Up until now for every project I have ordered all the parts needed for that project and kept all the left over parts in a Digikey box under my desk. This made it near impossible to find any parts if I ever needed them again since I had to sort through an unorganized box for a certain part. So one weekend I decided to try to organize my parts so that I could easily find parts that I have used before so I can reuse them on new projects.
There are many different ways to organized electronic parts; these component storage drawers are very popular but I don’t have a very big desk so I wanted something more compact and easier to search through since I don’t want to catalog my parts at this point.
I found these business card holder binders that I through would work great for holding components. I have seen similar ones specifically for SMT resistors and capacitors but I also wanted to store SMT ICs and through hole resistors and the business card sized pockets seemed great for that.
I bought a few from Staples and spent a weekend going through all my miscellaneous parts boxes and came up with this:
I have one for through hole resistors and capacitors, SMT passive parts (capacitors, resistors, inductors) and one for all my SMT semiconductors. One day I will probably need to put together an inventory database but this seems like a good start.
Since I am done with school I want to get back into doing some hobby electronics a project I posted about before was wanting to build a home automation system.
This was to consist of multiple wireless sensors and IO points around my apartment controlled by one central server.
To start this project up again I have designed a small battery powered temperature sensor. The idea would be that I could have one of these in each room of my apartment and they would measure and send the temperature back to the central server wirelessly.
This first board is going to be a prototype
I have designed it around the Microchip PIC24F16KA101 it’s a fairly low cost, low power 16-bit mircocontroller from Microchip. I have designed i two wireless trancievers, the XBee module I used on the Quad-copter and a module using the Nordic Semiconductor NRF24L01. The Nordic Semi one is much lower cost and lower power if it works out I will design another board with the chip right on it instead of using the module. But since I have experience with it and there is some risk the Nordic Semi part wont work out I designed in the XBee module as a backup.
This while thing is going to be powered by a singe CR2032 coin cell battery, so battery life will be a concern but with with some good software I think I can get it to last a good long time on that battery.
On April 13, 2013 I wrote the longest exam of my whole engineering career; The Fundamentals of Engineering (FE) exam in Seattle, Washington. This was an 8 hour exam consisting of a 120 question, 4 hour morning exam on basic general engineering questions and a 60 question, 4 hour afternoon exam which was discipline specific for which I chose electrical .I cannot talk about the questions in any detail but I will talk a bit about my thoughts of the exam and ho to prepare for it.
I spent the last 3 months studying for this huge exam in which I bought this book from amazon and went through practically all 900 pages:
The book is good and very detailed, I felt most of the questions in that book were much more difficult than the questions on the actual exam. So if you study from this and can do most of the questions in it you should be set for the exam.
I also bought a copy of the FE Supplied Reference Handbook. This is the formula book that they give you during the exam so it is important to know this book well and know where to find things in it.
Since the calculator I have used through my diploma and degree was not on the approved calculator list for the FE exam I had to learn to use a new calculator. I chose the TI 36X Pro. This is a great calculator it was able to handle everything on the exam with ease.
I arrived at Seattle center at about 7:00 am and was done by about 5:00 pm; it was a very long and exhausting day. None of the questions on either the morning or afternoon exam are particularly difficult individually but the length of the exam makes it mentally draining. The exam to me was more of a test of endurance than it was engineering aptitude.
A few words of advice to anyone planning on taking the exam in the future
Do lots of practice exams, and practice doing 120 questions in a 4 hour or less period of time using just your calculator and the FE Reference book. You need to know where thing are in the FE Reference book since you don’t want to spend too much time flipping through it searching for that one formula you need.
Don’t study the night before and go to bed early and get a good sleep; if you don’t know something the night before the exam you wont know it during the exam, cramming the night before is only going to stress you out.
Bring food and water, the exam is long and it’s nice to have something to snack on and drink during the exam
Relax and try to have fun :)
I am glad I took the exam and feel I did well, I should find out my results in the next few weeks. If I pass the next thing for me to do will be to apply to APEGBC to be an Engineer in Training (EIT), if I failed I will have to decide if I want to write it again.
One journey is over and the next one is just beginning I finally received my degree in the mail from BCIT; now to study for the Fundamentals of Engineering Exam so I can get my Engineer in Training (EIT) designation with APEGBC and work towards my Professional Engineer (P.Eng) designation.
The Fundamentals of Engineering exam is a huge 8 hour exam that pretty much covers every subject under the sun so I cam going to be very busy studying over the next 3 months and might not have time to work on my electronics projects.
I wrote a post about my design for a capactitive touch business card a few months ago but I have finally had time to build it up and test it out. overall it works well but I could make some improvements. Here’s a quick video of it working:
To implement the capacitive touch I used the PIC10F206 microcontroller. I chose this microcontroller over something bigger like a PIC12 or PIC16 or MSP430 because like the simplicity of this very low cost, low power, 6 pin micro controller.
Here’s the circuit for implementing the capacitive touch
The theory of how it works is that the timer in the microcontroller is used to send a train of pulses out of pin 4 of the microcontroller:
These pulses charge the capacitor made by the capacitive touch pad on the PCB. The voltage on this pad is monitored by the internal comparator on the mircocontroller on pin 1 and it discharges through the resistor R1. The next picture is a scope capture of the voltage on the capacitive touch pad when there is no finger on the pad. (Note that the capacitive of the oscilloscope probe does add enough capacitance to trigger the comparator but we still will be bale to see a difference when a finger is on the pad). Here we can see that it chages up fast when the output goes high and when the output goes low the capacitor cannot discharge through the output due to the diode blocking it, it can only discharge through R1. The larger the capacitance of the pad the slower the discharge which means the bottom value of the ripple will be smaller.
Here we can see the effect of a finger on the capacitive touch pad; there is more capacitance on the pad and that makes the minimum values of the ripple lower. The internal comparator on the mircocontroller has a 0.6V reference voltage so when the minimum values of the ripple drops below 0.6V it triggers the comparator. If the comparator does not get triggered for a certain amount of pulses set in the software it determines that the pad had been touched and it turns on the LED output.
That’s the basics of how the capacitive touch works on this board, which is one of many different ways it can be implemented.
Agilent Recent had a deal on that if you bought an e36xx power supply you would get an e1272a DMM for free which was a great deal since I needed a bench power supply and a new higher resolution multimeter. I decided to get the e3610a which has the following specs:
Linear Power Supply
30W power Output
Two Ranges: 0-6V @ 3A and 0-15V @2A
Noise: 2mV p to p
Load and Line Regulation: 0.01% + 2mV
It’s a nice solid power supply that has 10 turn potentiometers for the voltage and current limit adjust which feel great and give excellent control of the output, you can easily adjust the output to 10mV and 10mA resolution which can be difficult on power supplies with cheaper single turn potentiometers. Another thing I like about this power supply is that it’s fan-less, nothing is more annoying than test equipment with a loud fan and some I have used in the past can be very loud especially when outputting a lot of power.
This is an older design of power supplies so it doesn’t have some of the fancier features that newer digitally controlled power supplies have like being able to digitally set the output or have PC connectivity but I don’t really need any of those features anyway.
I measured the output step response with the oscilloscope and it shows no sign of overshoot.
Measuring the output noise of the power supply:
I think that’s more a measurement of the noise floor of the oscilloscope than the output noise of the power supply but that just shows the great performance of the supply.
I would recommend this supply to anyone looking for a solid linear power supply that is going to last them forever. I’ve done some looking around and if you don’t care about getting a used power supply these can be had for very reasonable prices on ebay. Also because of the simple design you could probably even pickup a broken one on ebay and repair it cheap. I know I’m considering getting a second one off ebay.
Here is a small teardown of the Power supply showing the high build quality.
I haven’t had time do blog anything for a while since I was busy with school but I finished my final exams last week which concludes my Bachelor’s degree. I have been working on this degree for five years now going to school at nights while working full-time during the day and now I am done. Since the Part-Time degree I did at BCIT is not fully APEGBC accredited my next goal is to write the Fundamentals Exam in Washington to get my EIT and work towards getting my P.Eng.
I also bought some new test equipment. Agilent had a deal for w e3610a power supply and an e1272a digital multimeter that I just couldn’t pass up. I will do a review of both pieces of test equipment in future blog posts.
I have also been working on my Capacitive Touch Business Card which I will blog about too.
Continuing with the Home Automation System I talked about in the last post I have been working on the datalogging server portion of the project. The purpose of this is to receive sensor data from the sensors in my apartment and server them on an internal websever and post them on Cosm for logging the data. I chose to use Cosm.com to log the sensor data since there is a very limited amount of onboard memory on the ATMega328 on the Arduino board and this way I don’t need to have external memory.
To test out the Arduino’s ability to function as my home automation system server I bought an Arduino Ethernet Shield and connected a 10K Ohm thermistor with 10K pull-down to the analog input on the Arduino board. I wrote a program that reads the analog input and posts it to my Cosm feed. I added a bit of software filtering to the ADC reading to smooth it out a bit, adding a capacitor to the ADC input may help as well but it’s working reasonably well for not
Here is a plot of the temperature in my apartment over the last 5 mins in degrees Celsius.
Using the Ethernet shield I also setup a little web server that posts the current temperature and pulls the graph from COSM to show the temperature over the last 5 mins. This webpage refreshes automatically every 5 seconds. I might try to setup dydns so I can access it from outside my apartment. I think I could also add controls to this web server so at some point I may be able to control the lights or temperature through it.
A project I have have wanted to do for a while is a home automation system for my apartment so I finally think I am going to do it. I have a general idea of how it will work shown in the block diagram below:
I will have a bunch of wireless sensors scattered around my apartment that will gather data about temperature, light, occupancy…etc. These will probably use the Digi Xbee module I used on the quadcopter and will transmit their sensor readings back to a central server. I’m thinking right now I want these wireless modules to be battery powered so they are going to have to be very low power so that the batteries will last a long time. I think the first one I’m going to do will be a temperature sensor, but I will talk about that more on a later blog post.
I’m thinking I could do other wireless modules like maybe a light switch to turn on and off the lights. Some other ideas include modifying my room fans to be able to control them through my home automation network, and even connecting my coffee maker to it ;)
For the server right now I’m thinking of using an Arduino with an Ethernet shield and an Xbee module. Now I’m not the biggest Arduino fan but it makes a quick easy setup for a small lightweight server and gateway to my home network and the internet. The wireless modules will send sensor data to the Arduino which will post it to the web server. An alternative to the on board web server would be to use Cosm I haven’t looked into it too much but that could be an alternate place for the server to post the sensor data to. Possibly I will use the Arduino web server for a LAN web server to connect to when I am home and the Cosm server to view data when I am away from my apartment.
Anyway I have ordered an Arduino Ethernet shield and I will start by connecting a temperature sensor to it and working on setting up the sever portion before working on the wireless modules.
I have been wanting a little digital storage oscilloscope for a while now and have been thinking about getting the ever popular Rigol 1052E but when I found an ATTEN ADS1042C on Craigslist for $200 I thought that seemed like too good a deal to pass up. Overall for a hobbyist this looks like a very decent oscilloscope:
Dual Channel Oscilloscope
40MHz Analog Bandwidth
500M Samples/Sec with 1 Channel, 250M Samples/Sec with 2 Channles
4K Sample Memory
USB Device and Host Ports
Math +,-,*,/, FFT
It’s definitely an older technology scope with the lower sample rate and smaller sample memory than the Rigol 1052E but for most things a hobbyist would do this scope would do just fine. It powers up fast and greets you with this screen in about 8 sec which is nice because a lot of the newest modern oscilloscopes like the Tektronix DPO serieis scopes take forever to boot up and when you want to take a measurement you don’t want to have to wait for the scope to boot up.
The scope has a fan but it’s fairly quite, from reading around about people who have the Rigol 1052E apparently it has a very loud fan; I have never used one in person so I can’t compare to be certain. but I have no complaints about the fan noise on this scope.
On to some measurements:
The noise floor of the two channels looks to be very low <2mVp-p but I did notice a funny DC offset as seem in the picture below. The DC offset doesn’t go away even if the inputs are AC coupled so I think this has to be a hardware problem in the scope but it’s less than 2mV DC offset so that’s not too bad.
I don’t have the best tool for testing the limitations of this oscilloscope but it measures a 4MHz sine wave just fine, which is the max mu function generator will put out:
The last two pictures are taken from the oscilloscope and written to a USB flash drive which works great but is it horribly slow to write a picture to the flash drive, it takes over 1 minute to write one picture, the pictures are about 220KB so that’s a write speed of around 3kB/s which is slower than the write speed of a floppy drive. It also has a USB device port on the back to connect up to a printer or a computer. I tried to install the drivers that came on the CD but it wouldn’t install on my laptop, my guess is that they are for a 32But OS and I have 64bit Windows 7. I will have to look around online to see if I can find 64bit drivers anywhere.
The FFT function seems to work well as shown below, this isn’t a feature I have used much on oscilloscopes and usually for this sort of thing a spectrum analyzer is a much better tool anyway.
I will do teardown on a later post, I am interested to see what ATTENs build quality looks like.
Overall I think this is a very decent oscilloscope for hobbyist work, it’s definitely not the best one out there; I think the Rigol 1052E is probably better value for money if you were going to buy one or the other new but if you can pick up a used ADS1042C like I did I don’t think you will be disappointed. I will probably upgrade to something nicer eventually but this will suit me just fine right now. My only complaints are that little DC offset on the voltage measurements and the horribly slow USB host port, I haven’t looked around but maybe there is a firmware update that fixes that.