Showing posts with label light. Show all posts
Showing posts with label light. Show all posts
Tuesday, September 24, 2013
Infra red Light Barrier Using 555
This is a short-range light barrier for use as an intruder alarm in doorposts, etc. The 555 in the transmitter (Figure 1) oscillates at about 4.5 kHz, supplying pulses with a duty cycle of about 13% to keep power consumption within reason. Just about any infra-red LED (also called IRED) may be used. Suggested, commonly available types are the LD271 and SFH485. The exact pulse frequency is adjusted with preset P1. The LEDs are pulsed at a peak current of about 100 mA, determined by the 47 Ω series resistor. In the receiver (Figure 2), the maximum sensitivity of photo-diode D2 should occur at the wavelength of the IR LEDs used in the transmitter. You should be okay if you use an SFH205F, BPW34 or BP104. Note that the photo-diode is connected reverse-biased! So, if you measure about 0.45 V across this device, it is almost certainly fitted the wrong way around.
The received pulses are first amplified by T1 and T2. Next comes a PLL (phase lock loop) built with the reverenced NE567 (or LM567). The PLL chip pulls its output, pin 8, Low when it is locked onto the 4.5 kHz ‘tone’ received from the transmitter. When the (normally invisible) light beam is interrupted (for example, by someone walking into the room), the received signal disappears and IC1 will pull its output pin High. This enables oscillator IC2 in the receiver, and an audible alarm is produced. The two-transistor amplifier in the receiver is purposely over-driven to some extent to ensure that the duty cycle of the output pulses is roughly 50%.
If the transmitter is too far away from the receiver, over-driving will no longer be guaranteed, hence IC1 will not be enabled by an alarm condition. If you want to get the most out of the circuit in respect of distance covered, start by modifying the value of R2 until the amplifier output signal again has a duty cycle of about 50%. The circuit is simple to adjust. Switch on the receiver, the buzzer should sound. Then switch on the transmitter. Point the transmitter LEDs to the receiver input. Use a relatively small distance, say, 30 cm. Adjust P1 on the transmitter until the buzzer is silenced. Switch the receiver off and on again a few times to make sure it locks onto the transmitter carrier under all circumstances. If necessary, re-adjust P1, slowly increasing the distance between the transmitter and the receiver.
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The received pulses are first amplified by T1 and T2. Next comes a PLL (phase lock loop) built with the reverenced NE567 (or LM567). The PLL chip pulls its output, pin 8, Low when it is locked onto the 4.5 kHz ‘tone’ received from the transmitter. When the (normally invisible) light beam is interrupted (for example, by someone walking into the room), the received signal disappears and IC1 will pull its output pin High. This enables oscillator IC2 in the receiver, and an audible alarm is produced. The two-transistor amplifier in the receiver is purposely over-driven to some extent to ensure that the duty cycle of the output pulses is roughly 50%.
If the transmitter is too far away from the receiver, over-driving will no longer be guaranteed, hence IC1 will not be enabled by an alarm condition. If you want to get the most out of the circuit in respect of distance covered, start by modifying the value of R2 until the amplifier output signal again has a duty cycle of about 50%. The circuit is simple to adjust. Switch on the receiver, the buzzer should sound. Then switch on the transmitter. Point the transmitter LEDs to the receiver input. Use a relatively small distance, say, 30 cm. Adjust P1 on the transmitter until the buzzer is silenced. Switch the receiver off and on again a few times to make sure it locks onto the transmitter carrier under all circumstances. If necessary, re-adjust P1, slowly increasing the distance between the transmitter and the receiver.
Saturday, April 13, 2013
Descrete Multistage Light Sequencer
The drawing below illustrates a multistage light sequencer using descrete parts and no integrated circuits. The idea is not new and I hear a similar circuit was developed about 40 years ago using germanium transistors. The idea is to connect the lights so that as one turns off it causes the next to turn on, and so forth. This is accomplished with a large capacitor between each stage that charges when a stage turns off and supplies base current to the next transistor, thus turning it on. Any number of stages can be used and the drawing below illustrates 3 small Christmas lights running at about 5 volts and 200mA. The circuit may need to be manually started when power is applied. To start it, connect a momentary short across any one of the capacitors and then remove the short. You could use a manual push button to do this.
Detailed operation:
Assume the circuit doesnt start when power is applied amd all lights are off and all three capacitors are charged to about 5 volts. We connect a jumper across the 220uF capacitor on the left which discharges the capacitor and turns on the 2nd stage transistor and corresponding light. When the jumper is removed, the capacitor will start charging through the base of the stage 2 transistor and stage 1 light.
This causes the stage 2 transistor to remain on while the capacitor continues to charge. At the same time, the capacitor connecting stage 2 and 3 will discharge through the 100 ohm resistor and diode and stage 2 transistor. When the capacitor charging current falls below what is needed to keep stage 2 turned on, the transistor and light will turn off causing the voltage at the collector of the stage 2 transistor to rise to 5 volts.
Since the capacitor connecting stage 2 and 3 has discharged and the voltage rises at the collector of stage 2, the capacitor from stage 2 and 3 will charge causing the 3rd stage to turn on and the cycle repeats for sucessive stages 4,5,6,7.... and back to 1. The sequence rate is determined by the capacitor and resistor values (220uF and 100 ohms in this case), load current (200mA in this case), and current gain of the particular transistor used. This arrangement runs at about 120 complete cycles per minute for 3 lights, or about 167mS per light. Faster or slower rates can be obtained with different capacitor values.
Sourced by : bowdenshobbycircuits.info
Saturday, April 6, 2013
LED Tube Light Using Transformer Circuit Diagram
Using white LEDs for illuminating our homes is becoming popular nowadays, due to the high power efficiency involved with these devices. The diagram shows a straightforward configuration involving many LEDs, arranged in series and parallel.The LEDs are driven by a general purpose 24 V power supply for illuminating the LED bank very brightly. The power supply incorporates standard bridge and capacitor network for the required rectification and filtration of the supply voltage to the LEDs.
The arrangement of the LEDs is done in the following way:
The supply voltage being 24, dividing it by the forward voltage of a white LED which is around 3 volts gives 24/3 = 6, meaning the supply voltage will be able to support at the most 6 LEDs in series.
However since we are interested to include many LEDs (132 here), we need to connect many of these series connected strings of LED through parallel connections.
Thats exactly what we do here.
Total 22 strings of LEDs having 6 in each are connected in parallel, as shown in the figure.
Since current limiting becomes an important issue with the white LEDs, a limiting resistor is added in series with each of the strings. The value of the resistor may be optimized by the user for adjusting the overall illumination of the LED tube light.
The proposed design will provide enough light for illuminating a small 10 by 10 room brightly, and will consume not more than 0.02 * 22 = 0.44 Amps or 0.44 * 24 = 10.56 watts of power.
24 Volt, LED Tube Light Using Transformer, Circuit Diagram
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