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Friday, May 30, 2008

The oscillator will be used to generate a square wave at a desired frequency. The wave is fed into a transistor that drives an infrared LED on and off very rapidly. Because the emissions are infrared and very fast, neither is visible to the human eye.

Inexpensive infrared receiver chips are available at 36 kHz, 38 kHz, and 40 kHz. The receivers are sensitive to oscillations several kilohertz to either side, although reception distance improves with a better signal to start with.

If used for object detection, the signal needs to travel the distance to the object, bounce off the object, and then travel the distance back to the receiver. So, distance becomes a factor.

Because infrared receivers amplify the signal to improve detection, electrical noise generated from the oscillator can leak into the receiver and trigger a false detection. This isn't a problem for VCRs or most consumer devices as they tend to contain either a transmitter (remote control) or a receiver (CD player), but not both.

Therefore, robot transmitter and receiver circuits must be carefully designed and positioned apart to be useful. Robots that chase electrical ghosts, spin in place, or jerk sporadically are initially amusing, but eventually frustrating.

The lower the power of the circuit, the more likely it will be lower in noise. Also, liberal use of decoupling capacitors and metal shielding helps a lot. Greater distance between the circuits makes an enormous difference.

The Popular 555

The 555 IC is an extremely popular timer. The low-power CMOS versions (TLC555, LMC555, and ICM7555) use less power than the older (555, NE555, LM555) versions and don't require a capacitor on the control pin. Although pin and functionally compatible, the component values differ between the low-power CMOS and older versions.

Infrared Emitter 555 Schematic

A portion of the configuration presented here is similar to an example in the Maxim ICM7555 datasheet. In this circuit, the 555 is used in astable multivibrator mode.

For maximum effect, over 60 milliamps pulses through the infrared LED. Adjust R3 as appropriate for your use and LED specifications.

When calculating current through the resistor, don't forget to first subtract the voltage drop across the LED and transistor. Let's say the LED uses 1.8 V (1.6 V to 2.2 V wouldn't be unheard of). Let's say the collector-emitter drop of the transistor uses 0.2 V.

5 V (total) - 1.8 V (LED) - 0.2 V (transistor) = 3 V remaining to drop across the resistor.

3 V / 47 ohms is about 64 mA. Because there's only one path, the current going through the resistor must be the same as what's going through the LED.

Now for the other trick: the word "pulses". The LED is only on half the time because it is blinking. If you use an ohmmeter, the average current is 32 mA (half).

Aside: The LED heats up faster than it cools off. As such, it's not possible to drive 100 mA through a 50 mA LED even though the average current is half. Depending on ambient temperatures, it's usually safe to drive only 125% or 133% of rated maximum at 50% duty. With smaller duty cycles and frequent pauses, it's possible to drive a lot more current in very short bursts.

Theoretical frequency can be calculated by:

f=1/(1.4 RC)

where f is frequency in kilohertz, R is resistance in kilohms, and C is capacitance in microfarads.

38 kilohertz = 1/(1.4 * 18.7969 kilohms * 0.001 microfarads)

Even if you could find a 18796.9 ohm resistor, it turns out the capacitance and resistance of the wiring and the wide tolerance (even at 1%) of the parts means a variable resistor (potentiometer) is a must! Also, the current being used to drive the transistor (Q1) alters the timing a bit.

Using a 1-nF (C1) [1 nF is same as 0.001 µF] capacitor and a 15-kilohm fixed resistor (R1) plus a 5-kilohm potentiometer (R2) does the trick. Not only does the potentiometer allow for hand tuning, but also the frequency can be varied from about 32 kHz up to about 42 kHz. The margin means the desired values of 36 kHz to 40 kHz should be attainable even with variations in parts and wiring.

Solderless Breadboard

There's a slight change from the official schematic presented above. On the breadboard, the timing capacitor (C1) is connected to +5 V rather than ground. Testing indicates the same frequency, voltage range, and power consumption regardless. Still, you should use a connection to GND.

On the left is a multiturn potentiometer. The small brass-colored screw rotates many times to perform the same adjustment as the white single-turn dial on the right. The multiturn allows for more precise adjustments and is less prone to shift out of position. Even if it does shift, less change results because it needs to take multiple turns around.

Multiturn potentiometers are more expensive, but worth it for timing circuits.

Surface Mount Components:

A very small infrared circuit can be created with surface mount components. The power usage and basic functionality is the same. Theoretically the electrical noise should be reduced since through-hole leads can act as transmitter antennas.

A couple of notes:

* R2 is a very small (4 mm) surface-mount multiturn potentiometer.

* A lot of extra drill holes exist in the board so that I could use up my small stock of through-hole parts if desired (for this board, I didn't desire). For example, C2 has extra holes to the left and right.

* This circuit differs from the breadboard and schematic as it is designed to drive a pair of dual emitters (four LEDs total). A tiny, green, surface-mount LED indicates when the oscillator is enabled.

create a surface-mount boards at home.

It's really not difficult. You should try it!

There are a few tricks that help me...

Using a toothpick, I place a small dab of silicone adhesive (which I suspect is just caulk in a smaller, more expensive tube) on each location of the board where a surface-mount component is going to be.

As far as I can tell, silicone is pretty friendly compared to the usual nasty PCB chemicals. The package indicates the material is stable up to 400 degrees Celsius. The wet viscosity holds components in place but allows for nudging. The thickness is perfect for bridging the space between the board and slightly raised component backs.

I then deposit each component using tweezers. After five minutes or so, the components can be soldered without them moving around. If a mistake is discovered, the component can be pulled off easily, as the silicone dries to a pliable, soft, rubbery consistency.

With small components, sometimes solder bridges form and sometimes the core flux misses the mark and cold solder balls or joints form. No problem, just place some flux paste in those locations. Reheat the joints with the tip of the soldering iron and they melt to perfection.

Which Oscillator Is Better?

The 555 circuit uses less power when turned on, but the total power usage of an infrared emitter device easily overshadows any minor power-on savings in the oscillator itself.

The NAND solution is cheaper and basically as easy to construct.

Obviously my optimized NAND circuit is better than my original NAND circuit. However, I can't say whether my 555 circuit is even better.

Since the 555 is specifically designed for timing and since it has been widely adopted, I assume there are benefits that I haven't perceived. Most likely the ability to vary duty cycle and other versatility is the real reason the 555 is so popular.

Wednesday, May 28, 2008

Cadmium-Sulfide Color Sensor

Over the years, a number of methods have been tried to create an inexpensive color sensor. One way is to surround an ordinary photocell with a red, green, and blue ultra-bright LED.

All three LEDs are never actually turned on at the same time. Each LED is turned on one at a time and the intensity of light reflected back to the cadmium-sulfide photocell is measured. An analog-to-digital converter measures the voltage divided between a fixed resistor (usually between 470 ohms and 10,000 ohms) and the photosensitive resistor (the photocell).

Ultra-bright LEDs are available from any electronics seller or eBay. Back when I first wrote this article, I got the LEDs from AllElectronics. I purchased red #LED-50 for $0.50, true green #LED-57 for $3.75, and blue #LED-58 for $3.50. Prices have come down considerably since then.

The advertised brightness of red is 3000 mcd, green is 3000 mcd, and blue is 1200 mcd. The resistor values that provided equivalent readings reflecting off white paper are red with 100 ohms, green with 800 ohms, and blue with 100 ohms. Either the green LED is a lot brighter than the others or the photocell's peak sensitivity is to green (or probably some combination of both).

The LEDs are water clear when turned off. Black electrical tape surrounds the photocell in the center of the LEDs. The tape blocks the direct light from the LEDs from reaching the photocell, thus detecting only reflected light.

After the amount of red light, green light, and blue light is measured, each component is individually scaled based on minimum and maximum values obtained at calibration. One-time calibration consists of aiming the completed sensor first at a white piece of paper and then at a piece of black conductive foam. The maximum and minimum values are plugged into the EEPROM of the microcontroller. Scaling based on actual data allows the individual attributes of that particular sensor and set of LEDs to be accounted for.

Alternatively, you can adjust the balance of the colors in hardware by using with three separate trimpots (trimmer potentiometers). Dialing a trimpot changes the brightness of a particular LED. For example, if there's too much red being sensed, simply increase the resistance to decrease the LED brightness by turning the trimpot attached to the red LED.

It's a good idea to always include a minimum fixed resistor value (100 ohms to 150 ohms) in series with each trimpot so that if you accidentally dial the trimpot to 0 ohms the LED won't be damaged.

The photo above includes an Atmel ATtiny45 microcontroller for turning on and off each of the LEDs, reading the results, and outputting the values to a personal computer. You can use any microcontroller of your choice. Or, if you just want a color mixer to play with various output colors, simply pull the microcontroller and feed the resistors 5V.

above is a pic of Regular and small cadmium-sulfide photocells.


The above readings were taken through a clear plastic case (not shown). By substituting a few black threads on which to rest the candy, the contrast between colors improved significantly. Perhaps the shiny plastic reflected too much LED light back into the sensor, regardless of the actual color of the object being examined.

Position Problem!

Later discovered a significant flaw with the sensor as currently designed. The candies had always been manually centered for reading. However, misplacement of objects causes more light to reflect from one of the LEDs than the other LEDs. This causes a false detection of color, since it now appears that the object has more of one particular color simply because that LED is closer to the object.

The design could be modified so that the LEDs can be placed together with all light appearing through a single tube or source. A disadvantage to this approach would be a reduction in brightness. An advantage would be that only one light source (the tube) needs to be aligned with the sensor for optimal and equal reflection.

For objects up close, the multicolor LED (also called an RGB LED) works pretty well for reducing object-position errors. Unfortunately, as the RGB LED is lifted up, it becomes apparent that the position of the individual color chips within the single lens causes the light sources to diverge. Perhaps this isn't as much of a problem with other RGB LEDs?

Speed Limitation

Only two or three complete color readings can be performed per second. The cadmium-sulfide photocell needs time to react to the brightness changes. Blinking the LEDs faster than this rate reduces contrast until all colors result in the same apparent reflective value, as though all LEDs were lit at the same time.

A visible-light phototransistor would provide superior speed. The infrared (remote-control quality) phototransistors I possess are all nearly insensitive to visible light, especially blue. Therefore, infrared diodes and infrared phototransistors won't work.

At first I thought I could use the "visible phototransistor" from Jameco Electronics (part number 120221, product number BPW77, for $1.99 each). However, the datasheet shows that the phototransistor is 100% sensitive for infrared, 50% sensitive for red, 33% sensitive for green, and even less sensitive for blue. This could be somewhat compensated for by using lower-value resistors on the green LED and blue LED so that they would emit more light.

A better choice is the family of TAOS light-to-voltage converters. Each consists of a fast true-visible-light photodiode and an amplifier in a hobbyist-friendly three-pin package. No external voltage-divider resistor is necessary.

At Mouser Electronics, you can find three major visible-light varieties that trade off speed vs. light sensitivity. (But even the slowest one is 1000 times faster than a cadmium-sulfide photocell.)

* TSL12S-LF or TSL250R-LF: Slower speed but more light sensitive.
* TSL13S-LF or TSL251R-LF: Middle speed and middle light sensitivity.
* TSL14S-LF or TSL252R-LF: Faster speed but less light sensitivity.

The [sloppy] paint job on the RGB LED is to prevent light from going directly to the TAOS photosensor. This sensor arrangement works by have each LED color (red, green, and blue) in the RGB LED turned on one at a time, the light then reflects off of an object, and is read by the photosensor. The next color is turned on, the results read, and so on.

Friday, May 23, 2008


Tiny motors are wonderful for driving little robots (like Appetizer or Chicago) or turning small parts (like sensors) on big robots. Illustrated above, from left to right:

* Blue m&m's candy for size comparison
* Cell-phone vibrating motor (salvaged)
* Solarbotics #TPM tiny pager motor. Replaced by TMP2 ($4.95) -- comes with clean shaft (no weight)
* Solarbotics #RPM pager motor. Replaced by RMP2 ($3.95) -- comes with clean shaft (no weight)

Electronic Goldmine has a number of pager motors with weights on their shafts: G12809 ($0.99), G13566 ($1.29), G15241 ($0.99), G15768 ($0.99), G15768 ($0.99 for 2), G16153 ($1.00).
BGMicro has a pager motor with a weight on its shaft: MOT1030 ($0.99).
All Electronics has a pager motor with a weight on its shaft: #DCM-204 ($1.25).

Solarbotics sells tiny geared pager motors!!

Geared motors are far superior to ordinary pager motors for robotics, since they have more torque (pushing power) and rotate more slowly. See the GM10 ($12) and GM15 ($19) in the Motors section of Solarbotics. Although slightly larger than most pager motors, the GM11, GM11a, GM12a, GM13a, GM18, GM19 ($19.75-$23 each) are still relatively small and are worth a look.


Before discarding a damaged or obsolete cell phone, pager, or force-feedback joystick (aka game controller), crack it open and recover the vibrating element! The vibrating part usually consists of a miniature motor with an offset-weighted shaft. Because the piece of metal on the shaft is not centered, when the motor spins it causes the device to shift back-and-forth as the weight of the metal piece shifts around and around the motor shaft. Vibration.

Dremel High-Speed Rotary Tool Failure

The offset weight must be removed to make an effective robot motor.

My first attempt at removal was to use a cutting wheel. Then, I tried to use a grinding stone. Although I successfully removed the weight, the process was difficult and took a long time. More significantly, the motor shaft got damaged. In the above photos, the shaft is nearly ground to half diameter. That's not good!

Someone with greater skill and tool-accessory knowledge could probably perform the operation better than I could. The Dremel isn't at fault.

Seriously, always wear goggles or protective eye wear when working with tools!

Locking Pliers

The metal attached to my cell-phone vibrating motors is extremely strong. It doesn't appear to be made of lead or some other malleable element. The metal ended up dulling or damaging the heads of standard pliers and cutters. Even when I could get a grip, I ended up pulling out the entire shaft of the motor. That's not good either!

While attempting to get a better grip on the motor, I accidentally discovered a reliable, repeatable, and easy way to remove the metal weight. Simply applying the locking force of locking pliers to the weight seems to crush or deform the metal very slightly, but enough to pop the crimp.

Unless you've got super powers, normal pliers won't work. The leveraged force of locking pliers is absolutely necessary.

Position, Squeeze, and Tug:

Grip the metal weight at the end of the locking pliers like popping off a beer cap with your molars. (The American Dental Association would like to point out that the prior sentence is very reckless and is likely to result in the enrichment of your local dental specialist.) Try to grip across only the crimped portion of the metal weight, so that it can squish out rather than crimp further. The motor body shouldn't be touching the pliers at all.

Use the greatest squeezing force the pliers can reasonably apply. The more the initial resistance to the squeeze, the easier it is to remove the motor shaft. When positioned and squeezed just right, I barely had to tug on the motor body to pull the shaft from the weight.

Use only your hand to pull on the motor body. No other pliers or tools should be necessary.

Alternate Method: Slitted Metal:

Depending on your access to precision machine tools (like a lathe and a milling machine), it may be possible for you to make a custom gear puller. If not, then a slightly more crude method can produce similar results.

Find the thickest piece of flat stock metal sheet (can be from a junk drawer) that will fit between the end of the motor and the gear or other object you want to remove. Saw or cut a slit part of the way through the metal sheet. See item (1) in above picture. The slit should be wide enough that the motor shaft can be slid on, leaving the gear on one side of the sheet and the motor on the other side of the sheet.

Then, find a rod (like from a consumed Dremel grinding bit) or make a punch tool that can fit through the object to make contact with the motor shaft. See item (2) in the above picture.

Place this setup on a vise or something similar to support the metal sheet. With the rod making contact with the motor shaft, gently tap the rod with a hammer. This should force the motor shaft out of the gear. At some point, the motor will fall to the floor. Be sure to put a blanket or something there to catch the motor.

Better still, if you have an arbor press, you can use the same tools to ease the motor free, rather than tapping on it with a hammer.

Monday, May 5, 2008

Robo's Think Like Humans

You know the future has arrived when scientists bring together two staples of science fiction: lasers and robots.

But rather than 50-tonne behemoths dealing death with a massive light cannon, the El-E robot is instead using lasers to think like a human.

Scientists at the Georgia Institute of Technology and the Emory University School of Medicine believe they have found the answer to the difficulties that robots have in processing the imperfections of the real world using laser pointers.

Ordering El-E to retrieve an item is as simple as shining a laser pointer on the object you want. The pointer can also be used a second time to tell El-E to put the object in a certain place or give it to a specific person.

Above, Charlie Kemp, director of the Healthcare Robotics Center at Georgia Tech and Emory, accepts a towel from El-E.

El-E, named after its arm's resemblance to an elephant trunk, as seen here, can grasp a range of household items including towels, pill bottles and telephones from floors or tables.

The robot and its ability to pick up items from both floors and shelves could be a lifeline for people who have mobility difficulties.

El-E's creators are gathering input from ALS (also known as Lou Gehrig's disease) patients and doctors to prepare El-E to assist patients with severe mobility challenges.

Researchers from Georgia Tech and Emory are working with an expert on human-computer interactions to ensure the robot will one-day be ready to be used in people's homes.

El-E uses a custom-built omni-directional camera to see most of the room. After it detects a selection has been made with the laser pointer, the robot moves two cameras to look at the laser spot and triangulate its position in three-dimensional space.

Once it has reached an object, sensors in its hands will guide it on opening and closing its gripper until it has a firm hold, as pictured here.

The robot is able to detect the difference between a face, a table or the floor so it is able to carefully present an object to a person or place it on a table or the floor.

Researchers say one of the key benefits of the system is that El-E does not need to understand what objects are called, instead relying on an array of sensors similar to those seen here.

El-E's power and computation is all on board and runs Ubuntu Linux on a Mac Mini.

Kemp said: "We humans naturally point at things but we aren't very accurate, so we use the context of the situation or verbal cues to clarify which object is important.

"Robots have some ability to retrieve specific, predefined objects, such as a soda can, but retrieving generic everyday objects has been a challenge for robots."

Georgia Tech and Emory researchers are now working to help El-E expand its capabilities to include switching lights on and off when the user selects a light switch and opening and closing doors when the user selects a door knob.


Those metal sculptures really looks great, and the best thing is that those weird mechanic’s have a lots of fire for you. Those are fire breathing robots and it looks too cool. These creative creators of those weird robots really do have some extra free time. Take a look at pictures and enjoy.

Jumping spiders, flaming bots and unnamed “things” inhabit the Greathouse Labs, providing lots of overheated excitement:

Terminator-like entities haunt the grounds:

Wicked-looking battle bots and robot crawlers lurk in the garage, the walking cannons scurry around like mechanized chickens:

Imagine meeting this thing somewhere in the country field in the middle of the night… You just might become a connoisseur of “grotesque” for the rest of your life.