Too much input current???
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Posts: 46,084
Hello,
I haven't posted in quite some time now. I have been busy
constructing my second mobile robot. Everything is working just
fine. But I do have a current question.
I have modified my robot to work with a cheap trans/receiver that I
got from an old RC car that I had. I have two separate supplies.
One driving the stamp(9V) and the other driving the two servos(4AA).
I have now taken power from the 4AA to drive the receiver board.
The receiver board has four wires that I am using to connect directly
to the stamp inputs. Do I have to put a series resistor to the input
pins of the stamp or is this o.k.? And if I do, what value of
resistor should I use? .....I have tested the output voltage of each
wire and it indicates that it goes no higher that 4Vdc. It sounds
like a safe voltage value but I'm not sure of current damage.
What do you guys think?
Thanks in advance and sorry for the long post.
Later,
Frank G>
I haven't posted in quite some time now. I have been busy
constructing my second mobile robot. Everything is working just
fine. But I do have a current question.
I have modified my robot to work with a cheap trans/receiver that I
got from an old RC car that I had. I have two separate supplies.
One driving the stamp(9V) and the other driving the two servos(4AA).
I have now taken power from the 4AA to drive the receiver board.
The receiver board has four wires that I am using to connect directly
to the stamp inputs. Do I have to put a series resistor to the input
pins of the stamp or is this o.k.? And if I do, what value of
resistor should I use? .....I have tested the output voltage of each
wire and it indicates that it goes no higher that 4Vdc. It sounds
like a safe voltage value but I'm not sure of current damage.
What do you guys think?
Thanks in advance and sorry for the long post.
Later,
Frank G>
Comments
As stated in the BS manual it is always wise to put a series resistor on the
input
pins of the BS, with any value from 10K to 22K.
Otherwise a pin could accidentally be set as output in the opposite direction of
the conected device, causing a short that may destroy the output driver.
The same if the output voltage of the conected device goes to more than 5V or
less than 0V.
Regards
ECO
Original Message
From: <fwankg@y...>
To: <basicstamps@yahoogroups.com>
Sent: mercredi 25 avril 2001 05:51
Subject: [noparse][[/noparse]basicstamps] Too much input current???
> Hello,
>
***
> The receiver board has four wires that I am using to connect directly
> to the stamp inputs. Do I have to put a series resistor to the input
> pins of the stamp or is this o.k.? And if I do, what value of
> resistor should I use? .....I have tested the output voltage of each
> wire and it indicates that it goes no higher that 4Vdc. It sounds
> like a safe voltage value but I'm not sure of current damage.
> Later,
>
> Frank G>
it operates at 5 volts. The receiver is powwered by 6 volts. It is
possible the stamp sees 6 volts on an input. This may or may not be
true. Applying more than 5 volts to any stamp pin is something
I would not do. The stamp may easily tolerate 6 volts on an input
pin. I would not do it. Safety first.
Because the input impedance is high on stamp input pins I would put
4700 ohms between the stamp and receiver.
Normally the stamp wont see the resistance, but if there is a problem
with your code, or if the voltage to the stamp goes low, and the
stamp resets, there would be input voltages on the pins while the
stamp powers down/resets. Resistors are a sensible precaution.
I look at it like this:
An ounce of prevention etc... In an application like yours, using
batteries that may go low, I would use optoisolators to protect the
stamp inputs. The optos would increas the current demand on the
batteries, but I prefer to be cautious when interfacing assemblies
that require different supply voltages.
There are folks out here way brighter than me. These guys could tell
you with certainty what you should or should not do. Because that's
not me I worry abiout doing things that will kill my stamps. That is
why I take extra care when interfacing my stamp to the outside world.
Good Luck
Rich
--- In basicstamps@y..., fwankg@y... wrote:
> Hello,
>
> I haven't posted in quite some time now. I have been busy
> constructing my second mobile robot. Everything is working just
> fine. But I do have a current question.
>
> I have modified my robot to work with a cheap trans/receiver that I
> got from an old RC car that I had. I have two separate supplies.
> One driving the stamp(9V) and the other driving the two servos
(4AA).
> I have now taken power from the 4AA to drive the receiver board.
>
> The receiver board has four wires that I am using to connect
directly
> to the stamp inputs. Do I have to put a series resistor to the
input
> pins of the stamp or is this o.k.? And if I do, what value of
> resistor should I use? .....I have tested the output voltage of
each
> wire and it indicates that it goes no higher that 4Vdc. It sounds
> like a safe voltage value but I'm not sure of current damage.
>
> What do you guys think?
> Thanks in advance and sorry for the long post.
>
> Later,
>
> Frank G>