ULN2003 question
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I want to drive an external power source using a BS2 and the ULN2003.
Decided to run a quick test. Set pin 7 of the BS2 as output,
connected a 6-volt external source to the ULN2003, connected pin 7 to
the input of the ULN2003 and wrote a test case that turns pin 7 on
for 10 seconds in response to an event.
When I tested the ULN2003 output, it registered apx. .5 volts for 10
seconds (the duration of the counter in my code). I'd expected 6
volts output for this duration.
I then set pin 8 of the BS2 as a second output pin, connected pin 8
to a second line on the ULN2003, revised my program (to handle both
pins 7 and 8) and tested the ULN2003 output on my multimeter. This
time it registered .6 volts for 10 seconds. (A .10 volt increase.)
I decided to check the amperage for the combined outputs; however,
upon switching the multimeter from volts (DC) to amps, I could hear
one of the AA cells in my external power supply begin to sizzle. Sure
enough, battery acid was leaking out of the base.
Two questions: 1) Why was I observing 1/12 the external supply
voltage from the ULN2003, and 2) What would cause the external power
supply to fail as described above?
Decided to run a quick test. Set pin 7 of the BS2 as output,
connected a 6-volt external source to the ULN2003, connected pin 7 to
the input of the ULN2003 and wrote a test case that turns pin 7 on
for 10 seconds in response to an event.
When I tested the ULN2003 output, it registered apx. .5 volts for 10
seconds (the duration of the counter in my code). I'd expected 6
volts output for this duration.
I then set pin 8 of the BS2 as a second output pin, connected pin 8
to a second line on the ULN2003, revised my program (to handle both
pins 7 and 8) and tested the ULN2003 output on my multimeter. This
time it registered .6 volts for 10 seconds. (A .10 volt increase.)
I decided to check the amperage for the combined outputs; however,
upon switching the multimeter from volts (DC) to amps, I could hear
one of the AA cells in my external power supply begin to sizzle. Sure
enough, battery acid was leaking out of the base.
Two questions: 1) Why was I observing 1/12 the external supply
voltage from the ULN2003, and 2) What would cause the external power
supply to fail as described above?
Comments
take it scratch, such as what your load was for the output.
The 2003 is a high-currrent sink device. In a typical configuration,
a load is connected from the output of the ULN2003 to +Vs.
Ouptut
/\/\/\
+Vs
And ground is connected to the Ground of the supply.
The ULN2003 does not output a HIGH, all it will do is act as a low to
allow current flow from source voltage to ground. It is essentially
an open-collector output of a transistor.
The ULN2003 can sink high current, and your load must limit current
to under 1A I believe (may be .5A, I forget precisely). Otherwise
something will smoke.
When the input is (from the stamp) is HIGH, the output will be LOW
sinking current, and you will measure about 0.6V for the C-E junction
of the output transistor.
This help?
Martin Hebel
Southern Illinois University
Beginners BS2 tutorial at:
http://imsinet.casa.siu.edu/bs2_tutorial/
--- In basicstamps@y..., "donnmoidaho" <donnmo@l...> wrote:
> I want to drive an external power source using a BS2 and the
ULN2003.
> Decided to run a quick test. Set pin 7 of the BS2 as output,
> connected a 6-volt external source to the ULN2003, connected pin 7
to
> the input of the ULN2003 and wrote a test case that turns pin 7 on
> for 10 seconds in response to an event.
>
> When I tested the ULN2003 output, it registered apx. .5 volts for
10
> seconds (the duration of the counter in my code). I'd expected 6
> volts output for this duration.
>
> I then set pin 8 of the BS2 as a second output pin, connected pin 8
> to a second line on the ULN2003, revised my program (to handle both
> pins 7 and 8) and tested the ULN2003 output on my multimeter. This
> time it registered .6 volts for 10 seconds. (A .10 volt increase.)
>
> I decided to check the amperage for the combined outputs; however,
> upon switching the multimeter from volts (DC) to amps, I could hear
> one of the AA cells in my external power supply begin to sizzle.
Sure
> enough, battery acid was leaking out of the base.
>
> Two questions: 1) Why was I observing 1/12 the external supply
> voltage from the ULN2003, and 2) What would cause the external
power
> supply to fail as described above?
martin@s... writes:
> The 2003 is a high-currrent sink device. In a typical configuration,
> a load is connected from the output of the ULN2003 to +Vs.
>
>
> Ouptut
/\/\/\
+Vs
>
> And ground is connected to the Ground of the supply.
>
Good morning, Martin
Not sure I followed you with the 2003 connections. I would say
Voltage - Load - 2003 collector. When input is high collector goes to ground
completing Load circuit. Drop across the 2003 will be about 1.3 volts
because of the two transistors in each Darlington.
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
channel of the device is triggered "on" by a logic high from the
stamp, it will conduct the selected outputs to pin 8 of the package
or ground. When you measured voltage on the device, I suspect that
you had your black lead of your meter on pin 8 and your red lead on
the desired output channel. What you are reading is probably correct
when the device was "on". In this case, it will not be 6 volts. When
you went to measure amps I think you may have left the connections
the same and by switching your meter to amps, you are applying a
direct short to the device.(through your meter in the amp mode)
Let's go back a little. You say that you are applying 6 volts to the
device. I will speculate that it is this 6 volts that you want to
switch. What is the current draw of the device that you are going to
power up from the 6 volts. Remember, the ULN2003 is only rated at
500mA.
---Guy
--- In basicstamps@y..., "donnmoidaho" <donnmo@l...> wrote:
> I want to drive an external power source using a BS2 and the
ULN2003.
> Decided to run a quick test. Set pin 7 of the BS2 as output,
> connected a 6-volt external source to the ULN2003, connected pin 7
to
> the input of the ULN2003 and wrote a test case that turns pin 7 on
> for 10 seconds in response to an event.
>
> When I tested the ULN2003 output, it registered apx. .5 volts for
10
> seconds (the duration of the counter in my code). I'd expected 6
> volts output for this duration.
>
> I then set pin 8 of the BS2 as a second output pin, connected pin 8
> to a second line on the ULN2003, revised my program (to handle both
> pins 7 and 8) and tested the ULN2003 output on my multimeter. This
> time it registered .6 volts for 10 seconds. (A .10 volt increase.)
>
> I decided to check the amperage for the combined outputs; however,
> upon switching the multimeter from volts (DC) to amps, I could hear
> one of the AA cells in my external power supply begin to sizzle.
Sure
> enough, battery acid was leaking out of the base.
>
> Two questions: 1) Why was I observing 1/12 the external supply
> voltage from the ULN2003, and 2) What would cause the external
power
> supply to fail as described above?