12 V Bidirectional Motor Control Circuit

This simple circuit drives DC motors with a maximum current of 1 A and can be built with readily available components.The output voltage is adjustable between 0 and 14 V and the polarity can be changed so that not only motor speed but also rotation direction can be adjusted by turning a knob. 

The circuit is also ideal as a controller for a DC model railway or small low voltage hobby tool. Power for the circuit is supplied by a 18 V mains transformer rated at 1.5 A. Diodes D1to D4 rectify the supply and capacitor C1 provides smoothing to give a DC output voltage of around 24 V. A classic ‘H’ bridge configuration is made up with transistors T1/T3 and T2/T4. Transistors T5 and T6 together with resistors R7 and R8 provide the current sense and limiting mechanism. The maximum output current limit can be changed from 1 A by using different value resistors for R7 and R8: IOUT = 0.6 V / R where R gives the value for R7 and R8. For increased current limit the mains transformer and diodes will need to be changed to cope with the extra current as well as the four transistors used in the bridge configuration. 

Circuit diagram:

  12 V Bidirectional Motor Control Circuit Diagram

 

Motor speed control and direction is controlled by a twin-ganged linear pot (P1). The two tracks of P1 together with R1/R2 and R3/R4 form two adjustable potential divider networks. Wiring to the track ends are reversed so that as the pot is turned the output voltage of one potential divider increases while the other decreases and vice versa. 

In the midway position both dividers are at the same voltage so there is no potential difference and the motor is stationary. As the pot is rotated the potential difference across the motor increases and it runs faster. The voltage drop across D5 and D6 is equal to the forward voltage drop VBE of the bridge transistors and ensures that the motor does not oscillate in the off position with the pot at its mid point.

http://www.ecircuitslab.com/2011/07/12-v-bidirectional-motor-control.html

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IR Remote Control Extender Mark 4

An Infra Red wired Repeater circuit to control appliances from a remote location.

Parts List:
R1: 1k Resistor (1)
R2: 3.3k Resistor (1)
R3: 10k Resistor (1)
R4: 15k Resistor (1)
R5: 2k2 Resistor (1)
R6: 470R Resistor (1)
R7: 47R Resistor (1) 0.5 Watt
PR1: 4.7k Preset (1)
C1,C3: 47u Elect(2)
C2: 1n Polyester 5% or better (1)
C4: 100u Elect(1)
Z1: 5V1 Zener (1)
Q1: BC549C or BC109C or 2N2222 (1)
Q2: BC337 or BC549 or ZTX450 (1)
IC1 : TSOP1738
IC2: 555 or 7555 (1)
LED1 5mm RED (1)
LED2,3 IR diode TIL38 or similar (2)

Alternatives to IC1 :
Everlight IR receiver module ELIRM 8621
Harrison electronics IR1
Vishay TSOP 1838
Radio Shack 276-0137
Sony SBX 1620-12
Sharp GP1U271R

Notes:
The signal emitted by an IR remote control contains two parts, the control pulses and a modulated carrier wave. The control pulses are used to modulate the carrier, a popular modulation frequency being 36 and 42KHz. The signal is radiated by an IR diode, typical wavelengths in the 850 and 950 nm region of the electromagnetic spectrum. Although this light is invisible to the human eye, it can be seen as a bright spot with a camcorder or digital camera.

In this circuit, the TSOP1738 IR module removes the carrier leaving only the slower control pulses ( 1 - 3KHz) which appear at the output. R1, C1 and Z1 form a smoothed 5 Volt supply for the IR module. Under quiescent conditions (no input signal) the output of the IR module is high. Transistor Q1 will be on, resulting in a low collector voltage, restting the 555 oscillator. Q1 also acts as a level shifter, converting the 5 Volt output signal to 12 Volts for the 555 timer. When an IR signal is received, decoded control pulses turn Q1 off and on. Each time Q1 turns off, pin 4 of the 555 timer goes high and an oscillation will be produced for the duration of each data pulse.

The 555 is wired as an equal mark/space ratio oscillator, the timing resistor R4, being connected back to the output of the timer, pin 3. The timing capacitor C2 is the other component in the timing chain. The pulse duration at pin 3 is defined as:-
 
T = 1.4 R4 C2

As the timing is crucialthe capacitor should have a tolerance of 5% or better and the power supply should be regulated. To allow for tolerance in components a 4k7 preset resistor is wired in series with R4. This adjustment allows R4 to be 15k to 19.7K creating output pulses of 21us and 27.58 us. As frequency is the reciprocal of periodic time then the oscillator adjustment is from 36.2Khz to 47KHz, allowing fine tuning for almost any appliance.

The final output stage uses a BC337 transistor in emitter follower. The output pulse will not be inverted, and the current through the IR photo emitters is around 30 mA dc. This is of course an average value, measured with a digital multimeter. The red led as always, is a visible indication that an input signal has been received. The circuit may be modified to use a fixed resistor in the timing chain as shown below. In this example a voltage regulator is also recommended to prevent changes in supply voltage altering the output pulse.

Setup and Testing:
Remove LED 2 and 3 and apply power. With no input signal LED 1 should be off. Press a button on a remote control in the same room as the circuit. LED 1 should flicker. If all is well, connect LEDs 2 and 3 and point them in the direction of the appliance (TV or VCR etc). The cable to the LEDs can exceed 100 metres if necessary, ordinary loudspeaker cable or bell wire is suitable. Set preset PR1 midway initially, it should work for all equipment. Most equipment is tolerant to within 5% so if you have for example a video that works at 42kHz and a TV that works at 38Kz tuning the modulation to 40KHz should allow both devices to operate. Any troublesome equipment, for example an Echostar receiver repeatedly press abutton on the handset while tuning PR1, you will find that it operates at some point. One IR LED may be used in place of LED2 & 3, but if there are two appliance in the same room, but in different locations, LED 2 can be aimed at a video, while LED3 aimed at a CD player for example. Below is how I discretely placed a photo emitter and plastered it directly into the wall:

Modifications:
An alternative output configuration is shown below. This uses a MOSFET to replace the original BC337 transistor. My thanks to Pete Griffiths for this modification and diagram.

Compatability:
If you make either the Mark 3 or 4 circuit please let me know if it works and the make and model of your remote control. I will add this to the database of compatible handsets below:-

Aiwa RC-ZVR01
Denon RC 554
Denon RC 921
Denon RC 924
Echostar T22605AA-00 * troublesome required careful tuning of PR1 to work
Kameleon One for all remote (URC-8060) Goodmans 97P1R2CPA1
Grundig SRC2
JVC LP20878-002
Matsui 28WN04
Mitsubishi 290P103A10
Mitsubishi EUR647003
NAD HTR2 (multi remote)
One for All 9910
Panasonic EUR511200
Philips RC6512
Pioneer AXD7323
Pioneer DV444
Pioneer VXX2801
Radioshack 1995
Saisho VR3300X
Sony RM-533
Sony RM-887
Sony RMT-V240
Sony RM-S325
Sony RM-DX50
Sony RM-U215
Sony RM-839
Sony RM-SCEX1
Sony RM-S336
Sony RM-D43M
Sony VCR
Technics EUR64713

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IR Remote Control Extender Mark 5

The latest addition to my collection of Infra Red (IR) Repeater circuits. The Mark 5 is a much improved version of the Mark 1 circuit and has increased range and sensitivity. It is also immune to the effects ofambient light, daylight and other forms of interference. In addition it works with IR modulation freuencies in the range 30 to 120kHz making the Mk5 circuit the best choice for compatibility with remote controls.

Parts List:
R1,R2: 5M6 RESISTOR (2)
R3,R5: 3k3 RESISTOR (2)
R4: 120k RESISTOR (1)
R6: 220R RESISTOR (1)
R7: 47k RESISTOR (1)
R8: 120R RESISTOR (1)
R9: 10k RESISTOR (1)
R10: 2K2 RESISTOR (1)
R11: 100R RESISTOR 1 W (1)
C1,C3,C4: 22n polyester CAP (3)
C2: 100u electrolytic 25V(1)
C5: 100u electrolytic 25V(1)
Q1 BC107 (1) alternatives, BC107A, 2N2222, 2N2222A
Q2 BC109C (1) alternatives, BC109, BC549
D1: 1N4148 DIODE (1)
D2: Red LED (1)
IC1,IC2 CA3140E opamp (1)
IR1: SFH2030: (1)
IR2,3: TIL38 (2) or similar.

Design Philosophy:
This time I have returned to "first principles" and built a wideband infra red (IR) preamp which receives and re-transmits the entire baseband signal from a remote control handset.

It is designed to work with IR controls using 30-120KHz and should therefore work with just about any handset. In addition I have separated ambient (surrounding) light from the modulated light used by a remote handset. The major problem with the Mark 1 circuit is that it reacts to all light sources, ambient light producing a continous signal from the IR photo diode and is amplified by the rest of the circuit. I have published a modification to the original Mark 1 circuit, click here to view.

Noise Immunity:
It is difficult working with Infra Red, you cannot see it, and it is difficult to measure. A major barrier with this circuit was how to differentiate between daylight and an IR signal. Ambient light produces an almost continuous signal, changing little over several hours. A signal from an IR handset contains control pulses modulated with a carrier frequency (typically 36kHz) transmitted using an Infra Red photo diode. My solution used here, is a simple RC filter formed by C1 and R3.

At low frequency i.e. 50Hz the impedance of C1 is high, around 144k. The voltage gain of inverting op-amp IC2 is approximately R4 / R3, but at low frequency C1 is in series with R3 so the gain is now 120k / (3.3k + 144k) or less than unity. Daylight or ambient light will change slowly over several hours, in frequency terms this signal would be millihertz or less and C1s impedance will be megaohms.

A signal from an IR handset will be modulated at around 36KHz. At this frequency the impedance of C1 is very low, around 200 ohms. This has little effect on the input impedance of the op-amp stage and voltage gain will now be R4 / R3 or about 34 times. The impedance of capacitor C4 also helps noise rejection as its impedance change will allow more signal to pass into Q1 base at high frequencies and much less signal at line frequencies.

Circuit Details:
Light photons are received at IR1, this is an IR photo diode type SFH2030. A SFH2030F, which contains a daylight filter,may also be used instead of the SFH2030. The photo diode is reverse biased and when light strikes it, the energy of the IR signal releases additional charge carriers within the diode, allowing more current to flow. This current is amplified and converted to a voltage by the first CA3140 opamp, IC1. IC1 is wired as a current to voltage convertor, see below.

In an ideal current to voltage convertor the output voltage would be the product Rf multiplied by the input current. The non-inverting input would be tied to ground. In the Mark 5 circuit the output voltage is iR1 or about 5.6 Volts/uA appearing at pin 6 of IC1. The current generated by the SFH2030 photo diode when receiving a signal from a handset several metres away is less than 50 nA and requires the extreme high input impedance to avoid shunting the signal. There are two reasons for using the CA3140, the first is its high input impedance, over 1000G. The second reason is that normally the non-inverting input would be at 0V when working from split + and - supplies. In this single supply version the non-inverting input is returned to negative supply via R2. This can only be done with a Mosfet input, hence the choice for using the CA3140.

IC1 converta all current from the photo diode IR1 into a voltage. Although the SFH2030 is most sensitive at infra red wavelengths, it will produce tiny currents from daylight and also the 50/60Hz noise fields from flourescent and mains lighting. To minimize this, C1 and R3 form a high pass filter, allowing a 30kHz and higher signals to pass but blocking low frequencies. The impedance of C1 increases with decreasing frequency being 31k at 50Hz. Daylight for example, produces a contstant luminence, changing slowly over several hours, to which the impedance of C1 is effectively infinite.

The signal voltage from IC1 is now further amplified by IC2, gain being the ratio R4/R3 or 31dB. All opamps have a limit called the gain bandwidth product. The gain will fall to unity at the highest usuable frequency and be a maximum value at dc. Between these limits the gain falls with increasing frequency as shown in the bode plot for the CA3140 below:

Looking at the chart above, at 100kHz the maximum gain can only be about 30dB. However this is ample and boosts the received range of signals from a remote handset to the photo diode which have worked well up to 4 metres apart. Because R5 is returned to the negative supply a Mosfet input opamp must again be used. The output is again filtered by a high pass filter comprising C4 and the associated input impedance of Q1. R6, C2 and C3 provide decoupling for the IR preamplifier, C3 is in parallel with C2 because an electrolytic is not always a low impedance at high frequencies.

The IR output stage is comprised of Q1 and Q2 and associated components. The output is arranged so that with no input signal, Q1 is on and Q2 off; the visible LED, D2 will also be off. With no signal the 47k resistor biases the driver transistor, Q1 into full conduction. Its collector voltage will be near zero volts and the output transistor Q2, which is direct coupled to Q1 collector will therefore be fully off. Power drain will be minimal.

When an IR signal is receieved from a handset, the complete modulated signal will be amplified and fed via C4 into Q1 base. This is sufficiently strong enough to overcome the positive bias supplied by R7 and switch off Q1. This will happen many times a second, at the same frequency as the IR modulating signal sent by the handset. As Q1 switches off, its collector voltage rises to near full supply switching on Q1 and lighting the LED D2. Pulses of infra red at the same modulating frequency are then transmitted by the photo emitting diodes, IR2 and IR3. Because the signal is cleaner, (i.e. no daylight or 50/60Hz lamp fields included) then the series resistor R11 has been incresed in value to 100 ohms. The range from photo emitter diode to the equipment to be controlled has proved successfull at over 4 metres when powered from a 12 Volt supply. D1 helps to improve the turn off speed of Q1, thereby ensuring that the output waveform will be "squarer". It can be omitted but the circuit will perform better if D1 is included. A simulated transfer characteristic is shown below:

AC Transfer Charcteristic

The ouput is measured between Q2 emitter and ground. A simulated transient response is shown below. Three graphs are produced with excitations of 40,80 and 120kHz.

Please note that the above waveforms are simulated using a perfect square wave input, with rise and fall times of zero seconds. The output is measured between Q2 emitter and ground with a 200 ohm resistive load. In the real world, the cable to the remote photo emitter LEDs will contain both capacitance and inductance. This will increase both rise and fall times of the output signal. As with the Mark 1 circuit I recommend using speaker wire or bell wire to be used to cable the remote photo emitters.

My Prototype

Note that the veroboard layout below only includes the componets from the left of the schematic to C4, I had Q1 and Q2 on breadboard during this testing phase.

Setup and Testing:
There is little to adjust in this circuit. First I suggest disconnecting the wiring to the emitters IR2 and IR3. Switch on and D2 should be off. Aim a remote in the direction of IR1 and press any button D2 should light and be seen to flash when a button is held on the handset and go off when unpressed. If all is well reconnect the wiring to emitters IR2 and IR3. Without lenses, the light is quite directional and so you will need to aim it carefully at the remote equipment you are controlling. A digital camera, or camcorder can "see" into the Infra red range. This is useful to prove that IR2 and IR3 are producing output.

Veroboard Layout:
Below is a picture of my veroboard layout for the Mk 5 IR extender using Ron Js excellent veroboard images. Special thanks to Derek Smith for checking the veroboard layout and pointing out one small error (which is corrected now).

Special Note:I have omitted Diode D1 in my prototype and also the veroboard layout above, and the two images below. Click the links below to view the actual veroboard layouts. The veroboard drawing above shows the component site, the yellow circles represent the breaks on the bottom (track side).

Component side (106k)
Track side (97k)Note that this is reversed from component side.
For more help on vero layouts see this Practical Page.

Fault Finding:
If your circuit does not work, first check that your circuit is receiving power. Next compare the voltages to my prototype below. These checks are all made with a digital multimeter with a supply voltage of 12V DC. All checks are made with respect to ground (i.e. the back or negative meter probe is always connected to the negative or 0V power rail).

With no input signal:

IC1   Pin6       1.15V
IC2   Pin6       0V
Q1    base       0.8V
Q1    collector  0.13V
Q2    emitter    0V


With a strong input signal (handset same room less than 2meters away):

IC1   Pin6       1.15V
IC2   Pin6       0.15V
Q1    base       0.65V
Q1    collector  3.16V
Q2    emitter    2.79V



A good tip from Derek Smith (UK, who had problems with poor noise immunity in this circuit. Derek cured his fault by replacing the SFH2030 photo diode, the new SFH2030 provided much better noise immunity. So, if your voltage levels are similar to my prototype above then try replacing IR1.

If you still have problems with noise immunity check the supply voltage. Special thanks to Roch who found out that his 12V power supply was actually running at 16V. After reducing the voltage to 9V the problems disappeared for him. My original circuit ran happily from a 12V regulated supply.

Compatible Handsets:
If you build the mark 5 circuit please let me know the make and model of your remote control. I will add it to the list of compatible handsets below:-

Aiwa RC-ZVR01
Echostar URC-39756
Kameleon One for all remote (URC-8060) Maplins 6 way Audio/Video Switcher Hub order code L63AB
One for all remote
Panasonic EUR511200
Panasonic DVD player model no N2OAHC000012
Philips RC6512
Pioneer AXD7323
Pioneer VXX2801
Pioneer DVD remote
RCA systemlink 8 A-V
Saisho VR3300X
Sanyo vhs remote
Sony RM1- V141A VTR/TV
Sony RM-533
Sony RM-831
Std Sky digi box handset
Technics EUR64713
Xbox Remote

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Power Circuit Breaker – Operation and Control Scheme

Power Circuit Breakers (PCB) break an electrical circuit to isolate faults. They also re-close to make a circuit after the fault is removed. To enable this opening and closing, it is operated by either a remote relay or a local switch. A remote relay is located inside the control room while the switch is located inside the circuit breaker junction box.Close and Trip Circuit of a Breaker



Understanding a breaker scheme is important if you plan on designing a substation. Quite often, it is overwhelming to make sense of the entire scheme at a glance. The figure below depicting a circuit breaker scheme will be used to explain various elements of the PCB’s design and its control.

Forms of Contact
Before explaining what each device in the scheme does, understanding the different forms of contact is necessary. A form ‘a‘ contact represents a Normally Open (N.O.) contact while a form ‘b‘ is a Normally Closed (N.C.) contact. Thus when a breaker is de-energized, its 52a and 52b contact position stay true to the statement above and as shown in Figure 1. However, when PCB is energized, the contacts switch their state i.e. 52a contact will be closed while 52b is open. Contact positions of all other auxiliary relays and switches – remote or local – stay unchanged unless, ofcourse, they operate on a fault or other desired condition.

Circuit Breaker Trip Coil
Figure above depicts a trip coil of the breaker. For brevity, I will cover the trip coil no.1 with trip coil no.2 identical.
From the diagram, the breaker is fitted with a 43 switch that toggles between local trip and remote trip. Positioning it in local allows the persons at the breaker junction box to trip the circuit by closing the Control Switch (CS). Switching it to remote position permits the relays in the control house to close their contact and trip the breaker.
Modern PCB’s employing Sulfur Hexa-Flouride (SF6) gas to extinguish an arc are fitted with ANSI ’63′ relay. To prevent breaker damage due to flash-overs during low gas conditions, tripping of breaker is cut-out by this relay’s contact. Notice in Figure 1 how the contacts from this relay are strategically placed in the close and trip circuit to cut out any signal from the relays or switches.
At this point, the reader should realize the importance of contact development. All contacts operate only when the trip coil of their respective relay is energized. For instance, consider the 63 relay and its contacts shown in in figure 1. This relay is energized by the same DC source as the one supplying the breaker. However its trip coil is actuated by a transducer that can sense a fall in SF6 gas pressure. When this occurs, it switches its contacts located in different circuits to prevent any breaker operation. Similarly, the 27 undervoltage relay trip coil is connected across the DC source. When this supply is interrupted, the relay switches its contact position. This change can be relayed to an alarm or initiate some other action.
To trip the breaker from a remote location, all contacts from relays at the remote location shall be hard-wired. Yes, this means laying a lot of copper from the breaker cabinet to the relays. Further, all tripping contacts are wired in parallel. When either relay’s contact close and thus complete the circuit, the breaker trips.

Target Devices
Now, you may notice the red target lamp is connected in a way that will essentially short out the remote relays and trip the breaker. Not surprisingly, this is not the case. The target lamps shown in the scheme have enough resistance in them (~200 ohms), limiting the current that can energize the coil.
Target lamps are used in circuits to convey certain conditions. With the breaker closed and energized, the red lamp illuminates to indicate a live circuit. When the breaker opens (due to a fault) the green lamp illuminates – the circuit complete with 52b contact switching from open to close.
Most modern circuit breakers are specified with two trip coils. Energizing either one leads to breaker’s trip. Since a good amount of redundancy is built into the protection and control of a power system, it is not too uncommon to see all primary relaying in the system tripping trip coil 1 and the back-up tripping trip coil 2.

Circuit Breaker Close Coil
This coil when energized actuates a lever that engages the closing mechanism (like a spring). A close circuit is optionally fitted with both 43 local/remote switch and a local trip switch. Remote relays are wired in as shown in Figure 1. Unlike the trip circuit, the relay contacts in the close circuit are always connected in series and present in normally closed position. Thus, when a relay trips, it also blocks closing of the breaker. Until the relay is reset, either manually or remotely, the breaker will not be operational.

Anti-Pump Relays
To prevent inadvertent multiple closing operation, breakers are fitted with anti-pump relay. Assume a scenario where a fault persists on a line and a person is looking to close a breaker on it. Although the person presses the close button for a second or two, for the breaker which operates in cycles, this duration is an eternity. With the close button pressed, the breaker attempts to close but because of the fault in the system it trips again, then closes, then trips. This trip/close operation repeats for the second or two the button is pressed. Since the motor in the breaker is not rated for continuous duty, serious damage can occur to it.

Modern breaker control relays are programmed to check for synchronism and also to reclose a breaker. A single contact from this relay is all that is needed to initiate one-shot, two-shot, or three-shot scheme. In old breaker schemes, 25 relay contacts and reclosing relay (79) contacts are typically wired into the breaker close scheme.

On a final note, keep in mind that not all relays can handle the momentary trip/close coil currents. Auxiliary relays like an electro-switches are typically employed to handle these currents.

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