My DIY Function Generator.

[DrNomis_44]

Hey Everyone,

Thought I would start a new thread about a piece of test equipment I built last year, based on a webpage article I found on the internet, so, what's the piece of test equipment and what does it do, I hear you ask?

It's a Function Generator, it puts-out a steady signal with a frequency-range of about 1Hz, or one cycle-per-second to about 1MHz, or one million cycles-per-second, and you can select one of three different signal waveforms, either Square, Triangle, or Sine.

Okay, so why do I think it's a pretty handy thing to have when it comes to building guitar amps?, the answer is pretty simple, since the frequency range of the Function Generator is from 1Hz to 1MHZ, that easily covers the full audio spectrum which is typically quoted as being from about 20Hz to 20kHz, or 20 cycles-per-second to 20,000 cycles-per-second, and this makes it very useful as a test-signal generator while you're performing setup-tests on your newly built guitar amplifier, or if you have to go back and troubleshoot it if it appears to be not working as it should, of course you could use your guitar as a signal-source if you wanted to, but let's face-it having to pick up your guitar, pluck a string, put the guitar down, and pick up your scope probe can get a bit tedious, what you need is some way of generating a steady known good signal so you have two hands free to check various points in your guitar amp's circuitry to see if the signal is making it's way all the way through the signal-path, that's where the Function Generator proves to be very handy.

I'm going to be doing a write-up of my DIY Function Generator in this thread, which will include some pics, and details for building one yourself.


Here's a couple of pics of my DIY Function Generator:






As you can see, there's not a whole lot inside the case, of course I could have used a smaller case to house all the internals, but I like the "aesthetics" of the case I chose, it has a Laboratory test-equipment look to it, my DIY Function Generator uses a mains power transformer to power it, but since I'm going to have to re-create the circuit board layout from scratch anyway, due to my old studio computer breaking-down last year and the original layout was amongst all the files I lost as a consequence, I'm going to re-design the circuit board layout from scratch so you can safely power it using a standard DC plugpack adaptor, I do need to make a minor mod to the original circuit so that you can control the output level of all three signal waveforms though, the Sine and Triangle waveforms are variable in level, but the Square wave level is a bit too high for practical use, I will include the mod in the re-designed circuit board layout once I know the mod works perfectly.


Stay tuned for more updates!......

[JohnH]

Looks like a fun project!

[DrNomis_44]

Here's a link to the webpage where I got the original design for my DIY XR2206 Function generator build, it includes a circuit diagram:

https://www.eleccircuit.com/xr2206-function-generator/



This design uses two ICs, an XR2206 Integrated Function Generator, and an SN74LS00 Quad 2-Input NAND Gate, I bought the ICs I used in my XR2206 Function Generator build from my local Jaycar Electronics store, they had some XR2206 ICs in stock but didn't have any SN74LS00 ICs in stock So I had to substitute a functionally equivalent one that they did have in stock, I ended-up settling on using a CD4093BE which is a CMOS Quad 2-Input NAND-Schmit Gate IC, the SN74LS00 Is a TTL IC, but as far as I'm concerned, the CD4093BE is practically functionally identical to the SN74LS00, although the CD4093BE includes hysteresis, anyway, in practice I can't see any difference in operation, it seems to function perfectly well in the circuit.

Over the years when Logic ICs were developed, a few different technologies were used to implement various logic gates and functions, TTL, or Transistor-Transistor Logic preceded CMOS, or Complementary Metal-Oxide Semiconductor Logic technology, which is what's commonly available nowadays.

So, what's a Logic Gate?, a Logic Gate is an electronic circuit that controls the flow of electricity much like a gate on a fence, you could also think of a Logic Gate as being functionally analogous to a switch which is either On, or Off, with no in-between state, a good example is a simple AND gate circuit made up of a battery, and two switches in series (we'll call them switch one and two respectively for this example) with a light bulb, if both switches one and two are switched to Off, then the light bulb does-not light-up, if either switch one or switch two are switched-on, the light-bulb does not light-up, however, if switch one and switch two are switched-on, the light-bulb lights-up because switch one and two are not interrupting the flow of electricity to the light-bulb, we can consider the switches Off-state as representing a Logic 0, or Low, and the switches On-state as representing a Logic 1, or High, similarly, we can consider the light-bulb being not lit-up as a Logic 0 or Low, and the light-bulb being lit-up as representing a Logic 1 or High, this is just a simple example of how an AND Gate works, in Digital Electronics there are lots of different types of Logic Gates that perform specific Logic functions, for example the AND Gate I just covered, as well as OR Gates, NAND Gates, NOR Gates, and Inverter Gates to name a few of the more basic ones.

[DrNomis_44]

Update:


Just finished working on doing the mods to my DIY Function Generator and everything appears to be working as I wanted them to, all three waveforms are now adjustable in output level, I may at some later-stage pad-down the square wave output a bit so it is roughly equal to the sine and triangle outputs, but for the time-being I'm happy with it, so I can get-on with doing a full write-up so that those of you who are interested can build one for yourselves.