Hey Guys,

So this project isn’t actually new, I did this around a year and a half ago, but it’s still cool (I think) and still relevant so I may as well share it. This is my homebrew GPS unit!

So the first thing you may notice is it’s not exactly neat, well hey? I did it with very few resources, and for what I made it with, I think it’s quite good!

The main micro-controller I’m using is an ATMega328, in the form of an Arduino Pro Mini (available from sparkfun). Now I know I’ve talked about this before but I really love this board, it’s small, perfect for embedding in projects, and cheap! What more could you want? The GPS I’m using is the Adafruit Ultimate GPS, which I believe is THE best hobbiest GPS. The OLED screen is also from Adafruit, and again is great value for money! It’s tiny (perfect for this project) but still has really high contrast and therefore readability. Both the GPS and screen have wonderful libraries written for them too, which makes the coding so much easier! Aside from the GPS, the screen and the Micro, the only other things are the batteries (AAA) and the buttons, which I soldered onto stripboard with 10K pull-downs (though later I realised it would’ve been easier to use the ATMega328’s internal pull-ups).

Most of the effort with this project was the code, which by the way is awful. I did this code when I was 14, and well it shows. So don’t be too scared! You can find the code on my GitHub page (link up top), so go take a look!

If you can’t stand the sight of such awful code (and I wouldn’t blame you), you can browse the pictures below, which are much more sightly!

So you may recall I was designing a tremolo effects pedal for my friend. Well I got the boards back (lovely quality from OSHPark) and soldered them up and, well see for yourself!

Above is the circuit for the project, which I have broken down into little bits. Hopefully it’ll be easier to understand that way!

So I’ll start with the simplest bit! The power section. It’s pretty much what it looks like, power comes in from headers, and is switched, with a switch.

The next simplest bit is probably this bit, which is just a voltage divider to give us a nice 4.5V, and some smoothing capacitors across the supply rails. We need the 4.5V because this is what the signal will be centred on, and putting it directly in the middle of the supply rails makes it easier on the op-amp. Op-amps generally don’t work as well closer to the supply rails, and most of the time don’t output near them, to do this, you need a special kind of op-amp, referred to as a rail-to-rail op-amp.

The next bit is the sine wave generator, this is a phase-shift oscillator configuration, with the op-amp for stability (without this op-amp if we were to try to draw any current out of the PSO the sine wave would collapse). RV1 and RV2 are potentiometers controlling the amount of modulation, and the frequency of modulation respectively.

The final section is the modulator itself! This is the bit where the sine wave is used to modulate the signal from the instrument. The modulation is actually applied to the feedback loop of the op-amp with the transistor (BC548) the op-amp then applies this to the signal itself. The capacitor on the output is to block the DC component of the signal (the 4.5V) and leave the signal as just the amplitude modulated input.

So that’s it! I will eventually be selling this as a kit, but until then, you can order the rev.1 board from OSHPark!

Cheers, Tom

So for my friends birthday, I decided I’d get him something a little more personal than just a bar of chocolate say, or some money. So I set out to design and build him a Tremolo effects pedal for guitar!

First of course, I needed to figure out how a Tremolo pedal works, I’d heard one in action before, but never thought about what was going on in any depth. Tremolo is an effect created when you change the amplitude of the waveform, which basically changes the volume of the sound. The speed at which you modulate (change) the volume can be changed on the pedal, as can the amount it varies it.

With this in mind, I got to work on EagleCAD (a free schematic and PCB layout software package) designing my pedal. Of course I didn’t design it all from scratch, I patched different circuits together to create it:

This circuit essentially works like this: The bottom section, with the four capacitors, is a sine wave generator. Hooked up to an op-amp (LM324), so as to make sure current could be drawn from it (without the op-amp, if you attempted to use the sine wave signal for anything, it would collapse). There are two potentiometers here, R1 is the potentiometer controlling the amount of modulation the sine wave applies to the signal, R2 is controlling the frequency. The modulation is physically applied to the feedback loop of the top op-amp (another LM324) through the transistor, which then applies it to the signal.

The power, ground, input, output and switch terminals are so they can be connected to their appropriate off board components.

After designing this schematic, I created a PCB:

I am currently waiting for my PCB to be built (by OSHPark), but when I get them back and test them, I will write another post. If they work, I may even sell them as a kit!

Leave any feedback (pun intended) below.

Cheers, Tom

Hi everyone,

If you haven’t heard, me and my co-partner are building a development board to embed into projects rather than using a full blown Arduino. For more details see this post.

Anyway, as one of the first projects for this little board, I have hooked it up to a DS1307 real time clock, and an AXE133Y OLED display to make a simple clock. As shown below:

I have simply connected the I²C lines to the same pins on the Arduino and wired up the ds1307 like the data sheet tells you to do. If someone asks I will draw up a schematic for you all, though many can be found online – like this one.

I hope to do many more projects in the coming weeks and months prior to the launch of this board next year so keep posted to see what else the SeedBoard can do. And as always you will be able to find the links to the Arduino sketches on our github page linked at the top of this page.

Thanks guys,

Jacob

Want to see what a SeedBoard can do? Check this post!

Note: SeedBoards are currently not for sale, but if you really want one drop me an e-mail and I will get in contact!

So big(ish) news guys! Me and my co-partner Jacob Rawson have been developing a small micro-controller dev board in our spare time, because we got sick of having to spend loads of money on an Arduino simply to embed it in a project and never see it again.

Now, there are other solutions to this rather than building your own, though much less fun, like the Sparkfun Pro Mini (which I have mentioned before)! For most of you this will be perfectly adequate but for me, living in the UK, it was just a tad too expensive to ship over here.

So why not build one? I got myself onto EagleCAD and started designing a board! This is the result! The SeedBoard (currently rev.2). With a small square form factor it’s ideal for embedding in a project, and (obviously) cheap enough! Costing us around £6 (~$10) non-profit. It can have any crystal you want in it, up to the chip limit of 20MHz, although if you’re feeling adventurous, you could try over-clocking it?

Thanks go to OSHPark for the amazing quality boards they consistently produce, this being one of them!

They are currently not for sale, but (as mentioned above) if you really want one, drop me an e-mail (tom@doayee.co.uk) and I’m sure we can work something out!

For those who don’t want one just yet though, we may be running a kickstarter sometime next year!

Look out for that!

Tom.