Paraphase Tone Controller

As opposed to the widespread Baxandall schema (dating back to 1952!) a ‘paraphrase’ tone control supplies a straight frequency response as long as the bass and treble controls are in the same position. This unique property makes the ‘paraphase’ configuration of interest if only treble or bass needs to be adjusted - it is not possible to adjust both at the same time! Essentially, it’s the difference in setting of the tone controls that determines the slope of the frequency response, and the degree of bass/treble correction. The schema is simplicity itself, based on two networks C1-C2-C3/R9-R10-R11 and C5-C6-C7/R12-R13-R14.

Picture of the project:

Paraphase Tone Controller Circuit

The first is for the high frequencies (treble) response, the second, for the low frequencies (bass). The roll-off points have been selected, in combination with C4 and C8, for the sum of the two output signals to re-appear with a ‘straight’ frequency response again at the output. Roughly equal output levels from the networks are ensured by R6 = 7.15 k and R8 = 6.80 k. However, the operating principle requires the input signals to the two networks to be in anti-phase. For best operation the networks are driven by two buffers providing some extra gain.

Circuit diagram:

  

Paraphase Tone Controller Circuit Diagram

The gain of IC1.D is slightly higher than that of IC1.C to ensure the overall response curve remains as flat as possible at equal settings of the tone controls. Because each network introduces a loss of about 1.72 (times), IC1.D and IC1.C first amplify the signal. The gain is set at about 8 (times) allowing input signal levels up to 1 V to pass the schema at maximum gain and distortion-free. The gain also compensates the attenuation if you prefer to keep the tone controls at the mid positions for a straight response.

Parts and PCB layout:

Parts and PCB Layout

To audio fans, the schema is rewarding to experiment with, especially in respect of the crossover point of the two networks. R3 and R4 determine the control range, which may be increased (within limits) by using lower resistor values here. The values shown ensure a tone control range of about 20 dB. IC1.B buffers the summed signal across R15. C9 removes any DC-offset voltage and R16 protects the output buffer from the effects of too high capacitive loads. R17, finally, keeps the output at 0 V. The choice of the quad opamp is relatively uncritical. Here the unassuming TL074 is used but you may even apply rail to rail opamps as long as they are stable at unity gain. Also, watch the supply voltage range. A simple schema board was designed for the project. Linear-law potentiometers may be fitted directly onto the board. Two boards are required for a stereo application. The relevant connections on the boards are then wired to a stereo control potentiometer.

Specification:

• Current consumption (no signal) 8 mA
• Max. input signal 1 Veff (at max. gain)
• Gain at 20 Hz +13.1 dB max. –6.9 dB min.
• at 20 kHz +12.2 dB max. –7.6 dB min
• Gain (controls at mid position) 2.38 x
• Distortion (1 Veff, 1 kHz) 0.002% (B = 22kHz) 0.005% (B = 80 kHz)

COMPONENTS LIST

Resistors

R1-R4 = 10k
R5,R7 = 1k
R6 = 7k15
R8 = 6k80
R9,R10,R11 = 8k2
R12,R13,R14 = 2k2
R15 = 1M
R16 = 100R
R17 = 100k
P1,P2 = 100k preset or chassis-
mount control potentiometer, linear law
Capacitors
C1,C2,C3 = 47nF MKT, lead pitch 5mm
C4 = 68nF MKT, lead pitch 5mm
C5,C6,C7 = 10nF MKT, lead pitch 5mm
C8,C10,C11 = 100nF MKT, lead pitch 5mm
C9 = 2µF2 MKT, lead pitch 5mm or 7.5mm
Semiconductors
IC1 = TL074
Miscellaneous
K1,K2 = line socket, PCB mount, e.g.
T-709G (Monacor/Monarch)

Author: Ton Giesberts - Copyright: Elektor Electronics

Stepper Motor Controller

Stepper Motor Controller Circuit diagram. Stepper motors are available in several versions and sizes with a variety of operating voltages. The advantage of this general-purpose controller is that is can be used with a wide range of operating voltages, from approximately 5 V to 18 V. It can drive the motor with a peak voltage equal to half the supply voltage, so it can easily handle stepper motors designed for voltages between 2.5 V and 9 V. The schema can also supply motor currents up to 3.5 A, which means it can be used to drive relatively large motors. The schema is also short-schema proof and has built-in over temperature protection. Two signals are required for driving a stepper motor. In logical terms, they constitute a Grey code, which means they are two square-wave signals with the same frequency but a constant phase difference of 90 degrees. IC1 generates a square-wave signal with a frequency that can be set using potentiometer P1. 

This frequency determines the rpm of the stepper motor. The Grey code is generated by a decimal counter in the form of a 4017. Outputs Q0–Q9 of the counter go high in succession in response to the rising edges of the clock signal. The Grey code can be generated from the outputs by using two OR gates, which are formed here using two diodes and a resistor for each gate, to produce the I and Q signals. Here ‘I’ stands for ‘in-phase’ and ‘Q’ for ‘quadrature’, which means it has a 90-degree phase offset from the I signal. It is common practice to drive the windings of a stepper motor using a pair of push-pull diagram for each winding, which is called an ‘H bridge’. 

That makes it possible to reverse the direction of the current through each winding, which is necessary for proper operation of a bipolar motor (one whose windings do not have centre taps). Of course, it can also be used to properly drive a unipolar motor (with centre-tapped windings). Instead of using a push-pull schema of this sort, here we decided to use audio amplifier ICs (type TDA2030), even though that may sound a bit strange. In functional terms, the TDA2030 is actually a sort of power opamp. It has a difference amplifier at the input and a push-pull driver stage at the output.

Stepper Motor Controller Circuit diagram:

Stepper Motor Controller Circuit Diagram

IC3, IC4 and IC5 are all of this type (which is economically priced). Here IC3 and IC4 are wired as comparators. Their non-inverting inputs are driven by the previously mentioned I and Q signals, with the inverting inputs set to a potential equal to half the supply voltage. That potential is supplied by the third TDA2030. The outputs of IC3 and IC4 thus track their non-inverting inputs, and each of them drives one motor winding. The other ends of the windings are in turn connected to half the supply voltage, provided by IC5. As one end of each winding is connected to a square-wave signal that alternates between 0 V and a potential close to the supply voltage, while the other end is at half the supply voltage, a voltage equal to half the supply voltage is always applied to each winding, but it alternates in polarity according to the states of the I and Q signals.

That’s exactly what we want for driving a bipolar stepper motor. The rpm can be varied using potentiometer P1, but the actual speed is different for each type of motor because it depends on the number of steps per revolution. The motor used in the prototype advanced by approximately 9° per step, and its speed could be adjusted over a range of approximately 2 to 10 seconds per revolution. In principle, any desired speed can be obtained by adjusting the value of C1, as long as the motor can handle it. The adjustment range of P1 can be increased by reducing the value of resistor R5. The adjustment range is 1:(1000 + R5)/R5, where R5 is given in k.If a stepper motor is switched off by removing the supply voltage from the schema, it’s possible for the motor to continue turning a certain amount due to its own inertia or the mechanical load on the motor (flywheel effect).

It’s also possible for the position of the motor to disagree with the states of the I and Q signals when power is first applied to the schema. As a result, the motor can sometimes ‘get confused’ when starting up, with the result that it takes a step in the wrong direction before starting to move in direction defined by the drive signals. These effects can be avoided by adding the optional switch S1 and a 1-k resistor, which can then be used to start and stop the motor. When S1 is closed, the clock signal stops but IC2 retains its output levels at that moment, so the continuous currents through the motor windings magnetically ‘lock’ the rotor in position. The TDA2030 has internal over temperature protection, so the output current will be reduced automatically if the IC becomes too hot. For that reason, it is recommended to fit IC3, IC4 and IC5 to a heat sink (possibly a shared heat sink) when a relatively high-power motor is used. The tab of the TO220 case is electrically bonded to the negative supply voltage pin, so the ICs can be attached to a shared heat sink without using insulating washers.

Water Pump Relay Controller Circuit Schematic

Water reservoir automatic level control, Simple schemary - 12V supply By means of a Relay, employed to drive a water pump, this schema provides automatic level control of a water reservoir or well. The shorter steel rod is the "water high" sensor, whereas the longer is the "water low" sensor. When the water level is below both sensors, IC1C output (pin #10) is low; if the water becomes in contact with the longer sensor the output remains low until the shorter sensor is reached. At this point IC1C output goes high, Q1 conducts, the Relay is energized and the pump starts operating.

Now, the water level begins to decrease and the shorter sensor will be no longer in contact with the water, but IC1C output will be hold high by the signal return to pin #5 of IC1B, so the pump will continue its operation. But when the water level falls below the longer sensor, IC1C output goes low and the pump will stop. SW1 is optional and was added to provide reverse operation. Switching SW1 in order to connect R3 to pin #11 of IC1D, the pump will operate when the reservoir is nearly empty and will stop when the reservoir is full. In this case, the pump will be used to fill the reservoir and not to empty it as in the default operating mode.

Water Pump Relay Controller Circuit diagram:

 Water Pump Relay Control Circuit Diagram

Parts:
R1 = 15K - 1/4W Resistors
R2 = 15K - 1/4W Resistors
R3 = 10K - 1/4W Resistor
R4 = 1K - 1/4W Resistor
D1 = LED - any type and color
D2 = 1N4148 - 75V 150mA Diode
Q1 = BC337 - 45V 800mA NPN Transistor
IC1 = 4001 Quad 2 Input NOR Gate CMos IC
SW = SPDT Toggle or Slide Switch (Optional)
RL1 = Relay with SPDT 2A @ 230V switch
Coil Voltage 12V - Coil resistance 200-300 Ohm
Two steel rods of appropriate length

Notes:

• The two steel rods must be supported by a small insulated (wooden or plastic) board.
• The schema can be used also with non-metal tanks, provided a third steel rod having about the same height of the tank will be added and connected to the diagram negative ground.