Custom Search

Sunday, February 3, 2008

Strobe Light

A simple electronic strobe light for dancing lovers can easily be constructed by using a timer 1C 555 and a triac. The cost of the circuit depends mainly on the nature of lamp used. A car headlight or an ordinary lamp of 100W with a good reflector will work well.
The 555 is a timer 1C which is set for the astable operation. In this mode the changing time will depend on
tl = 0.693 (Ra+2Rb) C
During charging period the output is high and the lamp is on. When charge across the capacitor reaches 0.67 Vcc, the output goes low and the capacitor discharges to a value of 0.33 Vcc, which is known as the trigger voltage level. As the trigger pin is connected to pin no. 6, it receives a negative trigger pulse and the next cycle starts.
Thus, the discharge time can be obtained as
tl = 0.693 x RB X C
and Duty Cycle is D = —————
Ra + Rb
Thus, by varying RA and RB, we can obtain strobes of required duration at required frequency.
This circuit can easily be converted into a photographic timer where the doorbell is replaced by the lamp and the values of Ra and Rb are kept fixed to get 5 second pulses.
To use a high-wattage flash tube, a bleeder resistor (Rx) should be added in place of the lamp, and connected to the trigger point of the Xenon tube. While purchasing the flash light or Xenon tube, select one with the lowest firing current. Standard values for firing voltage and current are 160V and 35mA; tube voltage is 230V.
To determine the values of resistors Rx and Ry, assume the tube firing current is 40mA.
Rx = (230-160)/0.04 = 1.75k (standard value: 1.8k)
Wattage = 70 x 0.04 = 2.8W
Select Rx of 1.8k and 5W rating.
Ry = 160/0.04 = 4k (standard value: 3.8k)
Wattage = 160 x 0.04 = 6.4W Select Ry of 3.8k and 10W rating.

No comments: