Conventional Headphone Amplifiers Most traditional headphone amplifiers used in battery-powered electronics are single-supply devices operating between a positive voltage and ground. This design results in an amplifier that can pass only positive signals. Audio signals, however, inherently swing positive and negative. So before a traditional single-supply amplifier can accept the audio signal, a DC bias must be added. This DC bias is typically half the supply voltage to allow maximum signal swing (Figure 1).

" />

Tkool Electronics

Conventional Headphone Amplifiers Most traditional headphone amplifiers used in battery-powered electronics are single-supply devices operating between a positive voltage and ground. This design results in an amplifier that can pass only positive signals. Audio signals, however, inherently swing positive and negative. So before a traditional single-supply amplifier can accept the audio signal, a DC bias must be added. This DC bias is typically half the supply voltage to allow maximum signal swing (Figure 1).

GXL-8HUB-C5_Datasheet PDF

Conventional Headphone Amplifiers Most traditional headphone amplifiers used in battery-powered electronics are single-supply devices operating between a positive voltage and ground. This design results in an amplifier that can pass only positive signals. Audio signals, however, inherently swing positive and negative. So before a traditional single-supply amplifier can accept the audio signal, a DC bias must be added. This DC bias is typically half the supply voltage to allow maximum signal swing (Figure 1).

Compressing sensor data prior to transmission can provide major reduction of transmission time. With sensor nodes such as temperature, water level, and light level sensors, the transmission of data on change or exception, rather than regular scheduled transmissions, is an effective way to reduce network traffic. In addition, having the ability to perform digital filtering or data compression at the sensor node is an effective way to reduce the data size and also frequency of transmissions. The availability of a 32-bit RISC CPU for data compression as part of the solution has significant benefit in these instances.

Interference and environment In some deployments, interference from other wireless technologies (such as Bluetooth or WLAN) may need to be addressed. Bluetooth uses channel hopping for data communications. Typically, this only presents a momentary state of interference to the wireless sensor network. The ability of an IEEE802.15.4 or ZigBee based network to perform automatic retries will likely overcome any effects of interference from Bluetooth. Equally, for sensor networks using infrequent transmissions and Bluetooth using frequency hopping, the probability of a packet collision is low.

GXL-8HUB-C5_Datasheet PDF

WLAN is designed to co-exist both in time and frequency with IEEE802.15.4., Using a collision avoidance principle, WLAN listens for a clear RF channel before it talks. If, however, there is particularly heavy network traffic on the WLAN then this can impose restrictive availability of the RF channel to the wireless sensor network due to a constant state of interference. In this case, the solution is to place the wireless sensor network on a different channel. This can be as simple as manually configuring the network to the alternate channel or by enabling the network coordinator to perform an intelligent channel scan on start-up to look for the clearest channel.

The type of building also dramatically affects the RF environment. Steel reinforced concrete floors, stonewalls and similar construction materials, for instance, introduce high levels of attenuation and multi-path fading. Likewise, the movement of people or machinery significantly varies the signal level at any particular location. The link budgets achieved by devices such as the Jennic JN513x wireless microcontroller allow for typical ranges of 20-40m indoors. Difficult building environments can be mitigated either by the use of a high power, high sensitivity module to gain a significant improvement in link budget, or by the use of additional router nodes in a mesh network, placed to bypass particular obstacles. In a typical densely populated network, there will be sufficient routing nodes that these issues aren't noticed.

Upfront site surveying and systems diagnosis assist with deployment challenges. The availability of evaluation kits that can support packet error rate testing and link quality measurements can be effective in gaining an understanding of the environment, identifying which RF channel is clearest and what is the best size of packet for transmission to minimize packet error rate.

GXL-8HUB-C5_Datasheet PDF

Security Recognizing the security issues that other wireless networks have experienced, the IEEE802.15.4 standard employs strong algorithms to protect data in the network. The adoption of the Advanced Encryption Standard (AES) with a 128-bit key length ensures data integrity and resistance to hacking, both highly important for commercial applications. AES security may be implemented in software, although a dedicated hardware encryption processor provides a better solution as this minimizes software overheads and allows faster encryption/decryption processing. This is important for sensor nodes that need to spend the shortest time possible awake (which is when they consume most power). Making the AES encryption processor accessible to the application software also allows higher level security mechanisms to be implemented.

In all cases, the key issue for widescale deployment of IEEE802.15.4/ZigBee wireless sensor networks will be how much of the above can be incorporated into a solution that can meet the 'magical' price point of $2 or less. Clearly, the availability of low-cost routers based on sub $2 chips will be of huge benefit in reducing the cost of large networks. This milestone should be reached by the end of 2007.

GXL-8HUB-C5_Datasheet PDF

About the Author Jimi Simpson is Product Manager at Jennic.

Related Articles How to compare proprietary and standards-based radio solutions

Compressing sensor data prior to transmission can provide major reduction of transmission time. With sensor nodes such as temperature, water level, and light level sensors, the transmission of data on change or exception, rather than regular scheduled transmissions, is an effective way to reduce network traffic. In addition, having the ability to perform digital filtering or data compression at the sensor node is an effective way to reduce the data size and also frequency of transmissions. The availability of a 32-bit RISC CPU for data compression as part of the solution has significant benefit in these instances.

Interference and environment In some deployments, interference from other wireless technologies (such as Bluetooth or WLAN) may need to be addressed. Bluetooth uses channel hopping for data communications. Typically, this only presents a momentary state of interference to the wireless sensor network. The ability of an IEEE802.15.4 or ZigBee based network to perform automatic retries will likely overcome any effects of interference from Bluetooth. Equally, for sensor networks using infrequent transmissions and Bluetooth using frequency hopping, the probability of a packet collision is low.

WLAN is designed to co-exist both in time and frequency with IEEE802.15.4., Using a collision avoidance principle, WLAN listens for a clear RF channel before it talks. If, however, there is particularly heavy network traffic on the WLAN then this can impose restrictive availability of the RF channel to the wireless sensor network due to a constant state of interference. In this case, the solution is to place the wireless sensor network on a different channel. This can be as simple as manually configuring the network to the alternate channel or by enabling the network coordinator to perform an intelligent channel scan on start-up to look for the clearest channel.

The type of building also dramatically affects the RF environment. Steel reinforced concrete floors, stonewalls and similar construction materials, for instance, introduce high levels of attenuation and multi-path fading. Likewise, the movement of people or machinery significantly varies the signal level at any particular location. The link budgets achieved by devices such as the Jennic JN513x wireless microcontroller allow for typical ranges of 20-40m indoors. Difficult building environments can be mitigated either by the use of a high power, high sensitivity module to gain a significant improvement in link budget, or by the use of additional router nodes in a mesh network, placed to bypass particular obstacles. In a typical densely populated network, there will be sufficient routing nodes that these issues aren't noticed.

Upfront site surveying and systems diagnosis assist with deployment challenges. The availability of evaluation kits that can support packet error rate testing and link quality measurements can be effective in gaining an understanding of the environment, identifying which RF channel is clearest and what is the best size of packet for transmission to minimize packet error rate.

访客,请您发表评论:

Powered By Tkool Electronics

Copyright Your WebSite.sitemap