Halloween Hacks!!!

I haven't had much time this month to work on my fun pending side projects: repairing and calibrating my Analogic AN3100 Voltage Standard, Repairing my Tektronix Type 491 Spectrum Analyzer, and cleaning up my Arduino based Function Generator code. My day job is getting in the way..... but my day job pays the bills so that is ok!

Below are some really cool Halloween Hacks I found on YouTube.

Happy Halloween!

Cool Design Idea of the Week - Power Selection Switch!

I was flipping through the latest issue of Electronic Design while flying back from Austin, TX and I came across a not obvious neat idea. On one of Parallax's Basic Stamp boards they intentionally placed the DC Power Jack in a location that would be blocked if a 9V Battery was installed.... thus preventing the 9V battery from getting reverse current if the DC Power Jack was plugged in as well. Brilliant!

It must be the EE in me but I would always think of adding a diode "OR", some FET, or a terribly complex circuit that disconnects power to the 9V battery when the DC Jack is plugged in. This approach, though not practical in all cases, is elegant and wins my Cool Design Idea of the Week award!!!

7400 Series Logic PLL Based Switch-Mode PSU

While building up a simple Seven-Segment LED Up-Counter Circuit a few weeks ago as a brain storming exercise, I thought a cool 7400 Series project would be to build up a "Buck" Switch-Mode Controller out of Logic Gates.

I had built up a few Analog & Digital PLL's before and I thought that might make a neat starting point for a switch-mode controller. Essentially a Digital PLL requires a Reference Frequency (Square Wave), a Digital Voltage-Controlled Oscillator, a Phase Detector (XOR Gate) and a Low Pass Filter. The Reference Frequency and the VCO outputs are the inputs to the XOR Gate (Phase Detector). The output of the XOR Gate is then feed into the Low Pass Filter which creates a DC error voltage. This error voltage is then feed into the VCO input; creating a feedback connection. As this circuit runs the error voltage will settle and the output of the VCO will become the same frequency as the Reference Frequency. What if the Low Pass filter was a typical Buck - Transistor, Diode, Inducator, and Output Cap. and the error voltage was the Output of the Buck Regulator? ..... that was my starting point anyway.

Below is what I came up with:

I built up a 90KHz reference Ring Oscillator using two 74HC04's. Then I built up a XOR Gate using 5 NAND 74HC00 gates. The VCO is based off the same 90KHz reference Ring Oscillator, but I added a capacitivly coupled MV2109 Varactor to vary the frequency when a DC voltage was applied through the 100K pot adjustment. The 5.1V zener diode was a vain attempt to prevent the Vout overshoot from affecting the VCO's output.... I'll explain this more later.

I used a TIP106 PNP transistor, a B321 Shottkey Diode, a 38uH 3A Inductor, and 3x47uF electrolytic caps as the "Buck" (filter) circuit. Since my XOR gate output was referenced to ground and the PNP transistor needed a Vinput based reference I used a 2N3904 NPN to couple the XOR output to the PNP.

Results:
I was able to get the basic converting circuit working. I used 16VDC as my input voltage and then adjusted the 100K pot to bring the VCO frequency closer to the Reference Frequency of 90KHz and I got 5VDC on the output.

 Below are the waveforms:

Issues:
With the feedback disconnected  (Vout to the input of the VCO) I was able to get the circuit to convert a 16VDC input voltage down to 5V reliably. With the feedback disconnected though any change on the input voltage will be seen on the output voltage and any load fluctuations will effect the output voltage as well. I wasn't able to get the VCO's output to stay stable enough when connected to Vout for regulation to work. The XOR Gate is a phase detector not a frequency compare; this means the output of the XOR gate when the VCO is 88KHz is pretty much the same as 92KHz. This is the overshoot problem I was hoping my Zener diode would take care of, but my VCO wasn't stable enough to not have the frequency overshoot and dialing in 5V was nearly impossible with the feedback hooked up.

Someone wise told me that "Experience is what you get when you didn't get what you wanted"... I got a lot of experience on this project. The XOR Phase Detector is probably not the right component to be used in this circuit since the phase polarity can not be distinguished and thus overshoot and run away is a problem when the feedback is hooked up. I ran out of time before the 7400 Series Logic Contest deadline, but I am still entering the "non-regulating converter" since I was able to get the 16VDC to convert down to 5VDC reliably (as long as the input voltage and load are constant).

Maybe I'll have an epiphany or  kind reader will give me some hints as to how to prevent the XOR Gate Output from switching when the frequency of the VCO is greater than 90KHz in the coming weeks.

EEweb Pulse Magazine Cover... Who is that guy!

Very Cool, I just had the neat opportunity to be on this month's EEweb's Pulse Magazine Cover. In the article I got the opportunity to discuss some generality's of my day job as a Design Engineer for a Weigh Scale company.... sorry no specifics about my latest and greatest project, our competitors probably read this magazine too. I also got to talk about some of my side projects and my Touchstone Semi. opamp design contest entry. Check it out!

Thanks EEweb for the opportunity!

The Benefits of Ancient Logic

I was catching up on reading my trade rag magazines from when I was in China the past week and a half and I came across this article on the benefits of 4000 Series CMOS Logic in today's designs. I thought it was ironic timing considering Dangerous Prototypes 7400 Series Logic Design Contest deadline is coming up..... I need to work on my entry. (I got all the pieces now I just have to build it and get it to work... the easy part!)

Enjoy!
The Benefits of Ancient Logic (Analog Devices: James Bryant)