we will leave it as is and continue by adding more logic circuitry to the robots.

The simplest logic circuits available are the same as the logic operators taught in any introductory computer class: NOT, AND, OR & XOR. These logic chips can be made to suit the purposes of the next stage in robotic life-form evolution, but would require a lot of additional support circuitry. Lacking space on the demo platform, we will instead opt for an integrated circuit that can accomplish our next task: which direction is the better power source?

To answer this question Herbert 1701 Species D will make use of a comparator chip. In simplest terms, a comparator takes two inputs and determines whether one input is higher than the other. Generally the inputs are voltage levels that are being compared. The comparison between the two voltages usually produces one of two outputs, either a ground level or an open circuit.

Herbert 1701 Species D Generation 1 SchematicFor Herbert 1701 Species D Generation 1, the two inputs will be the two variable voltage levels coming from photodiodes (and yes, the schematic shows the photodiodes properly biased for this purpose). This is similar to the variable levels used to "steer" Species C, only the voltage is going into the inputs of the comparator chip instead of the current going to the base of a transistor. The output from the comparator feeds the transistor used to turn a single motor on or off. In order to control both motors, and thus turn left and right towards a brighter light source, a dual comparator is employed with the second pair of inputs flipped from the first pair. The output of the second comparator then controls the other motor.

Herbert 1701 Species D Generation 1 Build 2Herbert 1701 Species D Generation 1 Build 1The dual comparator used is a LM393 variant. I tested out several different manufacturers and models of dual comparator chips using a simple distance test from a dead stop with no power. After three minutes in low light, I measured the distance that the robot platform had travelled. The winning dual comparator is a Texas Instruments TL393, which I had floating around in a parts bin. It is now an obsolete part, but with an inch more travel distance than the next closest chip it seemed worth keeping in the circuit. I did not test the newer LM393 from Texas Instruments, but I would imagine it would be an improvement over the TL393. One surprise was the TL393 outperforming the LM393 from National Semiconductor, which is usually the de facto standard for these types of ICs.

Herbert 1701 Species D Generation 1 SchematicThe Herbert 1701 Species D Generation 2 robotic life-form is a slight improvement over generation 1. The only additional circuitry is two more photodiodes, one for each side of the robot. Actually, the two original 180deg photodiodes were moved to point to the sides and the new photodiodes are angled forward. These additional photodiodes provide two benefits: First, the extra diode in series results in lower overall current levels and increased the distance test by nearly two inches. Second, having diodes point at the sides allows for a better comparison of light levels versus diodes only facing forward.

Herbert 1701 Species D Generation 2 Build 2Herbert 1701 Species D Generation 2 Build 2

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