A watchdog timer is a piece of hardware, often built into a Single Board Computer (SBC) or embedded PC that can cause a reset when it determines that the system has either hung up or is no longer executing the correct sequence of code.
A properly designed watchdog mechanism should, at the very least, catch events that hang the system. In electrically noisy environments, a power glitch may corrupt the program counter, stack pointer, or data in RAM. The software could crash, even if the code is completely bug free. This is precisely the sort of transient failure that watchdogs will catch.
Bugs in software will cause systems to hang — therefore it is better to fix the root cause rather than relying on a watchdog timer. In complex embedded systems it may not be possible to guarantee that there are no bugs. By using a watchdog, however, you can prevent those bugs from hanging the system indefinitely.
A good watchdog system requires careful consideration of both software and hardware. Make certain to decide early on in the design process how you intend to use it. You will reap the benefits of a more robust system when a failure is detected.
Cooling fans draw in dirt and dust from their operating environments, potentially causing catastrophic failures and/or costly interruptions and downtime. Stealth’s Fanless PCs are engineered to dissipate heat by utilizing the rugged aluminum chassis which acts as a heat sink. Additionally, some models use the latest heat pipe technology to cool and provide noise free operation.
How will fanless computers benefit you?
Save time/money and reduce the worry. No planned maintenance to clean cooling fans or discovering a clogged fan has shut down your application or process.
No noise! When used with SSD, the fanless PC is completely noise free making it ideal for control rooms, audio recording, board rooms, deep thinking and other areas that need to be low in ambient noise.
Numerous designs and configurations to meet your application needs. Deployable in limited space or in rack packaging offering multi I/O, sealed/waterproof, DC power, wireless and more.
Stealth’s fanless computer products are an excellent fit for many applications, including embedded control audio/video recording, digital signs, interactive kiosks, thin-clients, human/machine interface and your next applications.
Built to meet your applications
- No noise and low power consumption
- Solid state drives (SSD)
- Small rugged chassis designs
- Mobile, DC power input, multi I/O
- Sealed/waterproof, multi-LAN networking ports and 16×9 1080p models available
- Windows 7, 8 & XP Pro Compatible, *other O/S Options Available
The four most common touch screen technologies include resistive, infrared, capacitive and SAW (surface acoustic wave). Each technology offers its own unique advantages and disadvantages as described below. Resistive and capacitive touch screen technologies are the most popular for industrial applications. They are both very reliable. If the application requires that operators can wear gloves when using the touch screen, then we generally recommend the resistive technology (capacitive doesn’t support). Otherwise the capacitive technology (better optical characteristics) is more often recommended.
A resistive touch screen typically uses a display overlay consisting of layers, each with a conductive coating on the inner surface. The conductive inner layers are separated by special separator dots, evenly distributed across the active area. Finger pressure causes internal electrical contact at the point of touch, supplying the electronic interface (touch screen controller) with vertical and horizontal analog voltages for digitization. For CRT applications, resistive touch screens are generally spherical (curved) to match the CRT and minimize parallax. The nature of the material used for curved (spherical) applications limits light throughput such that two options are offered: polished (clear) or antiglare. The polished choice offers clarity but includes some glare. The antiglare choice will minimize glare, but will also slightly diffuse the light throughput (image). Either choice will demonstrate either more glare (polished) or more light diffusion (antiglare) than associated with typical non-touch screen displays. Despite the tradeoffs, the resistive touch screen technology remains a popular choice, often because it can be operated while wearing gloves (unlike capacitive technology). Note that resistive touch screen materials used for flat panel touch screens are different and demonstrate much better optical clarity (even with antiglare). The resistive technology is far more common for flat panel applications.
A capacitive touch screen includes an overlay made of glass with a coating of capacitive (charge storing) material deposited electrically over its surface. Oscillator circuits located at corners of the glass overlay will each measure the capacitance of a person touching the overlay. Each oscillator will vary in frequency according to where a person touches the overlay. A touch screen controller measures the frequency changes to determine the X and Y coordinates of the touch. Because the capacitive coating is even harder than the glass it is applied to, it is very resistant to scratches from (SIC) sharp objects. It can even resist damage from sparks. A capacitive touch screen cannot be activated while wearing most types of gloves (non-conductive).
An infrared touch screen surrounds the face of the display with a bezel of light emitting-diodes (LEDs) and diametrically opposing phototransistor detectors. The controller circuitry directs a sequence of pulses to the LEDs, scanning the screen with an invisible lattice of infrared light beams just in front of the surface. The controller circuitry then detects input at the location where the light beams become obstructed by any solid object. The infrared frame housing the transmitters can impose design constraints on operator interface products.
SAW (Surface Acoustic Wave)
A SAW touch screen uses a solid glass display overlay for the touch sensor. Two surface acoustic (sound) waves, inaudible to the human ear, are transmitted across the surface of the glass sensor, one for vertical detection and one for horizontal detection. Each wave is spread across the screen by bouncing off reflector arrays along the edges of the overlay. Two receivers detect the waves, one for each axis. Since the velocity of the acoustic wave through glass is known and the size of the overlay is fixed, the arrival time of the waves at the respective receivers is known. When the user touches the glass surface, the water content of the user’s finger absorbs some of the energy of the acoustic wave, weakening it. The controller circuitry measures the time at which the received amplitude dips to determine the X and Y coordinates of the touch location. In addition to the X and Y coordinates, SAW technology can also provide Z axis (depth) information. The harder the user presses against the screen, the more energy the finger will absorb, and the greater will be the dip in signal strength. The signal strength is then measured by the controller to provide the Z axis information. Today, few software applications are designed to make use of this feature.
Touch Screen Controllers
Most manufacturers offer two controller configurations: ISA Bus and Serial-RS232. ISA Bus controllers are contained on a standard printed circuit plug-in board and can only be used on ISA or EISA PCs. Depending on the manufacturer they may be interrupt driven, polled or be configured as another serial port. Serial controllers are contained on a small printed circuit board and are usually mounted in the video monitor cabinet. They are then cabled to a standard RS232 serial port on the host computer.
Most touch screen manufacturers offer some level of software support which include mouse emulators, software drivers, screen generators and development tools for Windows, OS/2, Macintosh and DOS. Most of the supervisory control and data acquisition (SCADA) software packages now available contain support for one or more touch technologies.
As in 1U, 2U, 4U … etc.
A “rack unit” or “U” is an Electronic Industries Alliance (EIA) standard measuring unit for rack mount type equipment. This term has become more prevalent recently due to the proliferation of rack mount products showing up in a wide range of commercial, industrial and military markets. A rack unit is equal to 1.75″ in height. To calculate the internal useable space of a rack enclosure you would simply multiply the total amount of rack units by 1.75″. For example, a 44U rack enclosure would have 77″ of internal usable space (44 x 1.75).
Stealth manufactures computers and peripherals that are designed to fit into a standard EIA size rack enclosures. Stealth’s rackmount PCs, LCD monitors and keyboards are available in many sizes and configurations. The slim space-saving series rack products are available in 1U (1.75″) and 2U (3.5″) in overall height. Since rack space is at a premium, these slim products represent significant cost savings to the end user. Standard rackmount products are available in 1U, 2U, 4U, 5U and 6U configurations.
Intrinsic safety is a protection concept deployed in sensitive and potentially explosive atmospheres. Intrinsic safety relies on the equipment being designed so that it is unable to release sufficient energy, by either thermal or electrical means, to cause an ignition of a flammable gas.
Intrinsically safe is achieved by limiting the amount of power available to the electrical equipment in the hazardous area to a level below that which will ignite the gases.
In order to have a fire or explosion, fuel, oxygen and a source of ignition must be present. An intrinsically safe system assumes the fuel and oxygen is present in the atmosphere, but the system is designed so the electrical energy or thermal energy of a particular instrument loop can never be great enough to cause ignition.
Traditionally, protection from explosion in hazardous environments has been accomplished by either using explosion-proof equipment which can contain an explosion inside an enclosure, or pressurization and/or purging which isolates the explosive gas from the electrical equipment.
Intrinsically safe equipment cannot replace these methods in all applications, but can provide significant cost savings in installation and maintenance of the equipment in a Hazardous area. The basic design of an intrinsic safety barrier uses Zener Diodes to limit voltage, resistors to limit current and a fuse.
Most applications require a signal to be sent out of or into the hazardous area. The equipment mounted in the hazardous area must first be approved for use in an intrinsically safe system. The barriers designed to protect the system must be mounted outside of the hazardous area in an area designated as “non-hazardous” or “safe” in which the hazard is not and will not be present.
Intrinsic safety equipment must have been tested and approved by an independent agency to assure its safety. The customer should specify the type of approval required for their particular application. The most common agencies involved are as follows:
Country – Agency
USA – FM, UL
Canada – CSA
Great Britain – BASEEFA
France – LCIE
Germany – PTB
Italy – CESI
Belgium – INEX
What it is and why I should care
by Ray Franklin
RoHS stands for Restriction of use of Hazardous Substances (ref. 1). The acronym is pronounced Rose, Roz, Ross, or is spelled out, depending on the speaker’s preference. RoHS is a directive issued Jan. 27, 2003 by the European Commission (EC). It directs European Union (EU) member nations to enact local legislation by Aug. 13, 2004, which will implement the RoHS directive as regulatory requirements before the activation date of July 1, 2006. And that means what?
The directive is a legally binding document for the EU member nations. It establishes regulations at the EU level, which flow to each member nation. Each government must pass its own laws, patterned after the RoHS directive, and do so by a deadline.
RoHS is part of a growing wave of environmental regulations or green initiatives. In addition to RoHS for Europe, there are similar regulations being written in China and other Asian nations. Japanese companies have created a non-governmental group to standardize green procurement requirements. In the U.S., individual states are passing laws restricting some substances and requiring recycling of certain classes of products. A common theme is the so-called “take-back” feature that requires manufacturers to accept old products from consumers and reuse or recycle the items.
The RoHS directive requires that six hazardous substances be removed from all electrical and electronic equipment. The substances may be present incidentally at certain levels as long as they are declared. The six substances are cadmium (Cd), hexavalent chromium (CR VI), lead (Pb), mercury (Hg), polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE). The maximum concentration of Cd is 0.01% by weight of homogeneous material, and 0.1% by weight for the other five substances. “Homogeneous material” means a material that cannot be mechanically disjointed into different materials (ref. 2). A substance is “present incidentally” if it was not intentionally added.
Some exemptions are declared in the RoHS annex, such as Hg in fluorescent lamps, Pb in certain alloys, and Pb in solder for servers (until 2010). All the details are in the RoHS directive text, with discussion and explanation in the dti RoHS guidance notes.
It all sounds pretty straightforward. There are, however, some kinks. For one, the EU member nations have not followed through and produced legislation. The Aug. 13 deadline is long past and only a few countries have passed legislation (ref 3). This delay is creating uncertainty among corporations striving for compliance. Compounding the confusion, local legislation could tighten restrictions and possibly remove exemptions. Any company counting on a particular exemption could run into trouble in countries that nullified the exemption. Furthermore, the EC failed to meet its own October 2004 deadline of finalizing the directive.
Though the regulatory climate is still unsettled, a few certainties have popped up. Compliance is not optional. If you don’t face regulation directly, your customers probably will, and they will push the requirements down to you. The safest strategy is to comply with the most stringent requirements — aim for RoHS with no exemptions. You are not alone. Every other business is in the same boat, and industry groups are working hard to formulate standards for compliance. Use the links on the RoHSwell home page to research RoHS in greater depth. Form your own plan, and get compliant.
1. From directive 2002/95/EC, of the European Parliament.
2. From dti RoHS Regulations, Government Guidance Notes, Consultation Draft, July 2004.
3. The Perchards Report, summary of the transposition of the WEEE and RoHS directives into law by EU member states, January 2005.