Hi all,
this is my first post and I'm a newbie trying hard to learn!
My project is a small fan activated for a certain length of time when a thermopile sensor detects a high temperature.
I use an LM358 to amplify the thermopile output from about 0-5mV to 0-5V (which corresponds to 0-100C). If a high temperature is detected it is supposed to activate a transistor switch which triggers a monostable 555 timer circuit (it is retriggerable). The output of the 555 timer uses another transistor switch to activate the fan.
The actual temperature is not important but its not supposed to activate at normal room temperature.
My problem is that the monostable circuit is triggered immediately and does not turn off. I replaced the transistor with a push button switch and it works fine so I think my problem is related to this transistor. (See the attached circuit diagram).
I've tried changing resistors R2 and R3 without effect. The NPN transistors are 2N3904 and the PNP one is a 2N2906.
I feel like I'm missing something obvious. Any advice appreciated! Thanks.
this is my first post and I'm a newbie trying hard to learn!
My project is a small fan activated for a certain length of time when a thermopile sensor detects a high temperature.
I use an LM358 to amplify the thermopile output from about 0-5mV to 0-5V (which corresponds to 0-100C). If a high temperature is detected it is supposed to activate a transistor switch which triggers a monostable 555 timer circuit (it is retriggerable). The output of the 555 timer uses another transistor switch to activate the fan.
The actual temperature is not important but its not supposed to activate at normal room temperature.
My problem is that the monostable circuit is triggered immediately and does not turn off. I replaced the transistor with a push button switch and it works fine so I think my problem is related to this transistor. (See the attached circuit diagram).
I've tried changing resistors R2 and R3 without effect. The NPN transistors are 2N3904 and the PNP one is a 2N2906.
I feel like I'm missing something obvious. Any advice appreciated! Thanks.
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