Part , Description , Radio Shack , Digi Key , Newark Notes IC1 LM741 Op-Amp 276-007 LM741CN-ND LM741CN NE741,µA741, etc. Q1 2N2222A transistor 276-2009 2N2222A-ND 2N3904 See text D1 1N4148 Diode 276-1122 1N4148GICT-ND 1N4001 1N4001, or others Th1 50K Thermistor KC005T-ND 96F3309 KC00 5T in prototype Re1 12V Relay 275-249 Z753-ND 83F8057 RS is 1A R1 15K, 5% resistor 84N2487 b rown-green-orange R2,R5 10 K, 5% resistor 84N2479 b rown-black-orange R3 150K, 5% resistor 84N2485 brown-green-yellow R4 4K7, 5% resistor 271-13 30 50N1628 yellow-pur ple-red R6 1K, 5% resistor 271-1321 50N6012 brow n-black-red R7 1K8, 5% resistor brown-gray-red P1 100K Trimmer Pot Bourns C1 10uF/25V Capacitor Electrolytic C2 0.01uF, Capacitor Ceramic Led Red, 3mm Light Emitting Diode Spare parts:Auto Fan Part on BoardQ1 = 2N3053, 2N3904, NTE123A, ECG123A, NTE128, ECG128, etc. D1 = 1N4001, NTE519, ECG519, NTE116 etc. Th1 = Thermistor, 22K – 100K. 50K used in the prototype. Re1 = Relay, Type 842-1C-C ―Fashion Electronics. Order # 50-333-0 (1.55 $) Reed relay works well. To give a better performance, the negativetemperaturecoefficient thermistor (NTC) as thetemperaturesensor should be placed as close as possible to t he IC power transistor to make sure a tight thermalcontact, installing it on theheat sinkis also a good idea. You also can set the VR1 at theheat sinktemperature (70degree Celcius). Another alternative (use at your own risk) is turn on your amplifier volume to maximum and use yourfingerto touch the heat sink regularly and adjust VR1 to activate the fan at heat intensity until the maximum temp you can stand to touch. And the LEDindicatorwill give you the information that the fan is active.
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Part , Description , Radio Shack , Digi Key , Newark Notes
IC1 LM741 Op-Amp 276-007 LM741CN-ND LM741CN NE741,µA741, etc.
Q1 2N2222A transistor 276-2009 2N2222A-ND 2N3904 See text
D1 1N4148 Diode 276-1122 1N4148GICT-ND 1N4001 1N4001, or others
Th1 50K Thermistor KC005T-ND 96F3309 KC005T in prototype
Auto Fan Part on Board Q1 = 2N3053, 2N3904, NTE123A, ECG123A, NTE128, ECG128, etc.
D1 = 1N4001, NTE519, ECG519, NTE116 etc.
Th1 = Thermistor, 22K – 100K. 50K used in the prototype.
Re1 = Relay, Type 842-1C-C ―Fashion Electronics. Order # 50-333-0 (1.55 $)
Reed relay works well.
To give a better performance, the negative temperature coefficient thermistor (NTC) asthe temperature sensor should be placed as close as possible to the IC power transistor to make surea tight thermal contact, installing it on the heat sink is also a good idea. You also can set the VR1 attheheat sink temperature (70 degree Celcius). Another alternative (use at your own risk) is turn onyour amplifier volume to maximum and use your finger to touch the heat sink regularly and adjustVR1 to activate the fan at heat intensity until the maximum temp you can stand to touch. And theLEDindicator will give you the information that the fan is active.
Th1 = Thermistor, 22K - 100K. Used 50K in prototype.
Re1 = Relay. A reed relay will work too.
Newark Electronics
Digi-Key
Radio Shack/Tandy
Radio Shack's pittyful selection of parts these days is a real headache.
So I'm no longer gonna waste my time looking for partnumbers. Unless I'm
sure
they carry the part. Too bad...
Couple Notes: Th1, the 50K thermistor, is a standard type. Mine was a bar or rectangular lookingthingy. Available from Tandy/Radio-Shack. Almost any type will do. I experimentedwith different models from 22K to 100K and all worked fine after replacing thetrimmer pot.The one used in the above circuit diagram was a 50K model made by Fenwal (#197-503LAG-A01). This 50K was measured at exactly 25 °C and with 10% tolerance. Theresistance increases as the surrounding temperature decreases. Tolerance for myapplication (cooling a large powersupply coolrib) is 10%. Another name for this thingis 'NTC'. NTC stands for "Negative Temperature Coefficient" which means when thesurrounding temperature decreases the resistance of this thermistor will increase. Youmay have to shop around to get the cheapest price. Some thermistors can be had for as
little as $4.00 but as much as $55.00 Canadian currency for the glass encapsulatedtype (the best).I replaced my thermistor for a 60K hermetically sealed glass type since theenvironment for my application may contain corrosive particles which may affectperformance on a future date.
P1 is a regular Bourns trimmer potentiometer and adjusts a wide range of temperatures for this circuit. I used the 10-turn type for a bit finer adjustment but theregular type may work for your application.
R1 is a 'security' resistor just in case the trimmer pot P1 is adjusted all the way to '0'ohms. At which time the thermistor would get the full 12 volt and it will get so hotthat it puts blisters on your fingers... :-)R3 feeds a bit of hysteresis back into the op-amp to eliminate relay 'chatter' when thetemperature of the thermistor reaches its threshold point. Depending on yourapplication and the type you use for Q1 and Re1, start with 330K or so and adjust itsvalue downwards until your satisfied. The value of 150K shown in the diagramworked for me. Decreasing the value of R2 means more hysteresis, just don't use morethen necessary. Or temporarily use a trimmer pot and read off the value. 120K workedfor me.
Transistor Q1 can be a 2N2222(A), 2N3904, NTE123A, ECG123A, etc. Not criticalat all. It acts only as a switch for the relay so almost any type will work, as long as itcan provide the current needed to activate the relay's coil.
D1, the 1N4148, acts as a spark arrestor when the contacts of the relay open andeliminates false triggering. For my application the 1N4148 was good enough since thetiny relay I used was only 1 amp. However, you can use a large variety of diodes here,my next choice would be a regular purpose 1N4001 or something and should be usedif your relay type can handle more then 1 amp.
If you like to make your own pcb, try the one below. The pcb is fitted with holes forthe relay but may not fit your particular relay. It was designed for a Aromat HB1-DC12V type. The variety and model of relays is just to great. How to mount it then?
Well, I left ample space on the pcb to mount your relay. You can even mount it up-side-down and connect the wires individually. Use Silicon glue, cyanoacrylate ester(crazy glue), or double-sided tape to hold the relay in place. Works well. Note that thepcb and layout is not according to the circuit diagram in regards to the hookup of thefans. The PCB measures approximately 1.5 x 3 inches (4.8 x 7.6mm)If you print the pcb to an inkjet printer it is probably not to scale. Try to fit a 8-pin icsocket on the printed copy to make sure it fits before making the pcb...
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Automatic fan controller circuit
This circuit will turn on/off 12V DC fan or CPU fan when temperature above normal temperature.You can set turn ontemperature by adjust VR1. This circuit use an NTC (Negative temperature coefficient)which is a thermistor is one inwhich the zero-power resistance decreases with an increase in temperature. So If temperature increate the voltage atpin 3 on LM311 will decreated .The resistance of NTC is about 10K at 25′c.
VR1 should be multi-turn potentiometer type such 10K/25 turn
Abstract:
The automatic temperature control system is a very essential feature of a factory
or an industry. In most of the case the temperature plays a vital role in the
process of manufacturing or the process carried in that factory or industry.
The most common and simplest way of controlling temperature is by using a fan
which is automatically connected to a network such as it is switched on when the
temperature of the surroundings increases.
The change in temperature of the surroundings can be sensed with the help of
thermistor or a sensistor. These electronic components sense the temperature of the surroundings. When there is a change in the temperatue tempetature then
these electronic components start to conduct the electric current. This is the main
principle of the automatic control devices. These devices can be extended to an
extent that we can set the temperature when the fan should rotate.
Overview
The circuits below are variations on basic thermostat designs that can
be used to control either heating or cooling devices. I've tried to make
them as simple, cheap, and thrifty with power as possible. I'm rather fond
of them. Potential applications include such diverse jobs as opening flaps
or controlling heat in greenhouses, powering automatic fans that only cut
in when needed, homebrew cooling and warming, air conditioning, space
heating, incubators, and just about anything electrical that needs athermostat to control it between the temperatures of -20 and 125°C. They
make use of small components called thermistors , which provide much
more accurate response to temperature change than traditional
mechanical thermostats.
Simple version
Choose this circuit unless you:
Need especially tight hysteresis (or control range—see explanationbelow)
Need to drive a heavier relay or other load that will draw more than
50mA
Are powering it with small batteries and want to minimise power
either a scale or set-point, adjust the hysteresis trimpot, VR2, to provide
an effect that suits your application. This change might throw off your
scale or set-point slightly, so go back and check.
My unit, which matches the above diagram, is adjusted for a minimumtemperature of about 18° Celsius. The main 5k panel-mounted pot
extends the range up to about 28°C, marked in increments of one degree.
If you want a wider range, use a 10k pot at VR3. If you wish to use the
circuit for much lower or higher temperatures (the thermistor is rated for -
20 to 125°C), you can subject the thermistor to the target temperature
range extremes, measure its resistances with a multimeter, and plan out
your pot values accordingly. The thermistor has lower resistance at
higher temperatures. Its rated resistance of 10k occurs at 25°C. At 30°C it
is more like 7k and at 17°C it's something like 14k. See note 6 below if
you want to work with much colder or hotter temperatures.
Warning: If you intend to use high voltage / household mainselectricity in conjunction with these circuits, make sure you complywith local laws. Do not attempt to work with mains power unless youare suitably competent or qualified. I take no responsibility fordamage or injury you might cause by electing to build, modify, oradd to these circuits.
Shopping: All parts used in these circuits should be readily available
around the world. Radio Shack in the US carries an equivalent thermistor,
for example, and possibly all the other parts too (or try Digikey —see
Postscript 3 below). Here in Australia, Jaycar and Altronics , stock
everything. Dick Smith only carry a 100k thermistor , which would suit a
modified circuit for higher temps (note 6 ), but last I heard they were
getting out of the components side of their business. Jaycar and Dick
Smith are in NZ too. Parts in yellow are used in the second 'versatileversion' circuit only.
Small-scale atmospheric circulation is the hot water boiler heating to forced
circulation by pump. Burned when boiler water temperature about 85 ℃, theneed to manually start the pump, so water began circulating heat exchange;
when the cycle of water temperature gradually dropped to about 50 ℃, the
need to manually turn off the pump, stop the water cycle, continue to burn
boilers; until the water temperature rose again to 85 ℃, and then manuallystart the pump to cycle. Kotelshchik need to always check the boiler
temperature, and then decide whether to start and stop the pump, so as not toboil the water inside the boiler caused by increased pressure within the heating
system safety hazard.
This example describes the atmospheric pressure boiler automatic temperature
controller that enables the boiler water temperature reaches 85 ℃ startautomatically when the pump work, the water temperature dropped to 50 ℃,the pump shut down automatically.
Circuit Work The atmospheric pressure boiler automatic temperature controller circuit consists
of power supply circuit, the temperature detection control circuit, trigger circuit
and control the work of the implementation status indication circuit, as shown.
Temperature detection control circuit by the temperature sensor RT, resistors R1
voltage of C points. When the water temperature below the set temperature, the
lower limit (eg 50 ℃),, C point voltage will be lower than the A point voltage,N1 output high level, so that point D goes low, V cut-off, K release, water pumps
stop operation.
Start the pump running, VL light; the pump stops working, VL off.
Component selection
R1 ~ R7 selected 1/4W carbon film resistors or metal film resistors.
RP1 and RP2 are made of a linear potentiometer.
RT NTC negative temperature coefficient selected thermistor (temperature is 5k).
C1 and C2 are selected voltage is 16V aluminum electrolytic capacitors.
VD use 1N4148 silicon switching diodes.
3mm or 5mm VL use light-emitting diodes.
UR chosen 2A, 50V rectifier bridge heap.
V use 58050 or C8050, 3DC8050 silicon NPN transistor.
IC1 LM324-based selection of quad op amp IC; IC2 use or CC4011 CD4011
NAND gate integrated circuit type four; IC3 use LM7805-type three-terminal
integrated voltage regulator.
T use 3 ~ 5W, the second voltage is 9V power transformer.
K selection JQX-14FF-type or 4098 Series 5V DC relay.
diode VD2 ~ VD4 and resistors R1, R2, R6 composition. In which R1, R2, C1 andIC clock oscillator circuit within the circuit, the oscillation period (T) R2 and C1 by
the value of the decision.
Control the implementation of the circuit by the transistor V, resistor R7, diode
VD1, AC contactor relays K and KM composition.
AC 220V step-down voltage by C2, UR
rectifier, VS regulator, R5 and C3-limiting filter, the relay K and the IC to provide
12V DC voltage, while VL lit.IC power work, the clock oscillator and the oscillation frequency count signal
processing, when the time delay on time (waiting time) at the end, IC of the Q14
side (3 feet) high output, so that V conduction , K, and KM pull, the load (the
controlled setting of the power) the power supply connected. At the same time,
IC has started regular working hours (working movement time) are counted,
R1 15k ohm resistor NTC Thermistor- 10k ohm, sold at Radio Shack in the states. P1 10k ohmpotentiometer - sets the low speed(voltage) of the fans at the cool temperature. P2 50K ohmpotentiometer - sets the gain of the circuit - how fast the voltage will rise to full output when the temp
is higher. TL082 a op-amp that I had handy, most any single voltage op-amp should work. The TL082is a dual op-amp if you want more then one controller on a board. note that the power and groundconnections for the op-amp are not shown on the schematic. R2 - The TL082 is a fast op-amp, neededR2 to reduce oscillation. IRF-510 A 4 amp mos-fet in a TO-220 case. Bascially as the voltage on thegate rises the mos-fet will conduct more current. note 1 there are also IRF-520 and 530 versions thatwill handle more current. note 2 Even at 5 watts the mos-fet will disapate some heat and will need tobe heat-sinked or at least in the air flow path. the large metal part of the fet will be at drain(D)voltage level. Do not attach to case. D1, almost any diode, 1N4001 should work,it conducts backaround the fan when the mos-fet turns off. As the fan continues spinning it will produce a voltage onthe drain lead of the fet. D1 will limit that voltage. Adjustment, easiest if you have a voltmeter but canbe done without. Get the thermistor at room temp. Adjust P1 for the low speed that you want yourfans to run at. Heat the thermistor to the high temp you want the fans at full speed. ( I stuck it undermy tongue) Adjust P2 until the fans are at full speed( with voltmeter the highest voltage you can get)then adjust P2 until the speed/voltage just begins to drop off. Most fan specs that I have seen show a
low voltage limit of around 7 volts. Some of the smaller 80mm fans have a lower limit of 8 volts. If you set the low voltage to low the fans may stall until the thermistor heats up enough. Let me know if you build this circuit and how it works for you. corrected, single voltage op-amps should be used, OP-07 is a dual voltage.