Hi,

i was thinking that i could build a speedometer
using the ospeedometer-object.
I have the reed-switch, but how big resistor should i use?
I found one 150 ohm and one 20 ohm, so is 170 ohm enough?
It should let trough 29 mah on 5 volts..

Thanks
------------------------------------



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The resistor acts as a pull-low resistor. A 10K-ohm or a 4.7K-Ohm is good
enough.

___________________
Ray Xu
r...@tx.rr.com
DPRG member
OOPic group member
Seattle Robotics
group member
My Blog

-----Original Message-----
From: o...@yahoogroups.com [mailto:o...@yahoogroups.com] On Behalf Of
oooopic
Sent: Monday, August 11, 2008 12:02 PM
To: o...@yahoogroups.com
Subject: [oopic] Reed switch help

Hi,

i was thinking that i could build a speedometer
using the ospeedometer-object.
I have the reed-switch, but how big resistor should i use?
I found one 150 ohm and one 20 ohm, so is 170 ohm enough?
It should let trough 29 mah on 5 volts..

Thanks

[Non-text portions of this message have been removed]
------------------------------------



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On Aug 11, 2008, at 11:38 AM, ray xu wrote:

> The resistor acts as a pull-low resistor. A 10K-ohm or a 4.7K-Ohm
> is good

If all I am doing is counting pulses I try not to tie inputs to Vcc at
least not without a series resistor. Drive the input as an output and
you could smoke the pin. I would use the reed switch to ground and a
pull-up resistor to Vcc/Vdd. I agree with your value of 10K.

Vdd
|
10K
|
pin<-----+
|
reed switch
|
Vss (ground)
Brian Lloyd
Granite Bay Montessori School 9330 Sierra College Bl
brian AT gbmontessori DOT com Roseville, CA 95661
+1.916.367.2131 (voice) +1.791.912.8170 (fax)

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At 05:44 PM 8/11/2008, Brian Lloyd wrote:
>If all I am doing is counting pulses I try not to tie inputs to Vcc at
>least not without a series resistor. Drive the input as an output and
>you could smoke the pin. I would use the reed switch to ground and a
>pull-up resistor to Vcc/Vdd. I agree with your value of 10K.
>
> Vdd
> |
> 10K
> |
>pin<-----+
> |
> reed switch
> |
> Vss (ground)
You could still hurt the micro if the pin is driven high and the reed
switch is closed. I'd add a protection resistor:

. Vdd
. |
. 10K
. |
pin<--330---+
. |
. reed switch
. |
. Vss (ground)
...Andy

------------------------------------



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