Door-Knock or Vibration Alarm Circuit Diagram

This is a simple circuit that activates an alarm when there is a knock on the door or there are any vibrations due to movement of heavy goods or furniture. The circuit uses readily available components.

Circuit and working

The circuit is built around quad-opamp LM324 (IC1), which is configured in amplifier mode. It uses the piezoelectric element of a piezo buzzer as the input sensor, two transistors BC547 (T1 through T2), a piezo buzzer and some other components for the alarm circuit. Fig. 1 shows the circuit diagram of the door-knock alarm.

The reference voltage at pin 3 of IC1 is set by trimming potmeter VR1. The piezoelectric element plate is fixed at the centre of the door using cello tape. Apply a small quantity of adhesive on the edges between the plates. Wires from the piezo element are connected at CON2. These generate an input pulse when vibrations are caused by knocking on the door. The pulse is amplified by op-amp A1 of IC1. Remaining three op-amps of quad IC LM324 are not used here.

The output of A1 of LM324 from pin 1 is further amplified by transistors T1 and T2 to drive the piezo buzzer or relay. Because of the presence of high-value capacitor C5, the buzzer remains active for a few seconds. The circuit is powered by 9V/12V power supply. Sensitivity of the circuit can be adjusted by 1M potmeter VR1.

Fig. 1: Circuit diagram of a door-knock alarm

In place of piezo buzzer PZ1, you can use 9V/12V single-changeover relay connected to an amplifier for louder sounds.

Construction and testing

An actual-size, single-side PCB for the alarm is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on the PCB, enclose it in a suitable plastic box.

Fig. 2: An actual-size PCB layout of the circuit

   

 Fig. 3: Component layout of the PCB

 

Before using the circuit, ensure that supply voltage is correct.

Sourced By: EFY Author :  Pradeep G

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Speed Controller for Small Cooling Fans

Small cooling fans are used in some equipment for cooling semiconductor devices. The circuit given here is of a simple automatic speed controller for a 12V, 0.6W (or 1.2W) cooling fan that increases the fan’s speed when temperature rises, and vice versa.

Circuit and working
Fig. 1 shows circuit diagram of the speed controller for a small cooling fan. Resistor R1 limits the initial current for the motor and lowers the speed of rotation, if needed. The temperature control is done with one or more NTC (negative temperature coefficient) thermistors connected in series with the electrical motor. The number of thermistors depends on their power dissipation.

Usually you cannot find low-cost NTCs with enough power dissipation. Therefore four of them in parallel are used here. This way power dissipation and self-heating of the NTCs are reduced. It is better to use NTCs with tolerance of ±2%. The NTCLE100E3 are available with nominal values of 3.3-ohm to 470-kilo-ohm and have maximum power dissipation of 0.5W at +55°C.

Table I shows easily-available NTC thermistors that can be used in the circuit. The resistors R2 through R5 are equalisation and limiting resistors. These resistors are usually between 3% and 15% of the resistance of the thermistors at +25°C.


LED1 is used as power on/off indicator for the circuit. LED2 indicates the speed of rotation of the fan. If speed of the motor is high, LED2 glows brightly, and vice versa. Diode D1 is used to prevent back EMF when power supply is removed.

Connector CON1 is used for the power supply. It is better to have power supply 10 to 25% higher than the nominal working voltage of the fan to compensate for the voltage drop across the resistors and the thermistors.

Voltage drop across resistor R8 is proportional to the current in the motor. Connector CON2 is used to connect a digital voltmeter to measure the voltage drop.

Construction and testing
An actual-size, single-side PCB for the circuit is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on a PCB, enclose it in a suitable plastic box.

Fig. 1: Circuit diagram of the speed controller

Fig. 2: An actual-size PCB for the speed controller

Fig. 3: Component layout for the PCB

Fix all the four NTC thermistors (NTC1 through NTC4) at appropriate locations, within the equipment whose heat is to be dissipated, for temperature sensing. On front panel of the speed controller fix switch S1 for power on/off, LED1 for power on/off indication and LED2 for fan-speed indication. Before using the circuit, verify that voltages at various points in the circuit are as per Table II.

Sourced By: EFY Author:  Petre TZV Petrov

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TDA1562Q 54 W Amplifier Circuit Diagram

This is the simple Using TDA1562Q 54 W Amplifier Circuit Diagram. The integrated output amplifier described in this article consists of little more than one integrated circuit. It is intended especially for use in motor vehicles and other battery operated applications. Although it appears simple and hardly worth looking at, the amplifier can produce an appreciable audio power output.[link]

Using TDA1562Q 54 W Amplifier Circuit Diagram

Data

PropertiesHigh power output through Class-H operation

Low power dissipation during reproduction of music signals

Proof against short-circuits

Protection against excessive temperatures

Standby switch

No power-on or power-off clicks

Visible error indication

Measurement results (at Ub=14.4 V)

Supply voltage 8–18 V

Sensitivity 760 mV r.m.s.

Input impedance 70 kΩ

Power output 54 W r.m.s.

into 4 Ω (f=1 kHz; THD+N=1%)

Harmonic distortion (THD+N) at 1 W into 4 Ω: 0.046% (1 kHz)

0.29% (20 kHz)

at 35 W into 4 Ω: 0.12% (1 kHz)

0.7% (20 kHz)

Signal-to-noise ratio (with 1 W into 4 Ω) 88 dBA

Power bandwidth 7.5 Hz – 185 kHz (at 25 W into 4 Ω)

Quiescent current about 135 mA (‘on’)

COMPONENTS LIST

Resistors:

R1 = 1MΩ

R2 = 4kΩ7

R3 = 1kΩ

R4 = 100kΩ

Capacitors:

C1,C2 = 470nF

C3,C4 = 10μF 63V radial

C5,C6,C8 = 4700μF 25V radial

(18mm max. dia., raster 7.5 mm)

C7 = 100nF, raster 5 mm

Semiconductors:

D1 = high-efficiency-LED

IC1 = TDA1562Q (Philips)

Miscellaneous:

S1 = single-pole on/off switch

Four spade connectors, PCB mount

Heatsink for IC1 (Rth<2.5>

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Battery-Discharge Measurement Circuit Diagram

Battery-life measurement for a portable system is a time-consuming task and many methods used for it do not give reliable results. Presented here is a circuit using which you can measure the battery-life very easily. Here, an analogue clock tracks the discharge time of the battery used in battery-powered portable devices.

Circuit and working
The circuit for battery-discharge measurement is shown in Fig. 1. It is built using low-power single-/dual-supply comparator MAX921 (IC1), MOSFET VN0300L (IRF1), an analogue clock and a few other components.

IC1 monitors the life of the BUT (battery under test) and controls the power supply for the analogue clock. When the BUT voltage falls below the threshold value set by VR1, IC1’s output becomes low, which turns off MOSFET IRF1. This means, power supply for the analogue clock is cut off and so the clock stops running. The reading on the clock at this point gives the discharge time of the BUT, provided you had set the clock to 12:00 before testing started. The circuit can test 2.5V to 11V batteries.

Fig. 1: Circuit diagram for battery-discharge measurement

Fig. 2: An actual-size PCB pattern for the circuit

Fig. 3: Component layout for the PCB

Construction and testing
 An actual-size, single-side PCB for the circuit is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on PCB, enclose it in a suitable plastic box. Connect positive terminal of the analogue clock to positive terminal of a 1.5V AA-size battery and negative terminal to the drain of MOSFET IRF1. Before using the circuit, verify that voltages at the test points are as per table.

For setting the threshold voltage, you need a variable DC power supply at CON1. For example, to measure the discharge time of a 6V battery (BUT), first decide its minimum threshold voltage, say 4.5V. Connect variable supply to CON1 and set it to 4.5V. Vary VR1 till the clock stops running. Now, remove the variable power supply, set the clock to 12:00 and connect the 6V battery at CON1. Connect the load across the battery. As the battery power is being consumed by the load, voltage level begins to drop. When BUT voltage drops below 4.5V, the clock stops running. The time shown on the analogue clock at this point is the discharge time.

Sourced By: EFY: Author : Bhaskar Pandey

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AM transmitter using Integrated Circuit

Many beginners give up playing with RF due to the difficulty of building coils and problems with self oscillations that are common in many electronic circuits of RF. I always point out to beginning the construction of a small FM transmitter, myself have made available a simple circuit and an explanatory tutorial in Article Micro FM Transmitter and Micro Spy FM Transmitter Spy Bug in SMD.

The RF is really a very critical area, but on the other hand, it is the most rewarding, especially when we see one of our creations give the air of grace and drop its waves through the air. I always say that we learn more from mistakes and making mistakes is part of the electronics, I even today burst capacitors and transistors see loose tufts of smoke, the difference is that today I have fun with these errors.

Here I will publish a simple electronic circuit RF, so simple that does not use a single coil. This is a small tone transmitter modulated (AM) for the band of medium waves (AM) using an integrated inverter hex 4049 and a crystal circuit. The circuit is very simple, but effective, as can transmit smoothly.

AM transmitter using Integrated Circuit

The operation of this AM transmitter is simple, the RF oscillator in the transmitter circuit uses an inverter (7-6), whose frequency is determined by the 1 MHz crystal, as we see in the scheme. Two more drives (9-10 / 11-12) amplify the 1MHz oscillator signal.

Have the two inverters (3-2 / 5-4) produce an audio tone, which is modulated with the RF signal by the last inverter (14-15). You can use a piece of wire as an antenna, the signal, a buzz, should be easily capitate until a few meters from the transmitter at 1000 kHz in any AM radio.

With this circuit it is possible to work with the fundamental frequency and its harmonics at all integer multiples of a 1 MHz (or 2 MHz, 3 MHz, ... 10 MHz). This circuit can also be used as a frequency standard to verify the calibration of the display of a short wave radio.

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Monitor for 6V/12V Batteries

Rechargeable batteries of 6V and 12V are used in a large number of applications. It is imperative that these are maintained properly to get maximum life out of them. Further, their permissible number of charge-discharge cycles must be fully utilised. Here is a circuit that gives a visual as well as an audible alarm if the battery voltage is higher or lower than acceptable limits, so that corrective action can be taken.

Circuit and working
As shown in Fig. 1, the circuit is built around dual-operational amplifier LM358 (IC1), hex inverting Schmitt trigger 74HC14 (IC2) and a few other components. The circuit can be divided into two parts—the input unit built around two operational amplifiers (op amps) in IC1 working as comparators, and audio alarm unit built around two RC oscillators and a transistor.

Voltage from the battery under test (BUT) is applied to connector CON1. It is divided by five by R1 and R2 for comparison with the threshold levels. the power supply of the circuit is limited to 5V ±2%. SPDT switches S1 and S2 simultaneously select between the preset threshold for 6V and 12V rechargeable batteries. potentiometers VR1 and VR2 set the highest allowable input voltage. For example, for a 12V battery, if you wish to activate the visual and audio alarms at 14.5V, you should set the potentiometer VR2 reference voltage to 14.5V/5 = 2.9V.

Potentiometers VR3 and VR4 set the lowest allowable input voltage. For example, for a 12V battery, if you wish to activate the visual and audio alarms at 10.8V, you should set the potentiometer VR4 reference voltage to 10.8V/5 = 2.16V. Similarly, you can obtain the reference voltages for a 6V battery by setting potentiometers VR1 and VR3.

When the input voltage is above the threshold set by potentiometers VR1 or VR2, the output at pin OUT1 of IC1 becomes low and the LED2 indicating a high voltage switches on. The output of gate N1 of IC2 becomes high and the RC oscillator built around gate N2 oscillates. The output, which is a square wave with frequency of approximately 1kHz, is amplified by gate N3 and transistor T1 and reproduced by the headphone loudspeaker (LS1) or an earphone. The frequency of the RC oscillator built around gate N2 can be set with the help of resistor R7 and capacitor C2 to an appropriate value.

When the input voltage is below the threshold set by VR3 or VR4, the output at pin OUT2 of IC1 becomes high. The output of gate N4 becomes low and the LED3 indicating a low voltage switches on. The RC oscillator built around gate N5 starts working. The produced square wave signal with frequency of around 1kHz is amplified by gate N6 and transistor T1 and reproduced by the headphone loudspeaker (LS1) or an earphone. The frequency of the RC oscillator built around gate N5 can be set with resistor R8 and capacitor C3 to an appropriate value.

Fig. 1: Circuit diagram of monitor for 6V/12V batteries

Fig. 2: Actual-size PCB layout for the monitor circuit

Fig. 3: Component layout for the PCB

When the input signal is within the range set by the selected potentiometers, both the oscillators do not work, and there is no sound from the loudspeaker and the LEDs LED2 and LED3 remain off.

Power supply for the circuit may be derived from 78L/M/05 (not shown) with 5V and ±2 per cent tolerance and connected at CON2. LED1 is the power indicator.

Construction and testing
An actual-size, single-side PCB for the voltage monitor for 6V/12V batteries is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on a PCB, enclose it in a suitable plastic box.
Fix CON1 on the front side of the case for connecting the battery under test (BUT). Fix CON2 on the rear side of the box for connecting a 5V power supply to the circuit.

Before use, check that voltages at the test points are as per the table.

Sourced BY: EFY Author Name:  Petre Tzv Petrov

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Electronical High Frequency Oscillator Circuit Diagram

This is the simple Electronical High Frequency Oscillator Circuit Diagram. Intended primarily as a building block for a QRI`transmitter, this 20-MHz oscillator delivered a clean 6-V, pk-pk signal into a 100-0 load. 

Electronical High Frequency Oscillator Circuit Diagram

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Simple Two 555 Timers Bell Circuit Diagram

This is the Simple Two 555 Timers Bell Circuit Diagram. This simple scheme uses two Bell 555 timer. The frequency controlled capacitors, which should be preserved are almost identical in value with each other to achieve the best results. Fine tuning is done with the R1 and R2. The decay time is controlled by R3.

 

Simple Two 555 Timers Bell Circuit Diagram

 

 

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Simple Ac line Voltage Announcer Circuit Diagram

This is the Simple Ac line Voltage Announcer Circuit Diagram. The range of this simple ac-voltage monitor is 100 to 140 Vac, with a resolution of 1 V. The speech processor interprets an 8-bit binary input code from an analog-to-digital converter. The processor`s pulse-code-mod ulated output then passes through a filter and an amplifier before driving tbe circuit`s speaker to vocalize the corresponding number. Each time switch S1 is _pressed, the speech-processor program enun ciates tbe monitored voltage readings from 100 to 140 V, depending on the code at the input of a 27C64 EPROM. 

 Simple Ac line Voltage Announcer Circuit Diagram

The voltage-monitoring circuit consists of a bridge rectifier, filter capacitors, and a 10-Kilload resis tor. A divider, RA and RB, limits the input voltage to a maximum 2.55 V. The aid converter, IC4, then sends the voltage reading to tbe 27C64 EPROM, ICS. Pressing Sl sends a negative transient pulse to the write, WR, input of the aid converter, IC4, which initiates a 100-ttS conversion process. [Link]

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Simple Stethoscope Circuit Diagram

The stethoscope is a medical or veterinary use tool, in which the professional can hear the heartbeat, breath or other bodily sound of his patient. We can say that the operation of the stethoscope is simple, the recorded sound is amplified and taken directly to the ear by a pipe. The stethoscope is also called phonendoscope, it has two different pickups sound the bell and diaphragm.

The traditional stethoscope is an acoustic equipment, and its pickup of sounds, are specific, the bell and one of the pickups that come in contact with the body, and its function is to capture bass. Have the diaphragm is used to capture the treble, all for a physical process, without the use of electronic circuits.
The Electronic Stethoscope

An electronic stethoscope or estetofone , has the ability to overcome low levels of noise, electronically amplifying body sounds. But this electronic system turns out to be limited the microphone audio frequency responses (pickup) and speaker, something that does not occur in acoustic stethoscopes.

Still there are a large number of companies offering electronic stethoscopes that rely on conversion of acoustic sound waves into electrical signals that can be amplified and processed making a faithful sound system, almost equal to the acoustic. Electronic stethoscopes sold commercially using various systems, the most common is a piezoelectric crystal placed in behind a foam rubber membrane as a pickup.

Simple Stethoscope Circuit Diagram

The evolution of electronic stethoscopes also made possible the emergence of new tests as the phonocardiogram and telemedicine which allowed remote diagnostics.

The circuit simpler and less effective sound detection is achieved by a set of a microphone, an amplifier and a speaker or earphone. This method suffers interference from environmental noise but can be used as a simple electronic stethoscope. Precisely, the simplest is that we show here in this article.

Above the electronic stethoscope circuit, its operation is as follows, one capsule, electret microphone is used as sound pickup, the U1A integrated circuit which is a TL072 has the low noise pre-amplifier function. Your gain is less than 3.9, which is due to the high output impedance of the electret microphone.

The capacitor C2 has a relatively large capacitance, as it filters, leaving only pass the low frequency (20-30 Hz) that are the sounds of a beating heart. The U1B mounted on a Sallen-Key filter low noise with a cutoff frequency of about 103 Hz. R7 and R8 set the gain level of the order of 1.6. The integrated circuit U5 which is a LM386 audio amplifier with an output of 0.25 watts. Part of the U4 integrated circuit can be optional, it is an operational amplifier 741 that controls the two-color LED.

Electronic Stethoscope components list

R1 - 10k ¼ W resistor
R2 - 2.2 ohm ¼ W resistor
R3, R9 - Not used
R4 ¼ W 47 Ohm resistor
R5, R6, R7 - 33K resistor ¼ W
R8 - 56 Ohm resistor ¼ W
R10 - 4k7 ¼ W resistor
R11 - variable resistor of 2.2 logarithmic
R12 - resistor 330 Ohm ¼ W
R13, R15, R16 1K resistor ¼ W
R14 - resistor 3.9 ohm resistor ¼ W
C1, C8 - electrolytic capacitors 470 uF / 16 V
C2 - electrolytic capacitor 4.7 uF / 16 V
C3, C4 - Polyester Capacitors 0.047 uF / 50 V
C5 - ceramic disc capacitor 0.1 uF / 50 V
C6, C7 - electrolytic capacitors 1000 uF / 16 V
U1 TL072
U2, U3 Not used
U4 - 741
U5 - LM386
MIC - electric microphone three terminals

The circuit is very simple and can be mounted on breadboard, on the microphone connection with the circuit should be used shielded cable to prevent noise pickup. You must mount the pickup so that the microphone is placed at a distance from the skin surface but one that is close to the body to protect the microphone from external noise.

Keep the microphone away from the headphones to avoid feedback. Unfortunately, the device offers a very limited application, use it only as a learning circuit, test or demonstration. Link

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Monitor and Protection Alarm Over Current Circuit Diagram

The electronic circuit described in this article's main function remote monitoring of power consumption (over current) in a domestic mains alternating current. This monitoring is necessary in many systems, especially in electronic counters, power supplies, AC, inverters, converters, etc.

The operation of the circuit is simple, to be connected to the power grid, and when the circuit detects a consumption in the electric network of more than 5 mA he lights LA1 signal lamp. The device can work with currents of several amperes, it depends on the diode used in D1 and D2. The Ti1 transistor is turned on when the D1 and D2 drop exceeds a certain level.

Monitor and Protection Alarm Over Current Circuit Diagram

Fuse F1 must of course be dimensioned to suit the application and current limit circuit. When Ti1 leads the alternating current can flow through the capacitor, and the triac is triggered, so that lights the lamp LA1.

The above circuit is a current alarm of some changes, there is a bridge rectifier formed by diodes D4 to D7, which was added only to supply the voltage to the coil of the relay Re1, that when the current through D2 exceeds a di-certain set level. The capacitor C1, may need to be resized to fit the sensitivity of the chosen relay coil.

Conclusion

Ti1 can be any transistor, just make sure that it can work with voltages up to 700 V. For D1 and D2, are recommended diodes 1N4000 series that can be used for currents up to 1 Amp or types 1N5400 supporting up 3 Amps. Watch out! This circuit works with the current network continues to play home that can be fatal, read our text on the Site Responsibility.

Sourced BY : www.CIRCUITSPROJECT.com

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MAX231 RS-232C LED Circuit Diagram

This is the simple MAX231 RS-232C LED Circuit Diagram. Use a pair of Maxim`s 5V-powered MAX231 RS-232C transmitters as drivers to obtain a 2-color LED. The transmitters require only a singleended, 5-V input to generate ± 10 V internally. 

MAX231 RS-232C LED Circuit Diagram

 

Their outputs are short-circuit-proof and can supply as much as 10 mA-enough to drive most LEDs. Depending on which LED you select, their currentlimiting feature might also eliminate the need for external series resistors.

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Simple Power-Saving Relay Driver Circuit Diagram

This is the Simple Power-Saving Relay Driver Circuit Diagram.In many circuits, the switching action is performed by a relay, which in turn activates an external load. The power consumed by the relay may be unsuitable for battery-powered applications. Here is a simple solution using some inexpensive components to considerably save power.

Circuit and working

Fig. 1 shows circuit diagram of the power-saving relay driver where resistor R1 and transistor T1 form a standard relay driver circuit.

  Fig. 1: Circuit diagram of the power-saving  relay driver

Once the relay is energised, its pole is pulled in to make contact with the N/O side, and it holds in that position with typically 75 per cent of its nominal-rated voltage. Power consumed by a relay coil during this holding time equals V²/R, where R is resistance of the relay coil and V is the voltage. Here resistors R2 and R3, transistor T2 and capacitor C1 lower the power consumption after actuation by applying less than the normal operating power.

Initially, when power is applied, capacitor C1 momentarily shorts resistor R2 and allows full voltage across the relay to pull the pole contact, and then slowly the current through the capacitor drops.

In the meantime, resistor R2 takes care of the current, ensuring it is just sufficient to hold the relay. The constant current mechanism formed by transistor T2 and resistors R2 and R3 effectively drives the relay at very less power.

Following calculations will help us understand how additional circuitry around relay driver transistor T1 saves power. Relay used here is a 12V, 400-ohm sugar-cube type. You can calculate the power saved as shown below:

 

Nominal current required for the relay (I)= 12V/400 ohm = 30mA

Power consumed by the relay=I2R=0.03A×0.03A×400 ohm =360mW

After introduction of the circuit:

The current through the coil (I) =VBE/R2=0.6V/47 ohm=12mA

Power consumed by the overall circuit = V×I = 12×0.012=144mW

Power saved=360mW-144mW=216mW

So, we conclude that considerable power can be saved using the additional circuitry.

This makes it fairly simple for anyone to re-design a relay driver to reduce its power consumption without the use of any expensive components.

Construction and testing

An actual-size, single-side PCB for the power-saving relay driver is shown in Fig. 2 and its component layout in Fig. 3.

Switch S1 is used to test the relay driver circuit. You can connect the output of a control circuit, such as a microcontroller, to CON2 for controlling the relay circuit.

CON3 helps in connecting to the electrical load. You can connect the load between N/O and pole contacts or N/C and pole contacts.

Fig. 2: An actual-size, single-side PCB for the power-saving relay driver

  

 Fig. 3: Component layout for the PCB

Before connecting the load to CON3, verify the test point voltages given in the table. You may reduce the value of R1 as per your requirement.

Sourced By: EFY Author:  T.A. Babu

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Nicad Battery Tester Circuit Diagram

This is the simple Nicad Battery Tester Circuit Diagram.This battery tester produces Nicad battery test at a speed of 500 mA. When an endpoint 1 V (defined by the setting of R3) is resolved, pin 2 of U2 becomes low, deactivating Ql and disconnecting the test battery from the circuit. Power for U3 comes from the 12-V regulator in series with the battery being tested. 

 Nicad Battery Tester Circuit Diagram

A clock or timer can be plugged into SI to indicate the time it takes to discharge the battery under test.

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