Showing posts with label activated. Show all posts
Showing posts with label activated. Show all posts
Friday, October 17, 2014
Simple Sound Activated Switch
Control by sound may be very useful, not just on a robot but also for a bit of home automation, for example a sound activated light responding to a knock on the door or a hand clap. The light will be automatically switched off after a few seconds. An alternative use is burglar protection — if someone wants to open the door or break some-thing the light will come on, suggesting that someone’s at home. The circuit can work from any 5– 12 VDC regulated power supply pro-vided a relay with the suitable coil voltage is used.
Sound Activated Switch Circuit Diagram
When you first connect the supply voltage to the circuit, the relay will be energised because of the effect of capacitor C2. Allow a few seconds for the relay to be switched off. You can increase or decrease the ‘on’ period by changing the value of C2. A higher value results in a longer ‘on’ period, and vice versa. Do not use a value greater than 47 µF. Biasing resistor R1 determines to a large extent the microphone sensitivity. An electret microphone usually has one internal FET inside which requires a bias voltage to operate. The optimum bias level for response to sound has to be found by trial and error.
Wednesday, October 1, 2014
Light Activated Switch Circuit Using IC 555
A very useful light activated switch circuit can be made by utilising a single 555 timer with its trigger and threshold inputs connected together.
The schmitt has a very low input current (1.5uA) and can directly drive a relay taking up to 200mA of current. The circuit shows a 555 schmitt being used to energise a relay when the light level on a photoconductive cell falls below a preset value; the relay energises when the voltage on pins 2 and 5 is greater than 2/3Vcc and de-energises when the voltage falls below I/3Vcc. This gives a hysteresis of 1/3Vcc, The circuit can be used in many other similar applications where a high input impedance and low out- put impedance are required with the minimum component count.
The schmitt has a very low input current (1.5uA) and can directly drive a relay taking up to 200mA of current. The circuit shows a 555 schmitt being used to energise a relay when the light level on a photoconductive cell falls below a preset value; the relay energises when the voltage on pins 2 and 5 is greater than 2/3Vcc and de-energises when the voltage falls below I/3Vcc. This gives a hysteresis of 1/3Vcc, The circuit can be used in many other similar applications where a high input impedance and low out- put impedance are required with the minimum component count.
Tuesday, September 9, 2014
Dark activated 230V Lamp
This device allows one or more lamps to illuminate at sunset and turn off at dawn.
Q1 and Q2 form a trigger device for the SCR, providing short pulses at 100Hz frequency. Pulse duration is set by R2 and C1.When the light hits R1, the photo resistor assumes a very low resistance value, almost shorting C1 and preventing schema operation. When R1 is in the dark, its resistance value becomes very high thus enabling schema operation.
Parts:
R1_____________Photo resistor (any type)
R2____________100K 1W Resistor
R3____________200K 1/2W Trimmer Cermet
R4,R7_________470R 1/4W Resistors
R5_____________12K 1/4W Resistor
R6______________1K 1/4W Resistor
C1_____________10nF 63V Polyester Capacitor
D1_________TIC106D 400V 5A SCR
D2-D5_______1N4007 1000V 1A Diodes
Q1___________BC327 45V 800mA PNP Transistor
Q2___________BC337 45V 800mA NPN Transistor
SK1__________Female Mains socket
PL1__________Male Mains plug & cable
Notes:
* R3 allows fine setting of operating threshold and R2 value can be raised to 150K maximum.
* Several lamps wired in parallel can be connected to the schema, provided total power dissipation of the load does not exceed about 300 - 500W.
* PL1 can be omitted and the input mains supply wires connected in parallel to any switch controlling lamps. In this case, if the switch is left open, the schema will be able to drive the lamps; if the switch is closed, the lamps will illuminate and the schema will be by-passed.
* Warning! The schema is connected to 230Vac mains, then some parts in the schema board are subjected to lethal potential!. Avoid touching the schema when plugged and enclose it in a plastic box.
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