Electronic Projects

Circuit Simulation

Sun, 06 Feb 2011 22:41:08 -0500

The link above will open a java app simulation of the H-Bridge circuit I have been discussing. Note the window will have to be resided to see the entire schematic. The simulation allows you to see how current flow through the circuit. You also can see the PWM waveform that is being generated. This simulation is completely customizable meaning components can be changed and moved. The parent site also has many more example circuits that can be simulated.

The image above is of the circuit from my last post constructed...

Sun, 06 Feb 2011 22:32:42 -0500

The image above is of the circuit from my last post constructed on a bread board.

The PWM generator, H-Brige, and control logic for the H-bridge...

Sun, 06 Feb 2011 20:52:51 -0500

The PWM generator, H-Brige, and control logic for the H-bridge mentioned in previous posts are all combined together into one circuit. This Circuit allow a switch to control the motor direction when connected to the motor direction input on the schematic. The Speed of the motor can be controlled by adjusting the duty cycle of the PWM with the duty cycle control potentiometer.

An H-Bridge can be operated with a PWM signal to vary the speed...

Sat, 05 Feb 2011 20:06:09 -0500

An H-Bridge can be operated with a PWM signal to vary the speed of the motor. To allow the motor to spin in both directions the PWM signal must be applied to either output A or output B but never both. This digital logic circuit allows one PWM signal to vary speed and a digital high or low to control direction.

Op-Amps can be used in may different configurations. The image...

Sat, 05 Feb 2011 19:30:51 -0500

Op-Amps can be used in may different configurations. The image above is of an op-amp configured as a PWM generator. The specific op-amp this circuit was tested with is an LS404CN but comparable models may also work. The op-amps in the schematic are run by a single sided 5v supply(5v and ground). A voltage divider is used to create a reference voltage of 2.5V.

The first two op-amps from the left of the image generate a triangle waveform. The amplitude of the triangle waveform output is set by the ratio of R1/R2 note R1 must be less than R2. The frequency of the triangle wave can be determined by the equation in listed on the schematic.

The third op-amp compares the triangle waveform to a variable reference voltage Vd generated by a potentiometer. When the triangle waveform is higher voltage than Vd the output is high. When the triangle waveform is lower voltage than Vd the output is low. This creates a PWM signal with a duty cycle set by Vd.

Operational amplifiers often called op-amps are a very import...

Fri, 04 Feb 2011 00:07:25 -0500

Operational amplifiers often called op-amps are a very import part of many analog circuits. Op-Amps are amplifiers contained within an IC chip which use external resistors to set the gain. Two of the most basic configurations of an op-amps are inverting amplifier and non-inverting amplifiers. The circuit diagrams for these amplifiers can be seen in the image above. The equations for choosing resistor values to obtain a specific gain is shown in the image above, beside the circuit they correspond to. The output voltage of the op-amp can be determined by multiplying the input voltage by the gain.

Like most other IC chips op-amps require a supply voltage to operate. Op-Amps are commonly used with 2 supplies a positive and negative voltage of the same magnitude. Some op-amps can be supplied with just 1 voltage and ground. The magnitude of the max output voltage of the op-amp will always be less than the magnitude supply voltage. How much less depend on the specific op-amp being used.

Op-Amps can also be used as comparators. A comparator compares the input voltage applied to the minus side of the op-amp to a another voltage such as a reference voltage generated by a potentiometer. If the input voltage is higher then the reference voltage the output will go high. If the input voltage is less then the reference voltage the output will go low.

Credit for the image goes to...

Wed, 02 Feb 2011 14:55:08 -0500

Credit for the image goes to www.cadvision.com/blanchas/hexfet/np-s.htm

An H-bridge as described in a previous post allow you to control the direction that a DC motor spins. An H-bridge can be built form discrete (individual) components or an H-bridge IC chip such as the L298 can be used. H-bridges built from discrete components generally are used a higher current motor control. For small motor under 3A-4A using a L298 or comparable IC is simpler and takes up less space on a circuit board.

For the discrete H-bridge in the image above there are two input A and B. To make the motor spin in one direction input A must be made high (a positive voltage applied) and B must be made low (grounded). To reverse direction A is made low and B is made high. A and B can’t both be high at the same time or a dead short will be created damaging the circuit.

The input can be driven by different means. Switched could be connected to the inputs or the output of another circuit could be connected the inputs.

Here is a simple explanation of how the circuit works. Current is provided to the motor through the MOSFETS. Diodes are place in parallel with the MOSFETS to prevent flyback currents from when the motor changes direction from damaging the MOSFETS. The bipolar transistors are used to allow a smaller voltages to operate the MOSFET switches. The resistor voltage divider between the the MOSFET gate and the bipolar transistor controls how fast the MOSFET can switch state. The resistor at the base of the bipolar transistor is used to limit base current. Finally the LED’s are used to indicate the motor direction.

Standard diodes are used to only allow current to flow in one...

Tue, 01 Feb 2011 23:37:50 -0500

Standard diodes are used to only allow current to flow in one direction. A diode unlike a resistor doesn’t have a resistance it has a voltage drop which is current independent. Most standard diodes have a voltage drop of between 0.4v and 0.7v depending on the model. Diodes have many uses one of the most common is in voltage rectification where a AC voltage is converted into a DC voltage. They also can be used in DC motor controls to prevent flyback voltage generated when the motor switches direction from damaging the motor driving circuit.

Another important type of diode is a zener diode. Zener diodes have very specific break down voltages (voltage at which they conduct current in the reverse direction). Because of this zener diodes are used in reverse bias to provide a static voltage reference independent of the current being drawn as long as the max power rating of the zener diode isn’t exceed.

The third type of diode is and LED or light emitting diode. LED’s have constant voltage drops just like normal diodes accept they are slightly higher usually between 2v-3v the exact voltage drop depends on the color of the led. So it is important to remember when using an led it is necessary to place a current limiting resistor in series to prevent excess current from burning out the led.

Two of the most popular types of transistors are Bipolar...

Tue, 01 Feb 2011 20:56:52 -0500

Two of the most popular types of transistors are Bipolar transistors and MOSFETS. The main difference between the two are that Bipolar transistor are current controlled devices meaning current flowing into the base activates them. MOSFETS are voltage controlled devices meaning the gate has a very high impedance allowing very little current to flow they are activated at a voltage potential at the gate.

Bipolar transistors come it two types NPN and PNP. NPN transistors are generally used to sink current (give it a path to ground). This is because to activate a NPN transistor the base voltage must be higher than the emitter voltage. If you where to use a NPN transistor to source current (supply it to the load) the base voltage would have to be higher than the voltage flowing to the load. This could be problematic and over complicate the design. The solution is to use a PNP transistor to source current to a load. With a PNP transistor the base voltage must be lower then emitter to activate it.

MOSFETS also come it two types N-Channel and P-Channel which are analogous to NPN and PNP bipolar transistors. MOSFETS are often used when switching higher currents.

An H-Bridge is a circuit used for controlling DC motors. It...

Mon, 31 Jan 2011 15:53:15 -0500

An H-Bridge is a circuit used for controlling DC motors. It allows you to run the motor in either direction. By closing 2 of the switches current is allowed to flow one direction this causes the motor to spin. If the first set of switches is opened and the other is closed current will flow through the motor in the opposite direction causing it to spin in the opposite direction.

This was my final group project for EMET 230. It’s a...

Wed, 26 Jan 2011 14:40:32 -0500

This was my final group project for EMET 230. It’s a Power Wheels car that is remote controlled through labVIEW over a Wi-Fi network connection. It also has a paintball gun turret with a camera.