AnalogTalk

Have you ever looked at the blinking light on your smoke detector at home wondering, how does that thing work, and why does it always go off when I’m cooking?  For most home smoke detectors there are two basic types, photoelectric and ionization.  What is the difference between the two?  Why is one preferred over the other in some regions?  I heard that the ionization smoke detectors have some radioactive material in them.  What is worse, the fire or being constantly bombarded by the radiation from my smoke detector?

Photoelectric smoke detectors operate on a simple principle of detecting smoke particles in a small chamber.  Infrared LEDs shine light into the chamber and is detected by a photo-detector.  If smoke particles enter the chamber, some of the infrared light is scattered and reflected to the photo-detector.  After a specified amount of light is detected (relative to a specified amount of smoke particles), then an alarm is sounded.

Ionization smoke detectors have a small amount of americium-241 (about 0.2mg or 1/5000 of a gram) that ionize the air between two plates causing free electrons to move through an electric field.  If smoke is introduced, then the number of free electrons is reduced.  This causes a change in the voltage across the plates and then an alarm is sounded.

So what is the difference between the two types?  Essentially there isn’t much difference because both types of smoke detectors have to meet the same standards for smoke detection.  However photoelectric detectors are typically better at detecting smoldering fires with more particles vs. ionization detectors which are better at gas type fires.  In this case, ionization detectors would sound an alarm with my cooking before the photoelectric detector.

Are you in danger of radiation poison from ionization smoke detectors?  No, you have more chance of getting radiation poisoning from standing outside in the sun.  The small amount of material radiates such a small amount that there is no danger for close exposure to the smoke detector.  However, some regions are concerned about the disposal of this material after the smoke detector has reached its end of life.  That is why Europe typically favors photoelectric smoke detectors and the Americas and Asia typically favor ionization smoke detectors.

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Smoke Detector ICs

News that’s be hitting the tech sites today =)

Microchip Technology Inc., a leading provider of microcontroller and analog semiconductors, today announced three new families of low-power, high-precision operational amplifiers (op amps); meaning the Company now has an extensive offering of high precision Op Amps with Gain Bandwidth Product (GBWP) from 10 kHz to 50 MHz. The MCP6051/2/4 (MCP605X), MCP6061/2/4 (MCP606X) and MCP6071/2/4 (MCP607X) op amps feature offset voltages of just 150 microvolts and are well suited for applications requiring low power consumption, low-voltage operation and high precision, such as those in the industrial, medical, consumer and other markets.

The MCP605X op amps have a GBWP of 385 kHz and a quiescent current of 30 microamperes. The MCP606X op amps have a GBWP of 730 kHz and a quiescent current of 60 microamperes. The MCP607X op amps have a GBWP of 1.2 MHz and a quiescent current of 110 microamperes.

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MCP6051

Faster than any RF spectrum analyzer, the device is ultra-wide band and can receive signals on and differentiate between a broad range of frequencies, like the human ear.  It also consumes 100 times less power than current state-of-the-art models. More Here and Here

The RF Cochlea mimics the neural signal processing of the human cochlea, which uses fluid mechanics, piezoelectrics and neural signal processing to convert sound waves into electrical signals which travel to the brain. “The more I started to look at the ear,” said Rahul Sarpeshkar, associate professor of electrical engineering and computer science at MIT, “the more I realized it’s like a super radio with 3,500 parallel channels.”

Picking up some bills at the ATM the other day got me wondering what sort touch screen tech was being used.  Understandable, inductive touch sensing is used.  Inductive touch sensing fundamental operating principles enable it to work through a front panel, such as plastic, stainless steel or aluminum. The technology also works through thick gloves and on surfaces where liquids are present. These characteristics make inductive touch sensing suitable for applications in the appliance market because of the possibility of a stainless steel front panel; the industrial market because of the technology’s robustness; and the automotive market because of the technology’s sleek aesthetics and ability to reduce accidental-touch triggers.

Why implement temperature control in your system?

Temperature sensors provide temperature feedback to the system controller to make decisions such as, over-temperature shutdown, turn-on/off cooling fan, temperature compensation or general purpose temperature monitor.

What type of sensor’s are there?

There are a number of passive and active temperature sensors that can be used to measure system temperature, including: thermocouple, resistive temperature detector, thermistor and silicon temperature sensors.

What type of products does Microchip support?

Microchip offers three flavors of silicon based temperature sensors:

Logic Output - A signal (logic HIGH or LOW) is asserted when a pre-defined temperature level is reached.

Voltage Output -  Outputs a voltage that is directly proportional to the measured temperature

Serial Output - Temperature is converted and communicated as a digital word (0’s and 1’s) through common communication interfaces such as I2C and SPI.

Why does Microchip support three different types of Temperature products?

This allows the system designer some flexibility when aligning a product to the needs of the application.  Some key features to consider when designing a temperature control system include high accuracy, low power, extended temperature range and small packages.

Here is a link to a Temperature Sensor Design Guide

There’s been quite some interest in what Microchip Technology has claimed to be the world’s first and only op amps to include mCal, an on-chip calibration circuit that calibrates offset voltage at power-up , or the use of an external pin. This results in a low initial voltage offset and a means to minimize drift over time and temperature, both extremely important specs for instrumentation and sensor conditioning applications.

So we’ve managed to get a hold of Kevin Tretter, senior product marketing manager in the analog and interface products division for Microchip to answer some questions.

What is the mCal feature?

The mCal circuitry within the MCP651/2/5 op amp family makes it possible to correct the input offset voltage of the operational amplifier.

How does the mCal feature work?

The calibration circuit is similar to a SAR ADC consisting of a comparator, reference, SAR logic, and a DAC to adjust the offset voltage of the amplifier.
During calibration, the inputs of the amplifier are disconnected from the pins and connected to the internal common-mode reference  or the common-mode based on the Vcal pin. The amplifier output is disabled to avoid glitching the output during calibration.

What does the Vcal pin do?

A low impedance voltage placed on the Vcal analog input pin will set the op amps’ common mode input voltage during calibration. If this pin is left open, the common mode input voltage during calibration is internally set to approximately Vdd/3.

Figure 1 MCP65X Block Diagram

When does the op amp perform a calibration?

A calibration sequence occurs at power-up and based on the state of an external input pin.
The power-on-reset circuitry within the amplifier will initiate a calibration sequence approximately 192 ms after it detects a power up condition. This delay allows for the external Vdd supply to stabilize.

Some devices also offer a CAL/CS pin, which controls the mCal/chip select circuitry. When this pin goes high, the device is placed into a low power mode and the output becomes high-impedance. When the CAL/CS pin goes low, a calibration sequence initiates. At the end of the calibration sequence, the output becomes low impedance and the part resumes normal operation.

How long does a calibration cycle take?

The total calibration cycle takes approximately 2 ms.

Is mCal the same as Auto-Zero?

No. Although both of these architectures provide for voltage offset correction, they are distinctly different. The auto-zero architecture implements a nulling amplifier which continuously corrects the offset of the main amplifier. mCal provides a digital calibration of the voltage offset, but this circuitry is only active upon start-up or when activated via the hardware pin.

How does mCal affect the noise performance of the operational amplifier?

The noise performance of a given amplifier is dependent on the actual op amp design and the process on which it is fabricated. The mCal circuitry will not affect the noise performance of the amplifier.

Have your own questions?  Leave them in the comments sections and we’ll search for the answer!

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MCP651

Looking for a Star Wars laser  blaster?  Maybe closer to a phaser on stun, Laser Energetics Inc. announced last Monday that it introduced its nausea-inducing Dazer Laser nonlethal laser weapon.  The Dazers operate at a range of up to 2400 meters, and work by emitting a green laser beam that fans out into a 1 x 8-foot “Dazer Zone.” When focused on a person’s eyes, his or her vision is temporarily impaired, their balance is effected, and they become overwhelmed by nausea that lasts for several hours!   Full story