于仁颇黎@机器人

日立金属全球最薄3轴加速度传感器

PC motherboards have always been attractive to robot builders because of their low cost compared to specialized embedded controller boards. But one of the big problems with adapting PC motherboards for use in mobile robots is the size. The new Mini-ITX form factor created by VIA Technologies solves this problem. Mini-ITX boards are just 17cm x 17cm making them ideal for use in mobile robots. In this review, we provide our first impressions of the VIA EPIA M10000 Mini-ITX motherboard.

The VIA EPIA M10000 Board with a quarter to provide scale

As with any PC motherboard, robot builders face the problem of supplying power to a board designed for an ATX power supply. The board requires +/-12vdc, +/-5vdc, and +3.3vdc. Fortunately, there are several 12vdc to ATX adapter boards available such as the small iTuner Pw-60 DC-DC convertor which is designed specifically for the VIA Mini-ITX boards. It plugs directly into the ATX PS connector on the motherboard and once you connect a 12vdc battery to it, you're all set to go. The VIA Technologies' website includes a page about the use of the Mini-ITX boards as car PCs that include additional information on operating the boards from 12vdc. The 1GHz M10000 consumes about 10 watts of power peak while the slower models peak at about 5 watts.

The VIA EPIA M-series boards include a lot of I/O options that can be used directly such as serial ports, USB connectors, and even an I2C port. There are also ports that can be repurposed by the creative robot builder. The fan connectors include pulse counters used to measure the fan RPM. These might be used with wheel encoders for odometery. The chassis intrusion connector would make a good general purpose input that could be connected to a bumper switch.

Some hands-on experience

The test setup at the DPRG Lab

I had brought along an ATX power supply, a 256MB DIMM, a spare hard drive and CD drive and associated cables. We connected all the parts in the DPRG lab, plugged in the power, and the EPIA M10000 fired up without a hitch. We did a fast and uneventful install of RedHat Linux 9 complete with X, GNOME, and all GNU development tools. In a robot, it would make more sense to use a slimmed down Linux distribution instead of a full-blown distribution like RedHat that's intended for server and desktop use. But as a way of testing out the board it worked great (in fact, the EPIA boards look like they'd be ideal as Linux servers).

The M10000 has a 1GHz CPU with a small fan. Other models of the EPIA Mini-ITX motherboards have slower CPUs and do not require a fan. For robots with limited power, it might be best to choose one of the models without a fan. None of the several heat sinks on the motherboard ever became more than slightly warm to the touch even after running steadily for over 24 hours.

While the VIA EPIA is very fast compared to the motherboards usually adapted for robotics, it doesn't have high performance graphics hardware. It was more than fast enough to run X but you probably wouldn't want to use this sort of board as a gaming machine. (As if the average robot builder has enough free time to play games anyway!)

The EPIA M10000, and a New Micros IsoPod

All sorts of ideas were floated for hacking the connectors and hardware to allow more interesting uses, many of which probably violate the warranty and some of which made the VIA representative cringe in horror.

But the easiest way by far to get a lot more I/O would be to use an add-on daugterboard. Several DPRG members suggested adding a New Micros IsoPod connected to one of the serial ports. This would instantly give the system a 40MIPs I/O subprocessor capable of running dozens of R/C servos, h-bridges, and monitoring all sorts of sensors and switches.

There was a lot of interest at the DPRG in using the I2C connector provided on the motherboard. A helpful blog entry by Dafydd Walters on I2C usage can be found at mobilerobotics.org.

As a final test of whether or not the VIA Mini-ITX form factor would work well with the average robot, I pulled out my own robot for a test fitting. When I built this robot in 1997, I used an NMI 8051 controller board mounted on a piece of foam core with several other small boards such as a Scott Edwards SSC. As it turned out the foam core panel was exactly 17cm wide and about 25cm long. I was easily able to fit the Mini-ITX board into the existing case without any changes. In fact, it fit so well, that I might just bring this robot to the next DPRG RBNO to use as a test platform for some more detailed experimentation with the Mini-ITX.

My robot with its original 8051 board	Swapping the 8051 and M10000
Robot with the M10000 in place	Closer view of the M10000

Conclusions

The VIA Technologies EPIA M10000 Mini-ITX motherboard is ideal for use in mobile robots. It fast, runs cool, draws minimal power, has lots of I/O, and is very small. There's probably no better PC motherboard around for robotics use at this time.

The specs:

CPU: 1GHz VIA C3/EDEN EBGA Processor
Chipset:

VIA CLE266 North Bridge
VT8235 South Bridge

2 UltraDMA 133/100/66 IDE HD connector
1 FDD connector
2 USB 2.0 connectors
2 IEEE 1934 (Firewire) connectors
1 IrDA Infrared Connector
1 RS-232 serial port
1 Audio connectors (Mic/Line out)
1 CD Audio-in connector
1 Wake on LAN connector
1 Chassis intrusion connector
1 I2C connector
1 LVDS connector
3 Fan connectors

1 PS2 Mouse ports
1 PS2 keyboard ports
1 Parallel port
1 RJ-45 Ethernet port
1 9 pin RS-232 serial port
2 USB 2.0 ports
1 VGA port
1 RCA port (TV our or SPDIF)
1 S-Video out port
3 Audio Jacks (line in, mic in, line out or 6-channel line out)

URLs mentioned in this review

VIA Technologies, Inc.
VIA Technologies' Robotics Initiative
iTuner DC-DC Convertor
VIA Technologies Information on 12vdc Automotive use of Mini-ITX boards
Dafydd Walters Article on the I2C bus
Dallas Personal Robotics Group

  光敏器件

Chinarobot

　　光敏器件包括光敏电阻、光敏二极管及光敏三极管等。光敏器件可以用来以可见光或红外光的形式控制报警器、测试仪、自动开关、继电器等多种装置或执行机构。因此光敏器件在自动化技术中起着极其重要的作用。
　　光敏电阻受光照后，其阻值会变小。光敏电阻的符号如图1所示，用来制作光敏电阻的典型材料有硫化镉(CdS)及硒化镉(CdSe)两种。光敏电阻的CdS或CdSe沉积膜面积越大，其受光照后的阻值变化也越大，故通常将沉积膜做成“弓”字形，以增大其面积。光敏电阻工作时的响应速度较慢，如CdSe光敏电阻的响应时间约为10ms，CdS的响应时间约为100ms。因此，光敏电阻通常都工作于直流或低频状态下。

　　光敏二极管是根据硅PN结受光照后产生的光电效应原理制成的，其符号如图2所示。光敏二极管工作于反向偏压下，其光谱响应特性主要由半导体材料中所掺的杂质所决定。光敏二极管的最大工作频率为几十MHz。

　　光敏三极管也是利用硅PN结的光电效应制成的。其符号如图3所示。光敏三极管使用时，其基极通常开路，基极－集电极产生的光感生电流直接馈入基极，并被光敏三极管自己所放大，因此光敏三极管的灵敏度比光敏二极管大得多，通常要大100多倍。光敏三极管的最大工作频率只有几百kHz。此外，还有用两个光敏三极管制成的达林顿式光敏三极管，这种器件的灵敏度又要比光敏三极管高十倍，但其最大工作频率更低，只有几十kHz。

　　光敏电阻、光敏二极管、光敏三极管与人眼的感光特性曲线如图4所示。从图4中可见，CdS光敏电阻的特性与人眼最为接近，因此，CdS光敏电阻比较适合用于照相机曝光表、空气烟尘检测器等可见光装置。光敏二极管、三极管的最佳响应特性在红外区(但目前，有些日光型的光敏二极管、三极管的特性与人眼的视觉特性更趋接近)，因此，光敏二极管、三极管最适合用于红外遥控系统、红外光束阻断报警器等装置。

　　光敏电阻是一种无结元器件，因此工作时无极性。图5示出了用光敏电阻构成的简单光控开关电路。在黑暗状态下，光敏电阻R3具有高阻值，因此三极管VT1的基极偏置电压近乎为零，VT1截止，继电器J释放。当有足量的光线照在光敏电阻R3上时，其阻值下降，VT1的基极有偏置电压加入，VT1导通，继电器J吸合，其触点可用来控制其它电路。

　　图6所示的光控开关电路使用了VT1、VT2达林顿放大电路，因此灵敏度较高。该电路利用继电器触点的其中一组进行自锁，使每次光照后继电器J保持吸合状态不变。如果要解锁，必须再按复位键S1。R2用于光控灵敏度调节。

　　图5和图6所示的光控电路为光亮时继电器吸合控制，图7则示出了光暗控制的光控电路。电阻R1、R2及光敏电阻R3构成分压电路，当光线暗至一定程度时，VT1的基极电压上升至使VT1、VT2导通，继电器J吸合。R1用于动作灵敏度调节。
　　图5～图7所示的电路的光触发电平受电源电压及环境温度的影响较大。图8所示的电路为一种精密光亮光控电路，其工作不受电源电压及环境温度的影响。电阻R1、R2、R6及光敏电阻R5共同构成惠斯顿电桥的两个桥臂，运放IC1用做高灵敏电压比较器。常态时，调节R6使R5、R6的节点电压V1略低于R1、R2的节点电压V2，IC1则输出高电平，VT1截止，J释放；此后，若光亮稍有增加(甚至人眼都感觉不到)，则V1>V2，IC1翻转输出低电平，VT1导通，J吸合。

　　精密光暗光控电路如图9所示。由于通过R5引入了少量正反馈，因而在光线变化时电路动作就会稍稍滞后，以避免光线亮度处于临界状态时继电器频繁抖动。

　　光来阻断报警器如图10所示。光敏电阻R4被照射时，阻值较小，因此三极管VT1及单向可控硅SCR均截止；当光束被阻断时，VT1的基极电压上升，VT1、SCR导通，蜂鸣器BZ得电发声报警。S1为复位开关。按下S1后，电路停止报警。

　　光敏二极管工作时处于反向偏压下。图11和图12示出了其典型偏置方式。图11中光敏二极管受光照时VOUT电压下降，而图12中光敏二极管受光照时VOUT电压则上升。

　　图13、14示出了光敏三极管的典型偏置方式，通常基极开路使用。图13中光敏三极管受光照时VOUT电压下降，而图14中光敏三极管受光照时VOUT电压则上升。若将光敏三极管的基极接地(图15)，则相当于光敏二极管的工作方式。如将光敏三极管的基极通过一个可调电阻接地(图16)，则可调节其灵敏度及最大频率响应。■

Several members of the TerraMax Team from Ohio State University have authored an article in the latest issue of IEEE Intelligent Systems titled, Ohio State University at the 2004 DARPA Grand Challenge: Developing a Completely Autonomous Vehicle (PDF format). The TerraMax robot was based on a 32,000 lb off-road military truck. The robot completed 1.2 miles of the 250 mile course before becoming stuck when it was unable to avoid a bush in its path. The TerraMax team will be returning for the 2005 Grand Challenge.

Chinese scientists have unveiled microscopic swimming robots designed to deliver drugs or clear arteries in humans. A NewScientist.com article says the prototype robots are 3mm long. A 1mm robot sub is under construction and the goal is developed a 0.1mm device eventually. The tiny submersibles swim by means of tiny paddles that are actuated by magnetic fields applied externally