008: FAN BLADE ELECTRONICS

THE INTAKE: ELECTRONIC PROPELLER CIRCUIT BOARD

As mentioned before, the electronics for the Falke will be from a simple off-the-shelve solution. I am going to use a 555/4017 IC combo, which is commonly used to make sequential blinking lights for certain TV Sci-Fi props in their heyday. To save time, I will not going to design my own board but use one that is already available in most stores. You can search for DIY electronic kit, which is described as “DIY Kit NE555+CD4017 Light Water Flowing Light LED Module” on most sites. To me, it’s just a 10 LED Sequential/Running Light, where a LED dot would ‘run’ from one end to the other repeatedly. The board supplied to me was the SMD version and so, which means smaller and much compact circuit board (aka PCB).

I also want to show to you how a normal DIY electronic kit can be used to achieve a realistic result as well. It’s only when the model calls for a very specific set of sequence or timing, then you will have to make the decision to go for full customisation.

THE (MODIFIED) CIRCUIT

Before I go on, I do need to tell you that the typical 555/4017 combo is a very common circuit on the Internet and can be easily found in the Internet. But I am going to modify this circuit. This section deals with the specific modification on the specific electronic kit which I bought on eBay. Those who are familiar with the 4017 IC would understand the modifications I am going to make.

There are two Integrated Circuit chips (aka IC) which makes the LEDs ‘run’; the 555 Timer and the 4017 CMOS Decade Counter. Briefly, the circuit uses the 16-pin 4017 IC (BCD to Decade counter) to turn ON the first LED, then turns it OFF before moving to the next LED. It does this for every LED until it reaches the tenth and last LED. Then the whole cycle repeats again. How fast it does this and how long the LED stays on depends on the ‘shape’ of the clock pulses sent by the smaller 8-pin 555 IC and its surrounding controlling components.

For this project, I only need to use five outputs and so, the circuit needs to be modified from its usual counting from ‘1 to 10’ into counting from ‘1 to 4’. The 4017 IC’s Datasheet tells me that I need to connect/short pin #10 to pin #15 where pin #10 is the 5^th output. Because at the 5^th count, that is when pin #10 is activated, it will reset the 4017 IC to start counting from 1 again.

STARTING WITH THE SMALLER COMPONENTS

Like any PCB board population, I need to start with the smaller components. I know things are not as easy if you’re not familiar with what I am going to do. So, let me explain some things first before we start:

PARALLEL LEDs.

I will be connecting three 7020 SMD LEDs in parallel for every one of the four 4017’s pin output. The IC has a limitation of providing only 15mA per output pin, which, is just enough to dimly light one single white LED. I will either have to reduce the current for all three LEDs to 5mA each, or use a transistor to control them, giving each LED their full 25mA.

I chose the former since I do not need the 7020 SMD LEDs to be very bright. And so, the 100 Ohm resistor is here to save the day.

THROUGH-HOLE RESISTORS

The 100 Ohm resistor will be a through-hole component and not as a SMD device which means I need to make some modifications to the board. I know the electronic kit has the SMD resistors of the same value but I was more worried it might get ‘warm’ over time since it is so small. There are a bank of soldering pads for the SMD resistors which I will need to modify. I need to connect these pads together so that they can extend the circuit to the through-holes soldering pad instead. This way, it is mechanically more secure to solder the 100 Ohm resistors via the holes instead of soldering at the SMD’s soldering pads.

Once that is done, I will continue with the soldering of the actual SMD components, starting with the smaller items, then with the two ICs and finally, with the largest components being the last, which is the variable resistor R4. There is a reason why these must be done in this order. If you soldered the larger/taller components first, they practically obstruct your soldering later on. The worse that will happen is that you will need to de-solder that component which, for some SMDs can be destroyed by heat, not forgetting other complications that may happen to the circuit board too.

TOOLS FOR THE JOB:

Before we start, there are some tools that I need. These are the basic tools for soldering and some circuit modifications.

1. 28~35 watt soldering iron with a Pencil Tip soldering bit
2. A pair of Tweezers with fine tips
3. 0.5mm rosin core solder
4. Rosin Flux
5. Solder Wick (optional but the more expensive ones, if you can)
6. De-Soldering pump (in case you soldered the resistors in the wrong place…)
7. Some thin wires, just like the ones we used for the LEDs earlier

RESISTOR CALCULATIONS

The 4017 IC can only give me a maximum current of 15mA before I need additional circuitry. So, let’s try to work with that. Moreover, the 7020 SMD LEDs are very bright at 20mA. With the limit of 15mA, this means each LED would get 5mA. And it’s still too bright!

WHY SURFACE MOUNT COMPONENTS?

A typical circuit board consists of electronic components such as resistors, capacitors, transistors and integrated circuits (ICs) to make it work. But when you need to put ALL that into a PCB to fit into a scale model, suddenly, that small PCB is unbelievably big. Let’s take the current PCB that I am using as an example. This typical 1 inch x 2 inch board in its ‘original’ form, would be twice the size at most (and longer) if it was using normal though-hole components. Of course, it can be smaller still if I use alternative solutions such as micro-processor ICs; we could be looking at a 1 inch x 1 inch PCB or smaller. However, due to costs, this will not happen; you need to invest in a specific microprocessor programmer, learn how to program and test it, apart from the usual PCB CAD design. Moreover, the typical output from a microprocessor is 25mA so, this design is still OK. But if it’s required to drive more LEDs, then size of the PCB changes.

I often involve SMDs components where possible in my designs for Scale Model Lighting because:
1. It really, really saves space and I can design a thin PCB to custom fit a specific model
2. Smaller components means less energy used and less heat dissipated
3. A microprocessor can do the job of a few ICs and has more functions, and personally,
4. It is a challenge for me to create compact custom PCBs (OK, and break all PCB Design rules, I supposed)

In the next article, I will show you how to solder SMD components onto a PCB.

SOLDERING SMD COMPONENTS

Here is a brief guide on how I solder the SMD components for this project. It is not difficult as long as you have plenty of practice. Soldering is a process transferring heat from the soldering iron to the solder to melt it. As for me, the faster the soldering is done, the better.

Working with those tiny SMD components are manageable as long as you always put the small loose ones in a container. Try not to take them out from their packages unless you are ready to solder them. Plus, a good pair of non-sticking, metal tweezers are essential.

Assuming the PCB that I bought has pre-tinned solder pads (where there is a thin layer of solder), it is not necessary to do Step A in the following section.

TINNING THE SOLDER PADS

This is how I solder normal SMD components onto the circuit board. All you need to do is to make sure the solder pads have a coat of solder. Then, it’s like laying logs to a cement base… well, OK, tiny logs, then.

On the other hand, looking back at Step 2, if you’re confident about handling the SMD component with the pair of tweezers, you can align the component on top of the solder blob with one hand, melt the blob with the soldering iron with the other hand and position it into place. This will definitely save some time.

SOLDERING SMD IC

Soldering SMD ICs are a little different due to their many repetitive leads and more importantly, their need to be oriented correctly. If you look at the diagram below, and then compare it with the actual PCB, there is a white silkscreened footprint marker for each IC. In the footprint, there is a small indentation or marking which shows the direction how the IC must be placed. For the SMD IC, it is represented by an inverted dimple on the top left which you need to match with marking on the the silkscreen. Once you have the IC’s direction sussed, you may start to position the IC where all its legs are aligned with their respective solder pads. Any misalignment will definitely cause damage/shorting to the chip or worse, to the whole circuit itself when power on your circuit.

Before we begin, let’s assume the IC’s solder pads are all pre-tinned. In fact, this is a standard feature in most manufactured PCBs. The term for this process is called tin-plating where the PCB goes into a machine which is literally just a set of hot rollers coated with melting solder. With the proper masking techniques, only exposed areas will get tinned.

If you are really interested in soldering SMD components, there are a lot of ‘how-to’ Websites and YouTube guides which you can look into. But ultimately, it’s, ‘Practice, Practice, Practice’. So, get some scrap PCBs and SMD components and try soldering and de-soldering them. De-soldering SMDs are not fun and can seriously go from SNAFU to FUBAR when other surrounding components are affected. Still, it’s a necessary technique to know. But not in this article. Heh.

OK, with the basics of SMD soldering done, let’s go to the next part where I start soldering with the PCB.

THE INTAKE: POPULATING THE CIRCUIT BOARD

With the soldering basics explained in above, let’s put it into practice and populate the PCB now. It is best to solder the smaller components first as they would be less likely to obstruct you when it comes to soldering larger components later.

THE 5-SECOND TIME LIMIT

I always try to keep my soldering time as short as I can. If you heat a component longer than it should be, it will be damaged and you will not realize this until you switch the circuit on and it is not working as it should be. My personal choice of soldering iron is usually a 30 to 35 watt Hakko Red with a sharp pencil tip soldering bit since my soldering is mainly for small stuffs and SMDs. Other people might disagree and have different setups instead. But you do you. Ultimately, a temperature controlled system would be ideal but this was never an option for me due to cost. And lastly, I like to use 0.5mm solder with rosin core flux too.

My Rule for soldering is simple:

Solder within 5 seconds (the longest) and if the soldering fails, let the components cool down and try again.

Oh, and use rosin flux wherever and whenever you can.

THE 555 TIMER IC

With the small SMD components successfully soldered, the next step would be the two IC chips and lastly, the R4 variable resistor. Let’s take a breather and look at the 555 Timer IC which can be used for a lot of things. For this project, it has been configured to generate square pulses. If you know how to ‘shape’ the 555 timer’s clock pulse (as in how long will the pulse be ON and what is the delay before the next pulse), you can change the resistor and capacitor value to get the type of pulses to suit your taste.

You can try one of the online 555 simulators here. Just RIGHT-CLICK on the Resistors and Capacitors to change their values as shown in the diagram below. Then observe the output waveform at the bottom!

http://www.falstad.com/circuit/e-555square.html

But the best was the simulator done by And Clarkson which unfortunately only worked up to Windows Vista.

Update: It is now available again:

(http://www.electroschematics.com/6482/555-timer-design-software/)

This is a very nice simulator where you can just enter the actual e24 resistor and capacitor values and see your results. However, you won’t find a 1.06K resistor and the closest is the e24 value which is 1K with a 5% tolerance.

(Of course you can get it, you just need to mix other resistors or get the e192 series, etc.)

So, the next best thing was to get the simulation from his old website (But you won’t get to see the shape of the output pulse):

OK, let’s continue with the Soldering!

TESTING THE CIRCUIT BOARD

With the modifications done as explained in the previous article, the board must now be checked for any potential mistakes. Let’s look at the image at the top and compare with your board:

1. Have you soldered the correct SMD resistors and capacitors in their respective solder pads?
2. Have the 4017 and 555 SMD ICs been placed in their correct orientation (see the position of the dimples)?
3. Have all the IC legs been soldered to their respective solder pads and there are no excess solder between the adjacent legs?

If the above three points are a resounding ‘YES’, lets prepare to connect the microUSB-to-DIL adaptor to power the board! Using the following image, you’ll need to do these steps:

1. Solder some red wires between the ‘+’ of the board and ‘VBUS’ of the adaptor.
2. Solder some black wires between the ‘-‘ of the board and ‘GND’ of the adaptor.
3. Get a micro USB cable and plug one end to your power bank.
4. Dial the R4 resistor to point to the middle (where the rectangle slot is perpendicular to the 4017 IC)

With that done, plug the other end of the microUSB cable to the adaptor and….. nothing happened. Yeah, if nothing happened as in smoke coming out or sparking, it should be ok. Remember, there are no LEDs soldered to the PCB so there are no other indications to prove that your PCB is a-OK. So, let’s prove that the PCB is working.

TESTING THE PCB WITH A MULTIMETER

A multi-meter is a dispensable tool and in a pinch, it can tell you a lot of things about your circuit. For me, an analogue multi-meter is the best since I am not measuring any voltage or current accuracy. The analogue meter also helps in testing the LED.

Unfortunately, I won’t even attempt to explain to you on how to trouble-shoot the problem as this will result in a very long article. Moreover, it will definitely result in more damages to the PCB if you tried doing it yourself.

But just in case, do check:

1. The correct position of the IC and its legs.
2. Are there really any solder blobs between the IC’s legs?
3. Do check on the four shorting pins soldered earlier. Put the Red Probe on them. If the needle moves and the ones in the red circle does not, it means there is a dry solder joint (and it’s a simple solution to just re-melt the solder again).
4. Touch the Red Probe to Pin #14 of the 4017 IC. If the needle does not jump (while the Pin #03 of the 555 did), try soldering the pin again. Then test it with the Red Probe.
5. Did you walk through a carpet or did you not temporarily Earthed yourself by touching the water pipes? The 4017 chip might have died due to static discharge from your body.

Assuming nothing did go wrong here, we’re going to really modify the circuit board to do what we want…

THE INTAKE: CIRCUIT BOARD MODIFICATIONS

The previous section has shown you how to test for the ‘standard’ PCB. Now, we need to modify the circuit to get it to do what we want. There are two modifications that needs to be done. The first is to set the 4017 IC to count up to four and then reset itself. The second is to provide a blinking LED for the Instrument cluster inside the cockpit (which is optional.)

COUNTING 1, 2, 3, 4 & 5 (AKA 3, 2, 4, 7 & 10)

The output from the 4017 IC follows a specific sequence and it’s reflected in its output pins: 3, 2, 4, 7, 10, 1, 5, 6, 9, & 11. This gives me a big headache when I was designing circuits around it on a single layer PCB. A double-layer PCB design will solve the problem but this would mean increased costs.

Sequence	1	2	3	4	5	6	7	8	9	10
Output Pin	3	2	4	7	10	1	5	6	9	11

When we count from 1 to 10, we would assume the outputs from the 4017 pins would follow the same pattern but they do not. Look at the table above and you will see what I mean. The first sequence starts at pin #3, followed by #2 and so on until to the final sequence which is pin #11.

In the case of the Falke’s Electronic Propeller, after the fourth count, the 4017 must start from the first sequence again. This means, we need to do something at the fifth count, which is to reset the chip. Look at the following image as it has two steps.

MODIFICATON STEP 1: THE 4017 IC

Take a short piece of wire, remove about 3mm of the plastic coating and put some solder blobs on its ends. Heat the 10^th leg of the 4017 IC and touch one end of the wire to it. Using the other end, melt the 15^th leg of the IC and join with it. You have effectively soldered a link between pin 10 and pin 15.

HOW TO IDENTIFY THE 4017 IC’S PINS

The pin layout of an IC goes in an anti-clockwise direction. Pin #1 always start from the bottom left side where there is a semi-circle, a white bar marking or in the case of SMDs, a small dimple indicator.

MODIFICATION STEP 2: THE FLASHING RED BUTTON

For this second part, I am using the 555 to give me a flashing LED. I can do this by tapping into its Pin 3 which is giving the clock pulses to the 4017 IC. So as not to disrupt the pulse, I soldered a current limiting 100 Ohm resistor to the pin and then lead it off to the LED. Ideally, using a transistor to switch the signal is a safer method.

About the blinking rate, the clock pulse from the 555 is 10 times faster than the 4017. So, in the later stage, I need to adjust the variable resistor to find a balance where the flashing rate of the light is noticeable and the fan is still spinning at a good speed.

Solder a small 0803 red LED (if you have not done this earlier) with wires about 8 inches or so and then twist it. At the Circuit board, unravel the twist a little so that you can solder a 100 Ohm resistor to the POSITIVE wire. Once that is done, slip in a heat-shrink sleeve to cover the resistor. Now, cut about 5mm off the other end of the resistor and tin it. Locate pin #3 of the 555 IC (as shown above) and solder the resistor to it. Cover up the resistor with the heat-shrink. Solder the (Negative) wire of the SMD LED to any NEGATIVE points in the circuit board. At this point, you need to be aware such soldering technique is physically weak and if you’re not careful, you can rip the resistor out or worse, the whole IC’s leg away.

CONNECTING THE ELECTRONIC PROPELLER

With the PCB now working, let’s connect the electronic propeller to it. I hope you have really, really labelled your four signal wires but if you did not, it’s still not a big problem. All you need to understand is this:

The 4017 IC turn ON and turn OFF each LED from each of its FOUR OUTPUTS, one by one in a sequence. You just need to solder ONE signal wire to the first OUTPUT. For the subsequent wire, touch it to the next OUTPUT and look at the electronic propeller. If the first set of blade turns to the next without any noticeable delay, then the second wire is correct. But don’t solder it yet as you need to test with the remaining two signal wires too.

First, let’s solder the Black Wire from the copper ring to the PCB as shown below. At the end of the day, the goal is to make sure the electronic propeller to spins ‘perfectly’.

Let’s begin:

1. Connect Wire #A (Green) to 4017’s Output #A (First 100 Ohm resistor from the left)
2. Connect Wire #B (Blue) to 4017’s Output #B (Second 100 Ohm resistor from the left)
3. Connect Wire #C (Beige) to 4017’s Output #C (Third 100 Ohm resistor from the left)
4. Connect Wire #D (Red) to 4017’s Output #D (Fourth 100 Ohm resistor from the left)

Once again, check that your soldering work is OK. Then power up the board, using the USB power bank. Your electronic propeller’s seamless animation would look like this. After frame #4, it is reset and starts from frame #1 again.

I wired this for clockwise spinning. If you need to wire it counter-clockwise, you will have to reverse the wire sequence from A, B, C, D to D, C, B, A.

Don’t worry about the fan’s ‘spinning speed’ for now. In the next section, I will show you how to do them.