Light Meter

[sdmuashr]

Hi,

Has anyone got experience with this circuit?
http://circuitswiring.com/bar-graph-light-meter-by-ic-741/
The circuit was built but does not work. The LEDs are supposed to turn on one by one as the intensity of light increases on photo-transistor. Can anyone tell me about how to make this work? Also if a two lead photo-transistor were to be used then how it should be connected?
The circuit works in Multisim but not in reality! (See the attachment.)
Thanks

[Kleinstein]

The circuit is made for a photodiode, that can provide a output voltage. The phototransistor needs a voltage drop to let a current pass. To make is work the Phototransistor should not go to ground, but with the collector to the positive supply and the emitter to the OPs input / resistor. Due to the higher current the 1 M value might be rather high.


The 741 OPs have a current limited output - so the LEDs will likely survive.
Today I would tend to use a single Supply OP like TLC271 oder LM358. Then a single 9 V battery is enough, as not negative supply is needed any more.