Wednesday, 25 December 2013

H Bridge simulation in NI multisim

H Bridge configuration has many applications in controlling a motor. Generally, a motor can be either switched ON or OFF(uni directional rotation) based on the needs and the direction of rotation depends on the polarity. But, in the field of Robotics and Medical applications, a single motor must have the ability to rotate in two directions(clockwise and anti clockwise). For this purpose, an H bridge configuration is preferred. As the name indicates, the circuit will be in the shape of alphabet “H”. The motor is made to rotate in two directions by changing the polarity of the motor.

Look at the following connections, 
Here, the direction of rotation of the motor varies with the change in its polarity. A simulation of the above schematic is shown below,

A combination of these two schematic gives a H Bridge circuit and the switching between polarities is done using the transistors(electronic switches) as shown below,

From the above circuit, it can be seen that when the switches(SW1 and SW3) closed, the motor will be in one polarity and when the switches(SW2 and SW4) are closed while the other switches are open, the motor will be in another polarity. And this is how an H Bridge circuit works and the transistors are used as the switches.  Below shown is the simulation of the H Bridge circuit in NI multisim,

Here, when the gate is ON, the MOSFET is turned ON, hence forms a closed circuit and the motor receives the polarity based on the above explanations. 

Sunday, 8 December 2013

Making of my Autonomous Vehicle

I have built an Autonomous Vehicle as a part of my final year project, which was sponsored by “Analog Devices, Inc”.The vehicle have the ability to move from one point to another point based on the GPS coordinates of both points and also plots the path it travels in google maps. In order to avoid obstacles in its path, the vehicle uses a grid of sensors that includes laptop based RADAR, camera, proximity sensors. Following are few snapshots of the prototype that was built (camera is not shown in the picture),

Front view

Side view

Here are some videos of making of my Autonomous Vehicle,

Initial obstacle avoidance algorithm testing 1 - outdoor

Initial obstacle avoidance algorithm testing 2 - outdoor

Optimized algorithm testing 1 - outdoor

Optimized algorithm testing 2 - indoor

Testing after changing vehicle dynamics 1 (vehicle turning radius test)

Testing after changing vehicle dynamics 2 (vehicle turning radius test)

Testing after changing vehicle dynamics 3 + Acquiring GPS data of start and end points

Image processing algorithm testing ( webcam+ MATLAB Simulink)

Plotted GPS data in google earth (while vehicle is moving)

Plotted GPS data in google earth (while vehicle is stationary)

Preliminary model built to test the algorithms 

Friday, 6 December 2013

Heart rate measurement in LabVIEW

This is one of my project in which I have designed a transducer that can measure the variations in oxygenated hemoglobin and deoxygenated hemoglobin ( simply known as an oximeter).The sensor was developed based on the key principle that these two parameters have two different optical spectra in the range of 500nm to 1000nm. Hence, two light sources of two different wavelength(red-660nm and infra red-940nm) are used. A photo diode was used to sense absorption rate and the output of the photo diode was obtained in the LabVIEW using a data aquisition card(NI 6211).  The photo plethysmograph(PPG) waveform was obtained in LabVIEW by driving the leds using PWM signals of 25% duty cycle. Hence, based on the PPG waveform, the heart rate(Beats Per Mintue) was found.
This is the video of the PPG waveform obtained in the LabVIEW. Since ordinary sensors was used, there were lot of noise interference in the reading and the BPM was very fluctuating.

(the PPG waveform in the video is a recorded measurement file of the actual experiment)
This is the PWM pulse which was generated to drive the LEDs from the LabIEW. LEDs are switched alternatively at same duty cycle.

Shown below is the transducing part which I have developed in my college laboratory,

“Simulation” is always a good idea before an actual execution of a project. I have simulated the transducing circuit in NI Multisim and it helped me a lot in actual implementation. Following is the video of the simulation. 

I have used the current source since the output of a photo diode is current and used an I-V converter to convert it into voltage( since input of NI 6211 must be in volts). Here I have also added a sample and hold circuit to hold one led`s value while other is being sampled and vice versa. The manual switch in the simulation was replaced with the control signal from the LabVIEW.

Though the acquired results got some flaws, obtaining a biological parameter was really awesome!

Thursday, 5 December 2013

The Free Radicals

Human body consists of n number of feedback loops right from a single cell to the  major parts of the body. Alteration to any of these cells, vessels or parts, leads the regular bio feedback loop to collapse and in some cases, may even results in death. These process often acts like a butterfly effect.

One of the major issue to consider is our immune system and free radicals. Our body`s defense system releases free radicals(a by-product of metabolic process of oxidation)to fight against viruses and bacteria. But the excess free radicals produced due to pollution, smoking, stress, along with the indigenous unterminated  free radical chain tends to steal(in order to get paired) electrons available in the body in every part of the tissue. And this chain goes on until all the free radicals are perfectly bonded.

This is the root cause for majority of heart disease, artery blockage and cancer since these free radicals are more fond of electrons in the region of heart and brain. Unfortunately there are no effective drugs have been developed so far to address this issue. And since free radicals are essential, it cannot be terminated too. But the excess free radicals bonded with the oxygen to form oxygen free radicals can be reversed or neutralized with proper intake of glutathione peroxidase and anti oxidants.

One of the impact of these excess free radicals is that, its tendency to steal electrons from the DNA. If this process is succeeded, the DNA is subjected to mutation and incase of pregnant women, it could even damage the fetus. Thus the effective control of the free radicals must be considered as a preventive step for proper health condition. To do so, keep away from stress and pollution. Also consume anti oxidant rich foods. Vitamin C, E and glutathione peroxidase can reverse the oxygen free radicals into pure oxygen and also prevent excess free radicals and heart blockage. Hope this information helps!!

(I have written this article for my college magazine during my third year of Engineering. These are my perception of free radicals and body chemistry. and I am not an expert in medicine or biochemistry)

Wednesday, 4 December 2013

Increasing the voltage levels of PWM signals

PWM signals are often used in robotics for the purpose of controlling the DC motor speed and to drive the servo motors. Most of the microcontrollers have the output voltage of 5V. When  the PWM signals are generated from these controllers, the average output voltage for maximum duty cycle will be around 3.3 to 4.2 V(approx). This voltage level cannot drive a 5 or 12V motor efficiently. Hence the voltage level must be boosted with appropriate external circuits.

Following is a simulation that demonstrates how to increase the voltage level of the PWM signals generated from a microcontroller. Here, I have used CCP module of PIC microcontroller to generate the PWM pulses. The DC motor is driven by the MOSFET based on the PWM signals. 

From the video, you can see the voltage level from the microcontroller and the boosted voltage in the oscilloscope.  It can be noted that only the amplitude is increased and the duty cycle remains unchanged. 
Voltage increase can also be seen by connecting a voltmeter across the motor terminals, as shown below,