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Ligth Sensitive Alarm

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New Member
Hey everyone, I'm new to the board and needing some help getting started on this electronics project. So here goes.

I need to design a circuit that responds to light intensity using op-amps, transistors, and photodiodes. The circuit needs to include an oscillator, using a transistor op-amp.

Here are the device requirements:
Output in sunlight: 1 W 500 Hz sinusoid into an 8-ohm speaker load
Dark output: Silence
Linear output voltage increase between extremes

I think I can figure out the correct component values, but what I really need help with is the schematic for the circuit.

Any thoughts, opinions, or ideas are greatly appreciated. Thanks.


New Member
What do you want to increase, the volume or the frequency of the output?

In both cases, you will need to convert the light intensity to a variable frequency or gain. You will need to use a 'transimpedance' amplifier to change the variable current from the photodiode to a variable voltage. This variable voltage will then need to vary the frequency of a voltage controlled oscillator, or it can vary the gain of an amplifier. Which photodiode are you using?

I do not have much time right now to help with a schematic, but when you answer your questions, I should be able to work something out.



New Member
Thanks for the reply.

I want the volume of the output to increase, not the frequency.
For the transimpedance amplifier I want my variable voltage to then vary the gain of an amplifier.
As far as the photodiode goes, I have no constraints on what kind I can use. This is a theoretical design problem so I do not need to find a specific photodiode, I can make up the components of it as long as they are reasonable.

What will the transimpedance amplifier consist of?
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