Robots w/Lasers

August 19, 2011

DIY OLED

Well, not completely DIY, I’m not making the OLEDs from scratch in a chemistry lab. But instead of buying an OLED from sparkfun for $37, or the OLED with a breakout board for $60, I found taobao, essentially a chinese version of ebay. Some seller was selling a very similar display for only ¥20.80 ($3.25). Below is a google-translated screenshot. Automated translation for chinese-to-english still has a way to go unfortunately.

Anyway, you can’t order directly from taobao.com, they only ship to people living in China. However a whole cottage industry has sprung up around exporting from taobao to USA, there are dozens and dozens of sites with poor english on them, who will buy from taobao, and then re-ship the package to you, for a nice fee of course. I went this route, choosing yoybuy.com (after seeing a review saying someone else used them successfully). I ended up paying all told $5 per OLED display.

Now the product page had zero technical info on the displays, and contacting the seller (in Chinese of course), they didn’t have any further information either. However I was able to track down the datasheet for both the display itself and the controller chip, which I’ve uploaded here:

OLED: UG-2828GDEAF02.pdf

Controller chip: SEPS225.pdf

The whole reason I started on this oled ordeal, is after reading this article on driving OLEDs via an AVR microcontroller by rossum. He gets pretty good results out of them, and I wanted to try something similar. I couldn’t find any US source of cheap OLEDs that fit the bill, after scouring ebay and so on. I did find mdfly.com which has a couple cheap oleds, but unfortunately the 1.5″ color display could NOT be driven by SPI, instead requiring a more complicated 8 bit parallel interface, that I didn’t want to have to fool with. SPI is ideal for AVRs since it can output data up to (Clock Speed/2) bits per second, meaning an AVR running at top speed of 20MHz could output at 10Mbit/sec (assuming you do nothing but output data, which means in practice it’s a bit lower). Rossum was able to output pixels fast enough to refresh the entire display at 30fps, which is great (check out the video on his page).

Speaking of rossum, he has some nice little breakout boards using a FAN5331 boost converter to generate the driving voltage for the OLEDs (which generally need 12-15V to drive the display), along with a buffer chip to allow you to interface 5V logic to the 3.3V OLED if you wish. Unfortunately the pinout and such of my OLED is different from his, including different connector size, so I couldn’t use it unchanged. Luckily he provides the source to his boards, so taking those as a starting point I’ve designed my own breakout boards:

Source: pdf, sch, brd (WARNING! These are a work in progress, have not been tested yet. It may short VCC to GND and set your cat on fire!)

I’ve sent away to have them made by laen’s pcb service, they should be back any day now, and I can start putting them together and see what happens! Watch this space for updates.

¥

 

Filed under: AVR,Hardware — davr @ 4:56 pm

July 7, 2010

Inexpensive PCB manufacturing for hobbyists

I just found this service which provides very inexpensive PCB’s for hobbyists. His pricing structure is very simple: $5 per sq inch, you get three copies of the PCB, and there’s no setup fees and free shipping. He’s doing kind of a BatchPCB thing, but somehow has made the cost less expensive. (BatchPCB is $2.5 per sq inch, you get one copy of the PCB, and there’s a $10 setup/shipping fee). I haven’t tried it yet, but he says he needs more people to use his service, otherwise he loses lots of money, so I think I’ll give it a go.

Oh, and did I mention, it’s with 6 mil minimum trace/spacing?

Filed under: Hardware — davr @ 4:25 pm

March 16, 2010

Comparison of PC-based logic analyzers

Here’s a comparison chart I’ve been working on that compares various PC-based logic analyzers. I made this mostly for myself because I’ve been wanting to buy a logic analyzer, but most of them are very expensive for a hobbyist’s budget. PC-based ones are a good compromise…they can be cheaper than standalone units since they don’t need all the processing and display hardware. I’m currently leaning towards the $120 Zeroplus unit, it seems to provide the best bang/buck. There is the $50 open source one, but I think I’d wait a bit for more reviews of it, to see how good it really works.

View Chart Full-Screen

I’ll write a review when I do decide on one. Also I know someone designing his own Logic Analyzer, if/when he finishes, I’ll give a link to that too.

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Filed under: FPGA,Hardware — davr @ 8:50 pm

May 18, 2009

Comparison of Entry-Level (aka cheap) FPGA boards

A while ago I decided I wanted to play around with a FPGA – Field-Programmable Gate Array, basically it lets you design new hardware ICs (Integrated Circuits), without needing a multi-billion dollar chip fabrication plant. So I set out to research the available pre-made development kits I could play around with. They’re quite a bit more expensive to get into than microcontrollers (where you can buy a $3 chip and build a programming cable out of some old scraps of wire), so I looked for the least expensive boards that still had a decent set of features.

I ended up making a comparison chart of FPGA development kits, like I said this was over a year ago, so it may be a bit out of date, but the low-end of FPGA’s doesn’t move all that fast. Most of the information is still valid, but you might be best to do some research yourself before you take the plunge. I only considered boards that featured FPGAs from Xilinx and Altera, since I found other vendors are not competitive in the low-cost arena (low-cost was the most important feature to me at the time, I didn’t want to spend $5000 just to play around. And yes, there are $5000 development boards).

View Chart Full-Screen

If you’re curious, I ended up getting the DE2 (with the educational discount). It costs a bit more, but it has significantly more features, such that I’ll probably never run out of stuff to play with.

The ones highlighted in green are the ones I feel provide the best value, and just coincidentally fall at the $50, $100, and $150 price points.
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Filed under: FPGA,Hardware — davr @ 3:26 pm

January 9, 2008

It Works!

I’ve finished assembling my little gadget…and it works! As a side note, Flux is super handy, it made soldering the tiny SMT stuff really easy, also I learned a few tips from this video.

I ran into one small problem: on the board, I added a JTAG port for in-circuit programming & debugging. However, my cheapo JTAGICE mkI (not mkII) doesn’t support the newer AVR chip I put on the board. So I had to hack in an ICSP port, hence the four ugly green wires coming out of the middle of the board. But once I got that in, I updated the program I had running on the prototype. There were just some minor changes, IO pins were mapped differently, and the syntax for using Timers was slightly changed.

Now that the hardware is essentially done, I need to write some more software, get a few polished minigames on there.

UPDATE: Please enter your email address, I’m trying to find out if there’s any interest in these devices. If enough people subscribe, it will encourage me to do something about it :)

You can download a short video, or watch it online here:

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Filed under: AVR,Hardware — davr @ 6:54 pm

January 4, 2008

PCB Received from Olimex

Over the christmas holiday I received my PCBs back from Olimex. They look very professionally made, it’s pretty neat knowing that I designed it completely myself. In the picture to the right you can see the board with a few of the components. I haven’t started soldering yet, but I’ve placed them on there so you can get an idea of how it will look when finished.

I’m waiting on the parts from Allegro before I can finish, I’ve requested samples of their surface mount pieces (previously I only got the ones in the DIP packages).

Filed under: AVR,Hardware — davr @ 12:00 pm

December 11, 2007

Designing my first PCB

So I built a pretty good prototype of my LED matrix, AVR-based toy (as you can see in my previous post, as well as this video). Now I’ve decided to get a PCB made, using mostly surface mount components, which will make it nice and compact. You can see to the right a 3D render of approximately what it will look like, right now a company in Bulgaria is fabricating my PCB, hopefully I’ll get it within another week or two.

Whether or not it actually will work once I get it & assemble it, remains to be seen.

I used cadsoft’s Eagle tool to design the PCB, and I used this plugin along with povray in order to create the 3d render. Also I sort of edited in the image of the LED matrix…since they didn’t already have a 3d part built for it. But it looks reasonable enough I think.

Filed under: AVR,Hardware — davr @ 5:01 pm

September 24, 2007

AVR Project update

I’ve had a little time to come back to working on my AVR ATMega-based project. First of all, I replaced a bunch of free wires with a ribbon cable, which makes things a lot easier to handle. I’ve also wired up the buttons, so now I can write little programs which can be controlled by user input. Right now you can just move the dot around and change its color, next I think I will make a 1 or 2 player pong game.

Download a short video of it in action (~700KB), or view it here:
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Filed under: AVR,Hardware — davr @ 7:48 am

July 17, 2007

Heart Monitor for NDS

I have a prototype of the hardware side of my Nintendo DS-based heart rate monitor. I’m using the awesome DSerial to interface an IR LED & IR phototransistor to the DS.

It works ok, but the signal is not strong enough. Slight movements can make the data unusable. I think I need to work on either amplifying the signal, or increasing the sensitivity of the DSerial. Also I need to rig up some velcro to stick the sensor to your finger, so you don’t have to hold it in place.

Here you can see my “sensor”:

Here is the connection to the DS:

And finally, here is a screenshot of the DS’s lower screen, which is just graphing the data coming from the DSerial’s ADC:

Check out this movie of it in action: dserial_heart_monitor.avi (1.5MB)

Filed under: DSerial,Hardware,Nintendo DS — davr @ 12:29 pm

June 29, 2007

Hardware I/O for Nintendo DS


A neat-looking device for DS homebrew development is natrium42‘s DSerial. The features include

  • 8051 microcontroller running at 24MHz
  • Reprogrammable from DS, premade firmwares available
  • Free development tools available
  • 18 GPIO lines, 2 status LEDs
  • UART with RS-232 level converter (can be disabled)
  • Full-speed USB 2.0 device (does not support USB host)
  • PWM and ADC available
  • 2D tilt sensor

I’m hoping to make some cool stuff with it…my first plan is to build a portable heart monitor, that can also tell you how stressed-out you are, based on your ‘coherence’ (essentially you take the FFT of your heart rate over time, and you want most of the energy to fall near to 0.1Hz)

Filed under: DSerial,Hardware,Nintendo DS — davr @ 12:37 pm
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