Bot Thoughts

JTAG ICE MkII Pinout

2012-01-27T07:00:00.003-07:00

So, you lucky soul, you have a JTAG ICE Mk II on the bench. And you're sick of trying to remember which squid cable wire color corresponds to MISO, MOSI, SCK, RESET, Vcc and GND for ISP (In-System Programming) your AVR? Me too. Here's a table that should help.

Squid			ISP		ATmega
Function	Squid Pin #	Color	Function	ISP6 Pin #	328P Pin
TCK	1	Black	SCK	3	19
GND	2	White	GND	6	8,22
TDO	3	Grey	MISO	1	18
VTref	4	Purple	Vcc	2	7
TMS	5	Blue	nc	nc	nc
nSRST	6	Green	RESET	5	1
Vsupply	7	Yellow	nc	nc	nc
nTRST	8	Orange	nc	nc	nc
TDI	9	Red	MOSI	4	17
GND	10	Brown	nc	nc	nc

Sources:
http://redmine.ruinwesen.com/projects/golem-public/wiki/JTAG_ICE_MKII_pinouts
http://www.atmel.com/dyn/resources/prod_documents/doc2562.pdf

Encoder Board Evolution

2012-01-20T07:00:00.000-07:00

The old encoder board I fabbed for Data Bus has failed. Rather than repairing several lifted traces on the old one, I felt that a more reliable approach was to order a professionally fabbed board via DorkbotPDX.

I took the opportunity to redesign using SMT components so I could shrink the board.

Old board above, new SMT board below

The old design was based on an LM393 dual comparator IC configured as a schmitt trigger. So is the new board, but instead of a single IC, it was easier to route traces using individual, Texas Instruments TL331, SOT-23 comparators. All the passives are 0603 size and the LEDs are 1206 size.

I'm still working on my technique for hand soldering SMT. Here are some things that seem to work so far:

Push components out of their tape using the point of a small nail
Tin the pads then suck off the solder with solder braid
Use a flux pen on all the pads
Use a really small tip and a decent iron
Use 0.015" solder; I use Radio Shack silver bearing solder
Use non-magnetic pliers/tweezers to pick and place parts
Use the nail tip to gently nudge them around on the board
Hold the parts down with the head of the nail while you solder
Tack down one side of the component, add solder if needed
Then add solder to the opposite side while holding it

Components tend to get pulled vertical by solder surface tension if you have too much solder on the pads so that's why it seems to work better to remove some solder and to hold the component down with a nail.

It's pretty darned tedious. I ended up reflowing the SOT-23 comparators using my reflow skillet. As I have two encoder boards to populate, I will try reflowing all the parts on one of them and see if that is any easier.

Hopefully the new board will hold up better to the rigors of testing and competition than the home fabricated board. Plus, I'll have spare boards in case something goes awry.

Geek Destinations: JB Saunders

2012-01-13T07:00:00.001-07:00

I had some time off during winter and I had a free day all to myself so I headed up to Boulder to meet a friend and visit JB Saunders. This place should be on every geek's bucket list. Holy cow...

The shop isn't huge, but it's jam packed with some new stuff and a lot of surplus parts. Loads of different potentiometers, transformers, relays, logic chips, SMD passives, wire, enclosures. It's really nice to be able to pick up and see and feel the part before you buy it.

Their collection of logic ICs. Well... part of it, anyway... 8-O

Think that's impressive? They have another wall of 'em. Yes, they have just about every DIP logic IC you can imagine in various families: F, S, LS, HCT, 4000, etc. I've had trouble finding some of the more obscure ICs lately. They had 'em.

A small sampling of the many parts bins

They also have a rack stuffed with used instrumentation, primarily oscilloscopes, but some other standard gear as well. I had to chuckle when I saw none other than a Hitachi V1050F just like mine sitting on the shelf. It was like finding an old friend.

Mmmmm, test instruments...

And they have tubes! Lots and lots of tubes. I didn't see a lot of the type of audio tubes that are really commonly used or popular. Sorry, no 12AX7's. But I recognized a few I've run across before. They have a ton of other miscellaneous tubes that I didn't even begin to recognize.

Loads of tubes

I ended up dropping $80 at the place, but I came away with useful stuff that I can't find elsewhere, or if I could, I'd have to pay for shipping. I got several microscopic Hammond 1551F enclosures, a handful of air gap variable capacitors in various values for some radio projects I'm doing, a couple of old control knobs, a bunch of LEDs (I hate to run out), magnetic coil wire, stuff like that.

In all a fun day. It's tough for me to get up to Boulder often. Not a lot of free time for that but I'll get back eventually.

If you're there, you can't miss a chance to visit this place!

AVC 2012: On The Waiting List

2012-01-07T17:00:00.000-07:00

Crap! I'm on the "backorder list" for the 2012 Sparkfun AVC!

That means several people have to officially drop out or I won't get to compete at all this year! I didn't see the announcement until a day after and apparently, by that time, all 50 slots had already been filled. I am in the top five on the waiting list, though, so there is still a glimmer of hope.

I don't know if I will get to compete but what is certain is that Data Bus development will continue and you'll read about it here.

Equally certain is that I will be hoping and praying that at least 5 other contestants fail miserably and give up... (is that wrong of me?)

LPCXpresso Surgery

2012-01-06T07:00:00.000-07:00

I have an LPCXpresso now. The board breaks out a 120MHz LPC1769 to DIP form. Attached to the board is an LPC-Link, a JTAG debugger. To use both boards conveniently, they need to be separated. One of my readers, Nemo, suggests an Xacto hobby saw and mitre box to split the boards apart. He achieved very nice, precision cuts this way.

My approach for cutting apart the LPCXpresso and LPC-Link involved use of a plastic cutter and utility knife shown above.

Use solder braid to remove the solder from the solder jumpers between both board halves.
Then score a line with plastic cutter on both sides using straight edge and (gently) vise.
Score until you can't easily go deeper.
Continue scoring with the narrower utility knife to score a bit deeper
Snap the board in half by hand without much effort.
Sand both edges.

Now mount male header pins on one side, female header socket on the other, et voila. Plus, no cables to deal with.

ARM for Hobbyists

2011-12-30T07:00:00.000-07:00

M0 mbed from mbed.org

ARM chips have gained a foothold in hobby electronics that I suspect will become significant, soon.

Certainly some projects (several of mine included) will benefit from more RAM, larger program space, faster clock speeds, and 32-bit processors.

What's required for widespread uptake of ARM are a combination of free tools that simplify programming and low cost development boards that make prototyping easier.

Leaf Labs began providing an Arduino-derived IDE for their Arduino-compatible STM32 ARM-based board some time ago.
The 96MHz ARM Cortex M3-based mbed dev boards with online compiler have been around for a few years now and are growing in popularity. A lower cost Cortex M0 mbed is coming very soon. The DIP package makes for easy breadboarding.
The LPCXpresso is a bit faster than the mbed at 120MHz and comes with a free IDE and features a DIP form factor, too.
Arduino and Atmel have teamed and announced the Due featuring a SAM3U, a 96MHz ARM Cortex M3. Not available yet.
The Wiring project (from which Arduino descended) will be introducing STM32 ARM compatibility soon.
Among a slew of hobbyist-unfriendly QFP packages, one ARM vendor, NXP, is soon to release a 28-DIP form factor Cortex M0, the USB-capable LPC1114FN28. NXP offers M0s in SOIC and TSSOP form factors as well.
There are more than a few low cost dev boards out there. Too many to list, in fact.

Not that ARM is the only 32-bit, high performance game in town but I've become very interested in the platform in the last few months. I know this isn't a comprehensive list. If you know of other ARM-based development hardware/IDE platforms I'd love to hear about it.

Pololu Goodies

2011-12-23T07:00:00.000-07:00

Happy Holidays to those who celebrate! Despite my fear of sounding like an advertisement, I love Pololu. Great people; they have always been friendly to me, and they come up with some really cool robots and components.

A few weeks ago I received a package with my Black Friday spoils and it was just like Christmas had come early.

Can't wait to try some high speed line following...

Mmmmm... tank treads.

Besides the above, I also ordered a 9DOF IMU and have implemented an AHRS using Pololu's sample code running on an ATmega328P.

Jingle Bells

2011-12-22T07:00:00.000-07:00

Ok, it's been done before, but why let that stop me?

Through the holidays, when you visit my blog, here, you'll add to the household festivities because a little bell in my office will jingle. And also, an angel will get its wings.

This version is a PC and Propeller-based holiday kludge-o-rama. Here's how...

Hardware

The 'bell tower' is made of some craft dowels and maple blocks. Since it's basically useless for anything more strenuous, the crap servo out of my ElectrixRC rings a little bell, one of the decorations left over from our wedding several years ago. Don't worry we have about 100 left. Want one?

I'm using one of my miniProp boards for Propeller power. The mass of wires on the breadboard has nothing to do with this project. I was experimenting with a very promising 20MSPS ADC and didn't have any free breadboards to play with. I guess now you know what to get me for Christmas...

The little red mini board houses a 1.5A 7805 regulator to step down from the ~9V from the protoboard power supply I threw together a long time ago. It features a ridiculously heavy transformer. Note the lethal, exposed AC lines. Please--don't do this at home. Seriously. I'm putting this POS in an enclosure the first chance I get.

Software

The bell rings when the propeller receives an "r" character over serial. It gets this message from a BAT file. The BAT file is called from a PHP script. The PHP script is run out of a lightweight PHP web server. The URL for this PHP script is referenced in an iframe on every page of my blog.

Here's the Propeller code (text and pretty versions):

{
 WebRinger -- Rings a bell when it receives a signal from the PC which detects visitors to a website

 Dependencies..: Servo32v5
 Author........: Michael Shimniok  www.bot-thoughts.com
}
  _clkmode = xtal1 + pll16x
  _xinfreq = 5_000_000       '80 MHz

  ms = 80000
  delay = 100
  
  bell = 9
  bellMiddle = 1100
  bellRight = 1000

OBJ
  servo : "Servo32v5"   ' Servo controller
  pc : "Simple_Serial"
  
PUB Start | pos, c

  pc.init(25,26,9600)

  servo.start
  servo.ramp

  repeat
    c := pc.rx
    if (c == "r" or c == "R")
      pc.str(string("ring!",13))
      ring
    waitcnt(cnt+500*ms)
    

PUB ring
  repeat 4
    servo.set(bell, bellRight)
    waitcnt(cnt + delay*ms)
    servo.set(bell, bellMiddle)
    waitcnt(cnt + delay*ms)

This is the BAT file. I have a Pololu AVR programmer sitting on COM9 talking to the Propeller

@echo off
mode COM9:9600,N,8,1
echo r >COM9

On my website, I include an iframe that sources my locally hosted php script.

And that's it. Perhaps in a later revision I'll set up a web server on an mbed so the whole thing is self-contained.

Magnetometers and Motors

2011-12-16T07:00:00.000-07:00

Test rig for current measurement

Now that I've got a mechanism for measuring motor current, it's time to try and quantify the effects of motor magnetic field on magnetometers.

Data Bus was cursed by Compass heading deflection earlier this year and I never discovered its cause. The error observed was on the order of 20 degrees or more.

As part of my ongoing work to get ready for the just-announced Sparkfun AVC 2012, I want to see if I can correlate motor current and magnetometer readings using a Honeywell HMC5843 3-axis magnetometer.

The Experiment

Test rig for measuring motor current.

Starting with the test equipment above, I added an HMC5843 magnetometer, and mounted it and the motor/prop on a wooden board for testing (first picture in the article; HMC is on the red board; LSM303DLH on the green one). The motor and magnetometer were separated by about 5.25 inches.

The values from the magnetometer were read by Data Bus' mbed microcontroller and printed over serial. I used a DMM to measure current while capturing X, Y and Z magnetic readings from the sensor for a range of current values.

Initially I used a 6V Speed 400, 380 brushed motor with a 7x3 propeller which drew on the order of 9A max. To measure the effects of higher current, I used Data Bus' original 20T, 540 brushed motor with a larger prop and was easily able to draw over 20A of current. Neither motor was equipped with a flux ring.

In the first test I used the 1800mAH NiMH battery pictured above, except on the 8A test where I switched to a 2200mAH 2S 25C Gens Ace LiPo. I continued to use that battery for the larger motor tests along with a bigger 30A SIG ESC.

Data Plots

The results of the first two tests are in. The plot below shows magnetometer effects for the smaller motor with ampere draws in the 0 through 8A range. Effects on 2D heading calculation are shown, too.

The 2D heading varied by less than half a degree between the 0A and 8A readings. Below is the plot for the bigger motor and ampere draws from 0 to 22A. Effects on 2D heading calculation are shown again.

The 2D heading varied by just over half a degree.

Conclusion

As expected, motor current appears to correlate with changes to magnetometer readings; however, the effect is minimal. The calculated heading suffers only minor error even up to 22A for a 540 size, 20T brushed motor with no shielding (flux ring), and at a distance of only 5.25" between motor and sensor.

As magnetic fields diminish with the cube of the distance, even a slight increase in distance should reduce the already minor effects to negligible levels.

The cause of the observed compass errors, it appears, is to be found elsewhere...

RadioShack? Yes.

2011-12-09T19:34:00.000-07:00

I've been visiting Radio Shack stores since I started dinking around with electronics in high school in the 80's. I'm not affiliated with them, but I've always been a loyal customer. Though I've heard many hobbyists dis them over the years, at least they've always had components on the shelves.

But nothing like this!

Arduino and Parallax gear including a Propeller board!

The venerable Forest Mims III books are back and better than
ever along with other promising titles

I almost missed this entire endcap of Arduino,
Make and Parallax goodies

Propeller boards, Arduino boards, Make kits, gyros, GPS, and on and on. Radio Shack is carrying a lot of really great hobbyist/roboticist/maker/electronics nerd gear. Go check it out.

Never have I been so excited to visit a Radio Shack since the days of blue Archer packages and speech chips hanging by the dozens.

Radio Shack has been saying recently that they're committed to DIYers. If this doesn't convince you, nothing will.

Constructing RoboTurkey

2011-12-02T07:00:00.002-07:00

Here are some construction details for RoboTurkey. Warning: lots of pictures and a video, to follow...

The body of the turkey is made from a tall, 4" diameter cookie tin I got at the Goodwill.

Jumbo sticks are used for wing crossmembers. The wing bones are mounted onto the horizontal stick, rotating on small nails as hinge pins secured with hot glue.

Wings, crossmembers, wing servo

The neck is a dowel with a smaller dowel sticking out of it at a right angle. This dowel has a hole drilled into it. Music wire linkage inserts into this hole and into the neck servo.

The neck inserts through a slot cut into the cookie tin on the top. A plastic hole plug at the bottom acts as a bushing.

The neck is held somewhat in place with sections of jumbo sticks hot glued into place.

The neck servo sits at the bottom rear of the body with linkage up to the neck dowel.

The beak is actuated by a mini servo you can see below. The servo moves a music wire linkage up and down. The linkage runs alongside the neck, and up to the lower jaw.

Here's the beak mechanism with the hole for the linkage in the lower jaw.

I put together a Sketchup animation showing how the parts go together since it's not obvious from the pictures.

The feet are just craft sticks glued to a small cube base, dowels for legs. The legs glue into a mounting base onto which the cookie tin is in turn mounted.

The bird is wrapped in a feather boa and has construction paper wings and tail that my daughter helped cut out and glue in place. The red thingy on the beak is a piece of cloth and the hat came from the craft store.

Sparkfun AVC 2012

2011-11-25T00:15:00.000-07:00

Data Bus is back and he's pissed.

Last April, Data Bus experienced crushing, embarrassing, humbling defeat. For six months, he's been nursing his wounds and stoking the fire in his belly while his thirst for victory has grown insatiable.

It's time.

I'm getting an early start on the 2012 Sparkfun Autonomous Vehicle Competition, greatly aided by the fact that I'm not starting from scratch. I'll chronicle the revisions over the next six months.

So far I've...

upgraded to a 2.4GHz radio system,
installed a brushless motor with LiPo battery,
reinstalled my CHR-6dm, 9DOF AHRS,
refurbished the wheel encoders,
installed steering link turnbuckles,
conducted some preliminary experiments,
blown up two GPS modules,
damaged my encoder board,
experimented with a Ground Control Station,
cleaned up the code, and
remounted the GPS to eliminate the sensor mast.

That and a few other things I may go into in more detail later. Presently, my primary concern, and biggest challenge, is to obtain a reliable and accurate heading reference.

Happy Thanksgiving

2011-11-24T03:20:00.001-07:00

A message to you from the newly completed RoboTurkey:

RoboTurkey's actual name is Oscar (all Thanksgiving turkeys are named Oscar in our family). At random intervals, he either moves his head around, flaps his wings, or speaks while moving his wings for emphasis. He simultaneously moves his beak while playing back audio clips of my daughter talking.

Here are some specs and info:

Wings and tail crafted by my 2 year old daughter
Plays back 8 phrases spoken by my daughter and recorded to a 2GB microSD card
Parallax Propeller on one of my miniProp boards
Software written in SPIN and PASM
LM386 audio amplifier with gain of ~20dB
Head, beak and wing movement controlled in parallel
3 hobby servos I had laying around
6 AAA batteries
NCP1117 LDO 5V regulator
Cookie tin from Goodwill
Feather boa, lots of craft sticks and hot glue from Hobby Lobby
Plays back audio from microSD

I'll post up build details in the near future.

Black Friday Deals

2011-11-21T17:26:00.001-07:00

Pololu is again doing a black Friday sale with lots of great deals and thought you might want to know.

I am going to try to be one of the first 50 people to get a 3pi robot, and I have a shopping list of other goodies I'd like to get like a $30 9-axis IMU.

Last year I scored a baby Orangutan, a couple of IR sensors, some nice voltage regulators, and a few other things.

[EDIT] oops, I listed black friday lists from years past. Try these:

Cheap Logic Analyzer SMD Clip Hack

2011-11-18T07:00:00.000-07:00

Cheap ebay clip, center, Selae Logic Analyzer clip, right

Want cheap SMD clips for your logic analyzer? One of my readers, Nemo, submitted a nifty hack to convert budget clips (above, middle) for use with typical female logic analyzer leads (above left).

The HP 1650A logic analyzer I was given a few years ago has been a huge help with my hardware hacking. I was talking to Nemo the other day and he has a Selae Logic Analyzer (I'm envious). His came with E-Z Logic clips that look identical to the HP/Agilent branded clips I got. Going rate is over $1 for the HPs and almost $3 for the E-Zs.

One of my HP logic analyzer clips

Instead, get yourself some cheap SMD clips from eBay, about $0.50 each. Also, get a right-angle 0.1" header. Pull pins out of the header, one for each clip.

SMD clip disassembled, with right angle pins ready for install

Disassembling the budget clips reveals a convenient hole into which the pin can be soldered. In fact, the hole is a sort of rivet. You want to carefully solder the pin to the rivet itself so it can rotate.

Once you've got the pin soldered in, trim down the soldered end of the pin (you can see it sticking out in the picture below). Then, reassemble, and now you have a place to plug in your female analyzer lead.

Pin is soldered to the rivet, needs trimming

Thanks for the tip, Nemo!

Electronic Candle with a 555 Timer

2011-11-11T07:00:00.000-07:00

Pokey my Trinity-style firefighting robot likes to blow out candles. It's his job. Whenever I demo Pokey at robotic events, I don't dare light a real candle lest I burn the place down.

Holding a flashlight for Pokey to track lacks drama, so here's a DIY electronic candle that you can actually blow out. You can build this yourself on a breadboard or on a simple home-etched pcb.

The 555 Timer

The candle is based on a 555 timer IC in monostable (aka one shot) mode. When the 555's trigger (TR, pin 2) goes low, the 555's Q output (pin 3) goes high for a set period of time, then goes low again until the next low TR. The Q output drives a PNP transistor so that the candle (a small incandescent lamp) is normally on.

Here's the schematic.

The time period that Q goes active is based on the time constant of an RC network: R1+VR1 between Vcc and DIS/THR (pins 6 & 7) and C1 between DIS/THR and ground.

I wanted a time range of about 1-10 seconds so I used Electronics Assistant to calculate some possible values and came up with 10k + a 100k potentiometer along with a 100uF cap.

Besides the basics, tie reset (R, pin 4) high, wire up ground and Vcc, and throw a 0.01uF cap from CV to ground. The trigger input is tied high and grounded with the wind detector switch.

The lamp runs off two AA batteries so I chose a TLC555 CMOS IC I had on hand because it will run off a Vcc as low as 2V.

Here's the simple 1-layer PCB design. I etched the board at home and you can too.

I prototyped the circuit on a breadboard before finalizing the board and etching it. I made sure it worked and the timing was close enough.

Driving the Lamp

The PNP is a 2N4402 BJT, 600mA capacity, plenty for the lamp. I chose the base resistor with a combination of back-of-napkin calculation, LTSpice simulation and breadboarding experimentation.

The transistor doesn't get warm and the lamp is bright so the BJT is probably in saturation. Or close enough. This isn't a mission critical application, after all.

Wind Detector

The wind detector is basically a custom mechanical switch that is normally open and momentarily grounds the 555's trigger pin, which is pulled up high with a resistor.

One half of the switch consists of a stiff piece of paper about 2"x2", taped to the switch lever, which is a length of 0.032" music wire with a spring on the other end and a loop for mounting.

The other half of the switch is a J shaped piece of wire mounted so the lever can bump into it when the wind catches the paper and moves the lever.

The Candle Base

I made the candle base out of some scrap wood with a hole in the bottom to hold the circuit board. A section of 3/4" square dowel mounts to the base. A lamp socket mounts to the top of this dowel. The lamp sits at a regulation 15-20cm height. A piece of brass bent in an L shape holds the AA battery holder to the side of the base. Wires route into the base from the back.

That's all there is to it. Just plug in the battery, the lamp comes on. Just a little airflow from you or a robot blows out the lamp for several seconds then it lights up again.

Road Testing an ARM LPC2101: Part 1

2011-11-04T07:00:00.000-06:00

I was graciously invited to participate in the Newark Product Road Testing Program and I'll be road testing two ARM microprocessors. First up is the NXP LPC2101, recently added to Newark's offerings.

While I relay my experiences, my hope is to make it easier for you, gentle reader, to jump into the wonderful world of ARM along with me. ARM processors have their place in robotics and electronics, can be inexpensive like this LPC2101, and can be very powerful. (You can find more NXP ARM processors from Newark here)

I hope to show that you don't need expensive breakout boards or cumbersome evaluation boards, and you can use free toolchains. So... let's get started...

Here's how this 32-bit NXP ARM7 microcontroller, and it's brethren, stacks up against a good ol' 8-bit AVR ATmega328P (e.g., Arduino Duemilanove):

Processor	Clock	Flash	SRAM	ADC	UART	I2C	SPI	Price
ATmega328P	20 MHz	32k	2k	80 kSPS	1	1	1	$4.41
LPC2101	70 MHz	8k	2k	400 kSPS	2	2	1	$3.80
LPC2103	70 MHz	32k	8k	400 kSPS	2	2	1	$4.40

That's just to give you an idea. Note that the AVR can only convert at 80kSPS at reduced resolution. Also, the ARM has a built-in boot loader. No need for scary JTAG programming. The LPC2102 falls between the '1 and '3 in flash/sram size.

Prototyping Circuit

Starting with nothing but a little 48-pin LQFP processor is a bit daunting. Don't panic. Building a circuit with all the necessary power and support components is actually pretty easy and not really different from other processors like the AVR ATmega series or the Parallax Propeller.

All you need is...

a 12MHz (or appropriate) crystal and two 16pF caps,
a 1k reset pull-up and 0.1uF debounce cap,
a serial in-circuit programming header,
3.3V and 1.8V power supplies, and
some decoupling caps.

The only thing really different versus a Propeller or AVR ATmega is that the LPC2101 needs an extra regulator for the 1.8V supply. Well, that's easy enough. Here's the schematic.

ARM LPC2101/2/3 schematic, click to enlarge.

The only thing you need to add to the schematic is a 5- or 6-pin TTL-serial header with RTS, DTR, ground and (optionally) power. Or you can use a Sparkfun FTDI breakout and manually select program mode for uploading your code. More on that shortly.

Prototyping Boards

Soldering surface mount, particularly QFP chips can be very tedious and irritating. You have to delicately line up the chip and hope you don't bump it when you try to tack down the first pin. And I've only messed with larger pitch QFPs, not a 0.5mm pitch like this LPC2101.

Enter Schmartboard products. Some time ago I received some Schmartboard products to review. The Schmartboard concept is to simplify surface mount hand-soldering so that anyone can easily do it.

The boards use a custom fabrication process, "EZ" technology, that creates grooves for chip leads to sit in. The pads are sunken, in other words, below the solder mask, and are pre-tinned. All you have to do is stick the chip in the grooved pads, and then, pin by pin, 'push' solder towards the pin. It works.

Here's how to implement the circuit above on a Schmartboard for QFP. I've color-coded the Schmartboard holes with a key in the upper right.Use the unused holes in the corners as needed to propagate Vcc, Gnd, etc.

After you add in the caps and pullups (my board has additional pullups, too), you can then solder your voltage regulators (I used simple 1117-type SOT-223 sized 3.3V and 1.8V regulators) onto another Schmartboard made for a variety of SOT, DPAK, etc packages. Then connect the power between boards and you get something like this:

Note the successful blinking LED on the red breadboard...

In-Circuit Programming

All you need for in circuit programming are 5-7 lines. You can use a 6-pin Sparkfun FTDI breakout board as I did.

Ground connect to, duh, Ground
TX (TTL serial) connect to RXI
RX (TTL serial) connect to TXO
!RST (connected to DTR
P0.14 (program mode selector) - connect to ground when ready to program
5V (ish) to your regulators (optional)

Either use the LPC2000 Flash Utility V2.2.3 (download) or, better yet, Flash Magic to download the code.

The next article will cover using the Flash Utility to upload a hex program, as well as covering a development environment for writing my first hello world program in C.

In a later article I'll review the second ARM Newark sent, a nice little Texas Instruments Stellaris 1000-family processor.

Thompson Robotics Expo 2011

2011-11-01T07:00:00.000-06:00

This past Saturday, my daughter and I had fun at the Thompson Robotics Expo up in Loveland and we set up a table for SHARC to demo Data Bus and Pokey.

Pokey, my Trinity-style firefighting robot, ran some demos where the little robot used rudimentary machine vision to search for a 'candle' (flashlight), drive forward to the white floor marker, and turn on the fan to 'blow out' the candle.

Data Bus, my Sparkfun AVC entry, was set up to send telemetry updates to the Happy Killmore Ground Control Station (HK-GCS) demonstrating GPS, attitude, odometry and heading sensors. I also set up a slide show on a digital picture frame to show Data Bus' anatomy as well as some pics from the 2011 AVC.

We got to watch some VEX and First Lego League (FLL) competitions and talk to a number of kids about the robots on display. It was fun to see young roboticists' eyes light up seeing what else is possible with robotics.

Sparkfun was there with some really cool displays and some real nice guys manning the booth. There were a few other booths, one with a 3d printing machine.

I was too busy manning the booth and keeping my little girl out of trouble to know what happened with the robotics competitions, but it was pretty obvious everyone was having a blast, us included!

Measuring Motor Current

2011-10-28T07:00:00.001-06:00

I need to measure the current going through brushed DC motors. One of the ways to do this is to use a shunt resistor, a low-value, precision resistor. Measuring the voltage drop across the resistor, one can calculate the current through the resistor.

I decided to make my very own, very simple, shunt resistor breakout board. It connects between the battery and Electronic Speed Controller (ESC) or other motor driver.

A header is included to measure voltage across the battery and voltage drop across the resistor either with a DMM or a microcontroller.

DMM test clips attached

I quickly drew up the design in Eagle, used toner transfer method and etched the board, soldered everything together and voila, simple current measurement.

Pretty simple circuit board, eh?

0.001 ohm, 1%, 3W = 50A+ (WSR31L000FEA)

The resistor is 0.001 ohms so 1mV = 1A (it's a Dale-Vishay WSR31L000FEA). My DMM has precision to 0.1mV, thus 100mA here. I selected a resistor with sufficient power handling to measure over 50A continuously.

So what the heck am I going to do with this thing?

Measure RC airplane propeller load on motor
Calculate battery internal resistance
Plot relationship between motor current and compass distortion
Calculate remaining battery capacity on an autonomous robot
Overcurrent protection
Create a digital ammeter with an MCU and LCD display

Some add-on hardware is needed to interface with a microcontroller. The AttoPilot shunt boards use a Texas Instruments INA-169 for amplifying voltage drop across the shunt to a suitable range for an analog to digital converter. (While I am using the simpler board above for bench testing, I decided to get the AttoPilot board for use on Data Bus)

AttoPilot current/voltage sense board

One has to be careful, of course, that the shunt presents substantially less resistance than the load. Some motors have very low resistance windings. For those cases, a hall effect sensor like the Honeywell CSLA2CD seems like it would do the trick.

Why The Wrights Flew First

2011-10-14T07:00:00.001-06:00

Orville demonstrating the flyer
to the U.S. Army, Fort Myer, Virginia
September 1908. Photo: by C.H. Claudy.
(Source: Wikipedia)

At the time the Wright brothers achieved the first powered airplane flight at Kitty Hawk1, the field of aeronautics had been buzzing with activity for years (perhaps not unlike the present DIY robotics community).

Why did they succeed where others failed?

Not by luck but by their methods. Rather than testing entire designs in total, as did many others, they developed and tested a component at a time following a repeating cycle of research, calculation, experimentation, and refinement.

Their successful powered flight and total control of the aircraft wasn't a surprise to them. It was the culmination of four years of intense, methodical, purposeful, and driven research and experimentation.

By the time they flew at Kitty Hawk under power, they had

tested many airplane control designs using kites,
created their own wind tunnel and balance for more sophisticated testing,
evaluated more than 200 different wing and airfoil designs,
piloted their own glider aircraft more than 1000 times
proven wrong, through experimentation, the established coefficient used to calculate lift, and
through wind tunnel testing, developed propellers that modern wood props can barely outperform

Breaking down complex problems into smaller problems is a recipe for success. So is designing and experimenting with individual components under controlled conditions prior to integrating the components into the finished design.

The biggest cause of my 2011 Sparkfun AVC failure wasn't due to its myriad flaky sensors. The sensor problems were merely a symptom. I didn't experiment enough with each sensor component.

For example, I encountered magnetometer (compass) errors. Was it because of accelerometer-based tilt-compensation distorted by linear acceleration? Distortion from nearby metal objects? Or DC motor magnetic fields?

I had no idea. Because I didn't experiment individually with the magnetometer sensors. I just slapped them on the robot and drove the whole thing around haphazardly. I tested the entire system, not its components.

So it's time to start over, experimenting in a more controlled fashion with each sensor, magnetometer first.

Sources:

http://en.wikipedia.org/wiki/Wright_brothers

http://wright.nasa.gov/overview.htm

1 Apparently there are some controversies about who flew first. I think the Wright's achievements, methods, and scientific contributions to aeronautics speak for themselves.

The miniProp Contest Begins

2011-10-11T07:00:00.000-06:00

miniProp. Win one.

It's time. Head on over to the Bot Thoughts facebook page and enter to win a miniProp, a Parallax Propeller on a DIP form factor with built in regulator, eeprom and crystal. Free IDE from Parallax, lots of community support, 8 cores (cogs), deterministic timing, easy to learn assembly, and more.

Next Tuesday I'll pick the winner at random out of the list of folks who comment on or like the contest post. Good luck!

Win A Propeller Board!

2011-10-07T07:00:00.000-06:00

Aww... so cute!

It's small, it's standalone, it's purple, and it's a Parallax Propeller, aka an experimenters dream. I designed this breakout board and I'm giving away a fully populated board to a lucky reader! I call it the miniProp board.

The Propeller has 8 cores (cogs) that operate together in perfect lockstep. The chip has perfectly deterministic timing and really simple assembly language. Writing device drivers on the Propeller is truly a piece of cake. And when you're done you have several cogs left to do lots of interesting things besides.

One can get a nice, inexpensive Propeller board from Schmartboard. They make soldering SMT devices really easy. And I think it's the cheapest board out there. I have and use one and I recommend it if you want to experiment with Propeller.

But I also wanted a DIP form factor for breadboard experimenting and heck, its fun designing boards. The PropStick USB looks great but it's too pricey for me. The inexpensive miniProp uses a Sparkfun FTDI breakout board programmer. Rev 0.2 is in the works at which point I'll post up the schematics and PCB layout in accordance with the Open Source Hardware definition.

The miniProp says "Hello World!" by blinking an LED

Want one of the Rev 0.1 boards, fully populated and ready to go? Keep an eye on the Bot Thoughts facebook page during the next week for a chance to win one!

I2C: mbed reading from Arduino

2011-09-30T07:00:00.001-06:00

Quite some time ago, I covered how to get two AVRs talking to each other using the I²C protocol.

Here's how to get an mbed and AVR talking with I²C, with the mbed acting as Master and the AVR acting as Slave.

Let's say you want the mbed to query the Arduino to respond with 4 bytes of data.

The mbed will write an address byte with the read bit set, using the Arduino's address, and then it'll request to read four bytes. The protocol exchange looks like this:

1. Send a start sequence
2. Send 0xC1 ( I2C address of the slave with the R/W bit high (odd address)
3. Read data bytes from slave
4. Send the stop sequence.
(source: I2C Tutorial)

On the Arduino, call Wire.begin(7), where 7 is the Arduino's I²C address. That tells the Arduino I²C peripheral what messages to listen for. Then call Wire.onRequest() specifying a handler function that is called when the master requests data.

void handleI2CReceive(int numBytes)
{
  char command = Wire.receive(); // pretty much just ignore the command

  return;
}

void handleI2CRequest()
{
  byte data[4];

  // the code below just sends
  // data from the global variable
  // box, a struct with 4 char members
  //
  data[0] = box.x1;
  data[1] = box.y1;
  data[2] = box.x2;
  data[3] = box.y2;
  
  Wire.send(data, 4);
  
  return;
}

void setup() {
  Wire.begin(I2C_ADDRESS);

  box.x1 = box.x2 = box.y1 = box.y2 = 0;

  Wire.onRequest(handleI2CRequest);
  Wire.onReceive(handleI2CReceive);
}

On the mbed, use the "raw" I²C library's start(), write(), read(), stop() methods and manually set the address. Take the I²C slave address, left shift once, and set bit 0 high to indicate a read operation. Then read four bytes. Like this:


        cam.start();
        data[0] = (0x7<<1 | 0x01); // send address + !write = 1
        cam.write(data[0]);       // send address
        data[0] = cam.read(1);
        data[1] = cam.read(1);
        data[2] = cam.read(1);
        data[3] = cam.read(0);    // don't ack the last byte
        cam.stop();

This only works when the slave has one "register". Suppose you have an Arduino that can respond with one of several ADC readings. The protocol exchange would first include the master writing the desired register number to the slave, sending another start, then reading the data. The Arduino would have to accept the register number and store that until the next read request, responding with the correct register's value.

AVR Low Power

2011-09-16T09:29:00.026-06:00

My RC airplane Lost Model Alarm (LMA) runs off a tiny CR1225 50mAH battery so low power operation was a must. Here's how to save power with your AVR or Arduino project.

Sleep Baby, Sleep

Let's say you want to poll a sensor periodically (think weather station, timer, etc). The MCU doesn't need to run continuously. You can make use of AVR sleep modes to save power.

AVRs can put themselves to sleep and will wake up under certain interrupt conditions. You can use timer/counters to fire interrupts to wake up the chip or use the watchdog timer to do the same.

The Lost Model Alarm goes into full sleep mode; the MCU and every peripheral is off until the watchdog timer wakes up the processor every second.

void enableWatchdog()
{
	// Enable watchdog interrupt, set prescaling to 1 sec
	WDTCR |= _BV(WDTIE) | _BV(WDP2) | _BV(WDP1);
}

ISR(WDT_vect)
{
  //do stuff here
}

//...

set_sleep_mode(SLEEP_MODE_PWR_DOWN);
sleep_mode();

Slow Down

If your processor doesn't need turbo speed, why use it? Higher clock speeds burn up power. You could set the AVR clock with fuse bits but flashing new firmware is a pain. So get the best of both worlds. Set the fuse bits for normal fast clock operation but, once the AVR starts up, your code tells the MCU to slow down the clock to a miserly speed.

I run the LMA's AVR at 9.6MHz but slow down to only 150kHz after the code initializes. Don't forget to redefine F_CPU in your code!


// 150kHz
void slowClock()
{
	CLKPR = _BV(CLKPCE);
	CLKPR = _BV(CLKPS2) | _BV(CLKPS1); // scale = /64
}

Low Power Circuits

Use the 80-20 rule to reduce current draw from designs.

When you're talking about microamps, the whopping 10-30mA draw of an LED is ghastly huge. Ditch the LEDs from any low power circuits.

Select components that minimize current draw. Choose low power versions of devices. For example, a CMOS 555 timer instead of a standard 555. Use high efficiency switching regulators (or no regulator) instead of linear regulators. In my case several buzzers were available with < 5mA current draw requirement and one with only 1mA draw so I chose that one.

Make sure voltage dividers have high enough resistance to minimize current. Leave MCU pins low or better in high impedance mode. Avoid circuits that default to a state that draws substantial current. For example, some transistor circuits, logic gates for certain logic families, etc.

XV-11 Imaging Sensor Revealed!

2011-09-12T07:00:00.000-06:00

Image from Random Workshop,
blog of XV-11 Hacking Guru Hash79

The XV-11 LIDAR has finally been completely cracked open.

Hobby roboticists are on the cusp of DIY, sophisticated, low cost, obstacle detection.

The XV-11 uses a laser-based "radar" that can map out the environment allowing the vacuum cleaner to navigate its environment avoiding obstacles like chair legs, sofas, cats, and more. With this kind of sensor your robot can also detect which room it's in.

Well, thanks to the winner of the Open Lidar Project, XV-11 hacking contest, now we can build our own: all the chips including the imager are known. Follow the link to find the details.