New MEMS Accelerometers for Industrial Condition Monitoring Apps

Analog Devices’s new ADXL1001 and ADXL1002 high-frequency, low-noise MEMS accelerometers are designed for industrial condition-monitoring applications. The accelerometers deliver the high-resolution vibration measurements needed for the early detection of machine failure (e.g., bearing faults).Analog ADXL1001

The ADXL1001 and ADXL1002’s benefits, features, and specs:

  • Deliver ultra-low noise density over an extended bandwidth with high-g range.
  • Available in two models with full-scale ranges of ±100 g (ADXL1001) and ±50 g (ADXL1002).
  • Typical noise density for the ADXL1002 is 25 μg/√Hz, with a sensitivity of 40 mV/g, and 30 μg/√Hz for ADXL1001 with sensitivity 20 mV/g.
  • Operate on single voltage supply from 3. to 5.25 V
  • Electrostatic self-test
  • Over range indicator
  • Rated for operation over a –40°C to 125°C temperature range.

The accelerometers cost $29.61 each in 1,000-unit quantities.

Source: Analog Devices

New Battery Pack Monitor Protects Multi-Cell Li-ion Batteries

Intersil Corp. recently announced the ISL94203 3-to-8 cell battery pack monitor that supports lithium-ion (Li-ion) and other batteries. The ISL94203 can monitor, protect, and cell balance rechargeable battery packs to maximize battery life and ensure safe charging and system operation. It works as a stand-alone battery management system for rechargeable Li-ion battery packs.Intersil-ISL94203

The ISL94203’s internal state machine has five preprogrammed stages that accurately control each cell of a battery pack to extend operating life. In addition, it integrates high-side charge/discharge FET drive circuitry.

Notable features and specifications:

  • Highest level of integration
  • Eight cell voltage monitors support Li-ion CoO2, Li-ion Mn2O4, Li-ion phosphate and other battery chemistries
  • Can operate as a standalone solution or with a microcontroller
  • Integrated charge pump controls cutoff FETs used to charge/discharge battery pack
  • Multiple cell voltage protection options up to 4.8 V
  • Programmable detection/recovery times for over-voltage, under-voltage, over-current, and short circuit conditions
  • Open wire detection
  • EEPROM storage for device configuration
  • Power saving algorithm activated when battery pack is not in use


The ISL94203 battery pack monitor is available now through Intersil’s worldwide network of authorized distributors. The ISL94203 comes in a 6 mm × 6 mm, 48-lead TQFN package, and is priced at $2.19 in 1,000-piece quantities. The ISL94203EVKIT1Z evaluation kit ($328) includes an evaluation board, interface board with USB-to-I2C interface, and software GUI that supports stand-alone operation or an external microcontroller.

Source: Intersil Corp. 

IoT Project: Wireless Sump Pump Monitor

Do you worry about your basement flooding? You can build a microcontroller-based, three-unit wireless system can monitor the water level in your sump pit. The Pump-Eye is a three-unit water level monitoring system built around a Freescale Semiconductor MC9S08GT60 and MC9S12NE64 microcontrollers.

1—A hose connects the Pump-Eye sensor unit to a copper pipe. The pipe gets fastened to the side of the sump pit.

A hose connects the Pump-Eye sensor unit to a copper pipe. The pipe gets fastened to the side of the sump pit.

The sensor unit monitors the water level in a sump pump pit, the sump pump’s AC power, and the sensor unit’s backup battery. The base unit receives status information from the sensor unit via RF. The sensor and base units use MC9S08GT60 microcontrollers; they communicate with each other via 2.4-GHz transceivers based on an MC13192 SARD board. The Ethernet link creates and sends timestamp and log messages to a host when the pump runs. The system sends a warning e-mail when the water level is high or there’s a power failure. An alarm sounds when the water level exceeds the normal maximum height by 10%.

In “Wireless Sump Pump Monitoring System”  (Circuit Cellar 189), David Kanceruk writes:

The Pump-Eye is a flexible system comprised of three electronic units: a sensor unit, a base unit, and an Ethernet unit. Let’s take a look at each unit.

Figure 1—The base and Ethernet units are optional. There are five ways to set up the Pump-Eye system without having to make any software changes.

Click to enlarge. The base and Ethernet units are optional. There are five ways to set up the Pump-Eye system without having to make any software changes.

The sensor unit monitors the sump pit’s water level (see Photo 1). Data is displayed on a 10-segment LED bar graph so you don’t have to remove the sump pit’s lid to determine the water level. An alarm sounds when the water level exceeds the height you program into the system. A switch enables you to cancel the alarm at any time. LEDs illuminate when the AC power is off and when the sensor unit’s 9-V backup battery needs to be replaced.

The base unit features the same indicators as the sensor unit. It sounds the same alarm signal as the sensor unit. I chose the SOS Morse code sound (an old sound that’s recognizable to some of us) because it’s notably different than the sounds generated by my appliances. Canceling the alarm on the base unit cancels the alarm on the sensor unit and vice versa. Because the units are connected wire- lessly, I can place the base unit anywhere in my house. Therefore, I don’t have to go to my basement to read the sensor unit’s front panel.

The Ethernet unit can connect to either the sensor unit or the base unit via an RS-232 connection. I can place the Ethernet unit in the most convenient location for connecting to an uninterruptible power supply (UPS) and network. The Ethernet unit receives commands from the unit to which it’s attached. It then sends syslog messages to a syslog server so that pump cycles can be time stamped and counted. A record is kept of the pump’s run times. The Ethernet unit can also send me an e-mail or text message regarding conditions that require immediate attention (e.g., high water levels and a loss of AC power).

The sensor and base units feature Freescale MC9S08GT60 microcontrollers. They communicate with each other via 2.4-GHz ZigBee transceivers based on a Freescale MC13192 SARD board using IEEE 802.15.4 MAC soft- ware. The sensor unit monitors the sump pump’s AC power and its 9-V back-up battery.

The front panel electronics on the two units are similar, but there are a few differences. The sensor unit is larger. It also has an extra connector that’s used for passing signals to the rear panel’s electronics for the sensors. Because the base unit simply acts as a remote display to show what’s happening on the sensor unit, it doesn’t need sensing electronics on the rear panel.

When you cover the top of a straw with your finger and place it in a glass of water, the air in the straw becomes pressurized. The amount of pressure depends on the height of the water in the straw, and this depends on factors such as ambient air pressure, the mass density of the water, gravity, and the height of the water outside the straw: P = Pa + rg∆h. In this formula, P is the pressure, Pa is the ambient pressure, r is the mass density of fluid, g is 9.8066 m/s2, and h is the height of fluid.

You can nullify the effect of a change in ambient pressure if you use a gauge pressure sensor to measure pressure relative to ambient pressure. The formula then becomes P = rg∆h. You can assume that the mass density of water and gravity are constants, so the pressure will be proportional to a change in the water’s height. The sensor unit measures this pressure with a Freescale MPXM2010GS temperature-compensated gauge pressure sensor. The pressure is then converted to a percentage of normal water levels observed in the sump pit.

I tried placing a hose in the sump pit to sense the water level, but I quickly discovered that it wasn’t too reliable. This was probably because of the surface tension of the water clinging to the inside of the thin hose (5/64 inches in diameter). Therefore, I decided to use a 0.5 inches in diameter copper pipe as a sensor interface. The ratio of the area affected by surface tension to the total area is less significant with the larger diameter. I bought a length 0.125 inches in diameter brass pipe to use as a nipple for the hose that connects the MPXM2010GS to the cop- per pipe. I soldered the brass pipe to a standard 0.5 inch copper cap in which I had drilled a hole. The cap is soldered to the top of the copper pipe.

The copper pipe solved the problem of holding the open end of the hose at a fixed height, and it also alleviated my concerns about dirt clogging the thin hose. A plastic clamp screwed to the side of the plastic sump pit holds the pipe in place. I had originally placed the pipe to the bottom of the sump pit, but I found a negative pressure developing in it after numerous pump cycles. I concluded that this was the result of scavenging around the bottom of the pipe because of water currents caused by the pump. Keeping the end of the pipe at the height of the low water level pre- vented this from happening.

Read the full article.

Wi-Fi-Connected Home Energy Monitor

The Kunzig brothers of Pennsylvania use the word “retired” loosely.

Donald and Robert are both retired—each from long careers in the telecommunications industry. And after retirement, each took on a new job (Donald developing software to track and manage clinical trials managed by BioClinica, Inc., and Robert at a large data center).

So while other semi-retirees might prefer relaxing in poolside chairs or on the couch, what do these two do? They eagerly take on some technologies they haven’t worked with before and build a Wi-Fi-connected device to monitor a home’s power usage. And after two years of trial, error, and, finally, success, they develop an e-commerce website to sell it.

“Robert’s son, Jay, a design engineer working in San Jose, CA, suggested the project,” the two brothers say in article they wrote for the May 2013 edition of Circuit Cellar. “The main purpose was to design a Wi-Fi-connected monitor that would be able to measure usage from both a utility and an alternate source of power such as solar or wind.”

Their article describes how they designed a usable device that offers programmability and function. They used a Microchip MRF24WB0MB 802.11 transceiver for Wi-Fi access and a Microchip Technology PIC24FJ256GB108 microprocessor in their design. They eventually wrote the article about the ups and downs of the process (which included five prototypes) because they felt elements of their work would help readers developing their own embedded electronics devices.

“All this effort has been rewarding, perhaps not financially (yet), but certainly intellectually,” the brothers say. “After almost two years of effort, we have produced a product with an excellent hardware design, coupled with software that is better than average. The platform can be used for just about any implementation.”

“We wanted to produce an energy monitor that was fully wireless, very accurate, extremely easy to use, and based on hardware and software that is very stable. We think we were successful on all counts.”

Check out the May issue of Circuit Cellar for their article. And for more information, visit their e-commerce website at

Microcontroller-Based Heating System Monitor

Checking a heating system’s consumption is simple enough.

Heating system monitor

Determining a heating system’s output can be much more difficult, unless you have this nifty design. This Atmel ATmega microcontroller-based project enables you to measure heat output as well as control a circulation pump.

Heating bills often present unpleasant surprises. Despite your best efforts to economise on heating, they list tidy sums for electricity or gas consumption. In this article we describe a relatively easy way to check these values and monitor your consumption almost continuously. All you need in order to determine how much heat your system delivers is four temperature sensors, a bit of wiring, and a microcontroller. There’s no need to delve into the electrical or hydraulic components of your system or modify any of them.

A bit of theory
As many readers probably remember from their physics lessons, it’s easy to calculate the amount of heat transferred to a medium such as water. It is given by the product of the temperature change ΔT, the volume V of the medium, and the specific heat capacity CV of the medium. The power P, which is amount of energy transferred per unit time, is:

P= ΔT × CV × V // Δt

With a fluid medium, the term V // Δt can be interpreted as a volumetric flow Vt. This value can be calculated directly from the flow velocity v of the medium and the inner diameter r of the pipe. In a central heating system, the temperature difference ΔT is simply the difference between the supply (S) and return (R) temperatures. This yields the formula:

P = (TS – TR) × CV × v × pr2

The temperatures can easily be measured with suitable sensors. Flow transducers are available for measuring the flow velocity, but installing a flow transducer always requires drilling a hole in a pipe or opening up the piping to insert a fitting.

Measuring principle
Here we used a different method to determine the flow velocity. We make use of the fact that the supply and return temperatures always vary by at least one to two degrees due to the operation of the control system. If pairs of temperature sensors separated by a few metres are mounted on the supply and return lines, the flow velocity can be determined from the time offset of the variations measured by the two sensors…

As the water flows through the pipe with a speed of only a few metres per second, the temperature at sensor position S2 rises somewhat later than the temperature at sensor position S, which is closer to the boiler.

An ATmega microcontroller constantly acquires temperature data from the two sensors. The time delay between the signals from a pair of sensors is determined by a correlation algorithm in the signal processing software, which shifts the signal waveforms from the two supply line sensors relative to each other until they virtually overlap.The temperature signals from the sensors on the return line are correlated in the same manner, and ideally the time offsets obtained for the supply and return lines should be the same.

To increase the sensitivity of the system, the return line sensor signals are applied to the inputs of a differential amplifier, and the resulting difference signal is amplified. This difference signal is also logged as a function of time. The area under the curve of the difference signal is a measure of the time offset of the temperature variations…

Hot water please
If the heating system is also used to supply hot water for domestic use, additional pipes are used for this purpose. For this reason, the PCB designed by the author includes inputs for additional temperature sensors. It also has a switched output for driving a relay that can control a circulation pump.

Under certain conditions, controlling the circulation pump can save you a lot of money and significantly reduce CO2 emissions. This is because some systems have constant hot water circulation so users can draw hot water from the tap immediately. This costs electricity to power the pump, and energy is also lost through the pipe walls. This can be remedied by the author’s circuit, which switches on the circulation pump for only a short time after the hot water tap is opened. This is detected by the temperature difference between the hot water and cold water supply lines…

Circuit description
The easiest way to understand the schematic diagram is to follow the signal path. It starts at the temperature sensors connected to the circuit board, which are NTC silicon devices.

Heating system monitor schematic

Their resistance varies by around 0.7–0.8% per degree K change in temperature. For example, the resistance of a KT110 sensor is approximately 1.7 kΩ at 5 °C and approximately 2.8 kΩ at 70 °C.

The sensor for supply temperature S forms a voltage divider with resistor R37. This is followed by a simple low-pass filter formed by R36 and C20, which filters out induced AC hum. U4a amplifies the sensor signal by a factor of approximately 8. The TL2264 used here is a rail-to-rail opamp, so the output voltage can assume almost any value within the supply voltage range. This increases the absolute measurement accuracy, since the full output signal amplitude is used. U4a naturally needs a reference voltage on its inverting input. This is provided by the combination of R20, R26 and R27. U5b acts as an impedance converter to minimise the load on the voltage divider…

Thermal power

PC connection
The circuit does not have its own display unit, but instead delivers its readings to a PC via an RS485 bus. Its functions can also be controlled from the PC. IC U8 looks after signal level conversion between the TTL transmit and receive lines of the ATmega microcontroller’s integrated UART and the differential RS485 bus. As the bus protocol allows several connected (peer) devices to transmit data on the bus, transmit mode must be selected actively via pin 3. Jumper JP3 must be fitted if the circuit is connected to the end of the RS485 bus. This causes the bus to be terminated in 120 Ω, which matches the characteristic impedance of a twisted-pair line…


DIY, Microcontroller-Based Battery Monitor for RC Aircraft

I’ve had good cause to be reading and perusing a few old Circuit Cellar articles every day for the past several weeks. We’re preparing the upcoming 25th anniversary issue of Circuit Cellar, and part of the process is reviewing the company’s archives back to the first issue. As I read through Circuit Cellar 143 (2002) the other day I thought, why wait until the end of the year to expose our readers to such intriguing articles? Since joining Elektor International Media in 2009, thousands of engineers and students across the globe have become familiar with our magazine, and most of them are unfamiliar with the early articles. It was in those articles that engineers set the foundation for the development of today’s embedded technologies.

Over the next few months, I will highlight some past articles here on as well as in our print magazine. I encourage long-time readers to revisit these articles and projects and reflect on their past and present use values. Newer readers should not regard them as simply historical documents detailing outdated technologies. Not only did the technologies covered lead to the high-level engineering you do today, many of those technologies are still in use.

The article below is about Thomas Black’s “BatMon” battery monitor for RC applications (Circuit Cellar 143, 2002). I am leading with it simply because it was one of the first I worked on.

For years, hobbyists have relied on voltmeters and guesswork to monitor the storage capacity of battery packs for RC models. Black’s precise high-tech battery monitor is small enough to be mounted in the cockpit of an RC model helicopter. Black writes:

I hate to see folks suffer with old-fashioned remedies. After three decades of such anguish, I decided that enough is enough. So what am I talking about? Well, my focus for today’s pain relief is related to monitoring the battery packs used in RC models. The cure comes as BatMon, the sophisticated battery monitoring accessory shown in Photo 1.

Photo 1: The BatMon is small enough to fit in most RC models. The three cables plug into the model’s RC system. A bright LED remotely warns the pilot of battery trouble. The single character display reports the remaining capacity of the battery.

Today, electric model hobbyists use the digital watt-meter devices, but they are designed to monitor the heavy currents consumed by electric motors. I wanted finer resolution so I could use it with my RC receiver and servos. With that in mind, a couple of years ago, I convinced my firm that we should tackle this challenge…My solution evolved into the BatMon, a standalone device that can mount in each model aircraft (see Figure 1).

Figure 1: Installation in an RC model is as simple as plugging in three cables. Multiple point measurements allow the system to detect battery-related trouble. Voltage detection at the RC receiver even helps detect stalled servos and electrical issues.

This is not your typical larger-than-life Gotham City solution. It’s only 1.3″ × 2.8″ and weighs one ounce. But the BatMon does have the typical dual persona expected of a super hero. For user simplicity, it reports battery capacity as a zero to nine (0% to 90%) level value. This is my favorite mode because it works just like a car’s gas gauge. However, for those of you who must see hard numbers, it also reports the actual remaining capacity—up to 2500 mAH—with 5% accuracy. In addition, it reports problems associated with battery pack failures, bad on/off switches, and defective servos. A super-bright LED indicator flashes if any trouble is detected. Even in moderate sunlight this visual indicator can be seen from a couple hundred feet away, which is perfect for fly-by checks. The BatMon is compatible with all of the popular battery sizes. Pack capacities from 100 mAH to 2500 mAH can be used. They can be either four-cell or five-cell of either NiCD or NiMH chemistries. The battery parameters are programmed by using a push button and simple menu interface. The battery gauging IC that I used is from Dallas Semiconductor (now Maxim). There are other firms that have similar parts (Unitrode, TI, etc.), but the Dallas DS2438 Smart Battery Monitor was a perfect choice for my RC application (see Figure 2).

Figure 2: A battery fuel gauging IC and a microcontroller are combined to accurately measure the current consumption of an RC system. The singlecharacter LCD is used to display battery data and status messages.

This eight-pin coulomb counting chip contains an A/D-based current accumulator, A/D voltage convertor, and a slew of other features that are needed to get the job done. The famous Dallas one-wire I/O method provides an efficient interface to a PIC16C63 microcontroller…In the BatMon, the one-wire bus begins at pin 6 (port RA4) of the PIC16C63 microcontroller and terminates at the DS2438’s DQ I/O line (pin 8). Using bit-banging I/O, the PIC can read and write the necessary registers. The timing is critical, but the PIC is capable of handling the chore…The BatMon is not a good candidate for perfboard construction. A big issue is that RC models present a harsh operating environment. Vibration and less than pleasant landings demand that you use rugged electronic assembly techniques. My vote is that you design a circuit board for it. It is not a complicated circuit, so with the help of a freeware PCB program you should be on your way…The connections to the battery pack and receiver are made with standard RC hobby servo connectors. They are available at most RC hobby shops. You will need a 22-AWG, two-conductor female cable for the battery (J1), a 22-AWG, two-conductor male for the RC switch (J2), and a three-conductor (any AWG) for the Aux In (J3) connector…The finished unit is mounted in the model’s cockpit using double-sided tape or held with rubber bands (see Photo 2).

Photo 2: Here's how the battery monitor looks installed in the RC model helicopter’s cockpit. You can use the BatMon on RC airplanes, cars, and boats too. Or, you could adapt the design for battery monitoring applications that aren’t RC-related.

Thomas Black designs and supports high-tech devices for the consumer and industrial markets. He is currently involved in telecom test products. During his free time, he can be found flying his RC models. Sometimes he attempts to improve his models by creating odd electronic designs, most of which are greeted by puzzled amusement from his flying pals.

The complete article is now available.