Th1, the 50K thermistor, is a standard type. Mine was a bar or rectangular looking thingy. Available from Tandy/Radio-Shack. Almost any type will do. I experimented with different models from 22K to 100K
and all worked fine after replacing the trimmer pot. The one used in the above circuit diagram was a 50K model. This 50K was measured at exactly 25 °C and with 10% tolerance.
Automatic Fan Controller - [Link]
The 555 Ic is wired as an astable and the frequency is constant and independent of the duty cycle, as the total resistance (R charge + R discharge, notice the diode) is constant and equal to 22Kohm (givin a frequency of about 1Khz, notice the hum).
Simple DC motor PWM speed control – [Link]
user “abbtech” writes:
The heart of the PWM Fan Controller is a PIC 12F675 microcontroller. This microcontroller is reading the analog output of a LM35 temperature sensor using a ADC (analog to digital converter) . The resulting digital value is converted to a temperature and a fan is powered proportionally to how hot the sensor is.
PIC 12F675 PWM Fan Controller - [Link]
This project is a PWM Fan controller based on PIC18F25K20. It offers a variable speed control, low acoustic noise, reliability, long lifetime, low power consumption, protection features. The MCU get the temperature from the sensor (D18B20), and after will do a conversion Celsius degrees and then it´s generated a PWM on PORTC.2 with 6 different levels.
PIC PWM Fan controller - [Link]
This project shows an 3-Wire DC Fan rpm regulator with intelligent duty cycle adjustment. The circuit will try to maintain the preselected rotation speed by adjusting duty cycle and receiving feedback from fan output. Check full project details on the link below.
PIC 3-Wire Fan RPM Controller - [Link]
To control the direction of a motor you have to be able to control the current flow throught it. To do this specialized ICs are used intergrating a circuit called H-Bridge. In the link below you can find a tutorial on how to use Texas Instruments L293NE or Texas Instruments SN754410. [via]
How to use L293NE to control a motor - [Link]
The EasyDriver is a simple to use stepper motor driver that is controlled using 5V pulses. There is two inputs, one for setting the direction and another for controlling steps of motor. It can drive bi-polar motors up to 750mA/phase. Power supply range from 7V to 30V and it is based on Allegro A3967 driver chip.
EasyDriver Stepper Motor Driver - [Link]
DTMF-remote – Activate relays with your smartphone - [Link]