BBC micro:bit Pedestrian Crossing

I started this project by trying out the pre-written code that came with the IET Pedestrian Crossing resource. The aim is to use the BBC micro:bit to develop a prototype for a pedestrian crossing for a local secondary school.   

Parts List

You will need the following:

• 1 x BBC micro:bit
• 1 x Kitronik Prototyping System
• 2 x Red LED’s
• 2 x Green LED’s
• 1 x Orange LED
• 1 x Piezo Sounder
• 1 x NPN Transistor
• 1 x 2.2kΩ Resistor
• 5 x Resistors suitable for your LED’s (I used 220Ω resistors)
• 7 x MF Jumper wires
• 3 x MM Jumper wires 

Stage 1 

First, I connected three LED’s to P0, P1 & P2 via series resistors.

Stage 1

BBC micro:bit Edge Connector Breakout Board	Breadboard Connection
P0 pin	Red Traffic LED via 220Ω Resistor
P1 pin	Orange Traffic LED via 220Ω Resistor
P2 pin	Green Traffic LED via 220Ω Resistor
0V Pin	Breadboard negative rail
3V Pin	Breadboard positive rail

Stage 2

This worked well so I thought I would try adding two more LED’s via series resistors to ports (P8 & P12).   I modified the pre-written program so that the two additional LED’s would also be controlled.

Stage 2

BBC micro:bit Edge Connector Breakout Board	Breadboard Connection
P0 pin	Red Traffic LED via 220Ω Resistor
P1 pin	Orange Traffic LED via 220Ω Resistor
P2 pin	Green Traffic LED via 220Ω Resistor
P8 pin	Green Pedestrian LED via 220Ω Resistor
P12 pin	Red Pedestrian LED via 220Ω Resistor
0V Pin	Breadboard negative rail
3V Pin	Breadboard positive rail

Stage 3

The final part of this project was to add a piezo sounder to simulate the crossing beeper.   I connected a piezo sounder to port (P16) via a driver transistor.  I modified the code once more to add this functionality. 

Stage 3

BBC micro:bit Edge Connector Breakout Board	Breadboard Connection
P0 pin	Red Traffic LED via 220Ω Resistor
P1 pin	Orange Traffic LED via 220Ω Resistor
P2 pin	Green Traffic LED via 220Ω Resistor
P8 pin	Green Pedestrian LED via 220Ω Resistor
P12 pin	Red Pedestrian LED via 220Ω Resistor
P16 pin	2.2k Resistor for Transistor
0V Pin	Breadboard negative rail
3V Pin	Breadboard positive rail

Stage 4

I have added an illuminated external push button which is connected to the button A pin (P5),this lets you trigger or detect a button "A" click externally.   The LED inside the switch is connected to port (P13) via  series resistor.

Stage 4

BBC micro:bit Edge Connector Breakout Board	Breadboard Connection
P0 pin	Red Traffic LED via 220Ω Resistor
P1 pin	Orange Traffic LED via 220Ω Resistor
P2 pin	Green Traffic LED via 220Ω Resistor
P8 pin	Green Pedestrian LED via 220Ω Resistor
P12 pin	Red Pedestrian LED via 220Ω Resistor
P16 pin	2.2k Resistor for Transistor
P5 pin	Button A – connected to an external  push switch
P13 pin	Pedestrian wait LED via 100Ω Resistor
0V Pin	Breadboard negative rail
3V Pin	Breadboard positive rail

Code

The code was originally written in Microsoft Touch Develop but this legacy editor is being discontinued so I have migrated the code to the new Microsoft MakeCode editor.  The code can now be found here.

Racal 836 Repair

Racal 836 

I picked up an old Racal 836 32MHz Universal Counter-Timer (circa 1972) at a radio rally last year. The unit looked good, powered up and all the digits worked. However having carried out some of the preliminary tests as outlined in the technical manual the unit would not perform the self-check function.   

Top side showing the various plug-in assemblies

Underside

I found this thread on the UK Vintage Radio Repair and Restoration forum and posted a reply for some help, I also posted on the Yahoo Racal Dana group.   Various helpful things were suggested to check which I did. All of the supply rails were correct, the 1MHz frequency standard was running and I replaced several tantalum capacitors. I finally discovered that motherboard was plagued with dry joints and that there was a dry joint on the gating control board connector so the signal wasn't getting to the high speed decade counter board. Having re-soldered these dry joints all of the functions now work correctly.

Overall I'm very happy with the unit, it is beautifully made though it can still be a bit temperamental. Usually re-seating the plug-in modules fixes the problem.  I have recently acquired a OCXO 10MHz frequency standard to check my counter with, it seems to be pretty much in calibration still after all these years.

RasPiO Pro Hat

I recently backed Alex Eames (@RasPiTV) Kickstarter campaign for a RasPiO Pro Hat which is a small add-on board for the Raspberry Pi and is designed to protect and put your GPIO ports in numerical order.   The Kickstarter campaign has been successfully funded so boards are starting to be shipped out, mine landed on the doormat the other day.  

The RasPiO®1 Pro Hat has the GPIO pins connected via a protection circuit to female headers but is also broken out to un-protected connections. There is a small breadboard for prototyping circuits.  The PCB is very nicely made and is complete with gold and white silkscreen text.

I tried out my board using the included RGB LED and a simple GPIOZero Python script. There is well written manual which contains some structured experiments for the included components.

Overall I very impressed with this great little add-on for the Raspberry Pi,  if you want one for yourself then you can find out more on the RasPiO website.