Hacked bumper mechanism

Having completed the new revisions of the circuit boards and sending them to be made by OSH Park, one of the few things that needs to be re-done/altered is the bumper required for operation as an Edgebot.

The hack, consisting of little more than a nail and rubber band

Previously it was unable to move backwards an forwards easily, this was because when you attached the bottom fastening plate, it sandwiched the slider between the bottom fastening plate and the top plate. I managed to fix this by applying a small amount of double sided tape to space the bottom fastening plate slightly and this provided the slider with enough room the slide relatively easily.

However, the micro lever switch does not have an adequate amount of force to push the slider forwards on its own. To fix this I made a slight hack to the design by adding a (blunted) nail through the back of the slider and attaching a small rubber band to the two screws either side of the newly added nail and the nail itself. This then provided a small amount of force to the slider to make sure that it is normally forwards, but with a small amount of pressure still allows it to move back and press the switch.

This hack will be implemented in the next version of the robot chassis.

Revised Photovore shield

The perfboard Photovore with diagnostic wires to figure the input/output wiring

As the Photovore shield failed, I had a look at the various components on it which could have failed, due to the little amount of parts on the modular Photovore PCB, it indicated that either the dual comparator was blown, or I had implemented the comparator chip into circuit incorrectly.

I started by simply swapping the comparator chip out and replacing it with another, completely new chip and the result? No difference in result. This caused me to presume that I had made an error when designing the PCB of the Photovore, so I made a mock-up of the circuit on a solderless breadboard which again, did not work, even when I attempted multiple circuits found online and within the simulation software.

Now without a Photovore shield, I needed another circuit that would perform similarly; I looked back through my notes on various original circuit design concepts and found a suitably simple circuit which I decided not to use previously as it required only 2 inverters and inverters are only packaged as a large hex NOT gate, therefore I would be using a large chip which could be replaced with a smaller DIP chip.

This new circuit is simple, it sets two LDRs up as a voltage divider, and the first inverter takes the split signal and turns it into a clean, digital signal, this is then fed to one of the motors, while that signal is inverted again for the other motor.

I quickly wired it up on a solderless breadboard to test the circuit, then continued to transfer it onto a perfboard shield. As you can see in the images, the perfboard shield is similar size, and no moderation to the headers was required to make them slot together correctly, due to the layout of the PCB.

The original Photovore PCB next to the freshly cut perfboard

The perfboard shield with the stackable headers in place

The finished DIY Photovore

The new Photovore shield on the chassis

As of the time of writing, it is fairly bright and it is hard to follow a light in bright light, as the difference between the two LDRs' resistance is minimal, so I will post a video when I have chance to.