Transistor Clock – Modification for 50Hz power

When I first brought my transistor clock kit, I wasn’t entirely sure how it’s timing circuit worked.  Assuming it was some type of internal crystal oscillator, I soon discovered that it runs off of the 60Hz sine wave present on 110V AC power.  This posed two important questions:

  1. Will it work in Australia, where we use 50Hz 220V power, and if not …
  2. How do I make it work?

Thankfully after spending the past few months building the power supply, prescaler, and seconds chain, I understood the circuit well enough to modify it to work at the correct speed.

The theory

The KABtronics manual shows the following diagram on page 25:

Transistor clock - Modification for 50hz - Original diagram
Transistor clock – Modification for 50Hz – Original diagram – Image (C) Copyright KABtronics

You can see the 60Hz signal coming from the wall, then dividing by 10 to get 6Hz, then dividing by 6 to get 1Hz.  In the case of a 50Hz input, it’s divided by 10 (giving 5), then divided by 6 to incorrectly arrive at 0.83Hz.  This means the clock effectively runs 17% too slow.  Not great.  If we modify the divide by 6 into a divide by 5, we’ll be all set:

Transistor clock - Modification for 50hz - Prescaler
Transistor clock – Modification for 50Hz – Prescaler – Image (C) Copyright KABtronics

Making the modifications

After cutting four traces and adding three links, the clock will work correctly, as described below.

On the front

1. Towards the bottom right of the board (where the prescaler is located), I cut two small traces, marked below with yellow dots:

Transistor clock - Modification for 50Hz - Front side cuts
Transistor clock – Modification for 50Hz – Front side cuts

Be careful with the cut between the diodes – there are two traces in there – you want the top most trace!  Don’t cut them both.  I could also have removed the diode (D52 to be precise) to the left of the yellow dot, but I didn’t want an empty space on my board.

On the back

2. I cut two more traces on the back, marked below with yellow dots:

Transistor clock - Modification for 50Hz - Back side cuts
Transistor clock – Modification for 50Hz – Back side cuts

3. Finally, I added three new traces to the back.  The points you want to link are marked below with green dots:

Transistor clock - Modification for 50Hz - Back side links
Transistor clock – Modification for 50Hz – Back side links

The final circuit is shown below.  Green lines are new traces, yellow dots are trace cuts.

Transistor clock - Modification for 50hz - Circuit diagram
Transistor clock – Modification for 50Hz – Circuit diagram


After I made these changes, I fired up my clock and it was now timing correctly.  You can see in the video below it’s not much more accurate compared to previously:

Next steps

Tens of seconds are next.  All the hard steps are now complete – I just need to power through soldering the 1,000+ remaining components and I’ll be done. ;)

Transistor clock – Display

The display consists of six seven segment LED components, along with 680Ω resistors for each segment.  The display simply takes the output from each decoder chain and lights up the corresponding  segment to create the digit.

How to build it

This portion of the clock contains 51 components:

  • 6 x 7 segment displays
  • 4 x red LEDs
  • 41 x 680Ω resistors (blue-gray-brown-gold)

With just 51 components, the display portion of the clock is the easiest to construct.

Things to watch out for

  1. Incorrect placement of the seven segment displays – There are 4 orientations possible, only one of which is correct.  The displays should be placed in the bottom most PCB holes, with the decimal digit towards to the bottom also (the decimal digit portion of the display is not used in the clock).
  2. Applying too much heat to the segment display pins – The manufacturer’s documentation states that the majority of display problems are a result over heating the pins.  The displays are easily replacement but best to avoid this problem with a low powered soldering iron.
  3. Seating of the segment displays – I found it best to solder each of the corner pins on the display, and make sure they are seated flush against the board before soldering the remaining pins.  Don’t forget point 2 above regarding over-heating.


Once I finished the construction of the seconds digit, I powered up my clock.  The display ticked over as expected with all segments lighting correctly.  As predicted, the clock is running 17% slower as a result of the 50Hz input signal from the 50Hz 240V AC power source.  This is easily visible in the below video:

Next steps

I’m going to try and correct the speed issue with some modifications to the prescaler circuitry.

Transistor clock – Seconds chain decoder

The seconds chain decoder takes the clock 1Hz clock signal from the seconds chain flip flops and converts it for display on the 7 segment displays.  There are two parts:

0-9 decoder

The four flip-flops (and their negated signals) from the seconds chain represent the binary value of the seconds counter.  The 0-9 decoder takes those signals and converts their values into decimal (0-9) in order to drive the 10 data lines for the 7 segment decoder. Towards the bottom of the photo below you can see the 8 traces.

Seconds chain decoder - 0-9 decoder complete
Seconds chain decoder – 0-9 decoder complete

7 segment decoder

This section takes the 10 data lines and uses those signals to light up the corresponding segment of the 7 segment display.  Towards the bottom of the photo below, you can see the 10 data lines.

Seconds chain decoder - 7 segment decoder close up
Seconds chain decoder – 7 segment decoder close up

How to build it

This portion of the clock contains 130 components:

  • 89 x ‘1N4148′ diodes
  • 20 x ‘2N3904′ – NPN transistors
  • 1 x ‘104’ – 0.1 mF capacitor
  • 20 x 10kΩ resistors (brown-black-orange-gold)

Their are a lot of tightly packed components in this part, so be careful with the orientation.


Again there isn’t a whole lot of testing to do in this step without an oscilloscope.  You can however apply power and make sure you still have no shorts.

Next steps

Display!  Finally I’ll get a chance to see whether my work up until now has been successful.

Transistor clock – Seconds chain

The seconds chain looks very similar to the first half of the pre-scaler, using most of the same components.   The seconds chain takes the 1Hz signal from the prescaler, and divides it into two parts:

  1. By 10 – to drive the seconds decoder circuit
  2. By six – to provide a 1/10Hz clock signal for the tens of seconds circuit

How to build it

The seconds chain portion of the transistor clock contains 81 components:

  • 24 x ‘1N4148′ diodes
  • 11 transistors:
    • 10 x ‘2N3904′ – NPN
    • 1 x ‘2N3906′ – PNP
  • 13 capacitors:
    • 12 x ‘221’ – 220 pF
    • 1 x ‘104’ – 0.1 mF
  • 33 resistors:
    • 17 x 10kΩ (brown-black-orange-gold)
    • 16 x 100kΩ (brown-black-yellow-gold)

The process is very similar to the prescaler construction.  Be careful with the PNP transistor as there is only one of them in this section – solder it first.  Same goes for the ‘104’ 0.1mF capacitor.


Unfortunately I still don’t have access to an oscilloscope which would be handy to determine whether this section is performing as expected.  I hope to get one in the next few weeks.

Next steps

The seconds decoder is next.

Transistor clock – Prescaler

The clock prescaler takes the 60Hz square wave signal from the second power supply comparator and divides it into a 1Hz signal accurate enough to drive the clock.  There are two parts – firstly dividing 60Hz by 10 to get 6Hz, then dividing that by 6 to arrive at the 1Hz square wave.

Given I’m in Australia (where 50Hz from the wall is the norm) I’ll need to make some modifications to this part once the clock is functional.  For now, I’m going to make the assumption that on 50Hz my clock will run 17% slower than expected.  50Hz / 10 / 5 = 0.83Hz = 17% slower.

How to build it

The prescaler portion of the transistor clock contains 153 components:

  • 41 x ‘1N4148′ diodes – These are oddly just referred to as ‘small diodes’ in the manual – no idea why the component name isn’t mentioned.
  • 20 transistors:
    • 18 x ‘2N3904′ – NPN
    • 2 x ‘2N3906′ – PNP
  • 23 capacitors:
    • 21 x ‘221’ – 220 pF
    • 2 x ‘104’ – 0.1 mF
  • 59 resistors:
    • 31 x 10kΩ (brown-black-orange-gold)
    • 28 x 100kΩ (brown-black-yellow-gold)

Here’s the process I used:

  1. Brought a plastic bending tool.  I don’t suggest even attempting to try to build this thing without one of these – it’ll look terrible.
  2. Cut the required number of components from each larger bag and double checked they were correct.
  3. Cut the components from the paper strips.  Do not try to just pull the components out – some of them such as diodes are fragile.  Do not cut the PNP transistors until you’re ready to insert them – they are easily mistaken for NPN.
  4. Bent the 1N4148 diodes using my bending tool – they are quite small so I cut my own notch in the side of the tool to match the PCB spacing.
  5. Soldered the diodes in place.  Diodes are polarised (only work one way) so it’s important they are aligned correctly.  One thing which may not be immediately obvious (and isn’t mentioned in the manual) is that the square PCB pads are for the cathodes – the side with the line on it.
  6. Soldered the resistors in place.  If you’ve bent them correctly (and consistently) they should stay in place once the board is flipped over – this saves an entire step of having to bend the terminals to make them stay put.
  7. Cut and soldered the PNP transistors – there are just two in the prescaler so make sure to place them correctly.
  8. Soldered the NPN transistors.  With the transistors I found it easier to solder the middle terminal first, flipping the board and them aligning them correctly, before soldering the other terminals in place.
  9. Soldered the capacitors in place.
  10. Cut off the spare component legs.  Get a decent pair of sharp pliers for this step.  You’ll have the excess component legs bloody everywhere after this step.
  11. Align all the components correctly – make it neat!


I then powered up the board and no magic smoke was released.  This at least means I don’t have any shorts.  If I had an oscilloscope, I’d be able to see a 1Hz (0.83Hz) square wave on the output of the top right of the prescaler.   You can see the trace fairly easily where the circuit jumps into the seconds chain.  If I measure the voltage on this point however I can see it swing from negative to positive, roughly every second – this is the best I can do until I get one of these.

Board warp?

When you’re at this stage of construction, be careful not to store the board ‘face up’ with the zip-tie underneath.  My board developed a noticeable warp from one corner to the other – which I’m hoping will fix itself over time.

Next steps

The seconds chain is next.  I hope to get faster at soldering, and also looking for a way to avoid the metal leads flying everywhere.

Driving simulator – The rebuild

I’ll be rebuilding my driving simulator using the following parts:

  1. Logitech G27 force-feedback wheel and pedals
  2. 2 x SCN5 mechatronic actuators made by Dyadic.  This will provide 2 degrees of freedom (DOF) meaning I can move the seat left, right, back and forward.
  3. 2 x Actuator mounting and dampening kits from SimXperience
  4. Universal motion seat kit from SimXperience
  5. Leather seat which I paid way too much for.  I’m not at all happy with it but it will do for now.  It’s heavy.
  6. Oculus Rift DK2 (ordered Aug 2014 – expected to arrive sometime in Oct 2014). Currently using the DK1 courtesy of Mr Lewis. (thanks! :))
  7. Software – probably a mix of Live for Speed and Colin McRae Rally to being with.

Time to get to work on a frame.

Transistor clock – Power supply

The first step to building the transistor clock is sorting the power supply stage.  There aren’t too many components in this stage and can be built in around 30 minutes.   I have a component bending tool which made installation a lot quicker.

The clock uses a 60Hz signal from the 9V AC 1A power supply, however in Australia we use 50Hz.   This is crucially important to the operation of the clock and I will be modifying the prescaler section to divide by 5 instead of 6.


I was happy to discover there were no fires or blown components on applying 9V power to the clock.  The capacitor measured 14.3V across its terminals which is good enough to continue onto the next step – the prescaler.



Transistor clock – The beginning

To give you an idea on how many components are required to make this clock work, here is the parts list:

  • 194 transistors
  • 566 diodes
  • 400 resistors
  • 87 capacitors
  • 10″ x 11.3″ PCB
  • Total parts - 1,247

The make the clock work, I need to make at least 2,500 good solder joints.

40TB PC build – Deconstruction and cleaning

With the October (LAN) long weekend approaching fast, I thought it a good time for a PC rebuild.    There are a few things I’ve wanted to do with this rig since I purchased it.    My build has the following parts:

  • Intel Core i7-3820 CPU @ 3.6GHz
  • Gigabte GA-X79-UD5 Motherboard
  • 32GB Corsair Vengeance DDR3 1600MHz RAM
  • 1200W Corsair AX1200 Power Supply
  • 1GB Gigabyte Radeon 6850 Graphics Card
  • Intel 120GB 330 SSD
  • 3 x 4TB (12TB) Seagate Barracuda ST4000DM001
  • 8 x 3TB (24TB) Seagate Barracuda ST3000DM001
  • A few smaller 2TB and 1.5TB drives

The current build works well performance wise with a WEI of 7.3 (if that still means anything).   It just needs some love on the construction side – it’s been hastily thrown together with no real thought on cable management or cooling.

24 hour filth

I never turn my machine off.  Ever.   Even though I’m a clean (non-smoking) person, thousands of hours of constant use takes its toll.  You can also see the terrible job I’ve done on the cabling.


Now that all the dust is gone, I can start the wiring.

Quadcopter build – Gimbal construction

The quad I have is based on the QAV540G (G == gimbal) so comes with all the gimbal parts as part of the kit.  Unfortunately I won’t have control over Yaw with this gimbal as it moves in 2 axes only, but it’s a start.

Whilst not particularly difficult, it can take some time to get the parts of the gimbal aligned correctly.  Make sure the motors are mounted corrected and all parts are oriented as per the manual.  I must have put it together at least three times incorrectly before getting all the parts to line up.  I haven’t worried too much about the wiring for the motors just yet.

Attaching the gimbal to the frame

This was relatively straightforward.  Below you can see my temporary motor connections to the controller (soldered).  I’ll be adding some plugs and socket shortly.  It doesn’t matter which order the wires at attached, but I just made sure the middle wire on the motor matched the middle solder join on the controller.

Firing up

After applying some power the gimbal just needed a few tweaks in SimpleBGC to get it to move correctly.   I’ve adjusted the power for the motors to ‘100’ (out of 255) which seems to give them enough torque for now without them getting too hot. The IMU provides real-time feedback of its position back to the controller, then moves the motors in the opposite direction to keep them level.  You can see the first test run below.

Ironically, YouTube has detected that my ‘video may be shaky.’  Still needs some work I think. ;)