Time away

For the next few weeks or so, I will be less able to carry on designing/building of the modular robotics project and keeping track of my other current projects as much, therefore I may post a little less frequently. This is mainly due to exams and work experience.

Two steps forward, one step back, another forward and then one back...

Can you see the error?

I'll start with the good news, I have now received all of the required components to build all the modules and have been constructing them when I have spare time.

I began to solder the Edgebot boards as soon as the parts started to arrived, and that process was completed without any hiccups, moreover when the quick build was finished I was able to test it using a few LEDs on the outputs, a switch acting as an the input and a small power supply, this enabled me to thoroughly test the Edgebot circuit and it appeared to function correctly.

When the components finished arriving I was also able to finish the Photovore, again without a problem, however I was then naive and reasoned that because it had few components and that I have worked with simple comparators before, that that board would work, more on that later.

Before I soldered each board I quickly looked over the tracks and layout again (having also done so when receiving them) and this time I noticed a fault with the motor controller;

Can you see it now? It is the short connecting all the pins.

This could be resolved relatively quickly using a lot a light, some magnification glasses, a scalpel and a steady hand. I made a shallow incision into the connecting track and then I was able to carefully peel back the track and sever it at the next pad, this completely removed the connection, this is easily seen with the track leading to the centre pin of the voltage regulator in the following image;

It isn't neat, but it gets the job done

I have since been able to solder the motor controller board completely and thoroughly test it both with and without motors, it seems that my worries about the L293D were unnecessary; it functions fine with a 6 volt input voltage (4x AA) and it also produces less heat than anticipated thus meaning there is no need for a heat-sink or other cooling method. Here are images of the (working) boards;

The fully soldered Edgebot module

The motor controller, without the confusion of the voltage regulator

Once the first chassis design has been finalised, a video of the robot shall be posted, this should be shortly. 

Stacking modular PCBs

The three boards stacked one upon another

This is another relatively quick post to show how to modular robotic boards are to come together to form a robot with modular behaviour. I have received packages in the post containing headers and some other various parts, but the main order has a back-ordered component, so it will take longer. 

As you can see from the first picture, the top two boards (the Edgebot and the Photovore) have a pair of Arduino 6-pin stackable headers, which are incredibly useful if you want multiple PCBs to have the ability to stack on top of each other, but unfortunately they are only sold in lengths of 6, 8 or 10 pins, so I had to design the boards around one of those sizes. These pairs of headers have two uses on these boards, the preliminary function is the transfer of electrical logic signals between various boards, the other purpose of the headers is to hold and stabilise the boards mounted on top and using a pair of headers is a lot more stable than a single row.

You can also see the right angle pins facing outwards from the upper boards, these are to attach various inputs/outputs to, such as touch switches, light sensors, logic outputs etc.

Here are some more images of the boards with a few components;

The three boards unstacked

Arrival of modular robotics boards

The three boards as seen from the top

This is just a quick post to say that the modular robots boards have arrived. I used OSH Park for these boards and although this is my third order with them, I am still highly impressed by the quality of the PCBs, I only ordered three of each board as they are the first physical version that I have and mistakes are relatively expensive. Here are some more photos of the boards;

The three boards as seen from the bottom

Drawdio

A finished Drawdio without a printed mount

Since even before I started the designs for the modular robots, I was greatly interested by the original Drawdio circuit concept, that you could use a simple circuit to interact with the surrounding world and for the world to, in turn manipulate the outputs of the circuit.

In this instance, it  the Drawdio is a basic electronic circuit which utilises the use of a 555 timer chip to produce an astable output frequency. The speaker frequency depends upon the resistance of the input circuit, which comprises of the graphite pencil and your body. As the line that you draw gets longer, the input resistance increases, therefore different tones can be heard.

The Drawdio was my very first circuit that I designed in Eagle, previously, I had used the very basic but easy to learn package called Fritzing, however, this provided very few components and little flexibility when it came to board layout. After attending a couple Cambridge PCB Makers sessions (Forum found here, Saar's blog here) I had a much greater (not yet great, just greater) understanding of PCB design software and decided to give Eagle a go. I then designed a derivative of the Drawdio circuit, but it functions the same.

The Schematic

There is no difference between PCB versions 0.1 and 0.2, except the fact that v0.2 had a general track layout clear-up as I got rid of the vias and added two ground planes.

The PCB

I also designed and developed a custom 3D printed mount for the Drawdio circuit board, it was designed in Solidworks and printed with transparent resin on a FORM 1. As you can tell from the following pictures, it took many revisions to achieve the correct tolerances on items such as the PCB and speaker, as they are designed to "clip in". I have not yet completely finished the mount however, as I intend to design a clip mechanism to allow for the CR2032 battery to be easily replaced when it runs out - it currently lasts ~500 hours with a TLC551 timer, (which works down to 1v for a coin battery to be used) so this action would be infrequent.

Top, left to right: PCB mounts v0.1, v0.2, v0.3, v0.4 and v0.5
Bottom, left to right: Speaker mounts v0.1 and v0.2

The bottom mount is the first "final" print, while the top is a more compact version

NOTE: I do not claim any credit for the original Drawdio circuit and the MIT project website can be found here. I did, however design the mount.

The latest Drawdio PCB design files (v0.2) can be downloaded from Dropbox.
The Drawdio 3D design files (v0.5) can be downloaded from Dropbox - (STL and Solidworks file types)