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temperature control unit

Discussion in 'General Electronics Discussion' started by wpaul, Apr 9, 2011.

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  1. wpaul


    Apr 9, 2011
    HI folks can anyone help me with the following project i will appreciate it very much i must build a temperature control unit.:)

    The temperature is to be controlled as a function of light intensity. This means that the darker the ambient
    light becomes, the more heat is to be generated by a heating element.
    • In order to conserve energy, the part of the system that heats up the element must have the highest
    possible efficiency.
    • A user interface must inform the user of all operational statuses (e.g. indicator for heater element

    Design constraints:

    • To meet the requirement of high efficient heating, the heater element must be supplied with pwm.
    For this a NE555 timer IC must be used.
    • The heater element to be used is a 12 VDC (60w) lamp (those used in motor vehicles) which provides good
    infra red radiation as a heat source.
    • The power supply for the system must be a +12 VDC source (battery or mains operated PSU).

    The unit should comply to the following specifications

    Heater element to be controlled: 60 W (connected externally to the unit via banana connectors and cables).

    Operating voltage: 12 VDC.
    • Control voltage: Chopped DC voltage.
    Light sensor: LDR or phototransistor.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Tell us about the feedback process.

    The heater will probably generate light, so there may be feedback there. Unless this is some sort of meaningless task where unspecified changes in light intensity need to be converted to unspecified changes in power to the element with no feedback then the light from the lamp, if not shielded from the sensor will result in you having a device that controls the light level and not the temperature.

    The only thing I can say is that it sounds like a school project, reading the constraints and specifications tell you everything you need to know, other than you need a pass element (bipolar transistor or mosfet) so that the output of the 555 can control a much larger load.

    You can figure out the maximum current to the bulb (but consider what happens if the bulb's filament is cold)

    Whether you use a bipolar transistor or mosfet would be up to you. One may seem to have benefits over the other, but if you are really going for high efficiency, you may need to find a way to compare Vce(sat) and Rds(on) in order to establish which device will be more efficient.

    You would also need to define efficiency and provide some way of measuring it, and preferably at different light levels.
  3. wpaul


    Apr 9, 2011
    hi steve .the feedback system according to me is a temp sensor must be mounted 3cm from the light source when it reaches 40 degrees celcuis must will switch of the 555 timer i attended to use pin 4 of the 555 the reset .the eficiency they want pwm to improve effiency so they want to improve the duty cycle. can i use a ldr on pin 5 of the 555 timer . the lamp will work as a day night switch when its dark it will come on and vice versa .
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