Simple Fire Alarm Circuit using transistor not simulating correctly

Question

there am student of BSSE but we studied Applied physics, our teacher give us project.

Am working on it but when i simulate it, this gives me error at Transistor and Speaker.

here is my circuit https://crcit.net/c/738382510e074fd987eb47e2a8859541

Thanks, help me to resolve this matter.

here i found article about it! https://www.electronicshub.org/simple-fire-alarm-circuit/#:~:text=Fire%20Alarm%20Circuit%20is%20a,damage%20to%20people%20or%20property

your battery is in the wrong place. Think about where you want the current to go — BeB00, Jun 08 '20 at 16:28
That circuit idea is rubbish from what I can tell. State what you are trying to achieve. — Andy aka, Jun 08 '20 at 16:29
@BeB00 i tried in both way but it still showing same output in simulated — lablnet, Jun 08 '20 at 16:29
@Andyaka the rubbish idea i get from here https://www.electronicshub.org/simple-fire-alarm-circuit/#:~:text=Fire%20Alarm%20Circuit%20is%20a,damage%20to%20people%20or%20property — lablnet, Jun 08 '20 at 16:30
I don't care where you got it from actually - I can see that it is rubbish without knowing who created it. However, I did take a look at that link but couldn't find your circuit so, how did you acquire the circuit you drew? As I said earlier - state what you are trying to achieve because a rubbish circuit with no description = no idea what you want = question closure. — Andy aka, Jun 08 '20 at 16:36
@MuhamamdUmerFarooq You have a cap where the origination for your idea uses a diode. — Aaron, Jun 08 '20 at 16:38
I don't know these things well I mentioned link in my above post documentation are there. — lablnet, Jun 08 '20 at 16:52

Leoman12 · Accepted Answer · 2020-06-08T21:45:29.187

There are a couple problems with the circuits used from that site. One, they are using an NPN transistor incorrectly and two, a speaker can't produce sound when you apply a constant voltage to it. The only circuit that would work is the one using the lm358.

Now onto your circuit. Couple problems with it: 1) Incorrect biasing of a PNP transistor or rather incorrect orientation. Also note you're using what seems to be a symbol of phototransistor (?). 2) Battery is in wrong orientation. 3) Speaker won't produce sound just because you apply voltage to it. 4) Don't see why you need a capacitor here.

Here is a more practical circuit which should work:

It uses a NTC thermistor which at 25 Celsius is about 10k but at about 70 Celsius is 1.7k. When the temperature is room temperature or at least way lower than flame, the NPN transistor is off and buzzer is off. When flame is present and within a few inches of Thermistor, its resistance drops to about 1.7k and biases the transistor on thus activating the buzzer. Note that flame should be a few inches away to achieve 70 degrees Celsius and not directly applied to thermistor. You can test this out when prototyping. Also circuit uses NPN transistor biases correctly and a piezoelectric buzzer not speaker. Circuit can be power off 3xAA batteries.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

Edit: To show how With some modifications to your circuit it should work:

Your new circuit:

schematic

^{simulate this circuit}

Simple Fire Alarm Circuit using transistor not simulating correctly

1 Answers1