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
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).
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.
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:
I’m going to try and correct the speed issue with some modifications to the prescaler circuitry.
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:
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.
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.
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.
Display! Finally I’ll get a chance to see whether my work up until now has been successful.
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.
18 x ‘2N3904′ – NPN
2 x ‘2N3906′ – PNP
21 x ‘221’ – 220 pF
2 x ‘104’ – 0.1 mF
31 x 10kΩ (brown-black-orange-gold)
28 x 100kΩ (brown-black-yellow-gold)
Here’s the process I used:
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.
Cut the required number of components from each larger bag and double checked they were correct.
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.
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.
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.
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.
Cut and soldered the PNP transistors – there are just two in the prescaler so make sure to place them correctly.
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.
Soldered the capacitors in place.
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.
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.
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.
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.
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.
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.
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.
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.
The gimbal build portion of the quad has been severely delayed due to technical problems with the hardware. I purchased two AlexMos Brushless Gimbal Controller with IMUs from GetFPV but they both worked terribly. Flimsy wiring, along with persistent IO errors meant they both went back for replacements. Six weeks later the replacements arrived and they worked much better. Below you can see the controller in action (green is good) along with the tiny Inertial Measurement Unit on the top left. The IMU will be mounted to the actual gimbal and provide inertia tracking and stabilisation.
I really can’t recommend the 8-bit AlexMOS boards based on my experiences – whilst they seem well-built I’ve a huge number of problems getting them to work. Go the 32-bit version instead with the added benefit of a third yaw axis.
I mounted the controller and knocked together a custom power cable to connect it to the dirty frame. I made some modifications to the plug and socket to make them sit flush on the frame. I probably shouldn’t have used a plug as it’s one more thing that can break apart in the air, but it’s not essential to safe flight so I think it’s OK.
With the controller board mounted, powered and at not throwing ten thousand IO errors per second, next up will be construction of the gimbal itself and mounting of the IMU.