Pathfinder Mini – Logic Gate Robot, no CPU!

Based off my larger walker, the Pathfinder Mini is a cost-reduced version which requires far fewer parts, much less plastic, and is a bit more simple to build. I will be releasing the plans for it as soon as I can, and considering the reduced part count, I may be able to sell complete kits instead of my usual plans or plastic-only kits.

If it were economically feasible, I would also like to make a batch of circuit boards to include with the kit. As of right now, it's too complex to build in point-to-point wiring, but a PCB with proper traces would be nice. I'd have to ditch the LEDs as a cost saving measure though as well. Or, you know, I could just use a microcontroller like a sane person.

This circuit was really just a fun project to prove I could build this idea from my head into an actual working robot. It does work quite well, and schematics and an explanation of the design is listed below.

Clock Gen

Astable 555 timer which generates the clock signal for SR04 Sonar Sensor and 4017 Counter.

Sonar Sensor

HC-SR04 Sonar Sensor. A clock pulse triggers a sonar ping. Pulse width on echo pin is proportional to echo time.

Missing Pulse Detector

The echo pin from sonar seamlessly refreshes the monostable 555 timer, keeping the output high. A resistor-capacitor circuit snubs out short pulses from close objects, causing the output of the 555 to go low. This causes a reset for the “Counter” and “First Loop” circuits.

First Loop

RS flip-flop “register” using a 555. Upon reset, the output is set high. The last output from the counter will set the output low


“Program Counter” using a 4017. Each clock pulse pulls one of 10 pins high, in sequence. A reset brings the output back to 0.

Diode “ROM”

Diode logic is used to hard-wire program instructions to each step of the counter. These instructions consist of “Left, Right, Stop, Up, and Load MEM”.

Light Sensor

Functions outside the program loop. Injects instructions for “Stop” and “Up” when light is above a threshold. Not strictly necessary, but adds a bit of interactivity.

Last Direction

RS Flip-flop “Register”. Retains the last direction executed from ROM after a reset.

MEM Compare

Combinational logic to determine the results of the MEM instruction. If the “First Loop” register is true, the “Last Direction” register is interpreted as either a “Left” or “Right” instruction. This provides obstacle avoidance when a reset is triggered by the sonar sensor, and is ignored in subsequent loops. Also only allows STOP instruction on first loop.

Motor Driver

A L293D motor driver circuit. I recommend capacitors on the motor outputs.

Servo Driver

A 555 timer in astable mode. The output is pulse width modulated via a voltage on pin 5, resulting in basic servo control for head tilt.



PG22 Short Update

Well, I built myself a second personal PG22 Short. Doing this allowed me to follow my own instructions, and find any remaining flaws in design or instructions. This did result in a minor revision of the location of the set-screw for the guide-rod, along with more explicit notifications on cleaning and sanding parts.

I’m happy to report that my second build not only fired properly on the first shot, but ejected and continued to function throughout 20 consecutive shots, with no visible wear or damage to any parts.

Because this gun is now a spare for me, I decided to have a bit of fun when printing it, and went for a more wild color scheme. I hope others find this as amusing as I do 🙂

PilotTrak V2 Mini

While the PilotTrak V2 is a huge improvement over the original PilotTrak, it is quite a bit bigger. There’s something about the cuteness of an absolutely tiny tank-like vehicle, and it’s nice to be able to pocket it and go anywhere. Solution? PilotTrak V2 Mini.

This version sacrifices a few features. There’s no secondary idler wheels, and there’s no servo tilt for the camera. The electronics are housed in the space freed up by the removal of the servo. While it’s a difficult build that requires de-pinned or micro receivers, it is not much larger than a standard TinyWhoop.

I’m probably going to add very fast (500rpm @ 3v) motors to make up for the lack of off-road ability.

PilotTrak V2

Currently very close to a final version 2 of the Pilot Trak. This version is FAR more capable than the original. It has greater ground clearance, wider tracks, better cog mesh, a battery cover, more room for electronics, grippier tracks, and overall reduced cost due to removal of ball bearings. Pulling cable through drop-ceilings is now a piece of cake with these improvements!

Once released, I may discontinue the V1 to focus on improving the V2. While the V1 was good for moderately flat indoor ground, it has a tendency to tip and has very little room for electronics, making builds difficult.

Posting from GeoWorks!

Using my WiPi Modem (available from my site), I was able to get my Brother GeoBook, a low cost 386sx laptop from the late 90’s, online! Software availability is not great, as it only runs GEOS / GeoWorks Ensemble, but there is integrated TCP/IP support via a PPP connection, which my Modem supports.
The only useful applications on the GeoBook are Emailer (A very, very basic SMTP/Pop3 email client), Web Browser, and a fairly nice, though limited, IRC client. While not extremely useful in today’s age, it is able to get enough connectivity to post to my blog via the WordPress email post. The WiPi modem is also able to provide me with an SSH client via terminal emulator, so I regularly use the GeoBook to configure my webserver! This machine would definitely get a few strange looks if I ever started using it in a coffee shop 🙂

PS2 Modchip

Modbo 5 Install complete! Nothing like dumping all your DVDs straight to a 500gb Internal HDD!