Transistor Comperator circuit - Electronic Circuits Projects Diagrams Free

Someone Electro · 8th July 2004, 02:18 PM

I need a cicuit whith transistors that compares the resistances of two LDRs.

Like this.
LDR1 = darker than LDR2 : LED1 = on
LDR2 = darker than LDR1 : LED2 = on

I searchd discover circuits and nothing (Just whith those comperator IC ones)

Roff · 9th July 2004, 01:12 AM

This should work. It won't have a huge amount of gain like an IC comparator.
VCC can be 5 to 9 volts, VEE can be -5 to -9 volts.
Balance it by placing the LDRs side by side and adjusting the pot until both LEDs glow at half brightness.
It is designed to deliver about 10ma to whichever LED is on.
If you need more gain, let me know and we can add another gain stage (it will be made of PNPs).
If you can't get 2N3904s, you can use almost any general purpose NPN.

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8th July 2004, 02:18 PM	(permalink)
Someone Electro	Transistor Comperator circuit I need a cicuit whith transistors that compares the resistances of two LDRs. Like this. LDR1 = darker than LDR2 : LED1 = on LDR2 = darker than LDR1 : LED2 = on I searchd discover circuits and nothing (Just whith those comperator IC ones) __________________ Il give you shocking experience.