This project ultimately just uses the power of the BBC Microbit to communicate via radio and control the LED strips, therefore this board started out purely as a passive breakout board to mount the MicroBit and connect it to the LED strip but quickly became more complex.
My Nixie tubes have 11 active pins each: a common anode and one cathode per digit (ten in total). The anode is connected to +180V via a 47k current-limiting resistor and each cathode is connected to the collector of a high voltage bipolar transistor (MPSA42) so that current can be controlled through each of them via the base of the transistor. This gives a total of 29 transistors that need to be individually controlled (24 hour clock requires 3 possible numbers for the first digit, 10 for the second, 6 for the third and 10 for the fourth). I chose to do this by using four 8-bit shift registers, connected in series to make one, 32-bit shift register.
One big change since I did the first version of the clock is my access to professionally made PCBs. At the time, I was only able to produce PCBs via hand etching or using my home-made PCB mill. A board like this requires at least a double sided design which is not easy using the above methods and so I used veroboard. This is painfully slow and messy.
For the new version I will use a professionally made two layer PCB.
I’m replacing the screen on the logic analyser for a few reasons: The CRT is heavy and bulky – replacing it would make the whole thing lighter, an LCD could be brighter and I can add colour to the monochrome display, and on top of this it’s just an interesting project. The most important thing is that the replacement screen is not worse than the old one!
The robot box needs to know when it has reached the limit of it’s motion. If motion continues past this point, the machine will literally rip itself apart. To stop this happening, I am using a limit switch that will be pressed if the robotic finger move too far. However, it seemed that a good portion of the time the robot would ignore this button and continue to rip itself apart. The reason for this lies in the way I was using interrupts to detect the pressing of the button.
For the Robox project, I needed a board to program and control a servo and a DC motor – I could probably have used something off-the-shelf, but I prefer to have a board specialised for the job.
The board I designed features an ATtiny828 microcontroller with 16 general use IO, two PWM outputs to control two 6V servos and an Allegro A3916 dual h-bridge to control two DC motors (or one stepper motor) at up to 1A per channel. This is more of a general use motor control board and could be useful in a bunch of projects.
The system needs a way to listen to the sound around it and the natural way to do this is with an electret microphone. I will probably include a 3.5mm jack input to allow you to plug music straight in too.