mindkits | Jethro Carr

As part of my project to make an Arduino based watchdog for my home server, I went and picked up a proper soldering iron today and assembled the RS232 Shifter Circuit I had purchased from Sparkfun/Mindkits.

I ended up getting a Goot soldering iron – it wasn’t too cheap, but the reviews I was reading online suggested it was the next best thing to a proper soldering station and a quality Japanese tool. It’s also 46W, so much better for the lead-free solder I’m using, compared to the crappy 15W DSE brand generic iron I was using previously.

Tool of the gods.

It made a massive difference to the soldering efforts, the lead-free solder melted without issue and flowed smoothly – plus the fine point conical tip made getting the solder into key areas a lot easier.

The tips are changeable and I’ve been advised by an electronics fixing friend to get a set of tip types, as certain ones suit different tasks better than others.

Whilst the new soldering iron is a huge improvement, my soldering skill is still a bit poor, I had a few text-book joins where the solder flowed perfectly and bonded with a smooth shiny surface, but a lot of my joins tend to be slightly one sided, where the solder hasn’t flowed right around the components lead and PCB hole which makes then a bit weak.

I’m also tending to leave too much solder on the component lead, which leaves larger joins than really needed, so need to work on how much solder I apply.

Parents, avert your children’s eyes from this soldering monstrosity!

On the flip side, the top looks great ;-)

After constructing the circuit, I gave it a test by connecting the TX and RX of the shifter circuit to the TX and RX on the Arduino, which basically uses the Arduino as an UART to RS232(over USB) adapter.

Then I connected the new DB9 port to my laptop and typed messages into the Arduino serial monitor, to have them passed through my new circuit and into my laptop’s DB9 port.

Amazingly, things worked first time and I’m able to successfully receive data via the shifter board – in my quick test TX from the shifter board wasn’t working, but it may have been a serial speed/config issue that I just need to tweak in the OS, rather than the board itself.

Arduino IDE to Minicom via an Arduino, my new shifter circuit and my laptop’s USB to RS232 adapter.

The next step is connecting this shifter circuit to the digital I/O ports on the Arduino and using the software serial library to add a second serial port to the device. I can then do the same to the HTC Magic serial break out and I’ll basically have an Arduno with 3 serial ports in total – the onboard UART, the DB9 PC via shifter and the HTC magic.

Once that’s done, it’s just a case of writing the software needed to turn the collection of hacks into a hardware watchdog and serial remote access system. :-)

And once that’s all working, I’ll build a final solution using one of the Arduino prototyping shields from Freetronics, which will include all the shifter circuitry onboard and just provide a 2×5 IEC pin header to plug a ribbon cable directly into the server’s motherboard serial port header.

As part of my efforts to learn more about electronics, I recently obtained a power supply kit that breaks the standard 5V USB output into 3.3V and 5V bread-board connectable outputs from Mindkits (who resell Sparkfun kits in NZ, amongst other stuff).

I went for a USB-powered model rather than a typical round-pin DC supply, since I have an abundance of USB power sources with me all the time (both laptop and wall adaptors) and it’s much better than having yet another damn power brick hanging around.

I finally managed to get around to making the time to try it out this weekend and dug out the soldering iron to tackle the challenge – past soldering exploits have never fared particularly well, but I figure sooner or later I’ll learn something and make a working device. ;-)

How hard could this possibly be? :-P

One of the biggest challenges I found was actually holding such a small PCB still, whilst trying to align solder and the iron – think one of my next purchases will be some sort of clamp to hold the board in place.

I’m not convinced that my soldering iron is particularly good either, need to do some research on the best type of soldering head (round vs chisel?). I’d probably go better with more gun shaped soldering iron than the round pencil design, I just tend to find it easier to align.

Ready, set, solder!

I started off doing the small components like resisters and small caps, before moving on to the voltage regular, switch, USB port and pin headers.

Apologies to any electrical engineers or skilled hobbyist reading this blog, but my soldering is pretty terrible, as you can see. Take note that this is the first thing I’ve soldered that actually works :-P

Oh god, oh god my eyes!

I started with the resisters in the middle, as you can see my soldering was pretty terrible there – used too much solder and ended up making large messy blobs.

Later I got better at briefly heating the legs and then applying the solder in a way that allowed it to run down and bond with the PCB, so my later joins got a lot better, eg the USB socket with it’s 4 close small pins.

I got an impromptu lesson to using a multimeter as the circuit wouldn’t work initially – I had managed to make a PSU that was always on (ignoring the switch status) and provided no 3.3V output.

Thanks to the simplicity of this kit, it was pretty easy to test each component to figure out where my bad joins were and I re-soldered a few of the bad earlier joins.

The only real headache was the voltage regulator – for some reason I had real difficulty getting the solder to bond with the middle pin and the PCB and had to redo it several times – it’s still not perfect TBH :-(

Assembled :-D

Shiny shiny! (OMG, an artsy picture without using Instagram!)

So far the kit seems pretty good, it was really easy to assemble with the clear silkscreen markings – most work I had to do was lookup the resister code/colors, which is trivial thanks to Electrodroid on my phone. :-)

The one design issue I do have with the kit, is that the positioning of the breadboard connectors requires you to break the header pins into single units, but doing this really weakens the design, since it’s just one tiny solder joint holding the pin to the PCB – I do fear the force of inserting and removing from breadboards will wear it down a bit over time.

To counter this a bit, I’ve stuck a blob of hot glue around the headers, to give them a bit more integrity – although the 3.3V pin soldering joint is playing up and might need redoing anyway.

Hot glue solves all! (also stuck some around the voltage regulator as one of the solder joints isn't that great, but I can't fix it without risking ruining the PCB trace)

Looking at the round-DC connector version of the kit, the design instead has two pairs of 2x pin headers, which I suspect will make it a bit more sturdy.

Overall whilst it’s a painful learning curve trying to get the soldering right, I didn’t burn myself *too* badly and whilst not a shining example of art, the board works and powers up.

Next time, I’ll be tackling the RS232 shifter kit and then working to hook up an RS232 power to an Arduino’s digital pins using a software serial driver. And after that, I might have a go at making some temperature sensor 1-wire boards to install around my server case using the small square prototyping boards I brought.

Hopefully by then my soldering will be an acceptable level. :-)