Holistic Detection

Measuring Supply Voltage

rsbohn — Tue, 29 Jul 2008 15:53:49 GMT

I'm running my latest handheld computer on solar power. It starts up when the sun rises and runs all day. I started wondering how I could measure the voltage coming in from the solar panel. I came up with a way to use a diode and a resistor and the ADC, but I wondered if there was a way to skip the ADC input.

I could time charging a capacitor, but since I don't know the supply voltage I don't think that would work. More voltage means more current, so the capacitor charges faster. On the other hand, when the capacitor discharges the time is based on the actual voltage. As long as the discharge resistance doesn't change I should be able to time it and get a reasonably accurate voltage.

I rigged up a test circuit using the Arduino. It charges the capacitor (33 uF) to 5 volts when I turn on pin 4. I let the capacitor charge for 1 second, then discharge it and measure the time until pin 4 goes low. The main discharge capacitor is 100K ohms.

I wanted to see what lower voltages would do, so I added a second 100K resistor on pin 3. This formed a voltage divider with the discharge resistor, so the capacitor would only charge to 2.5 volts. The software to drive this is cool: I set the charge pin (3 or 4) to output and drive it high. After 1 second of charging I turn the pin back to input mode. That makes it high impedance (but not high enough relative to the 100K discharge resistor...). Then I set pin 4 low and time how long it takes to read back as low. I'm getting about 172 milliseconds for 5 volts and 70 seconds for 2.5 volts.

I'm not sure about the input impedance of the Mega8 chip. I added another wire to pin 5 so I could charge the capacitor to 5 volts without switching the sense pin (pin 4) back and forth from input to output. When I did this the time went down to 160 milliseconds. I figure that the leakage back into the chip was the cause. All the resistances are in parellel. This means each time you add a pin to the circuit the overall resistance goes down. Perhaps keeping the charge pins high will change things.

Ten Pin ISP adapter

rsbohn — Thu, 17 Jul 2008 04:00:23 GMT

I've already built a six pin ISP adapter, but my Olmex cards use the ten pin ISP. I put a header on a scrap of perf board, added an LED for the heartbeat, and then connected the ten pin cable. Actually it is a fifteen pin cable, off a joystick adapter, but it works on one of my Olmex boards. I'll have to cut it down to fit the socket on the 28 pin Olmex board.

The 8 pin board has a 10 MHz crystal on it. I'm hoping that will give me a stable platform for my digital radio project (APRS to Morse Code).

Hello 5x7 Style

rsbohn — Tue, 17 Jun 2008 18:48:32 GMT

Wrote a new firmware for the 5x7 display. Now it scrolls out 'hello' over and over again. I'm running it on a solar panel, so it wakes up with the sun and runs all day long.

When I built the LED matrix I put resistors on the five columns. I'm starting to think it was a mistake. I like to light up a whole block at a time, and it makes sense to turn one row on at a time instead of one LED at a time. So if I had put in seven instead of five resistors I could have a five column refresh cycle instead of a seven row cycle.

The bitmaps for the characters are stored row-by-row. That way I can just load a byte from program memory and use it unprocessed to light the LEDs.

I might set the display sideways and then scroll it right to left. That would give me room for two 3x5 characters.

Provo, Utah

rsbohn — Mon, 02 Jun 2008 16:07:03 GMT

With a walkable downtown and access to two Universities, Provo Utah is a great location. I live next door in Orem.

Kipplinger: Provo: Pristine Tech Mecca (Video) (Text)

Another release of AVRISP sketch

rsbohn — Wed, 28 May 2008 22:48:14 GMT

There is a new release of the AVRISP emulation sketch for Arduino: avrisp.02.zip. This one should work with Mega8 and Mega168.

mega-isp

Sorting Out Page Sizes

rsbohn — Tue, 27 May 2008 17:31:05 GMT

There is a new release of AVRISP Emulation for Arduino. This is an Arduino firmware that allows you to program other AVR microcontrollers.

The new zip file (avrisp.01.zip) should compile on the current Arduino IDE, and I changed the comments that put the wrong labels on the SPI pins. Go ahead with this file if you use Tiny13, Tiny2313 etc. (any AVR with a 32 byte/16 word page size)

I'm building an Arduino for William on the Evil Mad Scientist business card. Monday I added the six pin ISP port to the card and built a cable for it. I took a 40 pin IDE cable and cut off one end of it. Then I soldered the other end to a pin header that I could plug into the Arduino.

I thought that my Mega8 chip was damaged because when I flashed it parts of the memory were not written. I tried using a fresh Mega168 chip and got similar results, so I took a second look at the software. When I developed the Arduino AVRISP emulation I was using chips with a 16 word page size. That means you write the flash 16 words (32 bytes) at a time. I had hardcoded that page size in my software. But the Mega8 uses a 32 word page size. My software would fill the zero page fine, then skip the bottom of page 1, resulting in the empty memory rows.
I already had the page size (AVRDUDE sends it to the programmer) so I just needed to change a function to return the correct current page based on the page size (instead of the hard coded 16 word page size).

It took some work to figure this all out. I even used Powershell at one point: I was wishing for a list of Atmel AVR chips with their flash page sized, when I realized that all the information is in avrdude.conf. I just had to find a way to summarize it. Powershell select-string saved the day select-string ("description", "paged", "page_size") avrdude.conf.

I saw that the various chips with paged flash use pages from 16 to 128 words, so I updated the current_page() function with the appropriate sizes and bitmasks. I would like to just calculate the bitmask, but with just a handful it was clearer just to return a value based on the current page size.

The updated code works with Mega8 (and should for Mega168 and other AVR Mega chips) and is available in the project SVN.

Flash Problems

rsbohn — Fri, 16 May 2008 20:56:03 GMT

I'm building a project using the AVR ATMega8 microcontroller. Once I got the thing wired up to where I could write firmware to it I found that it was always failing. I made a .hex file full of 0x10 values (256 bytes worth) and tried uploading that to the chip. The 0x20, 0x60, 0xa0, and 0xe0 lines were still blank (0xff). I guess the chip has some problems, so I rewrote my firmware to avoid the bad sections. I put the main routine at 0x30 and the sleep routine at 0x70. I found that the assembler uses word addresses, and that .org 0x70/2 is a valid address. I changed it to 0x38 just because the calculated address was weirding me out.

Then it also turns out I forgot to initialize the stack pointer (two bytes on Mega8 by the way). Got that fixed, adjusted the timing, and now it's working. Unfortunately I didn't select matching LEDs when I build the circuit board, so I think I'm going to start over with a new board, new LEDs and maybe even a fully functional Mega8 chip.

William's Arduino Board

rsbohn — Thu, 15 May 2008 13:26:05 GMT

I'm building an Arduino-compatible board for William. I'm building it on the Evil Mad Scientist MegaXX8 business card. It will have four built-in LEDs and a USB interface. It will also have connectors so he can use it with a breadboard. Perhaps we can connect it to some of his LEGO projects.

William wants a laptop. He thinks it would be cool if we could build one for him...

Cybord Signal Detector

rsbohn — Thu, 15 May 2008 13:20:24 GMT

Some digital radio signals use Frequency Shift Keying (FSK). This often has one frequency for a Mark and one for a Space. I plan to build a cybord or other chip that will decode an FSK signal, producing three different values: NO_SIGNAL, MARK, and SPACE. The signals would then go to a decoder chip to recover the original digital signal (a stream of zeros and ones).

Powershell Article on WindowsNetworking.com

rsbohn — Tue, 29 Apr 2008 13:40:01 GMT

Windows 2008 Powershell... on WindowsNetworking.com.

Nice to see more press for my favorite shell, but... the example commands in this article all use WMI. That's powerful but not the whole Powershell story. What about the drive providers? What about browsing and updating the registry? What about Get-Process and Get-Service? What about the .Net integration? I was disappointed with this article; it could have been so much more.

They do mention at the end that Powershell is more than a Windows Server 2008 feature. It is also available on XP, Vista, and Windows 2003. It really is more than a WMI wrapper and well worth your time to learn.

Blue Laser Pointer

rsbohn — Sun, 20 Apr 2008 23:00:42 GMT

DIY Blu-Ray Laser Pointer on Make Magazine blog.

Saw one advertised in Astronomy magazine (January 2008) for USD 1999.00. For a laser pointer? Seems like at that price they could include a DVD player.

(Tried to post this as a comment on the makezine blog. One has tried, one has failed; one can do no more.)

Nice work, I really like the constant current power supply.

Bynase on the Tiny2313

rsbohn — Sat, 19 Apr 2008 15:01:02 GMT

I put a bynase receiver on my Tiny2313 on the WOSP display board. I found an old source code that didn't work. It took me several hours to figure out how to get the LED driver code working. Now I can display the ramp chip in binary. I can also just put a long wire 'antenna' on the input and watch the lights flash. This could be a reasonable electromagnetic field detector!

But no, it's going to be part of the world's dumbest calculator. I still need to build the keyboard section which will read a bank of 8 switches. The current numeric input goes via bynase to the main processor. The plus and minus switches connect directly to the main processor.

The keyboard won't be a real bynase system because it won't have the pull-up resistors disabled. I'll probably put a switch in that line and a socket where you can plug in real bynase networks (or long-wire antennas). So the system is a dumb calculator but a usable bynase display.

Cybords Rule

Cybord PWM converter

rsbohn — Thu, 17 Apr 2008 13:52:23 GMT

I've built a cybord to PWM converter. It takes the bynase value on PI and converts it to a PWM signal on OC0A (Tiny13 pin 5). I hope to add the bynase-in code to my Tiny2313 display driver.

The current cyboard part runs at 1MHz on the Tiny13 chip. I'm driving it with the ramp generator I mentioned yesterday. I found that putting an LED on the PO line messed the signal up. Have to use a different pin (there are three more on Tiny13) for monitoring. Right now the PWM output is driving an LED, it goes from dim to bright, but when it goes dim again it sometimes goes dim in two steps instead of one. I suspect there may be a timing issue somewhere.

My PWM converter doesn't have PO at the moment. I should probably add it for completeness. I might try the Dice cybord and connect it to my PWM converter to see how that works.

When Cybords Attack

rsbohn — Wed, 16 Apr 2008 18:12:16 GMT

Cybords by Ward Cunningham.

I think I might use Bynase in my "World's Dumbest Calculator" project. I don't understand cybords, but I want to. I got the bynase2.inc file and built a simple cybord on a Tiny13 chip. I figured a ramp would be a good thing to have, so my first try was as follows:
main: inc byout rcall byop rcall bydle rjmp main

I put an LED and a current limiting resistor from PO to ground. Worked like a lead balloon (not at all).

Sat and thought awhile. Part of my problem is I don't understand how to debug these things. Perhaps I should download the pre-defined cybords and see if I can get them working.

After some thought I decided to slow my ramp down. I have a 256 count delay (decrement R17 until it underflows, then decrement byout). Not much better. So I changed it to decrement byout every fourth time through the loop. Now it goes from dim to bright slow enough to watch it. I put the voltmeter on PO and it was going from zero to about half a volt.

Took another look at the specification on c2.com. Bynase puts a high signal than waits hundreds of counts before repeating. I guess in a way I'm doing a very low-level PWM signal. So the LED lights up but not as much as I want. My next step is to add a second cybord chip that listens to signals on PI and translates the value to a real PWM signal. Have to figure out the settings for the timer to do PWM. Or I could just get the TV output ported to Tiny13. The ValueFilterMeter would help me see what is on the bynase circuit.

Eventually I plan to have a Tiny2313 read the 8-bit input switchbank and send the calculator status on two bynase signals. One for the input number and one for the accumulator. The Tiny2313 already on the display board will read the bynase signals and update the LED outputs.

uC Hobby and Wright Hobbies

rsbohn — Mon, 14 Apr 2008 19:29:52 GMT

uC Hobby and Wright Hobbies have a contest running. You could win a set of prototype circuit boards as shown. I'm hoping to win a set to use in my "pocket full of random bits" project.

uC Hobby: Six Prototype Boards

Updating my Profiles

rsbohn — Fri, 11 Apr 2008 16:27:13 GMT

Spent some time this week updating my profiles across the internet. I've got so many of them! Just ask Google.

Here's a new blog I like to follow: Digging Up Bohns.

This weekend I'm hoping to finish a project, the world's dumbest calculator. Just the thing for all your 8-bit arithmetic needs. I'll probably plant some peas in the garden also.

404 - Date Not Found

rsbohn — Fri, 04 Apr 2008 17:12:35 GMT

Suggestions:
-Try again tomorrow
-Use an alternate calendar

Clifford Stoll at TED 2006

rsbohn — Wed, 02 Apr 2008 12:05:08 GMT

Just saw this:

Clifford Stoll at TED 2006.

This guy is amazing!

View Adobe Illustrator Files

rsbohn — Fri, 21 Mar 2008 14:06:57 GMT

I just downloaded some files that were Adobe Illustrator images. How to view them? Turns out Adobe Reader (formerly known as Adobe Acrobat Reader) will display them. Looks like support for .ai files goes back to Acrobat Reader 6 at least.

Just thought you might like to know.

Relax with Powershell

rsbohn — Thu, 20 Mar 2008 15:52:34 GMT

I work better if I pause and stretch every 15 minutes or so. Here is how I use Powershell to help me remember:

while (([int]([datetime]::now).timeofday.totalminutes) % 15 -ne 0) { sleep 59} ; relax

My relax function wakes Merlin up and sends him scooting across the screen. So I get an audible and visual alarm every 15 minutes.

Arduino-0010 and arduino-avrisp

rsbohn — Thu, 20 Mar 2008 05:33:25 GMT

A defect was reported on the google code site for my arduino avrisp emulation. Seems to be specific to -0010 (or at least post -0008). Put a fix in svn, will publish a new zip after I get it tested.

Powerpoles

rsbohn — Sat, 15 Mar 2008 14:10:20 GMT

I'm building a power supply for Williams 2 Meter radio. Found a good article on using Anderson Powerpoles.

Anderson Powerpoles on flyrc.com

EMS Labs Biz Card

rsbohn — Wed, 05 Mar 2008 21:36:55 GMT

The Evil Mad Scientists are back.

Just ordered a five pack of boards!

Blinkenlights Video

rsbohn — Mon, 03 Mar 2008 16:10:28 GMT

Dark Activated Blinkenlights from Randall Bohn on Vimeo.

Readerboard LED Display

rsbohn — Mon, 03 Mar 2008 15:40:01 GMT

Found this on google: a 12x7 display driven by the ATTiny2313. They use the 74HC595 serial to parellel chip for the column drivers, and use transistors for the row drivers.

Readerboard by CPU Ready Consulting

My current firmware for my 5x7 board lights one LED at a time. I'm wondering if I could light a whole row at a time instead. My current limiting resistors are on each column, so it works better driving a row instead of a column. I used 330 ohm resistors, giving 15 milliamps per column with one LED on, that makes 75 milliamps out the row driver if all the LEDs are on. Too much to leave it on, bur perhaps the duty cycle is low enough I can get away with it...

Anyway I'm hoping to post a video of the blinkenlights firmware running sometime soon.