June 19th, 2009

Measuring Wind Speed

Measuring Wind Speed

The are a few ways to measure wind speed, some involving ultrasound transducers, some based on cooling effect of air flow but most common technique uses  spinning cups and measures their rotation speed. There are also a few ways to measure this rotation, some using a dynamo, some using Hall sensors but most use a photo-interrupter in a way much like it’s found in a computer mouse for example.

This kind of anemometer is presented in this project. Four hemispherical cups are attached to a rotating axis. At the other end of the axis there is a disc with  4 slits. Holes can also be used if they’re close enough to the edge. This disc’s slits or holes go in the photo-interrupter gap. Now when wind blows in the cups and spins the axis, the photo-interrupter will output a series of pulses whose period depends on the speed of rotation. Now you can either measure frequency, number of pulses within a time unit or the mean voltage of these pulses.

Note that the greater number the whole or slits are done in the disc the greater the resolution will be. The diameter of the disc is also an important factor in resolution.

The rotation speed is measured in this project by a PIC16F873 microcontroller. The photo-transistor has its collector connected to Port A0 from the PIC. The developer of the project is planning to display the measurement result on a screen but he also made an USB interface to send the data to PC. USBN9604 IC is used for this task. The article recommends that you ground the parallel input pins if not used so that it won’t cause interference.

The project right now is a work in progress but the principles of its operation have been stated. Also a schematic is provided and the circuit explanation. I for one, am waiting for complete article to check out the measurement algorithm.

Measuring Wind Speed: [Link]

May 25th, 2009

PIC-based Thermostat

PIC-based Thermostat

Summer is here for those of us in the northern hemisphere and heat becomes a problem again. Fear not for here is a project for you to build your own room temperature controller.

This device uses two sensors to monitor temperature at two locations, inside and outside for example and depending on the measurements, it controls two external devices like cooling fans for example. Relays are used to turn on or off these external devices. You can chose to trigger the relays when the outside temperature becomes too high or when inside temperature becomes too low.

The microcontroller used is a PIC16F873 and controls all functions of the device. Port B drives the 7 segment LEDs, Port C is used for device designation, Port A controls the Relays.

The temperature sensors are LM35DZ. These sensors can measure from 0 degrees to 100 degrees Celsius and outputs 10mV per Celsius degree. However the 0V level is given at 2 degrees Celsius and since the project doesn’t use a symmetric (+/-)  power supply it’s lowest temperature that can be measured will be the 2 degrees Celsius. The sensor’s output after being amplified by LM358 Opamp is sent to PIC’s analog input.

The 7 segment LED display will show the inside temperature, the outside temperature and the preset temperature. The preset value is the threshold that will trigger the external devices. While this project is designed to maintain the room temperature around a certain value, the principle can be used in many projects like in one of those incubators where u can control a fan and a resistive heating element.

In the end i must say this is a very well documented project and everything is explained in great detail. The information is very well structured and besides complete schematic and code everything is very well explained step by step, including the actual building process. Happy soldering.

PIC-based Thermostat: [Link]

April 13th, 2008

DC motor speed controller

 DC motor speed controller boardDC motor speed controller board

This motor speed controller powered by the PIC16F873 detects and controls the rotational speed of the motor. When lower than the specification speed, it increases a control electric current. When higher than the specification speed, it reduces a control electric current. It is possible to use when wanting to keep constant speed even if the load to the motor changes.

DC motor speed controller: [Link][Via]

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