Ice Warning Circuit for Automobiles

由于热敏电阻的易用性，对大气或流体热的变化作出反应的装置是简单的。这款汽车冰警告电路解释了如何实施热敏电阻like a transducer in a circuit that continuously blinks a warning lamp as soon as the atmospheric temperature drops to around 0 °C.

为什么冻结道路是危险的

Ice, specifically black ice, is among the most hazardous circumstances which motorists can easily come across during the cold months. Even when it might not look too chilly outside, snow can still land on the streets, that may unfreeze away sluggishly. Black ice may be specifically too dangerous at night time and morning hours, mainly because it may look like moist streets instead of icy. Black ice is incredibly elusive, which means for a vehicle this can easily end up skidding and accidents.

Keeping this in mind this circuit was developed, which can be applied to get an alerting signalregarding the temperature这可能会降至霜冻水平。或者，如该项目所述，电路可能习惯于警告冻结街道的汽车司机。

该设计

Besides a couple ofbipolar transistors, an npn and a pnp type, the circuit additionally employs 3 other forms of semiconductor devices. First of all, thethermistor涉及少量半导体物质，实际上是一种玻璃胶囊的负温度系数（NTC）风格。

Its tiny dimensions helps it to react quickly to temperature variations while the glass cover safeguards the semiconductor from the electrical conducting characteristics of liquids which can otherwise create misleading results.

Observe that an n.t.c. thermistor comes with an electrical resistance that rises as the temperature drops. Also, anop amp ICwhich is the recommended 741 kind is utilized as being a sensitive voltage change sensor around a Wheatstone bridge. One particular arm of which consists of the thermistor.

The thermistor can be any 100K NTC thermistor.

最后，ALED lamp is used as an indicator闪烁警告信号。这种光线紧凑，坚固，并且几乎不可用电流照亮。

Circuit Description

在上述图中揭示了“霜冻”警报的整个电路。它由来自12V汽车电池的电压驱动。或者，对于其他应用，9V电池可能足以运行电路。

电路基本上由虚线分解的几个元素组成。在这一行的左侧显示了temperature sensitiveWheatstone bridge, whose output is detected by the op amp operating like a差分放大器。

一旦热敏电阻延伸到预设温度，虚线就朝向虚线的右侧存在两个晶体管振荡器。

The Wheatstone bridge includes resistors R1 and R2 which fixes the voltage on the inverting terminal of the op amp at around 8V with reference to the ground line (for a 12V battery). The preset VR1 and the thermistor RTH1 create the second arms of the bridge.

这是因为热敏电阻是NTC规范，您会发现温度下降到其电阻增加，导致引脚3处的电压成比例地升高。

由于该电压仅通过引脚2的参考电平，运算放大器的输出变为状态并从零左右翻转到一些伏数。

The temperature where the output moves dramatically positive could be determined by fine tuning of the preset VR1. The quick increase in voltage at the output of theop amp turns oscillator电路显示在虚线的右侧。电阻R3使用该电压切换晶体管Tr1的基极。

The capacitor C1 helps with the positive feedback essential to hold the low-frequency amplitudes. Thepnp transistorTR2 powers LED in its collector terminal along with a calculated series resistor R5 which limits the current entering the LED at under the maximum rating.

TheLED flashing频率通过其自身的电阻在一定程度上建立到一定程度，尽管通过为CL选择适当的幅度可调节到所需的水平。晶体管TRI和TR2需要是电路最佳起作用的互补匹配。

CIRCUIT ASSEMBLY

Each of the elements, barring the battery, switch and the LED, could be assembled over a 0.1 inch matrix Veroboard as demonstrated in below, although the true design may well depend on the actual scale of the parts that are purchased by the user.

The thermistor should be positioned far away from any possible heat source or from the engine. It should be near to the floor of the car for easier sensing of the temperatures of the frosty icy patches on roads just a feet below.

热敏电阻必须从可能的水屏蔽或溅起雨, because chilling effect due to the water evaporating may cause sudden drop in it temperature below the actual surrounding temperature, leading to false alarms.

An effective placement of the thermistor is at the rear of the front bumper however the an even a better place could be identified depending on the type of car. Once the correct placement for the thermistor is found, you need to determine the wire distance needed between the thermistor and the control circuit.

Exercise caution while soldering the extension wire to the thermistor owing to the fact that the soldered joints must be protected using sleeving to shield against water contact. Sleeving with heat-shrinkable property may serve as the best option.

热敏电阻必须粘合到短塑料管的表面上，以确保在允许空气周围流动时，它从可能的水溅冷却。

只有任何微小的塑料盒都可用于封闭电路，也可以在汽车仪表板后面安全地定位它。三组输出电线应该通过索环终止盒子：几根电线将进入电池2到热敏电阻，2到LED。

Pick a location within the dash which may be most appropriate for visualizing theLED flashing。钻孔钻孔以使LED通过塑料索环可以轻松推动。

The LED should be joined accurately to the circuit in order that it TR2 is able to switching it on correctly with a forward bias.

您可以通过将多电表设置为其欧姆范围来轻松识别LED阳极引脚。在汽车内部电路的最终安装之前，必须通过实际冰温测试确认结果。

CALIBRATION

打碎一个小冰在一个碗里,直到它变m-liquid. Make sure that ice is actually in a melting condition which will provide the required 0 °C level for the test. Still to be sure verify the temperature using a thermometer if you an access to it.

将热敏电阻淹没在熔化冰内，细致预设电阻直到LED刚刚开始脉动。从冷冻水中取下热敏电阻，您可能会发现随着热敏电阻的温度向上移动LED终于停止闪烁。

或者，您可以为LED的闪烁阈值进行不同的温度。

电路对电源电压变化具有很强的耐受性，并且不会使LED在该设置之外的温度下闪烁。顺便说一下，电阻器R5还有助于在热敏电阻温度靠近设定电平附近时避免在时段中经常闪烁LED。该电阻为电容器提供缓慢的放电路线。

自定义电路

如果您觉得需要修改电路，以便它启用可听警告而不是LED闪烁，您可以简单地执行以下操作。

将C1值修改为约0.1μF（选择其理想频率的值），并用80欧姆小扬声器的LED替换R5，此时直接与TR2收集器直接加入。

To have a twin audio-visual signal, make the following customization but additionally change R4 with an LED. Practically you may find it fascinating to see that under likely conditions where ice is about to grip the road, the circuit quickly responds and begins signalling you with the alert warning.