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Constant Current Dummy Load

I just got my first oscilloscope. Complex analog circuits are now possible. As I mentioned in my last post, I working on a power distribution unit (PDU) for motorcycles, cars, and other DC applications. The project is very close to the testing phase and that means I will need to run this device at precise power levels and at precise temperatures. The testing protocol also includes vibration studies, but today we are just going to talk about precision current testing. This can be done many different ways. You can just put a resistor to ground and use Ohm's Law to tell you how much current you are burning. If you want to change the current in use though, you will have to change the resistor. That is not very handy if you want to test your power supply at multiple currents as you will need a lot of different resistors. Since my system is running at about 14V and I am talking about 15A of current, I'll need some pretty beefy resistors and those are expensive. Instead

"Making lemonade with lemons" or "Reworking your bad PCBs"

I've been working on a large project for a few months now. It's a DC power distribution unit, and as you can imagine it has need for relays. I've got the thing setup to accept cards to can perform many uses both input and output. One of the many cards I've designed for this system (dual low-side switching relay, 5V, 12V, audio sensor etc..) is a dual high-speed 12V solid state relay card. Rendering of PDU and fresh pile of PCBs from Circuitmart This is a photo of the relay on a breadboard.  single channel of dual high-speed 12V solid state relay on breadboard This is the card from both sides. The "empty" space is used for thick and wide traces to carry current. These will be built with 6oz copper and can source 23A @ 330W in theory. I've only pushed them to 100W so far but they showed no meaningful rise in temperature so I think I am on the right track. By the numbers, they are right where they should be. Because these cards are small and

Bench power supply project

I found myself needing a 480W power supply to test a high current project I was working on. A 500W bench/lab power supply will set you back $100s so I figured a PC power supply was the cheapest bet. For $80 you can get a Wonhunglow brand. I checked ebay and found Dell 500W server power supplies CHEAP. Like $2 cheap. I acquired a couple and figured out how to turn the thing on by shorting 3 pins together. Then I designed a simple little 4 rail power supply PCB and had it built by OSH Park. This power supply outputs 12V and 5V and 4V. I didn't have any use for the 4V so I skipped those pins but did add a 500mA 3.3V LDO to my board so I have 3.3V, 5V, 12V, and GND rails available. I left a large section of the solder mask missing so I could solder on some more current carrying capacity and called it done. I used a DPDT switch to short out the 3 pins required to turn on the 12V rail and added a little LED to indicate that the 3.3V regulator was running and put a small current limitin

Successful Launch of Classes on Meetup

A little over 2 weeks ago, we at Freeside Atlanta launched a series of classes on Meetup on everything from Linux to 3D Printing. They've been a huge success so far! Our 3D Printing class, shown above, was taught by 3D Printing Expert Anthony Aragues. We had 11 students sign up for the first class, where they covered the recent iterations of hardware and software and how to use them. In fact, every single class that we launched filled to capacity. Intro to Linux, Intro to Electronics, Intro to Arduino, CNC, and 3D printing. Thank you to all of the Teachers and Students that made this little experiment such a success! Because of how well this first round went we'll be launching more classes and workshops soon, so stay tuned!

Sharp Memory LCD - Arduino Library

This post extends the previous post . Source Code Released! I've got a little reflow oven simulation running on the LCD. I think its going to be great for the reflow oven project. The source for the sketch in the video is attached below. The library now does vectors in addition to text and bitmaps. I am now extending the Adafruit GFX library so I can use those vector drawing routines in addition to my PGM space bitmaps. I still need to clean up the unnecessary banging I am doing on one pin. I'll post up the code on the interwebz for all to use once that is cleared up. I need a darn oscilloscope to inspect that pin! If you need an early copy of the library and you don't know how to contact me, PM me from the youtube video. #include #include "SharpMemoryLcd.h" SHARPMEMORYLCD lcd; void setup() { Serial.begin(9600); lcd.LcdInitialize(); lcd.LcdAllClearMode();

Sharp Memory LCD - Musings

Update: Arduino Library Released If any of you guys were at Freeside this weekend, you would have seen me staring into the oscilloscope trying to make heads or tails of its output and comparing that to a couple of datasheets. One of those datasheets was for the Atmega328P microcontroller that is on the Arduino UNO, the other was the Sharp Memory LCD . These are cool because the are ultra low power 6uW and have extremely high contrast. The Sharp datasheet isn't what I would call straightforward, at least for the uninitiated (whom I count myself among). The power up sequence was pretty clear but once it came to pushing pixels it got a little vague. Really it was just a bunch of waves on the sheet. One of the waves is a constant 5-60Hz pulse. That is the sort of thing that would be very irritating to create if you are bit banging on the main loop of your program, so I needed to get the AVR to pump that out in an automatic way. Researching the interwebz and reading the Atme

ISP Programming Jig w/ pogo pegs

During one of the last projects I was working on, I found that the first programming jig I made had a serious draw back. It could only put the #1 pin of the programmer in two of the four corners. That meant that I could only program my board from one side. That was fine until I assembled the project in it's case. At that point, reprogramming was a difficult task that required disassembly, something I never considered when I designed the item and as it turned out it was almost impossible to do without destroying it. Annoying! Three weeks ago I decided I wanted to flash some new firmware on my motorcycle remote so I could use it to put a GPS on my Kindle Fire. That meant I needed take it apart and risk destroying it. Not an exciting prospect. Then I thought, why don't I just build another programming jig like the last one only upside down. That seemed like a winner, because it was fast, but I didn't have any more 2x3 ISP headers. Bah! Since I needed to wait on a shipm

Simple Chemistry

Inspired by THIS !SAFETY! This is some dangerous stuff. It will mess you up.   Zn + 2 HCl          > ZnCl 2  + H 2


This giant masonry blade has been sitting around Freeside forever: Rust and dust are indicators of abandonment. Please make use of the rusty and dusty. Note the diamond tipped edge I KNOW!  Let's make a giant scythe for my Halloween costume!!  (Never too early to plan)

Thingiverse: Anatomic Human Foot

Freesider's are evermore professional printistas of sorts.  As our sprints are ramping up, there seems to be a growing interest in "organic modeling".  Things often found in nature fall into this category for CAD artists. Here is a recent Thingiverse upload, which was made from some very simple modeling techniques in Newtek's Lighwave 3D application.  A little goes a very long way, indeed. per There are 26 proper bones in the human foot; 28 if you consider the sesamoids of the 1st metatarsal phalangeal joint complex. That's over 25% of your body's total musculo-skeletal anatomy, hitting the ground every time you go for a walk or run! Quite impressive, really. Read More: This anatomic foot model was designed in Newtek's Lightwave 3D, as part of the podcast @ Anatomic study models can be quite expensive,