Illum
Flashaholic
Source: http://www.electronic-circuits-diagrams.com/alarmsimages/alarmsckt2.shtml
Found this circuit online...and looking for ways to modify it to use a 2N3906 instead
I am not going to pay $6 shipping plus $5 fee to buy a $0.35 transistor when I have everything else...since it suggested at any general purpose PNP transistor will do, I have a jar full of 2N3906s so I'm hoping to use these
I believe the difference is the base biasing....but after looking at both datasheets for the last hour and I can't figure out what to change the resistor to, its telling me base cutoff current, not cutoff voltage, which I need for the resistor calculator.
I'm planning to power this with 9V, with the existing layout it doesn't matter whether I put 10KΩ or 3MΩ where R1 and VR1 is...the 2N3906 just will not turn off! :candle:
I hate testing with buzzers...so much
My understanding only goes as far as
To saturate the 2N3906
assume maximum load current = 100ma, HFE = 100 min
Minimum base current is 1ma, with 30% addition, 1.3ma.
Vin = 9V, the 1N4001 will drop 0.6V, so Vin = 8.4V
R1 is then calculated at
R1 = 9V / (.1/100 x 1.3)
R1 = 6923Ω, minimum 7KΩ
R2 = 10 x R1
R2 = 70KΩ
but in this case, the diagram isn't exactly consistent with the second picture above...I'm not sure whats wrong with it, the R1+vR1 in pic 1 is R2 in the picture, and the R2 in pic 1 is R1 in pic 2, but with two pots set at 7K and 70K but still...no dice
Any recommendations?
Found this circuit online...and looking for ways to modify it to use a 2N3906 instead
I am not going to pay $6 shipping plus $5 fee to buy a $0.35 transistor when I have everything else...since it suggested at any general purpose PNP transistor will do, I have a jar full of 2N3906s so I'm hoping to use these
I believe the difference is the base biasing....but after looking at both datasheets for the last hour and I can't figure out what to change the resistor to, its telling me base cutoff current, not cutoff voltage, which I need for the resistor calculator.
I'm planning to power this with 9V, with the existing layout it doesn't matter whether I put 10KΩ or 3MΩ where R1 and VR1 is...the 2N3906 just will not turn off! :candle:
I hate testing with buzzers...so much
My understanding only goes as far as
To saturate the 2N3906
assume maximum load current = 100ma, HFE = 100 min
Minimum base current is 1ma, with 30% addition, 1.3ma.
Vin = 9V, the 1N4001 will drop 0.6V, so Vin = 8.4V
R1 is then calculated at
R1 = 9V / (.1/100 x 1.3)
R1 = 6923Ω, minimum 7KΩ
R2 = 10 x R1
R2 = 70KΩ
but in this case, the diagram isn't exactly consistent with the second picture above...I'm not sure whats wrong with it, the R1+vR1 in pic 1 is R2 in the picture, and the R2 in pic 1 is R1 in pic 2, but with two pots set at 7K and 70K but still...no dice
Any recommendations?
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