Confusing Voltage Reading
JTB
Posts: 9
I am getting·a confusing voltage mesurement in the "What's A Microcontroller"·manual (page 79)·in the activity using the circuit set-up for "Readpushbutton State.bs2" program.··The Circuit is set-up with a pushbutton for the "active low" mode.· There is a 10k Ohm resistor (pull-up) connected between Vdd and the pole 4 of the normally open button.··This connection is shared with a220 Ohm resistor which is connected to P3
Here is the confusing part.· When the circuit is turned on I should be able to measure a voltage drop across the pull-up resistor.· Instead, I get zero volts across the resistor and 5 volts measured·between the top·and the bottom of the resistor·and ·Vss respectively.·· Its like the resistor is not even in the circuit.· I've checked to make sure connections a tight and even moved to alternate connection sites on the breadboard.· The resistor measures the correct resistance.· What am I missing?
Julian
Here is the confusing part.· When the circuit is turned on I should be able to measure a voltage drop across the pull-up resistor.· Instead, I get zero volts across the resistor and 5 volts measured·between the top·and the bottom of the resistor·and ·Vss respectively.·· Its like the resistor is not even in the circuit.· I've checked to make sure connections a tight and even moved to alternate connection sites on the breadboard.· The resistor measures the correct resistance.· What am I missing?
Julian
Comments
You don't have a path for current unless the button is pressed, therefore, you won't read a voltage.
Dave
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Dave Andreae
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dandreae@parallax.com
www.parallax.com
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Man do I feel stupid! Thanks for the info.
Julian