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] >>

Edward Isaac Bot: Sketchbook 3

Here's some sketches on motor encoders. The basic idea is that, back in the day when MCUs weren't affordable or readily available (the Motorola 68HC11 was popular, I recall), one had to plan for a pretty high chip count.

In this case, some type of counter that would track the number of slots in a disc that whizzed by an IR LED/Phototransistor pair. Remember I was still in college, with limited tools, etc.

So building any kind of precise disc with slots in it was not going to happen (since I didn't know any MechE's that could get me into their fancy machine shops).

But there are other ways to build encoders. You can print up an encoder wheel with a laserjet/inkjet printer and use an IR pair to read reflected light. Or you can print a transparency hoping that the printed spots are dark enough to block light. Or you can use one of these drain strainers or some other piece of hardware that has precisely predrilled holes.

Of course now, too, you can use an MCU to count pulses, and you can by tiny SMD-based IR circuits like those I used on Pokey. And what about broken inkjet printers? The two I've disassembled have excellent transparent encoder discs and IR sensors. (Not to mention a slew of motors, gears, rubber pieces, etc.)

Edward Isaac Bot: Sketchbook 2

Here's more silliness from the dusty Edward Isaac Bot sketchbook archives. This is a sort of block diagram for the robot. Various audio functions like record/playback and sound generation, as well as basic motor control of head, arms, wheels.

And the obligatory water pistol. Uh... right.

Truth be told, a water pistol feature would come in handy right now to discipline one of our cats who keeps jumping up on the kitchen counter. And in fact I am seriously thinking about refitting Pokey for that sort of guard duty... but that is another story for another blog entry.

So, yeah this was kind of crazy brainstorming. I mean, an air purifier? Really?