Friday, July 29, 2011

TS1001 Enabled Low Power 555 Timer Design

Touchstone Semiconductor TS1001 Coolest Opamp Design Contest Entry

I thought it would be fun to redesign the 555 timer using two TS1001 Low Power Opamps as comparators. The goal was to make the 555 Timer run on supply voltages below 1V and less than 5uA, so I could use a “fruit” Battery or Solar Cell to power the 555 timer in astable mode.

I started out by running some quick simulations with LTSPICE to prove out my circuit and size the resistors accordingly, so I could meet my 5uA current draw limit.
At the time of this contest no SPICE file was available for the TS1001 Opamp, so I just used the “Universal”  Opamp in LTSPICE; the majority of the current draw in my circuit is from the charge/discharge of the capacitor anyway.

I quickly made up a breadboard version of my circuit and tested it out to prove the concept.
I have two TS1001’s as the comparators and a Texas Instruments SN74AUC2G02 Dual-Nor Gate for the SR Latch.

I used DesignSpark’s PCB CAD program to create a Schematic & PCB of the 555 timer.

 Below I have my Low Power discrete 555 Timer running off an orange at 0.87V @ 4.4uA. 
Below is the square wave output of the 555 timer and the charge/discharge of the capacitor. This circuit is running at 18.4Hz. 
That is one of the downsides with this circuit; I was able to get it to run at a max output frequency of 525Hz with a 1V supply voltage before it pooped out. That is the whole power vs. performance trade off. Diodes Inc. has a Low Power 555 (ZSCT1555) that runs up to 330KHz @ 75uA; mine runs at 18Hz at 4.4uA… trade-offs.

I was also able to get the 555 timer running off of a Solar Cell pulled from a Light up Lawn Ornament. 

I hope you enjoyed my project entry; I had a lot of fun and learned a few things along the way.

DesignSpark Schematic & PCB files:
Gerber files:
LTSPICE files:

Saturday, July 23, 2011

Everything Including the Kitchen (current) Sink!

With almost every project/design I work on there is a switch-mode PSU that needs testing. In order to quantify the switch-mode PSU's performance you have to load it down to typical and worst case load conditions. This will allow you to make sure the Inductor is properly sized, the ripple current is acceptable, and just to make sure the supply is stable. In the past I would either grab a variable power resistor box or buy some 25Watt resistors and just make a load brick for the project.

The down side with using resistors as loads is you have to buy new values of resistors for every supply voltage you are testing. There has to be an easier way.... and there is!

I got the idea to make a variable Current (Sink) Load from watching one of Dave Jone's EEVBlogs.

This Variable  Current Load takes out all the "Ohm's Law" guess work when applying loads. If I need a 0.5Amp load, I just adjust the pot to set 0.5V across my 1 Ohm Current Sense Resistor and I have a 0.5Amp load irregardless of the Load Voltage. The Load voltage could be +3.3V, +5V, +12V, +24V and I still have a 0.5Amp Load...GREAT!
I grabbed some spare parts I had in my lab and an Altoids case and started hacking. I stacked 3 different size heatsinks and attached them to the pass FET; this will help pull the heat away better.

The terminal block provides the +10V, 0V, and -5V supply voltages. The Bar Graph panel meter displays the load current from 0-5Amps. Below I am using my Current Load to test a Linear Tech Flyback PSU eval board..

This was a fun project and the current sink works really well. The 10 turn pot allows some pretty precision current settings. I am pretty pumped to use my new Variable Current Load on Monday to test my new project at work.

Friday, July 22, 2011

Super LDMOS RF Transistor

I wish I would have had these parts when I was working on that 100W 900MHz Microwave Generator project 5 years ago.... I would have burned up a few less $30 transistors.

Wednesday, July 20, 2011

Arduino DS1621 Based Temperature Monitor

I just got some DS1621 I2C 5V PDIP-8 Temperature Sensors and with a quick google search I found some code from Jon McPhalen.

I added my LCD screen code and a Celsius to Fahrenheit float conversion and I had an easy Temperature Monitor built up in less than a 30mins. Fun lunch hour project! .... Now back to work :P

Click the link below to get to my modified code:

Now I have to clean up the code and combine the Real-Time-Clock and Temp Sensor into one build... but that is for another lunch hour;P

Sunday, July 17, 2011

DesignSpark PCB for Touchstone Contest

Well I finally finished up my PCB for my entry in the Touchstone Semiconductor TS1001 Design Contest... and not a moment too soon (the deadline is July 29th). I ordered a 5 day turn on the PCB and next day shipping from and should have just a couple days to build it up, test it, and get my video done for the contest.... always cutting it close.

This was my first PCB done with DesignSpark and I have to say I am pretty impressed. I easily created new library's for my custom components, edited the DRC rules, and kicked out some Gerber and drill files. I don't think DesignSpark has the full capabilities of EagleCad, but for just kicking out protoboards I am happy with DesignSpark.

Thursday, July 14, 2011

Work Hard.... Play Hard

Well I believe I have officially solved a doosy of an electronics problem, which now seems pretty obvious (Isn't that always the case).

I have been banging my head against the wall for weeks trying to understand why a bit of RF noise in the 100MHz range would cause a product I was working on to lock up? Also once I fixed that issue, why one type of display would work and the other would break?

It all boils down to the two displays even though schematically the same used different amounts of ITO to connect the SDA line and GND line of the Chip-On-Glass LCD controller to the metal flex cable. That increased resistance on the SDA & GND line (~400 Ohms on one display and ~200 Ohms on the other) casue the Ack I2C signal coming back from the LCD controller to read as a logic "1" instead of the proper "0". By changing the SDA & SCL to higher value pullups on the display the ITO resistance effect is less noticable. Obvious now right :p

Well I am going to celebrate with one of my favorite beers (Crow Peak Porter brewed in Spearfish, South Dakota, USA) and sulk a bit because I now have a lot of work ahead of me documenting this issue and updating the three pieces of my design that now need correcting.

Sunday, July 10, 2011

Free Beer Tomorrow.... The Sequel

Back in Sept 2010 I blogged about some of my favorite "Free" software tools and over the years I have just found a ton of neat tools that people have freely distributed, so here are some more!

I am defiantly a Texas Instruments Graphic Calculator lover. Even though I do have several Slide Rules... and know how to use them; I pick up and use my TI-89 daily.
I found this Virtual TI Calculator Emulator written by Rusty Wagner. This program uses a ROM image from the actual TI calculator and emulates it on a PC. He has also provided some picture "skins" to match the actual calculator.  This program comes in real handy when I'm in the lab or out of the office without my calc and need to crunch some numbers.

I've never been much for RPN calculators, but I do love the HP calcs easy Unit conversion function. This was one of the huge disappointments with the TI-89; you have to actually go into menus to assign units to be able to convert them; the HP calc does it with a couple quick button presses.  Below is a screen shot from the EMu48 HP Calc Emulator by Christoph Giesselink.

It has been a couple years since I've spun a set of PCB Gerbers for a home project; I've been busy trying to save the USA's Social Security program by having a few kids!

I was pretty familiar with Cadsoft's Eagle CAD but I figured if I am going to switch tools I might as well do it now while I am rusty. I downloaded and have started making a board with RS Components DesignSpark PCB. and I have to say for a Schematic/PCB tool that has no limitations on PCB size and is free.... I am impressed.

DesignSpark's Library and tool wizard is really intuitive and the pdf tutorials that come with the software are great. I would highly recommend checking out DesignSpark for an entry level SCH/PCB tool.

Friday, July 8, 2011

Ridiculously Simple Arduino LCD Clock

Well I got my Arduino Uno board a month or so ago and I've been dying to build up a quick project. I already got my Parallax Serial 16x2 Character LCD up and running, so I thought a simple add-on would be a basic Real-Time-Clock. The Dallas/Maxim DS1307 is a 5V I2C based RTC that looked pretty popular.

I soldered up the DS1307 to an Ardunio proto board and placed a CR2032 Coincell holder on the bottom. It fits nicely in between the boards when they are stacked.

(Schematic from

A quick search on Google brought me to Maurice's software and a cut and paste later with a few LCD tweaks I had a working Arduino LCD Clock. Too simple; this literally took me less than 30mins to throw together.... I did this over a lunch hour and still had plenty of time to finish my sandwich :-)