the Bluno beetle by DFRobot is an extremely elegant solution for wearable electronics. However, the inclusion of BLE on board and its small footprint also make it an extremely useful device for monitoring sensors.
In this instructable I will show you how to assemble a breadboard breakout that you can easily hook up to sensors and tuck away in narrow places, with little to no risk of damaging the board. Its prime purpose at my end has been code development, but I believe others may find it useful, hence this instructable.
I will be using a 170 points breadboard but there is no reason you can't use a larger one. If you do, all the instructions herein should still apply, but it is worth noting that many steps and the overall design only make sense in the context of a minimalistic project.
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Step 1: Soldering the GND and VCC Pins
Let's start by soldering the power pins. They serve as supply to the breadboard and therefore we'll want them to protrude away on the underside of the board. Alternatively you may want to use the tall 'stackable' variety, but make sure the plastic crown sits on the underside if you do (or insert spacers on both sides).
Insert pins upside down into the breadboard as shown. For now their exact locations are not important as long as their relative positions are so that the beetle slots snugly on top.
Note that while the pitch between the terminals on the PCB is non standard, conveniently the '+' and '-' cut into the board allow the beetle to almost perfectly align with the breadboard.
Solder the pins in place - this should be an easy job!
Step 2: Adding a I2c Terminal
Next is another straightforward task, adding a dedicated i2c terminal by soldering angled pins to the SCL and SDA contact zones situated on the underside of the beetle.
Use blu tack to sit the pins in position as shown in the picture.
Step 3: Soldering the I/O Pins
Now that you are hopefully warmed up, let's tackle by far the most fiddly part of this hack: soldering 8 individual pins for the I/O.
The difficulty here is that the distance between the I/O points drilled into the board does not correspond to a standard pitch. This does not matter too much for the end result but it means the pins will be unconnected until they are soldered down and therefore will possibly move to a side or another while you are performing the task.
Again, using blu tack to sit the pins and board is going to be your best option. Rest the beetle on the power pins on a flat surface, position the pins into the holes with the shortest side going through it (we are soldering the I/O on the opposite side of the board compared to the GND/Vcc pins). Then press down a piece of blu tack folded in half gently onto the pins and board. Solder the pins from the underside.
Tip: the easiest way is probably to present the pins 4 at a time, A then D (or vice versa), but it's up to you how you approach this. Whatever you do, just take your time or the pins will be misaligned later when we assemble the breakout terminals.
Step 4: Adding a Vin Point
This step is only required if you wish to supply power to the board by other means than the USB port, but I think it is useful to have and not too tricky to perform.
Note that I am using an angled pin but you may want to replace the pin altogether with a longer, stackable, variety. My preference was to have the Vin point clearly separate from the I/O and I tend to use those kinds of 'contact soldering' often There are no other reasons, use whatever is best for your situation.
Note that you may wish to file a little the plastic crown around the 'through hole' pin soldered previously, to allow it to slide back down all the way. It will work without this extra step, but it will make for a nicer job.
Step 5: Adding 3-pin Terminals
The last soldering job is not the easiest to perform and in a way is not critical. As such, you may or may not want to struggle with it, although with a little application it is not that difficult a step and it will give you more mileage out of your breadboarded bluno.
Either way, start by removing one of the pin out of a common 2x3 male/pins header, and replace it by one of the long 'stackable' variety, as shown in the picture. Repeat the operation 3 more times. These blocks will serve as the basic breakout terminals and help holding everything together. Center roughly all the pins around the spacers.
The second photo provided depicts the result of the soldering job described in the next step, so you know what you are throwing yourself into. I suggest you have a go as the worst that can happen is that you ruin a couple of pins, easily replaceable.
Step 6: Creating the Fork
If you've gone this far with this instructable then nothing can stop you, right?
The tricky part of this soldering is that you have to be very specific how you assemble the connections, where the solder must go, and how much of it you apply. It's a lot less fiddly than soldering the I/O pins though, but if you haven't got the right tools this could quickly prove to be an exercise in frustration.
The important part here is that you will want the angled pin to go on the outside of the terminal block, but solder it from the inside. If you don't do it that way you'll either make some of the pins difficult to use, or risk shorting signals on the edge of the PCB.
Again, blu tack is here to the rescue. Lay the angled pin on it and push it in gently. You may want to remove the plastic crown if your soldering iron is quite bulky, but leaving it on will allow you to avoid having to bury the pin in the blu tack, so, if you can, keep it around for now.
Next, sit the terminal block on top, more specifically the tall pin needs to cross the angled pin just right. What you are looking for is a 3-storey high structure on top of the angled pin, so that the fork splits to one side rather than extend it.
Adjust the distance by eye so that only a tiny part of the angled pin extends past the tall pin. Don't worry too much however, as there is a bit of jiggle room - just try to get a nice right angle so that the fork looks nice and parallel.
Note that the angled pin used is quite important, try to find one with a short-ish side and one that peaks high enough to match the height of the tall pin in the terminal block.
You'll need to repeat this step 3 more times, or more exactly once, then make mirror images for the remaining 2. If you are not quite sure what I mean here, have a look at the next step where I show you how it all comes together, and hopefully it will then make more sense.
Step 7: Wiring the Breadboard
Now is the time to put the soldering iron away, congratulation, you've made it through!
This is the 'fun' part, depending on what you have at hand to do the breadboard wiring. I recommend spending a little time on this step, the effort will be worth it!
Regardless of your method, reproduce the wiring shown in the picture, keeping in mind that the beetle will slot on top, meaning the power pins will need to be unobstructed, and their close neighbourhood adequately clear of wires as well.
You also need to keep the areas reserved for the breakout terminals as clear as possible. I have marked their location in the picture for your convenience, so if you can't reproduce the wiring verbatim have a good look at it first and make sure your wires are not in the way before going any further.
Note that you do not have to colour code the wiring as long as you link the points as shown. In the picture, white will serve the ground lines, while red will supply the breadboard with 5V (or other voltage if using the Vin pin).
Step 8: Assembling It Together
Let's see if it all fit together shall we?
Just slot in the terminals into the breadboard as shown. If you find that something is not quite right, try swapping pins around inside the terminal blocks, adjust them around the spacer, or go back to the drawing board, you've done something wrong ;-)
Last plug in the beetle and it should all come together beautifully. If not, pull and push some things around until it works, you've done something wrong ;-)
More seriously, I realise that some earlier steps are not visually documented as well as I could have, but if you can get your head around the principle it should be easy to go back and try again.
Step 9: Using Jumpers
This step explains how and why I designed the breadboard-beetle the way I did.
The first thing you may notice is that the I/O pins are not bridged into the terminal blocks. Typically you would use GND+VCC from the terminal blocks + Signal sourced directly on the beetle pin, This is how I tend to use it as many sensors I use don't comply with the G/V/S pin ordering and it is often necessary to use single jumper wires to hook them up anyhow.
That said, I wanted to be able to hook up sensors to the terminal only pins and switch input on the fly. This is useful when trying to refine code, as you can quickly A/B the results. It's also practical if you wish to flash the microprocessor with a multipurpose program that allows you to relocate the setup elsewhere, where conditions require a different programming.
This is how it works: by using jumpers you may decide which I/O is hooked up to the sensors. Choices are between A0 and A1, A2 and A3, D2 and D3, D4 and D5. The pictures attached show you a jumper swap between A0 and A1 as an example.
Of course a jumper solution is not strictly necessary and you could (almost) as easily swap jumper wires instead, but when using a combination of alternative programming it becomes highly practical to colour code your jumpers to clearly identify what the board is currently running.
So there you go, I hope you enjoyed this instructable, keep on eye on my ID for more in the future!