Lie detector circuit

This is a false capture circuit or Lie detector circuit. The basic principle of the resistance of human skin. While dry skin is a resistance of about 1 Mega ohm but if the skin moisture resistance is reduced. When the body are excited or scared or not sure the skin is moist than usual.
Operation of the circuit is a circuit of R1 and R2 divide the line voltage and probe used to measure the resistance of the skin, which is parallel with R2.So voltage drop across R2 is based on the resistance of the skin with is if the skin dry (people do not lie), the resistance of about 1 mega ohm to a strong drop across about 4.5 volt, but if the skin moist (liar), the resistance is less than 1 mega ohm to a voltage drop across less than 4.5 volts.It uses the pressure is on bias voltage to flow in Q1 – BC548, where Q1 and R3 buffer circuit to circuit.

Dew sensitive switch with opto-coupler

Here is a simple circuit that can be used to switch ON or OFF a device when the dew present in the surrounding atmosphere crosses a set value.The circuit uses a dew sensitive resistive element and a comparator based on LM 358 to perform the above said operation.
At normal condition the resistance of dew sensor element will be low and so the voltage drop across it.So the voltage at the non inverting pin of LM358 (IC1) will be less than the voltage at the inverting input of the LM358.So the output of the opamp will be low.This keeps the opto-coupler (MCT2E) deactivated.When the dew increases the resistance of the element increases and so do the voltage across it.Now the voltage at the non inverting pin of LM358 (IC1) will be higher than the voltage at the inverting input of the LM358.So the output of the op amp will be switched to high.This in turn activates the optocoupler.The LED glows to indicate it. As a result we get an optopcoupler activated and de activated according to the amount of dew in the atmosphere.The output pins of optocoupler pin (5&4) can be used to control the external device.

Temperature Sensitive Switch For Solar Collector

This circuit can be used to turn the pump on and off when a solar collector is used to heat a swimming pool, for example. This way the water in the collector has a chance to warm up significantly before it is pumped to the swimming pool. A bonus is that the pump doesn’t need to be on continuously. The basis of operation is as follows. When the temperature of the water in the solar collector is at least 10 °C higher than that of the swimming pool, the pump starts up.
The warm water will then be pumped to the swimming pool and the temperature difference will drop rapidly. This is because fresh, cool water from the swimming pool enters the collector. Once the difference is less than 3 °C the pump is turned off again. R10/R1 and R9/R2 each make up a potential divider. The output voltage will be about half the supply voltage at a temperature around 25 °C. C7 and C8 suppress any possible interference.
The NTCs (R9 and R10) are usually connected via several meters of cable, which can easily pick up interference. Both potential dividers are followed by a buffer stage (IC1a/IC1b). IC1c and R3, R4, R5 and R6 make up a differential amplifier (with unit gain), which measures the temperature difference (i.e. voltage difference). When both temperatures are equal the output is 0 V. When the temperature of the solar collector rises, the differential amplifier outputs a positive voltage.
This signal is used to trigger a comparator, which is built round an LM393 (IC2a). R7 and P1 are used to set the reference voltage at which the comparator changes state. R8 and P2 provide an adjustable hysteresis. R11 has been added to the output of IC2a because the opamp has an open collector output. A power switch for the pump is created by R12, T1 and Re1. D1 protects T1 against voltage spikes from the relay coil when it is turned off.
A visual indication of the state of the controller is provided by IC4 (UAA170), a LED spot display driver with 16 LEDs. The reference voltage for the comparator is buffered by IC1d and fed to input VRMAX of the UAA170. R20/D21 and R23/D22 limit the input voltages of IC4 to 5.1 V, since the maximum permissible input voltage to the UAA170 is 6 V. When there is no temperature difference, LED D20 turns on.

Battery Tester For Deaf and Blind Persons

Many blind and deaf-blind persons use portable electronic devices to assist their everyday lives but it is difficult for them to test the batteries used in this equipment. Talking voltmeters are available but there is no equivalent usable by deaf-blind persons. This battery tester uses vibration and a user-settable control to enable blind and deaf-blind persons to test both ordinary and rechargeable AAA, AA, C, and D cells and 9V batteries. For ease of use and maintenance the device is powered by the battery under test.
The design is dominated by the fact that the pager motor will operate down to only 0.7V. With a 0.3V drop from the switching transistor, a weak cell, at 1.0V, will only just operate the motor. This means that the 1.5V cell sensing circuitry cannot be isolated from the 9V test terminals using steering diodes – they would introduce too great a voltage drop. The solution was to duplicate the level sensing circuitry for each set of test terminals. On the 1.5V side of the circuit, a resistance network consisting of two 10kO multi-turn trimpots (VR2 & VR3) and user control VR1a produces an adjustable proportion of the voltage of the cell under test.
VR1a selects a division ratio between the low and high limits set by the trimpots. The resistance of VR1a is 10 times larger than the resistance of these trimpots to minimise the interaction between their settings. The voltage from the resistance network is applied to a combined threshold detector and current amplifier formed by Q1 to Q4 and associated components. When the threshold (about 0.6V) is exceeded the pager motor is energised, causing the battery tester to vibrate. In use, VR1 is first set to its fully counter-clockwise position, then a cell is connected.
If the cell’s voltage exceeds the 1V low threshold set by the 1.5V LOW trimpot (VR2), the battery tester will vibrate. Rotating VR1 clockwise applies a progressively lower voltage to the threshold detector until a point is reached when the threshold is no longer exceeded and the pager motor switches off. The angle of rotation of VR1 then indicates the voltage on the battery. VR1 is fitted with a pointer knob to make the angle of rotation easy to feel. Having the pager motor switch off rather than switch on ensures that the voltage of the battery is sampled while it is supplying the load of the pager motor.
This gives a more accurate indication of the state of the battery than its open-circuit voltage. To ensure that the user turns VR1 clockwise during the test, the circuit is designed so that once vibration has ceased, it cannot be made to start again by rotating VR1 counter-clockwise. This also eliminates any possibility of user confusion arising from any hysteresis in the circuit. This feature is implemented by Q5, which forces the base of Q2 high if Q4 ceases to conduct strongly. A 1µF capacitor between the base and emitter of Q5 forces it off when power is first applied, to give Q4 a chance to conduct.
The parallel 1MO resistor discharges the 1µF capacitor when power is removed, to reset the circuit. To prevent the pager motor being driven through the base-emitter junction of Q5, the base of Q5 is connected to the collector of Q4 via 10kO resistor. Another 10kO resistor is connected in parallel with the pager motor to ensure that Q5 switches on when Q4 switches off. The 9V test circuit is similar to the 1.5V circuit. A 68O 1W resistor limits the current through the motor to prevent it from being over-driven by the higher voltage.
In addition, there is a series diode to protect the 9V circuitry against reverse polarity. A diode is not possible for the 1.5V side of the circuit because it would introduce too great a voltage drop; fortunately, it is also unnecessary since 1.5V is below the reverse breakdown voltage of the transistors used. The 1µF capacitor across the pager motor smoothes the load provided by the motor so that measurements made by the circuit are consistent from one trial to another. The 1N4001 diode across the pager motor clips any back-EMF generated by the motor.
A D-cell holder and an AA-cell holder connected in parallel were used for the 1.5V test terminals. The 9V test terminals are the studs from a standard 9V snap screwed to the box. To calibrate the battery tester, start with VR1 fully counter-clockwise. First adjust the 1.5V LOW trimpot by turning it fully counter-clockwise, then apply 1.0V to the 1.5V test terminals and turn the trimpot slowly clockwise until vibration just ceases. Now turn VR1 fully clockwise and adjust the 1.5V HIGH trimpot similarly with 1.6V applied to the 1.5V test terminals.
There is a small amount of interaction between the low and high settings, so repeat the adjustment of the 1.5V LOW trimpot. Similarly, calibrate the 9V side of the circuit for a range of 6.0V to 9.6V. To test a battery, rotate VR1 fully counterclockwise before connecting the battery to the appropriate set of test terminals (1.5V or 9V). If the device does not vibrate, the battery is completely dead. Otherwise, rotate VR1 slowly clockwise until the device just ceases to vibrate. The position of VR1 then shows the condition of the battery under test.

Body Charge Detector

It is well known that through such simple everyday activities as walking on a carpet or moving in a chair, the body accumulates a static charge – sometimes many thousands of volts. Due to its extreme sensitivity, this circuit will detect not only such charges but also EMF-induced voltages in the body, which are generally far smaller. This means that, whether you happen to be “charged up” on any particular day or not, your body will almost certainly trigger this circuit. An interesting twist is that the sensor does not need to be made of metal. Provided it is isolated from ground, the sensor can be any conductor, including a plant in a pot. The circuit is a comparator based on an LF351 FET-input op amp (IC1). The has the benefit of a high impedance input which is crucial for detecting a static charge. The other aspect which is crucial is that the 0V side of the circuit must be connected to earth (eg, a metal stake driven into the ground). Without the grounded connection, the circuit will yield poor results.

Soil dry tester circuit

This Check this dry soil circuit For the Blind. Because it will alert on clay. Circuit has less detail. It production the low frequency pulse, the IC CMOS 4001. is primary device,internal structure consists of NOR Gate.When added to RC circuit will be on low frequency oscillator. It is divided into two series, the first low frequency pulse generator. Then sent to another set. , A set of audio source through the C4 and then out to the speakers.You can apply the display devices as needed. Special about this circuit is to use solar cells as power supply to the circuit.Use only probes. Into the soil, we want to examine.

Pump Controller For Solar Hot Water System

This circuit optimises the operation of a solar hot water system. When the water in the solar collector is hotter than the storage tank, the pump runs. The circuit comprises two LM335Z temperature sensors, a comparator and Mosfet. Sensor 1 connects to the solar collector panel while Sensor 2 connects to the hot water panel. Each sensor includes a trimpot to allow adjustment of the output level. In practice, VR1 and VR2 are adjusted so that both Sensor 1 and Sensor 2 have the same output voltage when they are at the same temperature. The Sensor outputs are monitored using comparator IC1.
When Sensor 1 produces a higher voltage than Sensor 2, which means that sensor 1 is at a higher temperature, pin 1 of IC1 goes high and drives the gate of Mosfet Q1. This in turn drives the pump motor. IC1 includes hysteresis so that the output does not oscillate when both sensors are producing a similar voltage. Hysteresis comprises the 1MO feedback resistor between output pin 1 and non-inverting input pin 3 and the input 1kO resistor. This provides a nominal 12mV hysteresis so that voltage at Sensor 1 or Sensor 2 must differ by 12mV for changes in the comparator output to occur.
Since the outputs of Sensor 1 and Sensor 2 change by about 10mV/°C, we could say that there is a degree of hysteresis in the comparator. Note that IC1 is a dual comparator with the second unit unused. Its inputs are tied to ground and pin 2 of IC1 respectively. This sets the pin 7 output high. Since the output is an open collector, it will be at a high impedance. Mosfet Q1 is rated at 60A and 60V and is suitable for driving inductive loads due to its avalanche suppression capability. This clamps any inductively induced voltages exceeding the voltage rating of the Mosfet.
The sensors are adjusted initially with both measuring the same temperature. This can be done at room temperature; adjust the trimpots so that the voltage between ground and the positive terminal reads the same for both sensors. If you wish, the sensors can be set to 10mV/°C change with the output referred to the Kelvin scale which is 273K at 0°C. So at 25°C, the sensor output should be set to (273 + 25 = 298) x 10mV or 2.98V.
Note:
The sensors will produce incorrect outputs if their leads are exposed to moisture and they should be protected with some neutral cure silicone sealant. The sensors can be mounted by clamping them directly to the outside surface of the solar collector and on an uninsulated section of the storage tank. The thermostat housing is usually a good position on the storage tank.