[quote author="sa5bke"][quote author="Tuomas"]I made a USB function generator over the summer[/quote]
I might, when I get time, try to replicate this. But I wonder, why is the upper limit ~3MHz in your build? I thought it was 12.5 MHz on the AD9833.
Eric[/quote] The AD9833 can go all the way to 12.5MHz, but the sine wave gets very distorted above 3MHz. Something they don't mention in their datasheet... If you added some aggressive lowpassfiltering with a cutoff somewhere around 5-12MHz, you could probably get a decent sine wave up to that point. I just added a RC lowpass at ~3MHz. The sine wave is good enough up to that point.
Another annoying thing with the chip is that the amplitude of the sine and triangle is 0.6v, but the amplitude of the square wave is 3.3v (if I recall correctly) out of the chip. I used an opamp to amplify the signal. Sine and triange get amplified, square is clipped by the opamp. That's how they both end up with about the same amplitudes. Ugly...
Still quite new to this, and don't have a lot of income so building my own equipment is often a good option.
I used to have a self-made power supply, but that was replaced by a "real" lab supply, with current limiting.
I made a USB function generator over the summer: [attachment=0] Still sort of work in progress. No variable amplitude. Can't change the offset. But it's come in handy quite a few times already. (More info on my website).
I've had a project idea on my mind for a while now that would probably need some capacitive touch buttons, but I've never used them before. About a month ago I started looking at some of the possibilities out there. After ruling out external controllers as an option, I noticed that Atmel provides a library for using a normal AVR ADC peripheral to do capacitive touch sensing, with only a single external component. The library is provided as a binary blob, however, and I couldn't find any source code for it. So I decided to try implementing it myself.
As far as I could figure it out, the idea is to take advantage of the sample&hold capacitor inside the ADC block.
I ended up making a dedicated PCB with an ATMega32u4 microcontroller for testing out the capacitive touch sensing (it's amazing having access to a PCB router at the university, transforming a PCB design into a physical board is simply a matter of some clicks of a mouse and waiting 30 minutes. Except for vias, they need to be painstakingly riveted one at a time...): [attachment=0]
I've got a full writeup of the experimentation on my website, including my understanding of the theory of operation and code (and a video of the board in action, the three buttons controlling the three colors of an RGB LED): http://tuomasnylund.fi/drupal6/content/ ... le-adc-pin
I'm sure this has been done before many times over, but I had fun trying to figure it out myself and it seems like a pretty elegant and reliable solution in my opinion. I'll probably end up using this in a project in the near future.
Thoughts, comments and corrections are always welcome.
I actually finished this more than two weeks ago, but a trip abroad got in the way of writing about it. Today I finally got around to posting about it onto my website.
I did encounter a problem with it, it doesn't seem to work with the only IR device I have in my apartment. I wrote about this on the link given above, but the short story is, I can capture and re-send a signal from the remote, but it doesn't seem to work.
That would seem like the obvious problem, but what is causing it?
On the other hand, that signal on the scope is of course after the demodulator, so the problem could also be something else. For example, I use a 38KHz demodulator on the irtoy / attached to the scope. What if the original remote uses a different frequency? Could that explain my problems?
If you have any ideas, feel free to post.
Also, thanks for the free PCB, kind people of Dangerous Prototypes!
Interesting topic with some nice links! especially the latest one.
I've been meaning to make a GPIB-USB converter for a while myself, Ialready bought the centronics connector and looked at some projects online. I've been thinking of using a at90usb162 as the microcontroller, because I've got a couple of spare ones lying around and am quite familiar with that particular chip.
I've also got a couple of pic18f2550s lying around aswell (for a IR toy free pcb build), though, and that project posted uses that chip. With the code already done, I wouldn't have to do that myself. I'm in Austria right now for a university course, but I'm tempted to try and design a simple pcb of my own (with SMT components) during this week if I have time. I'll be back in Finland next week and could try to mill the pcb with the PCB mill at my University, then solder and program it.
The reason for this is that I own two old HP devices, a HP 54201D digitizing oscilloscope and a HP1631D logic analyzer. I wouldn't mind being able to control them with my computer. I'll try to post something here if I get anything done at some point.
I don't have nearly as impressive collection as some of you guys, but here's my stuff anyways: -Bus Pirate v3 -Open Bench Logic Sniffer -Bus Blaster v2 -USB IR Toy (built from a free PCB, finished it last weekend. I need to post something about it online soon) -2x XC9572XL CPLD dev board (one of them is fried) -XC2C64A CPLD dev board
I'd take a picture, but I'm currently abroad, so most of those devices are in my home country (but not all of them! I took My IR Toy and Bus Pirate with me. You never know when you need them).
