EDM machining is a process where a shape is obtained from a piece of metal by using sparks to remove material! If you have a shape that you wish to reproduce-you make a copper positive of the shape you wish to reproduce (hereafter called the electrode), and by passing a high voltage spark between the electrode and the process material (will become the finished part), erode the process material to exactly match the shape you want.

This book by Ben Fleming is really well written and has great schematics and explanations for how the circuitry works. If you’ve ever had to trace a circuit with a highlighter and a red pen in order to analyze how a circuit is supposed to work, the explanations are appreciated.

There’s a lot going on in this project with high voltages, indicator dials, AC, DC and signals. The brain of the whole thing…

(drumroll)

The 555 timer.

Ollie’s EDM machine is coming out really well.

Here is the electrode in the chuck. My cell camera didn’t pick up the sparks, but the electrode is sparking a deep hole in the process material in this photo.

Today we went to Ollie’s workshop to tune the spark timing.

On the front of the machine, there are two dials, one for ON time and one for OFF time. They work independently of each other. They are wired to the R1 and R2 on the 555 timer chip for asynchronous control.

We used the scope to see how fast the spark was across the gap in the electrode and the process material when it was doing the best job of removing material.

It seemed like it was on the order of a few microseconds (as in…under 4)! As we turned the ON and OFF times to different values, at times, the electrode shorted completely to the process material.

Altogether, a very impressive project!

The post DIY EDM Machine appeared first on .

The first fish, Goldie, died just a few days after she came home. She wasn’t very excited by food, so she was probably sick to begin with. I was strangely depressed over her death, even though she lived and died in another city, and I never even got the opportunity to know her.

Lex just came home with new fish!
Check out the video of Goldie II and Goldie III – right-click and save as wmv in order to view.

The Hungry Fish small

The post THE HUNGRY, HUNGRY FISH appeared first on .

I’ve decided to write about one of my most useful lab tools, the oscilloscope. An oscilloscope lets you see invisible electrical signals, usually showing how they change over time. The X- axis is time (inverse of frequency) and the Y- axis is amplitude. Other useful things an oscilloscope will show you is how much noise there is in the area of interest, how much of the signal is AC or DC and if your component is not working.

Actually seeing if your component is not working at all is pretty easy- just put the scope on the output and see if anything happens. It’s way more annoying when the component is working just a little bit and puts out an unclear signal.

Photo of a Teledyne LeCroy oscilloscope –
for the purpose of the photo, it’s showing a calibrated 1kHz signal from the scope itself.

Typically, modern oscilloscopes are digital oscilloscopes. Old oscilloscopes are analog. Simply put, this means that analog oscilloscopes display the original signal and that digital oscilloscopes process the signal from analog to digital. There’s tons of information out there about the differences between them. Let us know in the comments if you find some interesting trivia!

There are a few specifications to look for when buying an oscilloscope, over the next few posts, I want to discuss the following: bandwidth, sampling rate, triggering, memory. We’ll also discuss probes and the different kinds you can get. I’m going to be visiting a lab next week where they look at picoVolts and they use special probes for less noise.

I bought my first oscilloscope off of eBay for $140 in 2006. It’s an analog oscilloscope and made by a company called SPECO, which I’m not even sure if it exists anymore. It also looks like I may have paid too much- as I wrote this post, I looked for a link to it, and you can now buy it on eBay for $35.

You’ve heard the expression you get what you pay for?
In the case of the cheap SPECO, it’s true.

The SPECO has a bandwidth of 20 MHz, the LeCroy pictured above has a bandwidth of 200 MHz! I also have another oscilloscope made by OWON that has a bandwidth of 60 MHZ.

The ultimate goal is to get your input signal represented accurately on the screen of the oscilloscope! So you need to choose a scope with a bandwidth large enough to show your signal range. So what does bandwidth mean exactly in the context of oscilloscopes? What can you even look at with such a small bandwidth of 20 MHz? What kinds of signals need the resolution of 200 MHz?

Bandwidth is defined as the frequency at which a sinusoidal input signal is attenuated to 70.7% of its original amplitude. This is also called the -3 dB point. At the -3 dB point, the signal of interest will start to distort so you need to choose your scope so that it has a frequency range large enough to not lose any signal amplitude.

I’ve seen a number of slightly different recommendations around- but most online recommendations agree that buying an oscilloscope with bandwidth with at least 5 times the highest frequency component in your signal will achieve good results. If I want to look at a signal of 40 MHz, then the LeCroy oscilloscope pictured above is a good choice. If I am only going to look at signals to troubleshoot if a switch is on or off, then a lower bandwidth oscilloscope is fine.

Some of the signals I look at are:
RF detection chips- low MHz to GHz! Needs a high bandwidth oscilloscope like the one in the picture above

555 timer signals- microseconds/ high-KHz, low MHz! Can get by with the Owon, although I would never recommend that oscilloscope to anyone. After I wiggle some wires around, I can get good results with my analog scope too.

PIC Microprocessors- nanoseconds/ high MHz Needs a higher bandwidth oscilloscope

That’s it for today- my next post will discuss sampling rate and what it means.
What kind of oscilloscope do you have and more practically, what kind of signals are you looking at?

The post Oscilloscopes -Part 1 appeared first on .

~Sophi

The post The Super Green Dot Project appeared first on .

Recently, I had the opportunity to talk to people who do RF layout. It was then that I was introduced to the concept that a 4 layer board will require a much thinner transmission line (for a matched 50 ohms) than a 2 layer board.
My RF circuit requires 50 ohms for the best power transfer between the antenna and the rest of the circuit. You can read more about impedance matching on Wikipedia, but the basic idea here is when the antenna and the circuit have the same impedance, it is like a seamless wire. Ideally, you want your power source, transmission line and load to match, otherwise … it won’t work!

Unmatched impedances will cause your input signal to attenuate in power by varying degrees depending on how bad your impedance match is.
This concept is one of the first things I learned in Electromagnetics class in school, but there is no substitute for learning like hands-on!

There are a number of transmission line calculators online. I chose the one from EE Web. I think it’s pretty clear from the diagram what the inputs mean, but just quick: the trace thickness is the thickness of your trace. You get this from the weight of your PCB. OSH Park, where I get my boards fabbed, has 1 oz copper on the top layer. My transmission line is on the top layer, which is 1 oz copper. Substrate height is the height between the bottom the trace to the next layer. Trace width is what controls the transmission line impedance, so you have to change this until your output reads the desired impedance. And the substrate dielectric is also available from your board house. It’s the Greek symbol εr and it means relative permittivity.



The width of my needed transmission line on a 4-layer board turned out to be 0.03mm. On a 2-layer board, the transmission line size needed is 3mm. I decided to go with a 4-layer board on my next round. My PCB layout software is a lite version of Eagle ($70), but Eagle doesn’t allow 4 layers with this version. I could pay $169 for a Hobbyist version which includes 6 signal layers, but I sell boards. The standard is $820, which is still an excellent price, considering many PCB software packages are thousands.

KiCAD is an open source, free software that allows multiple layers. For this circuit, it turned out to be an obvious choice. I learned enough of the software to make a board within 2 weeks, and
sent it off to be fabbed. I am impressed with how intuitive KiCAD is to learn, and will continue to use it on all of my boards that require more than 2 layers.

Link to part 6 in this series
Link to part 5 in this series
Link to part 4 in this series
Link to Diode Detector post
Link to part 3 in this series
Link to part 2 in this series
Link to part 1 in this series

The post Cell Phone Signal Detector – Part 7, transmission line width… and KiCAD! appeared first on .

I have gotten several emails from people who question how I have time to make so many projects.
So how am I doing this?

After working as a Design Engineer for several years, I came to the realization that no one would ever hire me as an engineer with a flexible schedule, or for less than 50 (60?) hours per week. A Design Engineer job means you belong to the company that hires you. In return, you get a sweet salary, health insurance, 2 weeks of paid vacation and some sick time. Plus retirement money in many cases.
I decided to take a chance, jump out of Engineering and into in Sales, where I work about half-time. The schedule is more flexible simply because I’m dealing with people all over the world and in different time zones. I gave up the health insurance (I pay for my own) and the 2 weeks paid vacation (I take as much unpaid vacation as I want).
I am lucky to pick up freelance design work on the side and have recently started Marketing consulting for New Products. Want to hire me? Email Me

So if you’re in an job and desperately want to have time for your own projects or start a business, going part time is an excellent option. You don’t completely give up your income, which is helpful. If your job won’t let you go part time or flex-time, then you have to look for one that will- or switch fields. It’s a definite risk AND you have to find the part time job that pays enough to pay your bills.
I will reach my 2 year anniversary of Not Working Full Time at An Engineering Job on July 2nd. I think these have been the best two years of my life so far.

UPDATE: My sister Ana Kravitz has a Analytical Marketing Consulting practice for website analytics and she is called MIX Analytics!

The post A personal post + blogging at Engineer Blogs appeared first on .

The students had a small issue, their Nose Poke module plugs into a larger instrument, that collects data and does a bunch of other stuff. Unfortunately, since it’s part of the larger system, the Nose Poke module needs 28V to work.

All they need for many of their experiments is a Nose Poke that puts out an active high or low that runs on 5V. In fact, because of the difficulty in interfacing with the larger instrument, their rig to get to 5 Volts is complicated and is prone to mechanical error.

Today, I started building them a simple 5 Volt Nose Poke system that they can easily add into their existing data collection system.
I started at my favorite store, Radio Shack. Radio Shack is the only local place around here that sells components. They pretty much have most of the basics and for $3.79, I walked out with part number 276-0142, Infrared Emitter and Detector. With 2 resistors and a display LED to show that the circuit is working, I came up with this circuit:



When you put your finger in between the Emitter and Detector, the display LED (the red one) shuts off.



It was good to run a quick test on the circuit- I hadn’t specc’d IR components before and Digikey (my next stop after Radio Shack) provides many options. I wanted to get a sense of the important specifications to shop for. It is clear that the further away the emitter and detector are from each other, the more power is needed. By the way, the 100 ohm resistor that I used in the above circuit for the Emitter makes a nice bright beam but gets hot (and its a 1/2 Watt). Using more resistance didn’t allow the Emitter to provide enough power to get to the Detector.

Next steps: choose parts and design PCB.

Thanks to Rick Eh? for the mouse photo

The post Mouse Nose Poke! An IR Beam-Break circuit appeared first on .

Ollie and I brought a blown-up version of this product to get some Market and Technical research from a large crowd with different cell phone providers and cell phone models. Our blown up version is a bar graph which bounces up and down with the cell phone signal levels.

The 8′ bar graph is being triggered by a child texting the sensor circuitry in the globe.

Since the idea of the product is to detect transmitted and received signals from a good distance, I made sure that there would not be any cell towers too close to the Maker Faire site ahead of time. It was fun looking at maps of where cell towers are located!
Unfortunately, since cell service where Maker Faire is located (San Mateo fairgrounds) is poor, a temporary tower was brought in, and placed very close to the building we were exhibiting in.

Check out the cell tower serving up extra radiation!


After setting up the exhibit, we realized that it was full on all the time, the cell tower was overpowering the exhibit and we weren’t going to be able to show anything except a big, red, bright light.
Not only that, my circuitry was now getting hot since it was designed for pulsing high amps but not running 13 amps through the circuit all the time. UGH.

My new friend Álvaro Prieto made shorter antennas out of solder and tried to fix the situation with the one 5dB attennuator I had brought with me. No joy at all. Over dinner after setup, my friend Pete Doktor suggested we put tin foil around the exhibit to block the cell tower. I laughed at the low-tech suggestion but my wheels were turning. My brother Lex Kravitz, who is one of my favorite project partners, then suggested we build a Faraday cage around the sensor circuitry to keep out the cell tower. He works in a lab that happens to have Faraday cage materials lying around.

Here’s Ollie and Lex making the cage on Saturday morning ONE HOUR before Maker Faire opened.


And here’s what it looked like during the fair. Not bad, eh?



We put my cell phone under the Faraday cage and told people to text the project. Over the course of the weekend, we received over 400 texts!

I’ve had a few email questions about how Ollie built the bar graph to diffuse the light so well, so I’ll detail how he did this in another post.

The post Texting Trapper at Maker Faire 2012 appeared first on .