Help on low voltage indicator circuit

In summary, this circuit has a light sensitive switch that controls the output of a buzzer. If the light is not shining on the photo diode, then the voltage across the buzzer is low. If the light is shining on the photo diode, then the voltage across the buzzer is higher.
  • #1
banerjeerupak
123
1
I can't understand where to put the input terminals in this circuit. can you help me with this...
 

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  • #2
This is my guess.

It is a light sensitive switch. So the input is light on D2 which is a photodiode. If it is not conducting then there will be high voltage across BZ1 (buzzer?) If it is conducting then there will be a lower voltage across the load at BZ1.


I believe that photo diode can be either light on or dark on, so I can't tell you which state will be conducting.
 
  • #3
There is no photo dioded in the circuit. Why would you think that? The voltage that is sensed is the voltage powering the circuit. That voltage is between the arrow on the upper right and the ground. BTW, it is a high voltage indicator. No beep from the beeper until the voltage passese above a threshold.
 
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  • #4
Int, I think that you got your arrows backward. I don't know much of anything about electronics, but I've had to read a schematic or two in my time. D2 is an LED; a photodiode is indicated by the arrows pointing toward it rather than away. It looks to me as if the grounds are the negative connection, and positive connects to BZ1 where the top arrow is.
I'm not sure, but I think that I'm right.
 
  • #5
As supernova says, the output asserts (low) and turns on the LED and buzzer when the overall supply voltage reaches a threshold. The threshold is set with potentiometer R2 versus the zener reference voltage from D1.

This is obviously meant to be a simplistic circuit, but I wanted to point out a common error in this schematic that is often made by people designing with potentiometers. Potentiometers have a minimum wiper current that is required to keep that interface clean and low-resistance. If you connect a pot as shown in the schematic, with the wiper only connecting to the input of an opamp (especially if it is a CMOS opamp with very low input bias current), then over time the wiper contact will become unreliable. If the wiper is adjusted daily or something, then it is less of an issue. But in a circuit like this one, where you set the threshold once and leave it there for years, the operation of the circuit is likely to fail eventually.

Just an FYI for you design-types.
 
  • #6
berkeman said:
Potentiometers have a minimum wiper current that is required to keep that interface clean and low-resistance. If you connect a pot as shown in the schematic, with the wiper only connecting to the input of an opamp (especially if it is a CMOS opamp with very low input bias current), then over time the wiper contact will become unreliable. If the wiper is adjusted daily or something, then it is less of an issue. But in a circuit like this one, where you set the threshold once and leave it there for years, the operation of the circuit is likely to fail eventually.

What would you normally do to prevent that? Just load it a bit with a resistor or something?
 
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  • #7
triden said:
What would you normally do to prevent that? Just load it a bit with a resistor or something?
Yes. One variation that works well is to put the pot in series with another resistor to ground. Tie the wiper of the pot to the midpoint between the pot and the resistor, and also tie that midpoint into the opamp input. The midpoint tie should be the CCW end of the pot in this application, so that when you turn the pot control clockwise, that shorts out more and more of the pot, and raises the setpoint going into the opamp.
 

1. What is a low voltage indicator circuit?

A low voltage indicator circuit is a circuit designed to monitor and display the voltage level of a power source. It is commonly used in electronic devices to indicate when the battery or power supply is running low.

2. How does a low voltage indicator circuit work?

A low voltage indicator circuit typically consists of a voltage comparator, a reference voltage, and a display such as an LED. The comparator compares the input voltage from the power source to the reference voltage and triggers the LED to light up when the input voltage drops below the reference voltage.

3. What are the components needed to build a low voltage indicator circuit?

The components needed for a low voltage indicator circuit may vary, but typically include a voltage regulator, a voltage comparator, a reference voltage source, a display such as an LED, and necessary resistors and capacitors.

4. Can a low voltage indicator circuit be adjusted for different voltage levels?

Yes, a low voltage indicator circuit can be adjusted for different voltage levels by changing the reference voltage or using a voltage divider circuit to adjust the input voltage range for the comparator.

5. What are some common applications of low voltage indicator circuits?

Low voltage indicator circuits are commonly used in electronic devices such as portable chargers, power banks, and battery-operated devices to inform the user when the battery or power supply is running low. They can also be used in automotive and industrial applications to monitor the voltage level of batteries or power sources.

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