The Schematic
Fig. 1 - The schematic for the APC, parts list below - click here for a bigger version
The Parts List
Capacitors
The Build
The schematic above is actually pretty close to how the final build comes out. I'm building mine on perfboard and to make my wiring easier (because I'm a beginner and absolutely winging it...) I actually make a rail across to the top and bottom rows for the positive and negative power. Usually I'll just use the old, cut-off legs from components to make a connection from one side to the other across the board - this circuit is only small so it'll only take a couple to get from one side to the other.
The other thing I do with these is to put all my components on the top of the board and then put most of the wiring on the underside.
both of these are just my own choices and shouldn't be taken as the absolute best way of doing something. If you've got your own methods, then use those - whatever works for you.
The next step I take is to mount the two IC holders. As I'm putting things on both sides of the board, I find that I'm flipping the board over a lot. To keep my orentiation correct I find it helpful to put a little mark next to pin 1 of both IC holders on both side of the board. I find that this just keeps me from wiring up the wrong pin because I've confused myself as to which side of the board I'm soldering on.
With those in place we can start wiring up the ICs and the various bits. I've done this in a table form so hopefully it'll be easier to follow where each bit goes and what it's connected to. I've included a little 'Done' column so you can tick off the wiring as you go.
| Let's Wire! | |||
|---|---|---|---|
| From | To | Then To | Done |
| IC1 Pin 2 | IC1 Pin 6 | - | |
| IC1 Pin 6 | Resistor R1 | IC1 Pin 7 | |
| IC1 Pin 2 | Capacitor C1 | Negative Rail | |
| IC1 Pin 3 | IC2 Pin 2 | - | |
| IC1 Pin 4 | Positive Rail | - | |
| IC1 Pin 8 | Positive Rail | - | |
| IC1 Pin 7 | LDR R2 | Postive Rail | |
| IC1 Pin 1 | Negative Rail | - | |
| IC2 Pin 6 | IC2 Pin 7 | - | |
| IC2 Pin 3 | Capacitor C3 | Output (positive) | |
| IC2 Pin 6 | Capacitor C2 | Negative Rail | |
| IC2 Pin 4 | Positive Rail | - | |
| IC2 Pin 8 | Postive Rail | - | |
| IC2 Pin 7 | LDR R3 | ||
| IC2 Pin 1 | Negative Rail | - | |
| Jack Tip | Output (positive) | - | |
| Jack Sleeve | Output (negative) | - | |
| 9v Positive | Postive Rail | - | |
| 9v Negative | Negative Rail | - | |
But What About Using Potentiometers Instead Of Light Dependent Resistors?
The orignal design of the APC used potentiometers, and the simplicitiy of this design makes it very straightforward to swap them back in. You will lose the light-controlled aspect, but what you lose by that you'll gain back in predictability.
Each LDR can be replaced by a 500k potentiometer and 1k resistor pairing. Simply connect the 1k resistor to pin 7 of the IC, then to the middle leg of the pot. Then connect the right leg to the positive rail. It's really that simple. We need to include the 1k resistor to ensure that the resistance between pin 7 and the positive rail doesn't got 0 ohms - if it does the 555s start to get really hot and (I'm assuming) bad things will happen if left unchecked, so we stick on the 1k to keep things all happy. If you wanted to - and you may notice it in the picture of my build below - you can include the 1k with the LDR - it'll do no harm and won't affect the sound in any noticible way.
The Optional Bits
In my build I decided that I would like to have a switch to turn it on and off - I know, decadent right?... So I spliced in a push-button swtich on the positive wire going from 9v battery to the positive rail.
I also decided that I'd put an LED on it too - mainly so I could see if it was turned on, but as it was using LDRs it'd also affect the amount of light they'd receive. To put an LED I connected it as follows -
| Let there be light! | ||||
|---|---|---|---|---|
| From | To | Then To | Then To | Done |
| Positive Rail | 330 ohms resistor | LED (positive leg) | Negative Rail |
The Final Outcome
Fig. 2 - it's not pretty, nor is the noise it makes
And that's it really. All you need to do is to put it in an enclosure and start making a racket. To be honest, you should probably start thinking about an enclosure before you build it - I've built a few of these now and every time I wish I'd thought about the enclosure first.
All work © Darren Shaw 2021 (except where noted)
darren@anexium.com
Back to the index