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Science Forum Index » Electronics - Basics Forum » transistor base input
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| Peter Bennett |
 Posted: Wed Apr 30, 2008 9:08 pm |
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Guest
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On Wed, 30 Apr 2008 21:55:53 GMT, Randy Day <randy.day@shaw.cax>
wrote:
Quote: lerameur wrote:
[snip]
just as 5 volt.
When the voltage from my source is between 6v and 9 volts, my chip
reads high (or 5v)
otherwise the chip reads low or zero.
like I said, the source is the voltage going to the siren, so it is
almost always ZERO.
When siren goes off, the voltage jumps anywhere between 6 to 9 volts.
Then the chip should read high
Just use your micro as a digital input; no analog required.
6-9vdc in --10K-----+------ micro
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/\ 5v zener diode
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Gnd
HTH
Another thought - perhaps the 6 to 9 volts going to the siren is
actually AC or pulsed DC, rather than plain DC. In that case, you
would want a diode in series with the 10K resistor in the above
circuit, cathode towards the Zener, and a capacitor (0.1 uF or so,
perhaps) and a 100K resistor, both in parallel with the zener. This
would give a steady DC voltage to the microcontroller input while the
siren is operating.
(The "jumps anywhere between 6 to 9 volts" bit makes me think that the
siren drive is not DC.)
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca |
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| Randy Day |
| Posted: Wed Apr 30, 2008 10:00 pm |
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Guest
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Peter Bennett wrote:
Quote: Just use your micro as a digital input; no analog required.
6-9vdc in --10K-----+------ micro
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/\ 5v zener diode
|
Gnd
HTH
Another thought - perhaps the 6 to 9 volts going to the siren is
actually AC or pulsed DC, rather than plain DC. In that case, you
would want a diode in series with the 10K resistor in the above
circuit, cathode towards the Zener, and a capacitor (0.1 uF or so,
perhaps) and a 100K resistor, both in parallel with the zener. This
would give a steady DC voltage to the microcontroller input while the
siren is operating.
(The "jumps anywhere between 6 to 9 volts" bit makes me think that the
siren drive is not DC.)
Good point. |
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| gearhead |
| Posted: Thu May 01, 2008 9:27 am |
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Guest
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On Apr 30, 2:55 pm, Randy Day <randy....@shaw.cax> wrote:
Quote: lerameur wrote:
[snip]
just as 5 volt.
When the voltage from my source is between 6v and 9 volts, my chip
reads high (or 5v)
otherwise the chip reads low or zero.
like I said, the source is the voltage going to the siren, so it is
almost always ZERO.
When siren goes off, the voltage jumps anywhere between 6 to 9 volts.
Then the chip should read high
Just use your micro as a digital input; no analog required.
6-9vdc in --10K-----+------ micro
|
/\ 5v zener diode
|
Gnd
HTH
You should rethink the 10k resistor.
You chose to make your input signal the max specified impedance for
the chip -- without even allowing for the additional impedance of the
source signal, or just plain old wiggle room; which you can easily
afford. You should also consider zener current. A smaller resistor
is in order, maybe by an order of magnitude. |
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| John Popelish |
| Posted: Thu May 01, 2008 4:42 pm |
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Guest
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gearhead wrote:
Quote: On Apr 30, 2:55 pm, Randy Day <randy....@shaw.cax> wrote:
Just use your micro as a digital input; no analog required.
6-9vdc in --10K-----+------ micro
|
/\ 5v zener diode
|
Gnd
HTH
You should rethink the 10k resistor.
You chose to make your input signal the max specified impedance for
the chip -- without even allowing for the additional impedance of the
source signal, or just plain old wiggle room; which you can easily
afford. You should also consider zener current. A smaller resistor
is in order, maybe by an order of magnitude.
Why?
The lower the resistor, the more the source will be loaded.
--
Regards,
John Popelish |
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