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Sunday, September 1, 2013

Metal Detector Based on the TDA0161

These metal detector circuit diagram is based on the TDA0161 monolithic integrated circuit , designed for metallic body detection by detecting the variations in high frequency Eddy current losses. For detecting metals , TDA0161 require an external LC tuned circuit .

Metal Detector Circuit diagram

Output signal is determined by supply current changes. Independent of supply voltage, this current is high or low according to the presence or the absence of a close metallic object. This metal detector circuit use two LEDs , which offer an visual indication of presence or absence at a metals ,around the coil . To adjust the circuit you need to make sure there is no metal near the coil and then set the fine adjustment to a "Mid position". After that you need to adjust the course adjustment to turn on the LED and , adjust the fine adjustment to turn off the LED.

This detector electronic circuit operates over a wide range input voltage of 4 -35 volts . If you want you can use other values for the Cx capacitor and for L1 inductor ( changing this value will affect the frequency oscillation and the detection range ) .

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Thursday, April 11, 2013

On Demand WC Fan Using 555

In most WCs with an extractor the fan is hooked up to the lighting circuit and that is swaped on and off either in sympathy with the light or with a brief prolong. Since rest rooms are every so often used for laundry the fingers or simply for a fast seem within the reflect, it is no lengthyer at all times necessary to alter the air within the smallest room in the house. The following circuit robotically determines whether there truly is any want to run the fan and reacts appropriately. No odour sensor is needed: we just appoint a small contact that observes when and for a way lengthy the bathroom seat lid is lifted.

If the seat lid is left up for no much less than some presettable minimum time t1, the fan is set working for another presettable time t2. In the instance shown the contact is made using a small magnet on the lid and a reed change established on the cistern. The leisure is straightforward: IC2, the acquainted 555, forms a timer whose period can also be adjusted up to roughly 10 to 12 minutes using P2. This resolves the fan running time. There are three CMOS NAND gates (type 4093) between the reed switch and the timer enter which generate the desired set off signal. When the lid is within the ‘up’ place the reed swap is closed.

$\"http://4.bp.blogspot.com/-hJuHHa6khu0/UIum3PsoQSI/AAAAAAAAJmY/EYdHAQTTsjo/s400/Voltage+Inverter-Circuit+diagram.PNG\"$ Capacitor C1 costs via P1 unless it reaches the level the place the output of IC1a switches from good judgment 1 to logic 0. The output of IC1b then goes to logic 1. The fringe of the zero-1 transition, handed during the RC community fashioned with the aid of C2 and R2, leads to the output of IC1c going to common sense zero for a 2d. This is taken to the set off enter on pin 2 of timer IC2, which in turn changees on the relay which lead tos the fan to run for the time frame decided by using P2. The circuit is powered from a small transformer with a secondary winding turning in between approximately eight V and 10 V. Do no longer omit to incorporate an acceptable fuse on the main facet.

The circuit round IC1b and IC1c ensure thats that the fan does no lengthyer run continuously if the bathroom seat lid is left up for a protracted length. The time constant of P1 and C1 is set so that the fan does no lengthyer run as a result of lavatorial transactions of a extra minor nature, the place the lid is opened and then closed quickly afterwards, before C1 has a possibility to cost sufficiently to trigger the circuit.

Circuit Source: DIY Electronics Projects

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Friday, April 5, 2013

Power On Indicator

Some types of electronic equipment do not provide any indication that they are actually on when they are switched on. This situation can occur when the back-light of a display is switched off. In addition, the otherwise mandatory mains power indicator is not required with equipment that consumes less than 10 watts. As a result, you can easily forget to switch off such equipment. If you want to know whether equipment is still drawing power from the mains, or if you want to have an indication that the equipment is switched on without having to modify the equipment, this circuit provides a solution.

One way to detect AC power current and generate a reasonably constant voltage independent of the load is to connect a string of diodes wired in reverse parallel in series with one of the AC supply leads. Here we selected diodes rated at 6 A that can handle a non-repetitive peak current of 200 A. The peak current rating is important in connection with switch-on currents. An advantage of the selected diodes is that their voltage drop increases at high currents (to 1.2 V at 6 A). This means that you can roughly estimate the power consumption from the brightness of the LED (at very low power levels). The voltage across the diodes serves as the supply voltage for the LED driver. To increase the sensitivity of the circuit, a cascade circuit (voltage doubler) consisting of C1, D7, D8 and C2 is used to double the voltage from D1–D6. Another benefit of this arrangement is that both halve- waves of the AC current are used. We use Schottky diodes in the cascade circuit to minimise the voltage losses.

Circuit diagram :

Power On Indicator Circuit Diagram

The LED driver is designed to operate the LED in blinking mode. This increases the amount of current that can flow though the LED when it is on, so the brightness is adequate even with small loads. We chose a duty cycle of pproximately 5 seconds off and 0.5 second on. If we assume a current of 2 mA for good brightness with a low-current LED and we can tolerate a 1-V drop in the supply voltage, the smoothing capacitor (C2) must have a value of 1000 µF. We use an astable multivibrator built around two transistors to implement a high-efficiency LED flasher. It is dimensioned to minimise the drive current of the transistors. The average current consumption is approximately 0.5 mA with a supply voltage of 3 V (2.7 mA when the LED is on; 0.2 mA when it is off). C4 and R4 determine the on time of the LED (0.5 to 0.6 s, depending on the supply volt-age). The LED off time is determined by C3 and R3 and is slightly less than 5 seconds. The theoretical value is R × C × ln2, but the actual value differs slightly due to the low supply voltage and the selected component values.

Diodes D1-D6 do not have to be special high-voltage diodes; the reverse volt-age is only a couple of volts here due the reverse-parallel arrangement. This voltage drop is negligible compared to the value of the mains voltage. The only thing you have to pay attention to is the maximum load. Diodes with a higher current rating must be used above 1 kW. In addition, the diodes may require cool-ing at such high power levels. Measurements on D1–D6 indicate that the voltage drop across each diode is approximately 0.4 V at a current of 1 mA. Our aim was to have the circuit give a reasonable indication at current levels of 1 mA and higher, and we succeeded nicely. However, it is essential to use a good low-current LED.

Caution: the entire circuit is at AC power potential. Never work on the circuit with the mains cable plugged in. The best enclosure for the circuit is a small, translucent box with the same colour as the LED. Use reliable strain reliefs for the mains cables entering and leaving the box (connected to a junction box, for example). The LED insulation does not meet the requirements of any defined insulation class, so it must be fitted such that it cannot be touched, which means it cannot protrude from the enclosure.

http://www.ecircuitslab.com

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