Saturday, July 18, 2009

Mini Function Generator: Part 1

[Part 1 2 3] >>

Right off the bat I'll admit this Mini Function Generator electronics project isn't strictly a robotics thing. But, having a tiny square wave and triangle wave generator on hand could be useful for audio repair and for demonstrating oscilloscopes I put up for sale.

My main goals for this project was to try out a short run, cheap PCB fabrication company, play around with Eagle circuit CAD and LTspice simulation, and make a simple, small, but useful function generator.

I started with a single supply function generator op amp circuit diagram from Circuit Suggest and then drafted it up in Eagle and then wired it up on a breadboard. Originally I was going to include a switch to select multiple frequencies. Without going into the gory details, suffice it to say that, in the real world, getting a multiple frequency function generator to work is a bit trickier than LTspice led me to believe.

So instead of trying to do everything at once, I decided on an ultra simple, one frequency generator. With a little trial and error and with help from my oscilloscope I got it set up where I want. The device will output a 2kHz square and triangle wave signal which is right in the middle of the audio frequency range. I can't use it for ESR testing but maybe I'll add that capability in the next version.

It'll be really small. The circuit board is the size of a 9V battery. Because that is what's going to power it. A 9V battery holder will attach to the bottom of the PCB, while the top contains components, including a on/off switch, LED power indicator, waveform symmetry adjustment potentiometer, and... two BNC connectors. This is gonna be one de-luxe device!

Since I want to use this thing with an oscilloscope, I thought it'd be really handy to just build in a pair of BNC connectors from the get go. It also has wire pads in case I want to hook up anything else. Like RCA connectors for injecting signals into audio gear, perhaps?

So, I've submitted it to BatchPCB (which I discovered browsing Sparkfun) and looks like it'll cost $7 for the board. I put together a project (collection of components) at Mouser using their cool Project Manager tool. Cost for components is about $11 before shipping. So I am going to pull the trigger and order the board soon.

I'll tell you more about the circuit in the next part. Hopefully I'll have it built and working by part 3...

[Part 1 2 3] >>

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