Jay's Technical Talk » Technology

Boost Converter Schematic

Jay — Sun, 22 Jan 2012 14:43:56 +0000

I have drawn up a schematic (click to enlarge) of the high current and sensing portions of my maximum power point tracking (MPPT) 2-phase boost converter battery charger circuit. The schematic does not include the micro-controller, MOSFET gate driver IC, and associated power supplies, as those items are on the (relatively) low-power side of things.

What do all of these things do?

L1, Q1, and D1 – These three components make up the heart of the boost converter. When Q1 turns on, power builds up in L1 as the current rises. When Q1 turns off, all of that power exits via the only available route (out past D1) and the voltage is boosted as the inductor (L1) resists the current change. If you turn Q1 on and off very quickly (under control of the micro-controllers’ PWM output via a MOSFET gate driver) it raises the output voltage higher than the input voltage.

L2,Q2 and D2 – See L1,Q1, and D1 above. These three guys act in the same way, but Q2 is turned on and off 180 degrees out of phase from Q1. So while one half of the circuit is drawing power in, the other half is pushing power out, and visa-versa. This doubles the power capacity of the circuit, and reduces the size of the filter capacitors that are needed, as they are shared between the two phases.

C1 & C2 – Ceramic & Electrolytic capacitors that work together to filter the input power (i.e. they provide short bursts of current needed when Q1 or Q2 turn on)
C3 & C4 – Ceramic & Electrolytic capacitors that work together to filter the output power (i.e. they absorb the short bursts of current leaving L1 and L2 when Q1 or Q2 turn off)

R1, R2, and C5 – Voltage sensing. R1 and R2 are a classic voltage dividing resistor network. Because R1 is so much larger than R2, the high voltage output (up to 200 volts) is reduced to a low voltage output on the “VOLTAGE SENSE” output (between 0-5 volts), suitable for a microcontroller input (A2D) pin. Because it is coming out of a switching boost converter, the output voltage has a lot of noise in it, so capacitor C5 helps to reduce this. I still had to make multiple sense readings on the microcontroller input pin and average them to get a reliable reading. I expect that if I made an analog low-pass filter on the voltage sense output it could fix this with a higher component count.

R3, U2, R4,R5, Q3 – These are the current sensing subsystem. R3 is a 0.1 ohm 5watt resistor that is acting as a current shunt. 1 amp flowing through this resistor equates to a 0.1 volt drop from one side of the resistor to the other. U2, the AD8212 chip amplifies this small voltage, and together with Q3, converts it to a low voltage signal suitable for a microcontroller A2D input pin. Currently R5 (at 100K) is set up for a 100x gain in the amplification, but I may reduce that as I start to test at higher power levels.

In reality, I have not yet soldered D2 and Q2 onto my pref-board, so the circuit is currently a single phase boost converter. This is fine, as I am not yet testing it at full power and my current microcontroller isn’t powerful enough to output a proper 2 phase control signal anyways. On the software side, I have gotten my micro-controller to regulate the circuit to output a (relatively) constant voltage regardless of the input voltage by controlling the PWM duty cycle. I have measured the current-sense output using a multi-meter and it is working, but I have not yet integrated current sensing into the control software. Here is a picture of the pref-board. The current sense module is still on a solder-less breadboard next to it.

My lack of progress on the software side is due to a lack of the proper development tool (PIC Kit 3) which is required to program the newer PIC microcontroller that I selected (PIC16f1824) to drive both phases of the boost converter. When I ordered the new PIC’s I didn’t read the specifications closely enough and just assumed that my eight year old PICKit1 would be able to program it. Silly me….Apparently Microchip has made some improvements in the last eight years. Of course, when I got the new chips, I ripped my code apart to make it work with the dual ECCP PWM modules and faster internal clock, and by the time I figured out that I couldn’t program the new chip I had already gotten the code to a state where I didn’t want to reverse all of my changes just to be able to play with the old microcontroller for a few days until the new programmer arrived. On the plus side, the new chip has an internally generated 32Mhz clock which will (eventually) let me run two PWM channels 180 degrees out of phase with a duty cycle of 125 kHz and 8 bits of resolution. It also has a UART, so I can easily use a serial LCD module for displaying status information.

Using the Microchip PIC Kit 1 with Linux

Jay — Sun, 01 Jan 2012 22:15:40 +0000

The PICKit 1 is a combination programmer and development board for midrange PIC micro-controllers. In addition to being able to program FLASH pic devices, it also allows them to run and access 8 (charlieplexed) LED’s, a pushbutton switch, and a potentiometer. It’s a great little board for learning the basic of micrcontroller programing, but unfortunately it is not supported by Microchip’s new MPLAB X software (that is written in Java, and supports Linux/Mac in addition to Windows).

You CAN however use the PICKit 1 under linux. The piclab software is supposed to support it (I have not tested this). I use version 1.6 of the PicKit1 flash usb programmer for unix. Even the newest 1.6 version reports checksum errors after writing the hex file, but it does work correctly.

To make it work as an external program in MPLABX I had to select the “format HEX file for download” option under the Linker so that it would not fill all 2048 flash bytes when the program was smaller than that. I am able to manually run the usb_pickit command after building to flash the code, but it’s kind of annoying, as that program has a problem verifying the checksum and reports an error every time (which is interpreted as a build failure) plus, I have to run mplab X with root permissions to be able to access my USB port.

Solar Panels on the Electric Truck

Jay — Wed, 16 Nov 2011 10:16:13 +0000

I purchased two used GE Energy GEPVc-175 watt solar panels and mounted them to the bedcover of my truck using 10-24 machine screws and T cone washers as rubber vibration dampers. Each panel weighs 31 pounds, and is rated to deliver up to 175 watts of power in full sun (at around 36 volts each, or 73.4 volts at 4.7 Amps in series). I am still waiting on a group of Georgia Tech ECE students for the magic box that does maximum power point tracking (MPPT) and voltage boosting to charge my 120 volt battery pack, but I hope to be generating 1-3 miles of my daily commute from the sun soon. As my daily commute is 4 miles, this can be a significant percentage of my total energy usage.

I have calculated that in the summer the panels are far enough behind the cab that they will not be shadowed by it, even if I have to park facing south. In the winter and early spring / late autumn I need to park facing north to avoid shading a strip of the solar panels.
I still need to figure out a way to tilt the panels towards the sun to collect as much energy as possible. This is especially critical during winter, when the solar angle is way off of vertical. As the bed cover tilts, AND the bed of the truck can tilt (the other way) I figure I can work something out (with a few pieces of wood cut to the correct height, or linear actuators if I want to get fancy.

Ferrofluid Sculpture test 2

Jay — Mon, 07 Nov 2011 01:28:50 +0000

After buying some strong rare earth magnets I re-tried my ferrofluid levitating sculpture. The main problem is that the ferro-fluid moves to the poles of the magnets (top and bottom, with gravity favoring the bottom) and does not surround the sides of the magnets. It was also hard to get enough small magnets to fit under the main magnet (as they repel each other), so I had to include a screw in the middle to get the weight correct.

Note: Working with Ferro-fluid is dirty and messy. If magnets snap together they can throw dark oily fluid which stains just about anything. Be sure to have lots of paper towels on hand, jars/shields under/around everything, and don’t work in a nice room. Dish detergent and abrasive scrubbing will eventually get it off of most surfaces that are not porous. Wear disposable rubber gloves and use disposable pipettes. Wear disposable clothes. Don’t use any of your wife’s kitchen appliances or instruments that you can’t afford to replace.

Update: After floating under the magnetic levitation for 24 hours, the ferro-fluid became much less “spiky” and eventually the drops at the end of the magnets became spherical.

Also, cleaning ferrofluid from a magnet is almost impossible.

Tracking individual battery voltages

Jay — Sun, 16 Oct 2011 19:14:37 +0000

This graph shows the voltage (multiplied by 10, so 65=6.5 volts, and 50 = 5.0 volts) batteries 1-6 of my electric pickup while accelerating. My first battery (blue) is consistently 0.1 volt below the others, so I am keeping an eye on it. But this graph shows that although it is a 1/10th of a volt lower, it does not sink lower than the other batteries under load, so it appears to be holding up well so far.

The graph also shows off my new (to me) Pak Trakr system. The Pak Trakr system connects to each battery in your pack with small remotes that daisy chain together. Each remote monitors six batteries and transmits the voltage levels once a second to a display and optional serial data logger.

Ubuntu 10.04 AMD Radeon M6 chipset and Extron Electronics video multiplexer

Jay — Sat, 24 Sep 2011 00:37:29 +0000

After working perfectly for 4.5 weeks with the same podium setup, my Thinkpad X31 laptop refused to output VGA video to the Extron Electronics video multiplexer box at school.
It appears that the Extron Electronics box is not sending out proper Extended Display Identification Data (edid) which tells the laptop what resolutions it supports. My xrandr command finds the data for my laptop video display screen, but not for the VGA-0 port:

VGA-0 connected (normal left inverted right x axis y axis)
LVDS connected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   1024x768       60.0*+   60.0
   800x600        60.3     59.9
   640x480        59.9     59.4

I have no idea why this started today. I don’t remember applying any patches to X-org in the last two days, and the technicians in charge of the podium swear that they didn’t change out anything.

I figured out a fix to make it (mostly) work. Tell xrandr to go ahead and force the VGA-0 port to a specific resolution with the following command:

 xrandr --addmode VGA-0 1024x768

This mostly works, but the sync signal is slightly off, leaving a black bar of 20-30 pixels on the left side of the screen. It is also annoying to have to run that command every time I want to display to the podium.

NetMedia iViewHD 2M POE Camera Review with ZoneMinder

Jay — Sun, 31 Jul 2011 11:17:33 +0000

I have recently purchased a NetMedia iViewHD 2M power over Ethernet (POE) camera (retail price $105) for use with ZoneMinder.

This small camera must be hard-wired into a switch that provides power over Ethernet (which will cost another $80-100, but allows you to power up to 4 POE devices). I bought mine used, and plan on buying (up to three) more, but not at retail prices. If I find a similar POE camera with a better lens at the same price I would probably try it out, but at used prices the NetMedia iViewHD 2M is a good deal despite my image quality complaints below.

Image Quality
Note that the fancy looking lens in the image is actually a sticker around a small (almost pinhole really) plastic lens that would not look out of place on a cell phone. That being said, I have been mostly happy with the image quality for the price. The camera has a 2 Mega-Pixel sensor which provides images up to 1600×1200 in size. The large images look good, but are unsuitable for security systems due to the relatively long exposure time the small aperture requires. This leads to motion blur on important things such as people walking by. This motion blur happens even in full daylight with the camera set to “best for day” frame rate and exposure settings. If you want to make a time lapse movie of a construction site or flower bed growing at 1600×1200 the iView HD 2M will work great, but don’t expect to get usable images of things in motion at the highest supported resolution. I have found that by using it set to 1024×768 resolution the exposure time is small enough to capture good pictures of moving people. (I have not yet tried it on cars.) This is still 2.5 times the resolution of a typical 640×480 network camera, and looks very clear when displayed full-screen on a 720p TV monitor.

Using it with ZoneMinder.
As this is a megapixel camera, you are likely going to need to increase your maximum amount of shared memory that can be allocated at a single time (/proc/sys/kernel/shmmax) before you can use it. The camera works well with ZoneMinder using the “single image” grab url:

/image.cgi?CAPTURE=YES&STREAM=0&COMMAND=

When I tried turning on MJPEG (STREAM=1) the connection would “glitch” several times a day leading to phantom events. Not a show stopper, but things appear to just work better for ZoneMinder when dealing with single image capture. I have not measured which (stream or single images) setting uses more CPU time on the ZoneMinder server.

On-Dash voltage guages

Jay — Mon, 16 May 2011 01:01:42 +0000

I received a VWRAS2-D12-D9-SIP isolated DC/DC power adapter from Digikey and built an updated voltage gauge module with dual gauges (one for the 12 volt accessory pack, and one for the 120 volt traction pack). The gauges were slightly too large to fit inside the dash, so I built an enclosure out of craft plywood that sticks out flush with the bottom of the radio.

One of my best decisions while building it was to use a tow light plug inside the dash that allows for easy removal of the gauge unit for updates, fixes, and general repair. This was very useful because the accessory voltage gauge did not work correctly at first. Unfortunately, the “isolated” power supply was not isolated enough for my 12 volt gauge. The first one gave inconsistent results and eventually fried. The second one I bought had the capability to use either a 5 volt power supply with a common ground or an isolated 9v supply. I tried it with the VWRAS2-D12-D9-SIP and it had the same problems, so I broke down and added a 5v linear regulator to power it using the shared ground mode. Problem solved. In the photo below you can see the two power regulators soldered up dead bug style and the back of the gauge holder.

One fun but unplanned feature of this system is that it has a “heads up” mode at night. The red LED traction pack voltage display is positioned so that it reflects off of the back window, directly into the field of view for the rear view mirror. So at night I can read the voltage gauge by quickly glancing at the rear view mirror.

Update: I have upgraded this system again with self powered digital panel meters.

HOWTO: Full Disk encryption on Ubuntu 10.04

Jay — Sat, 26 Mar 2011 21:15:15 +0000

How to set up an entirely encrypted disk using Ubuntu 10.04 (LTS):

Use the Alternative installer (text based) ISO image so that you have access to the LVM and Encrypted Disk options.

Assuming you want to keep a windows partition or some other pre-existing partitions intact, you will have to manually partition things instead of using the guided partitioner, so select “manual”.

Set up two partitions. One will be your /boot partition and should be around 250MB. This is the only data that will be unencrypted on the disk. The other will be your encrypted volume, that will hold an LVM physical volume that will contain all of your other partitions such as your swap partition, / (root) partition and any /home /var etc partitions that you want to set up. You should select “Use as:” “physical volume for encryption” when setting it up.

Then go back up to the top of the menu to the “Configure Encrypted Volumes” option, select the large partition and set up a pass-phrase for it.

This will create an encrypted volume (defaults to using ext4). Select it and change the “Use as:” to “Physical volume for LVM”

Now, go back up to the top of the menu to the “Configure the Logical Volume Manager” option. Create a volume group (vg0 is as good of a name as any) using the /dev/mapper encrypted volume you created above.

Create a logical volume (I named mine “swap”) that will hold your swap partition. It should be at least as large as the maximum amount of RAM you ever intend on installing in your computer if you want to suspend to disk (hibernate).

Depending upon how many other partitions you want (one big root, or /home and /var, etc…) create other partitions using the rest of the space inside of your LVM volume group.

Once you leave the LVM configuration area, you will see all of the LVM logical partitions that you have created. Select each of them and configure their mount point and file system type. (or use as Swap in the case of your swap partition.)

Write everything to disk (which will also format partitions) and you are ready to continue with the rest of your installation!

S-10 Electric Pickup

Jay — Sun, 27 Feb 2011 23:26:51 +0000

Our new commuter vehicle (and my new toy) is a second-hand electric conversion S-10 pickup. We purchased it from the original converter after he had upgraded to a Ford Ranger EV.

It is powered by 20 six-volt lead acid (PbA) golf cart batteries wired in series, giving a nominal 120 volt system. Sixteen of the batteries are stored in boxes under the tilt-up pickup bed. The remaining four batteries are under the hood, where the radiator would be on an internal combustion engine (ICE) vehicle. It can be charged via either the QuickCharge 120V charger plugged into a standard 15Amp outlet (which takes 13 hours) or the Zivan NG3 high frequency 240V charger (which takes 7 hours and a 240 volt outlet).

The traction batteries power a Curtis 1231C motor controller rated at 500 amps driving an FB1-40001A series wound motor that generates up to 90 HP. Also under the hood is a 12v accessory battery that is continuously recharged from the 120v traction battery pack by a MeanWell SD-350D-12 DC/DC converter.

Future projects include:

Digital volt meter on the dash
A 120 volt external plug for the convenience charger.
Larger capacity vacuum reservoir
Vacuum Gauge in the instrument cluster
LED Daytime Running Lights
Temperature sensing in the battery boxes
Switch to selectively silence the back-up beeper when reversing in the morning