While browsing dangerousprototypes.com I saw an interesting little gadget by Mark Frejek at www.mikrocontroller.net. Mark had made a transistor and component identifier using an AVR ATMEGA8, a few resistors and a 16x2 LCD. Always wanting one of those expensive Atlas testers I was intrigued.
I saw a few examples of people building the circuit on the net and the operation of the gadget seemed to be really well done. The software seemed very polished and comparable to the Atlas devices that I've only seen in person at trade shows. Also, having all the required parts in my bins and the long standing niggle in the back of my brain telling me to try and find a use for that ATMEGA8 DIP uC I've had floating around for a while, it was almost a match made in heaven.
Here is a small update on a project I'm working on for a client.
I've subsequently dropped the split quadrature encoder set up and added another shaft encoder on the actual lead-screw. So now I can actually use a stepper or a servo and I close the control loop using my own shaft encoder. I've still got to put up with the non-realtime kernel but it's a lot better and good enough for what I need.
What got me started on wanting to increase my RF knowledge was this article by Dave Richards. I was originally looking for interesting ways to make project cases and happened to find his glorious "double-sided PCB case" technique. The technique has been around for a while, but the circuit he built in it was just so pretty I had to have a go. His little story about using shortwave radio as a kid piqued my interests enough to actually sit down and build one.
So here are some short videos of my attempts at the WBR receiver originally designed by N1BYT.
Once again *many* thanks to the guys on Twitter for their assistance. It turned out I had a bunch of dodgy MPF102 j-fet transistors which hampered my initial testing.
I decided recently that RF was a field I had very little practical knowledge of. I know the basics, the methods and the general ideas, but I've never actually put together a circuit other than a pre-purchased kit.
Thanks Alan Yates and the guys on twitter I set out to be a simple RF oscillator. I also really wanted to build something using the "manhattan" construction style.
You can see above I'm using the CRO probe to inductively couple with the tank coil.
I've still got the circuit bouncing around my desk, I'm going to attempt to build a Direct Conversion receiver with it when I have some time.
Further work on my "Alarm Clock" I wanted an alarm function that could play WAV files from an SD card. This will allow tailored alarms for each alarm to be played.
I needed to output some debugging from a micro controller, usually this is easy. Just plug in a MAX232 and connect up a USB to Serial cable and you're away. But in this case I was using 3.3v making the MAX232 useless. I didn't have any MAX3232's in my boxes and I didn't want to fiddle around with resistors etc to make a rudimentary level converter. I needed something, and I knew it was something I would use time and time again in the future so I set out to make a LVTTL USB to Serial cable.
Looking at the various USB to Serial cables I had, I came across one that I could clearly see had a FT232BM. Looking up the data sheet for the FT232BM I found in the app notes that this chip can be configured to be 5V bus powered, 5V self-powered, 5V bus powered with 3.3V I/O and 5V self-powered with 3.3V I/O.
I've been working on a small project of late that utilises an ATMega32 and plays WAV files from a SD card. I'm using ELM Chan's Petit FatFS to do the FAT translation, but I was having issues with the SD card configuration and communication. Getting frustrated I started using my S3E development board as a SUMP Logic Analyzer for a while until I splurged and bought an Openbench Logic Sniffer which is based on the SUMP LA.
It cost me $46 AUD with free shipping from SeeedStudio. The "free" shipping took about 3 weeks to get from Hong Kong to Sydney Australia so I was less than impressed with that, but I'm more than impressed by the little board.
After setting up "the alternate" SUMP client and connecting up my SD card logic lines I soon had a sample of where my problems were. Also the SPI decoding build into the client was a joy to use and very very handy. The S3E version does have the advantage of the larger capture buffer (512K vs 4K) but using 115200bps serial as opposed to the 1Mbps of the OLS's USB connection this limitation is soon forgotten.
Having this board on my bench for a week or so, I was starting to worry about damage from things being dropped on the board while in use. So I set out to make a Perspex case similar to my Bus Pirate case. And here is the result...
Hey all, been a while, very busy at work. Anyway, my friend Tyson gave me a bag of these Siemens PD3435 LED displays. They are a really neat retro LED display that's remarkably good. They would have been expensive in their day. I needed a way to test the devices as all 20 or so were jumbled together in a bag with no anti-static protection. I ended up making a simple testing shield for an Arduino.
The devices are very feature-full and much nicer to deal with than the DLG2416s I have laying around. They have features like display dimming, display blinking, character blinking that the DLG simply doesn't. Plus the characters are larger and much easier to read for the given package size.
I intend to use two displays to make a 8 character clock. Here is a video showing the concept and also me fiddling with a gray-code rotary encoder.
I haven't been posting much lately because I've been busy helping out a friend with some handy little boxes of tricks.
The first one is a simple toggle button controller that uses an ATtiny13 to form a push-on push-off control button with LED and a dry-contact reset to turn the toggle off. The PCB was designed with gEDA PCB and the NC GCode was created with it's GCode export function. It generates passable GCode, but you do need to verify that the tool can make it through all the small clearance gaps otherwise you end up with bridged traces (especially around pads).
gEDA PCB GCode export also doesn't produce a very good outline code to route the board out. It for some reason includes all the drill holes etc etc. So I manually edit the file and remove all the unneeded stuff. I also have to manually add "tool diameter offset" with the G40 and G42 commands otherwise it will run the tool exactly on the outline and not compensate for the tools width. With the G42 command EMC2 will offset the tool width and cut the board out at the correct size. It's a bit of fiddling but the results are great otherwise
Also since I dialled out the backlash the machine is back to being accurate once again. My circular pads are circles again! Also the drill alignment is much much better.
Anyway, the second PCB (box still pending) is a two host to one device USB switcher. It's for a audio-visual automation system that requires to switch a device between two computer outlets. It takes a dry-contact to make the switch. The LEDs where added just to show the selection, otherwise they're not needed.
The board uses telephone grade 5V relays so the contacts should be more than adequate for USB. The device seems to work just fine with the box in line so so far so good.
After finding the DLG2416 quite useful it's also a very I/O hungry display to use. It's pretty obvious when looking at the spec sheet (7 data lines, 4 address lines, write latch, clear etc.) that the display was designed to live on a nice fat bus with heaps of I/O room, but in micro-controller land we have to be fugal with our use of I/O.
