Remember to click G+1 if you like a post... It will make me happy :-)

1 March 2015

Breadboarding the Piezo Buffer

I'm back! Today I'm going to reveal a few more of my adventures in building my piezo buffer circuit. Let's get to it!


My new challenge of becoming an electronics wizard is full of firsts. Everything I do requires research and learning. I'm finding that I can't take anything for granted and often the simplest things are the hardest to get right.

The picture above shows a new skill I've been working on: "Breadboarding".

Breadboarding is a means of prototyping a circuit without actually having to solder anything. Because everything is temporary, you're free to move things about and experiment. Ideal! ...or so you'd think...


How do breadboards work?

I haven't broken mine apart to have a look inside, but plenty of other people on the internet have. Within the plastic case you will find strips of metal clips. These metal clips are laid out in the pattern of the holes that you see on the surface of the plastic box. There are often special lengthways strips that are intended for using as power rails (i.e. easy access to positive and ground) and lots of 5-hole strips to be used for whatever you want.

The holes are all spaced out at 0.1 inch which conveniently ties up with the standard sizes of the pins on components you will be working on.

The challenge is to stick wire through the holes (which can be the legs of resistors, or capacitors, or transistors, or jumper wire) in such a way as to make all the connections of the circuit.

I talked previously about my struggles in making that leap from circuit schematic to real circuit. Well, breadboarding is a great way of making that transition.


Having had all sorts of problems with my breadboard prototyping I've had to resort to lots of research on breadboards to try and debug my circuit. Yes... I only went and put the whole thing together and the bloody thing didn't work!

Who ever learnt anything from things working first time anyway ;-)

It turns out that breadboards are prone to a number of issues including the horribly sounding "parasitic capacitance" which refers to a problem where current can drain between strips that are next to each other.

Actually, most people's issues with breadboarding are more ones of not understanding how breadboards work, or simply sticking things in the wrong holes. If you're messy with your layout and wiring then you're probably going to make mistakes and when you do, it is going to be a sod to unravel.

Guilty!


I was saddened to hear of Leonard Nimoy's death earlier this week. What a great guy. I've been a long-time fan and can't help but feel that we've lost something special here.

I think that this painting by John Jacobsmeyer is a fitting tribute to the enigma that was Leonard Nimoy. I've told Mrs Uke that I'm going to buy it to hang above the fireplace. Live long and prosper my friend! :-D


My piezo buffer circuit involves an audio-in which you can see here is connected to my Sharkfin Ukulele piezo pickup; an audio-out which is connected to my guitar amp and a 9vDC-in which I'm feeding with a standard guitar effect pedal power supply.

Here's an interesting observation:

I can plug my Sharkfin directly into the amp and it gives sound with a single lead, but if I take the in and outs I'm using on the breadboard circuit and join them together to effectively bypass the circuit (i.e. two leads joined together), I don't get any sound through the amp. Something about this arrangement is completely degrading the signal. Right now, I don't understand why this should be.

Having got everything together, nothing worked. How bloody frustrating! My crude attempts at debugging failed, so I started to experiment to try and simplify the circuit and get a sound out of the JFET. My thinking was that if I could at least prove that the JFET was working, I could then build upon this. I threw the laws of science out of the window and plugged things in any which way until at last I got sound! YAY! ...and then it started making a sort of squelching noise ...and then it went dead altogether. BOO!

Try as I might, I couldn't get it to work again. More debugging required...


I've been honing my debugging skills but there is definitely a lot more for me to learn here.

The most basic test I've been doing is to ensure that everything is connected as it should be. This obviously requires giving it a visual once-over, but an important test is to check for continuity. This involves unplugging the power and with the multimeter set to "continuity" testing that there is a connection between all the parts of the circuit that there should be.

The technique I've developed is to find the furthest apart points that are checkable and checking them. You can't check continuity through capacitors or resistors or transistors, so the legs of these are good starting and end points. I check large stretches of circuit; If there is continuity across a long stretch then you've proved that you have continuity through all the little connections along the way. Working through this sort of test is pretty painless, but it only proves so much.

All my connections seemed to be good (once I'd fixed them). Still nothing. Next, I figured that I must have a broken component. The most obvious one to check was the 2n5457 JFET itself. I swapped it out for another I had and TADA it worked! And it's been working ever since!

I think I must have blown the first JFET in my careless random experimentation. Perhaps the squelching I was hearing was the sound of too much current being supplied to it before it went pop?


Here's an interesting sync. Last week I told you I was reading King City by Brendon Graham. Check out this picture. Top is a drawing in the book. Bottom is my profile pic from a period in 2012. What's this mean then?


"Don't bloody believe it. 40,000 capacitors and not one larger than .1 micro farads." ~ King Uke, on his ill-fated expedition to Mars

Hear my frustration as I realise that I don't have all the parts I need to get this circuit built as per my original specifications. Damn you capacitors!

Capacitors are still a bit of a mystery to me, but I've ended up using larger ones than my specification requires while I wait for parts to arrive. I think that the only downside to this one is that the unit will use more power charging up the capacitors; I think that the circuit itself will only draw the current that it needs, so everything else should be fine. Stop me now if you know better!

And that's where I've left the project... right on the verge of experimentation. The circuit is a little noisy on the breadboard, but I've read that this is to be expected. It will be interesting to see whether this changes when I move it to a fixed arrangement. Is the buffer doing what it should be doing to match input and output impedance? It's impossible for me to tell at the moment. I'm not sure right now how I can test this without an oscillator. I'll keeping thinking about this and see what I can come up with.


Finally, I'm going to end with mention of another electronics project. This one comes courtesy of Geoff Eggins and it involves electronics. Geoff's pimped his ukulele to turn it into Iron Man!

You can find all the details on the Iron Man Ukulele website. Geoff says that he has no other projects in the works. COME ON GEOFF! YOU CAN'T LEAVE IT HERE! Ha ha.

I think he's done a great job. At the heart of the project is a kit ukulele that's been ripped open and put back together again with added wires. I call out the wonderful job that Geoff's done with the headstock inlay and also the distinct lack of information on how he wired up the LEDs. Fix it Geoff! ;-)

Go see for yourself.

No comments:

Post a Comment