Voltase hobby: control

Showing posts with label control. Show all posts

Thursday, September 4, 2014

3 φ Full Wave Controlled Rectifier circuit to control DC Motor Speed

In the given Block and schema diagram of a 3 φ Full Wave Controlled Rectifier schema to control DC shunt motor is shown.

In this schema diagram the field and armature diagram are connected through three phase full wave Controlled rectifier schema.

In three phase supply, each phase is different form other one in 120°, therefore at each out put terminal a, b, & c give the following Sine wave voltage.

Through the three phase controlled rectifier, the three phase supply is converted to a DC and provided to the armature and field of the DC shunt motor.

Through the 3φ full wave Controlled Rectifier, the 3φ AC supply converted to a DC voltage and provide to the armature and field of the DC motor, which flow in shape of T_A (Armature Current) through the ckt (DC motor) due to this controlled Dc the motor start in low speed.

If the DC motor start through ordinary way, then an external resistance is connected in the armature ckt, these resistors in armature ckt controlled the speed of the motor, (Gradually decreases the resistance form the armature ckt) and when total resistance (Resistors) remove form the armature ckt, the motor is rotate at its full speed (RPM). The main purpose of the resistance with the armature ckt is that, to match armature current with internal current (emf) to decreased value.

In case of the controlled rectifiers the resistors are not connected because at motor starting time the SCR connected in armature ckt set the delay angle value ,that the armature resistance controlled the voltage drop in the armature. The armature controlled method is mostly used as compare to the field controlled method,

In armature controlled method the field voltage is kept constant, while the armatures voltages changes.

In the given ckt rectifier converted to the in put DC supply (Full wave) , the rectifier is consistof SCRs , the out put of the SCR is Directly apply to the Armature in a variable shape. The applied voltage can be change form the changing the firing angle of the SCR.

Low Power Amplifier with digital volume control

Amplifier with digital volume control can we make predictably because the circuit is made simple with just single chip TDA8551. The series of Mini Amplifier With Digital Volume Control is a type BTL amplifier with 1 Watt.

Techniques for adjusting the volume in this series has been provided with a pin path control that is controlled by providing an input voltage VCC and GND. The series is also equipped with a selector mute, standby and operating.

Mini amplifier with digital volume control schematics

Tuesday, September 2, 2014

Contrast Control for LCDs

The adjustment control for the contrast of an LC-Display is typically a 10-k potentiometer. This works fine, provided that the power supply voltage is constant. If this is not the case (for example, with a battery power supply) then the potentiometer has to be repeatedly adjusted. Very awkward, in other words. The schema described here offers a solution for this problem.

The aforementioned potentiometer is intended to maintain a constant current from the contrast connection (usually pin 3 or Vo) to ground. A popular green display with 2x16 characters ‘supplies’ about 200 µA. At a power supply voltage of 5 V there is also an additional current of 500 µA in the potentiometer itself. Not very energy efficient either. Now there is an IC, the LM334, which, with the aid of one resistor, can be made into a constant current source. The schema presented here ensures that there is a current of 200 µA to ground, independent of the power supply voltage. By substituting a 2.2-k? potentiometer for R1, the current can be adjusted as desired.

Circuit diagram:The value of R1 can be calculated as follows: R1 = 227x10-6 x T / I. Where T is the temperature in Kelvin and I is the current in ampères. In our case this results in:
R1 = 227x10-6 x 293 /
(200x10-6)
R1 = 333R

Note that the current supplied by the LM334 depends on the temperature. This is also true for the current from the display, but it is not strictly necessary to have a linear relationship between these two. Temperature variations of up to 10° will not be a problem however. This schema results in a power saving of over 25% with an LCD that itself draws a current of 1.2 mA. In a battery powered application this is definitely worth the effort! In addition, the contrast does not need to be adjusted as the battery voltage reduces. When used with LCDs with new technologies such as OLED and PLED it is advisable to carefully test the schema first to determine if it can be used to adjust the brightness.

Contrast Controller Circuit Diagram For LCDs:

Contrast Controller Circuit Diagram For LCDs

The value of R1 can be calculated as follows: R1 = 227x10-6 x T / I. Where T is the temperature in Kelvin and I is the current in ampères. In our case this results in:

R1 = 227x10-6 x 293 /
(200x10-6)
R1 = 333R

Note:

The current supplied by the LM334 depends on the temperature. This is also true for the current from the display, but it is not strictly necessary to have a linear relationship between these two. Temperature variations of up to 10° will not be a problem however. This schema results in a power saving of over 25% with an LCD that itself draws a current of 1.2 mA. In a battery powered application this is definitely worth the effort! In addition, the contrast does not need to be adjusted as the battery voltage reduces. When used with LCDs with new technologies such as OLED and PLED it is advisable to carefully test the schema first to determine if it can be used to adjust the brightness.

Fan on off Control by Light Wiring diagram Schematic

This schema lets you turn on/off a fan by just directing torchlight or other light toward its light-dependent resistor (LDR). The schema is powered from a 5V power supply.

Preset VR1 and a light-dependent resistor (LDR) work as the potential divider. Normally, the LDR’s resistance is high (20 kilo-ohms) in darkness and low (2 kilo-ohms) in light. This value of high and low resistances varies for other LDRs. Preset VR1 is used for setting the intensity of light, while preset VR2 is used for setting the output time period of IC1.

Fan on/off Control by Light Circuit Diagram

When light falls on the LDR, the monostable (IC1) triggers at pin 2, making its output at pin 3 from low to high. This low-to-high transition forms a clock for D flip-flop. The D flip-flop is operated in toggle mode by connecting its Q output to D point. The flip-flop output goes to an inverter (N1). The inverter output is fed to the relay driver transistor.

When the inverter output is low, diode D1 conducts and the current is diverted into the inverter. Hence the relay does not energise. When the inverter output is high, diode D2 conducts and the current is diverted into transistor T. Hence the relay energises.

One terminal of the fan is connected to the normally-open (N/O) contact of the relay, while another terminal is connected to the neutral (N) of mains. The mains live (L) is connected to the pole of the relay. When the relay energises, the fan turns on. Otherwise, the fan remains off.

Switches S1 and S3 are for initial resetting of the monostable (IC1) and D flip-flop (IC2), respectively, and switch S2 is used for setting the D flip-flop. Paste a piece of paper on the face of the LDR so that it doesn’t get activated by ambient light. Use a torch to light the LDR.

After initial resetting of the monostable and D flip-flop, the inverter output goes high and the fan turns on via the relay. When light falls on the LDR, the fan goes off. If torchlight is again directed toward the LDR, the fan turns on. The sequence repeats.

Initially if switch S2 is used to set the D flip-flop, the fan is held ‘off’. The relay does not energise as the Q output of D flip-flop goes high to make the inverter output low. Directing the light towards the LDR at this moment turns the fan ‘on.’

Sourced By: EFY Author: V. Gopalakrishnan

Monday, September 1, 2014

Heater and Ventilation Control

This is a guest post by our visitor Etienne F. For any questions please contact the author (email address link is given below). This schema control a heater and a fan at variable speed and intensity with over temp and under temp alarm. The control work with a thermistor for the temperature reading and the setpoint is variable. The speed and intensity work with a difference between the temperature reading and a setpoint. At all time, only one of the system works (heat or ventilation) or if the temperature is near the setpoint, none of them work.

1st block: temperature reading and setpoint voltage:

The reading of the temperature to generate voltage

Difference between set point and temeprature reading:

For the first PWM voltage value, the input from the LM324 subtract the temp reading and the setpoint. The result is multiply by the pot between the out and the + input of op amp U2b (ratio from the resistance and the pot.) (Value in ohms). The result is send to the – input of Op amp U2c and the second 100K pot is use to set the offset voltage (2Vdc in my schema). The result is send to the input of the PWM control block. The correct ratio should be around 2 :1 (multiply by 2 the voltage) The 1N4007 Diode keep the voltage over 0V (the result of the subtractions can be negative but the PWM need a voltage between 0 and 12V DC)

The voltage for the LM324 is +12 and -12VDC (pin 4 and 11) The second block subtract the setpoint voltage to the temperature reading. The result is multiply by the pot. (Depending of the value of the potentiometer). The ratio between the 56K resistance and the value of the potentiometer define the multiply ratio. The output equation is Vin X (Pot /R1) = -Vout The next op amp input add a voltage value to the result (2V) and the last amp is used to reverse the result.

3rd block: voltage generator proportional to a high temperature (PWM)

The block consists of an LM324 (quad op amp) which is used as a comparator (compare the temperature reading at set point), a square wave generator whose frequency varies according to the set point and the temperature reading. This square wave into an oscillator schema which, after being compared to the set point (which is a triangle wave that varies between 4V and 9V has a frequency of 45Hz). The triangular wave enters into a schema to be compared to the value of reading. When the reading exceeds the value of the triangular wave form is a square wave and the output is 12V.

More reading approaches the set point, the longer the 12V signal is activate and when the reading exceeds the maximum of the triangular wave (9V), the fan runs at maximum speed. The square wave into a MOSFET to be amplify (the ratio of on / off is increased). The duration of the excess voltage determines the duration of 12 V. The 0.1uF capacitor (C3) between the + and – of the load makes the signal clearer.

High and Low Temp Alarm:

Part list :

U1, U2, U3, U4, U5 : LM324 quad amp
Q1 : IRF521 MOFFSET
Q2 : TIP31C
D1, D2, D3, D4 : 1N4007
C1 and C2 : 1uF capacitor
C3 and C4 : .1uF capacitor

47K thermistor
Resistance :
19X 56K
10X 100K
2X 3.3K

Author: Etienne F

Monday, August 25, 2014

Wiper Speed Control

A continuously working wiper in a car may prove to be a nuisance, especially when it is not raining heavily. By using the schema described here one can vary sweeping rate of the wiper from once a second to once in ten seconds

http://www.electronic-diagram-diagrams.com/carsimages/2.gif

The schema comprises two timer NE555 ICs, one CD4017 decade counter, one TIP32 driver transistor, a 2N3055 power transistor (or TIP3055) and a few other discrete components. Timer IC1 is configured as a mono- stable multivibrator which produces a pulse when one presses switch S1 momentarily. This pulse acts as a clock pulse for the decade counter (IC2) which advances by one count on each successive clock pulse or the push of switch S1. Ten presets (VR1 through VR10), set for different values by trial and error, are used at the ten outputs of IC2. But since only one output of IC2 is high at a time, only one preset (at selected output) effectively comes in series with timing resistors R4 and R5 connected in the schema of timer IC3 which functions in astable mode. As presets VR1 through VR10 are set for different values, different time periods (or frequencies) for astable multivibrator IC3 can be selected. The output of IC3 is applied to pnp driver transistor T1 (TIP32) for driving the final power transistor T2 (2N3055) which in turn drives the wiper motor at the selected sweep speed. The power supply for the wiper motor as well as the schema is tapped from the vehicle’s battery itself. The duration of monostable multivibrator IC1 is set for a nearly one second period.

Sunday, August 24, 2014

Low Power Amplifier with digital volume control

Mini amplifier with digital volume control schematics